Copyright �2001 W3C� (MIT, INRIA, Keio), All Rights Reserved. W3C liability, trademark, document use and software licensing rules apply.
This is a W3C Recommendation of a specification of animation functionality for XML documents.� It describes an animation framework as well as a set of base XML animation elements suitable for integration with XML documents. It is based upon the SMIL 1.0 timing model, with some extensions, and is a true subset of SMIL 2.0. This provides an intermediate stepping stone in terms of implementation complexity, for applications that wish to have SMIL-compatible animation but do not need or want time containers.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. The latest status of this document series is maintained at the W3C.
This document has been reviewed by W3C Members and other interested parties and has been endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited as a normative reference from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.
The SMIL Animation specification has been produced as part of the W3C Synchronized Multimedia Activity and was written by the SYMM Working Group (members only) of the W3C Interaction Domain, working with the SVG Working Group (members only) of the W3C Document Formats Domain. The goals of the SYMM Working Group are discussed in the SYMM Working Group charter (members only), (revised July 2000 from original charter version).
The SYMM Working Group (members only) considers that all features in the SMIL 2.0 specification have been implemented at least twice in an interoperable way. The SYMM Working Group Charter (members only) defines this as the implementations having been developed independently by different organizations and each test in the SMIL 2.0 test suite has at least two passing implementations. The Implementation results are publicly released and are intended solely to be used as proof of SMIL 2.0 implementability. It is only a snap shot of the actual implementation behaviors at one moment of time, as these implementations may not be immediately available to the public. The interoperability data is not intended to be used for assessing or grading the performance of any individual implementation.
There are patent disclosures and license commitments associated with the SMIL 2.0 specification (and thus with the SMIL Animation specification also), these may be found on the SYMM Patent Statement page in conformance with W3C policy.
Please report errors in this document to<EMAIL_ADDRESS>The list of known errors in this specification is available at http://www.w3.org/2001/09/REC-smil-animation-20010904-errata.
A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR.
2. Overview and terminology
����2.1. Basics of animation
����2.2. Animation function values
����2.3. Symbols used in the semantic
descriptions
3. Animation model
����3.1. Specifying the animation
target
����3.2. Specifying the animation
function f(t)
��������3.2.1. Animation function timing
��������3.2.2. Animation function values
��������3.2.3. Animation function calculation
modes
����3.3. Specifying the animation effect
F(t)
�������3.3.1. Repeating animation
�������3.3.2. Controlling the active duration
�������3.3.3. The min and max attributes
�������3.3.4. Computing the active
duration
�������3.3.5. Freezing animations
�������3.3.6. Additive animation
�������3.3.7. Restarting animations
����3.4. Handling syntax errors
����3.5. The animation sandwich
model
3.6. Timing model details
3.6.1. Timing and real-world clock times
3.6.2. Interval timing
3.6.3. Unifying event-based and scheduled timing
3.6.4. Event sensitivity
3.6.5. Hyperlinks and timing
3.6.6. Propagating changes to times
3.6.7. Timing attribute value grammars
3.6.8. Evaluation of begin and
end time lists
3.7. Animation function value
details
3.8. Common syntax DTD definitions
4. Animation elements
����4.1. The animate element
����4.2. The set element
����4.3. The animateMotion element
����4.4. The animateColor element
5. Integrating SMIL Animation into a host
language
��� 5.1. Required host language
definitions
��� 5.2. Required definitions and
constraints on animation targets
��� 5.3. Constraints on
manipulating animation elements
��� 5.4. Required
definitions and constraints on element timing
��� 5.5. Error handling semantics
��� 5.6. SMIL Animation
namespace
6. Document Object Model support
��� 6.1. Events and event model
��� 6.2. Supported interfaces
��� 6.3. IDL definition
��� 6.4. Java language binding
��� 6.5. ECMAScript language binding
7. Appendix: Differences from SMIL 1.0 timing model
8. References
This document describes a framework for incorporating animation onto a time line and a mechanism for composing the effects of multiple animations.� A set of basic animation elements are also described that can be applied to any [XML]-based language. A language with which this module is integrated is referred to as a host language. A document containing animation elements is referred to as a host document.
Animation is inherently time-based. SMIL Animation is defined in terms of the SMIL timing model.� The animation capabilities are described by new elements with associated attributes and semantics, as well as the SMIL timing attributes. Animation is modeled as a function that changes the presented value of a specific attribute over time.
The timing model is based upon SMIL 1.0 [SMIL1.0],
with some changes and extensions to support additional timing features.
SMIL Animation uses a simplified "flat" timing model, with no time containers
(like <par>
or <seq>
). This version of
SMIL Animation may not be used with documents that otherwise contain timing.
See also Required
definitions and constraints on element timing.
While this document defines a base set of animation capabilities, it is assumed that host languages may build upon the support to define additional or more specialized animation elements.� In order to ensure a consistent model for document authors and runtime implementers, we introduce a framework for integrating animation with the SMIL timing model. Animation only manipulates attributes and properties of the target elements, and so does not require any specific knowledge of the target element semantics.
The examples in this document that include syntax for a host language use SMIL, SVG, XHTML and CSS. These are provided as an indication of possible integrations with various host languages.
Animation is defined as a time-based manipulation of a target element (or more specifically of some attribute of the target element, the target attribute). The animation defines a mapping of time to values for the target attribute. This mapping accounts for all aspects of timing, as well as animation-specific semantics.�
Animations specify a begin, and a simple duration that can be repeated. Each animation defines an animation function that produces a value for the target attribute, for any time within the simple duration. The author can specify how long or how many times an animation function should repeat. The simple duration combined with any repeating behavior defines the active duration.
The target attribute is the name�of a feature of a target element as defined in a host language document. This may be (e.g.) an XML attribute contained in the element or a CSS property that applies to the element.� By default, the target element of an animation will be the parent of the animation element (an animation element is typically a child of the target element). However, the target may be any element in the document, identified either by an ID reference or via an XLink [XLink] locator reference.
As a simple example, the following defines an animation of an SVG rectangle shape.� The rectangle will change from being tall and thin to being short and wide.
<rect ...> <animate attributeName="width" from="10px" to="100px" begin="0s" dur="10s" /> <animate attributeName="height" from="100px" to="10px" begin="0s" dur="10s" /> </rect>
The rectangle begins with a width of 10 pixels and increases to a width of 100 pixels over the course of 10 seconds. Over the same ten seconds, the height of the rectangle changes from 100 pixels to 10 pixels.
When an animation is running, it should not actually change the attribute values in the DOM [DOM-Level-2].� The animation runtime should maintain a presentation value for each animated attribute, separate from the DOM or CSS Object Model (OM). If an implementation does not support an object model, it should maintain the original value as defined by the document as well as the presentation value. The presentation value is reflected in the display form of the document. Animations thus manipulate the presentation value, and should not affect the base value exposed by DOM or CSS OM.�This is detailed in The animation sandwich model.
The animation function is evaluated as needed over time by the implementation, and the resulting values are applied to the presentation value for the target attribute.�Animation functions are continuous in time and can be sampled at whatever frame rate is appropriate for the rendering system. The syntactic representation of the animation function is independent of this model, and may be described in a variety of ways. The animation elements in this specification support syntax for a set of discrete or interpolated values, a path syntax for motion based upon SVG paths, keyframe based timing, evenly paced interpolation, and variants on these features. Animation functions could be defined that were purely or partially algorithmic (e.g., a random value function or a motion animation that tracks the mouse position). In all cases, the animation exposes this as a function of time.
The presentation value reflects the effect of the animation upon the base value. The effect is the change to the value of the target attribute at any given time. When an animation completes, the effect of the animation is no longer applied, and the presentation value reverts to the base value by default. The animation effect can also be extended to freeze the last value for the remainder of the document duration.
Animations can be defined to either override or add to the base value of an attribute. In this context, the base value may be the DOM value, or the result of other animations that also target the same attribute. This more general concept of a base value is termed the underlying value. Animations that add to the underlying value are described as additive animations. Animations that override the underlying value are referred to as non-additive animations.
Many animations specify the animation function
f(t)
as a sequence of values to be applied over
time. For some types of attributes (e.g. numbers), it is also possible to
describe an interpolation function between values.
As a simple form of describing the values, animation elements can specify a from value and a to value. If the attribute takes values that support interpolation (e.g. a number), the animation function can interpolate values in the range defined by� from and to, over the course of the simple duration. A variant on this uses a by value in place of the to value, to indicate an additive change to the attribute.
More complex forms specify a list of values, or even a path description for motion. Authors can also control the timing of the values, to describe "keyframe" animations, and even more complex functions.
f(t)
F(t)
defines
the mapping for the entire animation, f(t)
has a simplified model that just handles the simple duration.F(t)
F(t)
combines the animation function
f(t)
with all the other aspects of
animation and timing controls.This section describes the attribute syntax and semantics for describing
animations. The specific elements are not described here, but rather the
common concepts and syntax that comprise the model for animation.� Document
issues are described, as well as the means to target an element for animation.
The animation model is then defined by building up from the simplest to the
most complex concepts: first the simple duration and animation function
f(t)
, and then the overall behavior
F(t)
.� Finally, the model for combining
animations is presented, and additional details of animation timing are
described.
The time model depends upon several definitions for the host document: A host document is presented over a certain time interval. The start of the interval in which the document is presented is referred to as the document begin. The end of the interval in which the document is presented is referred to as the document end. The difference between the end and the begin is referred to as the document duration. The formal definitions of presentation and document begin and end are left to the host language designer (see also Required host language definitions).
The animation target is defined as a specific attribute of a particular element. The means of specifying the target attribute and the target element are detailed in this section.
The target attribute to be animated is specified with
attributeName
. The value of this attribute is a string that
specifies the name of the target attribute, as defined in the host
language.
The attributes of an element that can be animated are often defined by
different languages, and/or in different namespaces. For example, in many XML
applications, the position of an element (which is a typical target attribute)
is defined as a CSS property rather than as XML attributes. In some cases, the
same attribute name is associated with attributes or properties in more than
one language, or namespace.� To allow the author to disambiguate the name
mapping, an additional attribute attributeType
is provided that
specifies the intended interpretation.
The attributeType
attribute is optional. By default, the
animation runtime will resolve the names according to the following rule: If
there is a name conflict and attributeType
is not specified, the
list of CSS properties supported by the host language is matched first (if CSS
is supported in the host language); if no CSS match is made (or CSS does not
apply) the default namespace for the target element will be matched.
If a target attribute is defined in an XML Namespace other than the default
namespace for the target element, the author must specify the namespace of the
target attribute using the associated namespace prefix as defined in the scope
of the animation element. The prefix is prepended to the value for
attributeName
.
For more information on XML namespaces, see [XML-NS].
attributeName
has an
XMLNS prefix, the implementation must use the associated namespace
as defined in the scope of the animation element.An animation element can define the target element of the animation either explicitly or implicitly. An explicit definition uses an attribute to specify the target element. The syntax for this is described below.
If no explicit target is specified, the implicit target element is the parent element of the animation element in the document tree. It is expected that the common case will be that an animation element is declared as a child of the element to be animated. In this case, no explicit target need be specified.
If an explicit target element reference cannot be resolved (e.g. if no such element can be found), the animation has no effect. In addition, if the target element (either implicit or explicit) does not support the specified target attribute, the animation has no effect.�See also Handling syntax errors.
The following two attributes can be used to identify the target element explicitly:
targetElement
= "<IDREF>"href
=
uri-referenceWhen integrating animation elements into the host language, the language
designer should avoid including both of these attributes. If however, the host
language designer chooses to include both attributes in the host language,
then when both are specified for a given animation element the XLink
href
attribute takes precedence over the
targetElement
attribute.
The advantage of using the targetElement
attribute is the
simpler syntax of the attribute value compared to the href
attribute. The advantage of using the XLink href
attribute is
that it is extensible to a full linking mechanism in future versions of SMIL
Animation, and the animation element can be processed by generic XLink
processors. The XLink form is also provided for host languages that are
designed to use XLink for all such references. The following two examples
illustrate the two approaches.
This example uses the simpler targetElement
syntax:
<animate targetElement="foo" attributeName="bar" .../>
This example uses the more flexible XLink locator syntax, with the equivalent target.
<foo xmlns:xlink="http://www.w3.org/1999/xlink"> ... <animate xlink:href="#foo" attributeName="bar" .../> ... </foo>
When using an XLink href
attribute on an animation element,
the following additional XLink attributes need to be defined in the host
language. These may be defined in a DTD, or the host language may require
these in the document syntax to support generic XLink processors. For more
information, refer to the "XML Linking Language (XLink)" [XLink].
The following XLink attributes are required by the XLink specification. The values are fixed, and so may be specified as such in a DTD. All other XLink attributes are optional, and do not affect SMIL Animation semantics.
type
= 'simple'actuate
= 'onLoad'show
= 'embed'Additional details on the target element specification as relates to the host document and language are described in Required definitions and constraints on animation targets.
Every animation function defines the value of the attribute at a particular moment in time. The time range for which the animation function is defined is the simple duration. The animation function does not produce defined results for times outside the range of 0 to the simple duration.
The basic timing for an element is described using the begin
and dur
attributes. Authors can specify the begin time of an
animation in a variety of ways, ranging from simple clock times to the time
that an event like a mouse-click happens. The length of the simple duration is
specified using the dur
attribute. The attribute syntax is
described below. The normative syntax rules for each attribute value variant
are described in Timing attribute value
grammars. A syntax summary is provided
here as an aid to the reader.
This section is normative
This section is normative
This section is informative
The begin value can specify a list of times. This can be used to specify multiple "ways" or "rules" to begin an element, e.g. if any one of several events is raised. A list of times can also define multiple begin times, allowing the element to play more than once (this behavior can be controlled, e.g. to only allow the earliest begin to actually be used - see also Restarting animations).
In general, the earliest time in the list determines the begin time of the element. There are additional constraints upon the evaluation of the begin time list, detailed in Evaluation of begin and end time lists.
Note that while it is legal to include "indefinite" in a list of values for begin, "indefinite" is only really useful as a single value. Combining it with other values does not impact begin timing, as DOM begin methods can be called with or without specifying "indefinite" for begin.
This section is informative
The use of negative offsets to define begin times merely defines the synchronization relationship of the element. It does not in any way override the time container constraints upon the element, and it cannot override the constraints of presentation time.
This section is normative
The computed begin time defines the scheduled synchronization relationship of the element, even if it is not possible to begin the element at the computed time. The time model uses the computed begin time, and not the observed time of the element begin.
This section is normative
The element will actually begin at the time computed according to the following algorithm:
Let o be the offset value of a given begin value, d be the associated simple duration, AD be the associated active duration. Let rAt be the time when the begin time becomes resolved. Let rTo be the resolved sync-base or event-base time without the offset Let rD be rTo - rAt. If rD < 0 then rD is set to 0. If AD is indefinite, it compares greater than any value of o or ABS(o). REM( x, y ) is defined as x - (y * floor( x/y )). If y is indefinite, REM( x, y ) is just x. Let mb = REM( ABS(o), d ) - rD
If ABS(o) >= AD then the element does not begin. Else if mb >= 0 then the media begins at mb. Else the media begins at mb + d.
If the element repeats, the iteration value of the repeat
event has the calculated value based upon the above computed begin time, and not
the observed number of repeats.
This section is informative
Thus for example:
<animate begin="foo.click-8s" dur="3s" repeatCount="10" .../>
The animation begins when the user clicks on the
element "foo". Its calculated begin time is actually 8 seconds
earlier, and so it begins to play at 2 seconds into the 3 second simple
duration, on the third repeat iteration. One second later, the fourth iteration
of the element will begin, and the associated repeat
event will
have the iteration value set to 3 (since it is zero based). The element will end
22 seconds after the click. The beginEvent
event is raised when
the element begins, but has a time stamp value that corresponds to the defined
begin time, 8 seconds earlier. Any time dependents are activated relative to the
computed begin time, and not the observed begin time.
Note: If script authors wish to distinguish between
the computed repeat iterations and observed repeat iterations, they can count
actual repeat
events in the associated event handler.
If no begin
is specified, the default value is "0" - the
animation begins when the document begins. If there is any error in the
argument value syntax for begin
, the default value for
begin
will be used.
If the animation does not have a dur
attribute, the simple
duration is indefinite. Note that interpolation will not work if the simple
duration is indefinite (although this may still be useful for <set>
elements). See also Interpolation and indefinite simple
durations.
If there is any error in the argument value syntax for dur
,
the attribute will be ignored (as though it were not specified), and so the
simple duration will be indefinite.
If the begin is specified to be "indefinite" or specifies an event-base, the time of the begin is not actually known until the element is activated (e.g., with a hyperlink, DOM method call or the referenced event). The time is referred to as unresolved when it is not known. At the point at which the element begin is activated, the time becomes resolved. This is described in detail in Unifying event-based and scheduled timing.
The following examples all specify a begin at midnight on January 1st 2000, UTC
begin="wallclock(2000-01-01Z)" begin="wallclock( 2000-01-01T00:00Z )" begin="wallclock( 2000-01-01T00:00:00Z )" begin="wallclock( 2000-01-01T00:00:00.0Z )" begin="wallclock( 2000-01-01T00:00:00.0Z )" begin="wallclock( 2000-01-01T00:00:00.0-00:00 )"
The following example specifies a begin at 3:30 in the afternoon on July 28th 1990, in the Pacific US time zone:
begin="wallclock( 1990-07-28T15:30-08:00 )"
The following example specifies a begin at 8 in the morning wherever the document is presented:
begin="wallclock( 08:00 )"
In addition to the target attribute and the timing, an animation must specify how to change the value over time. An animation can be described either as a list of values, or in a simplified form using from, to and by values.
attributeType
domain.If a list of values is used, the animation will apply the values in order over the course of the animation (pacing and interpolation between these values is described in the next section). If a list of values is specified, any from, to and by attribute values are ignored.
The simpler from/to/by syntax provides for several variants. To
use one of these variants, one of by
or to
must be
specified; a from
value is optional. It is not legal to specify
both by
and to
attributes - if both are specified,
only the to
attribute will be used (the by
will be
ignored). The combinations of attributes yield the following classes of
animation:
from
value and a to
value
defines a simple animation, equivalent to a values
list
with 2 values. The animation function is defined to start with the
from
value, and to finish with the to
value.from
value and a by
value
defines a simple animation in which the animation function is defined to
start with the from
value, and to change this over the
course of the simple duration by a delta specified with the
by
attribute. This may only be used with attributes that
support addition (e.g. most numeric attributes).by
attribute. This may only be used with
attributes that support addition.to
attribute. Using this form,
an author can describe an animation that will start with any current
value for the attribute, and will end up at the desired to
value.The last two forms "by animation" and "to animation" have additional semantic constraints when combined with other animations. The details of this are described below in the section How from, to and by attributes affect additive behavior.
The animation values specified in the animation element must be legal values for the specified attribute. See also Animation function value details.�
Leading and trailing white space, and white space before and after semicolon separators, will be ignored.
If any values (i.e., the argument-values for from
,
to
, by
or values
attributes) are not
legal, the animation will have no effect (see also Handling Syntax Errors). Similarly, if none
of the from
, to
, by
or
values
attributes are specified, the animation will have no
effect.
If the simple duration of an animation is indefinite (e.g., if no
dur
value is specified), interpolation is not generally
meaningful. While it is possible to define an animation function that is not
based upon a defined simple duration (e.g., some random number algorithm), most
animations define the function in terms of the simple duration. If an
animation function is defined in terms of the simple duration and the simple
duration is indefinite, the first value of the animation function (i.e.,
f(0)
) should be used (effectively as a constant)
for the animation function.
Examples
The following example using the values
syntax animates the
width of an SVG shape over the course of 10 seconds, interpolating from a
width of 40 to a width of 100 and back to 40.
<rect ...> <animate attributeName="width" values="40;100;40" dur="10s"/> </rect>
The following "from-to animation" example animates the width of an SVG shape over the course of 10 seconds from a width of 50 to a width of 100.
<rect ...> <animate attributeName="width" from="50" to="100" dur="10s"/> </rect>
The following "from-by animation" example animates the width of an SVG shape over the course of 10 seconds from a width of 50 to a width of 75.
<rect ...> <animate attributeName="width" from="50" by="25" dur="10s"/> </rect>
The following "by animation" example animates the width of an SVG shape over the course of 10 seconds from the original width of 40 to a width of 70.
<rect width="40"...> <animate attributeName="width" by="30" dur="10s"/> </rect>
The following "to animation" example animates the width of an SVG shape over the course of 10 seconds from the original width of 40 to a width of 100.
<rect width="40"...> <animate attributeName="width" to="100" dur="10s"/> </rect>
By default, a simple linear interpolation is performed over the values,
evenly spaced over the duration of the animation.� Additional attributes can
be used for finer control over the interpolation and timing of the values. The
calcMode
attribute defines the method of applying values to the
attribute. The keyTimes
attribute provides additional control
over the timing of the animation function, associating a time with each value
in the values
list (or the points in a path
description for animateMotion
- see The animateMotion element). Finally, the
keySplines
attribute provides a means of controlling the pacing
of interpolation between the values in the values
list.
calcMode
= "discrete | linear | paced |
spline"calcMode
attribute is ignored and discrete interpolation is
used.
calcMode
.paced
" is specified, any
keyTimes
or keySplines
will be
ignored.values
list to
the next according to a time function defined by a cubic Bezier
spline. The points of the spline are defined in the
keyTimes
attribute, and the control points for each
interval are defined in the keySplines
attribute.keyTimes
= "<list>"values
attribute list, and defines when the value should be
used in the animation function. Each time value in the
keyTimes
list is specified as a floating point value
between 0 and 1 (inclusive), representing a proportional offset into the
simple duration of the animation
element.
If a list of keyTimes
is specified, there must be
exactly as many values in the keyTimes
list as in the
values
list.
Each successive time value must be greater than or equal to the preceding time value.
The keyTimes
list semantics depends upon the
interpolation mode:
keyTime
associated with each value defines when the value is
set; values are interpolated between the
keyTimes
.keyTimes
.If the interpolation mode is "paced", the keyTimes
attribute is ignored.
If there are any errors in the keyTimes
specification
(bad values, too many or too few values), the animation will have no
effect.
If the simple duration is indefinite, any keyTimes
specification will be ignored.
keySplines
= "<list>"keyTimes
list, defining a cubic Bezier function that
controls interval pacing. The attribute value is a semicolon separated
list of control point descriptions. Each control point description is a
set of four floating point values: x1 y1 x2 y2
, describing
the Bezier control points for one time segment. The
keyTimes
values that define the associated segment are the
Bezier "anchor points", and the keySplines
values are the
control points. Thus, there must be one fewer sets of control points
than there are keyTimes
.
The values must all be in the range 0 to 1.
This attribute is ignored unless the calcMode
is set to
"spline".
If there are any errors in the keySplines
specification
(bad values, too many or too few values), the animation will have no
effect.
If calcMode
is set to "discrete", "linear" or "spline", but
the keyTimes
attribute is not
specified, the values in the values
attribute are assumed to be
equally spaced through the animation duration, according to the
calcMode
:
n-1
even periods, and the animation function is
a linear interpolation between the values at the associated times. Note
that a linear animation will be a smoothly closed loop if the
first value is repeated as the last.This semantic applies as well when the keySplines
attribute is
specified, but keyTimes
is not.
The times associated to the keySplines
values are determined as
described above.
The syntax for the control point sets in keySplines
lists
is:
control-pt-set ::= ( fpval comma-wsp fpval comma-wsp fpval comma-wsp fpval ) fpval ::= Floating point number comma-wsp ::= S (spacechar|",") S
Control point values are separated by at least one white space character or a comma. Additional white space around the separator is allowed. The allowed syntax for floating point numbers must be defined in the host language.
For the shorthand forms from-to animation and from-by animation, there are only 2 values.� A discrete from-to animation will set the "from" value for the first half of the simple duration and the "to" value for the second half of the simple duration. Similarly, a discrete from-by animation will set the "from" value for the first half of the simple duration and for the second half of the simple duration will set the computed result of applying the "by" value. For the shorthand form to animation, there is only 1 value; a discrete to animation will simply set the "to" value for the simple duration.
If the� argument values for keyTimes
or
keySplines
are not legal (including too few or too many values
for either attribute), the animation will have no effect (see also Handling syntax errors).
In the calcMode
, keyTimes
and
keySplines
attribute values, leading and trailing white space and
white space before and after semicolon separators will be ignored.
The three illustrations 1a, 1b and 1c below show how the same basic
animation will change a value over time, given different interpolation modes.
All examples use the default timing (no keyTimes
or
keySplines
specified).�All examples are based upon the following
example, but with different values for calcMode
:
<animate dur="30s" values="0; 1; 2; 4; 8; 15" calcMode="[as specified]" />
�
Figure 1a: Default discrete animation.
There are 6 segments of equal duration: 1 segment per value. |
|
Figure 1b: Default linear animation.
There are 5 segments of equal duration: n-1 segments for n values. Spline interpolation is a refinement of linear, and is further illustrated in Figure 2, below. |
|
Figure 1c: Default paced animation.
There are 5 segments of varying duration: n-1 segments for n values, computed to yield a constant rate of change in the value. |
The following example describes a simple discrete animation:
<animate attributeName="foo" dur="8s" values="bar; fun; far; boo" />
The value of the attribute "foo" will be set to each of the four strings
for 2 seconds each. Because the string values cannot be interpolated, only
discrete animation is possible; any calcMode
attribute
would be ignored.
Discrete animation can also be used with keyTimes
, as in the
following example:
<animateColor attributeName="color" dur="10s" calcMode="discrete" values="green; yellow; red" keyTimes="0.0; 0.5;" />
This example also shows how keyTimes
values can interact with
an indefinite duration. The value of the "color" attribute will be set to
green for 5 seconds, and then to yellow for 5 seconds, and then will remain
red for the remainder of the document, since the (unspecified) duration
defaults to "indefinite".
The following example describes a simple linear animation:
<animate attributeName="x" dur="10s" values="0; 10; 100" calcMode="linear"/>
The value of "x" will change from 0 to 10 in the first 5 seconds, and then
from 10 to 100 in the second 5 seconds. Note that the values in the
values
attribute are spaced evenly in time with no
keyTimes
specified; in this case the result is a much larger
actual change in the value during the second half of the animation. Contrast
this with the same example changed to use "paced" interpolation:
<animate attributeName="x" dur="10s" values="0; 10; 100" calcMode="paced"/>
To produce an even pace of change to the attribute "x", the second segment
defined by the values list gets most of the simple duration: The value of "x"
will change from 0 to 10 in the first second, and then from 10 to 100 in the
next 9 seconds. While this example could be easily authored as a
from-to animation without paced interpolation, many examples (such as
motion paths) are much harder to author without the "paced" value for
calcMode
.�
The following example illustrates the use of keyTimes
:
<animate attributeName="x" dur="10s" values="0; 50; 100" keyTimes="0; .8; 1" calcMode="linear"/>
The keyTimes
values cause the "x" attribute to have a value of
"0" at the start of the animation, "50" after 8 seconds (at 80% into the
simple duration) and "100" at the end of the animation. The value will change
more slowly in the first half of the animation, and more quickly in the second
half.
Extending this example to use keySplines
:
<animate attributeName="x" dur="10s" values="0; 50; 100" keyTimes="0; .8; 1" calcMode="spline" keySplines=".5 0 .5 1; 0 0 1 1" />
The keyTimes
still cause the "x" attribute to have a value of
"0" at the start of the animation, "50" after 8 seconds and "100" at the end
of the animation. However, the keySplines
values define a curve
for pacing the interpolation between values. In the example above, the spline
causes an ease-in and ease-out effect between time 0 and 8 seconds (i.e.,
between keyTimes
0 and .8, and values
"0" and "50"),
but a strict linear interpolation between 8 seconds and the end (i.e., between
keyTimes
.8 and 1, and values
� "50" and "100"). See
Figure 2 below for an illustration of the curves that these
keySplines
values define.
For some attributes, the pace of change may not be easily
discernable by viewers. However for animations like motion, the ability to
make the speed of the motion change gradually, and not in abrupt
steps, can be important. The keySplines
attribute provides this
control.
The following figure illustrates the interpretation of the
keySplines
attribute. Each diagram illustrates the effect of
keySplines
settings for a single interval (i.e., between the
associated pairs of values in the keyTimes
and
values
lists.). The horizontal axis can be thought of as the
input value for the unit progress of interpolation within the
interval - i.e., the pace with which interpolation proceeds along the given
interval. The vertical axis is the resulting value for the unit
progress, yielded by the keySplines
function. Another way of
describing this is that the horizontal axis is the input unit time
for the interval, and the vertical axis is the output unit time. See
also the section Timing and real-world
clock times.
| keySplines="0 0 1 1" (the default) | keySplines=".5 0 .5 1" � |
||
| keySplines="0 .75 .25 1" | keySplines="1 0 .25 .25" |
To illustrate the calculations, consider the simple example:
<animate dur="4s" values="10; 20" keyTimes="0; 1" calcMode="spline" keySplines={as in table} />
Using the keySplines values for each of the four cases above, the approximate interpolated values as the animation proceeds are:
| keySplines values� | Initial value | After 1s | After 2s | After 3s | Final value |
| 0 0 1 1 | 10.0 | 12.5 | 15.0 | 17.5 | 20.0 |
| .5 0 .5 1 | 10.0 | 11.0 | 15.0 | 19.0 | 20.0 |
| 0 .75 .25 1 | 10.0 | 18.0 | 19.3 | 19.8 | 20.0 |
| 1 0 .25 .25 | 10.0 | 10.1 | 10.6 | 16.9 | 20.0 |
For a formal definition of Bezier spline calculation, see [COMP-GRAPHICS].
The keyTimes
and keySplines
attributes can also
be used with the from/to/by shorthand forms for specifying values, as
in the following example:
<animate attributeName="foo" from="10" to="20" dur="10s" keyTimes="0.0; 0.7" calcMode="spline" keySplines=".5 0 .5 1" />
The value will change from 10 to 20, using an "ease-in/ease-out"
curve specified by the keySplines values. The keyTimes
values
cause the value of 20 to be reached at 7 seconds, and to hold there for the
remainder of the 10 second simple duration.
The following example describes a somewhat unusual usage: "from-to animation" with discrete animation. The "stroke-linecap" attribute of SVG elements takes a string, and so implies a calcMode of discrete. The animation will set the stroke-linecap property to "round" for 5 seconds (half the simple duration) and then set the stroke-linecap to "square" for 5 seconds.
<rect stroke-linecap="butt"...> <animate attributeName="stroke-linecap" from="round" to="square" dur="10s"/> </rect>
As described above, the animation function
f(t)
defines the animation for the simple
duration. However SMIL Animation allows the author to repeat the simple
duration. SMIL Animation also allows authors to specify whether the animation
should simply end when the active duration completes, or whether it should be
frozen at the last value.� In addition, the author can specify how
each animation should be combined with other animations and the original DOM
value.
This section describes the syntax and associated semantics for the additional functionality. A detailed model for combining animations is described, along with additional details of the timing model.
The period of time during which the animation is actively playing,
including any repeat behavior, is described as the active duration. The active
duration may be computed from the simple duration and the repeat
specification, and it may be constrained with the
end
attribute.� The complete rules for computing
the active duration are presented in the section Computing the active duration.
Repeating an animation causes the animation function
f(t)
to be "played" several times in sequence.�
The author can specify either how many times to repeat, using
repeatCount
, or how long to repeat, using
repeatDur
. Each repeat iteration is one instance of
"playing" the animation function f(t)
.
If the simple duration is indefinite, the animation cannot repeat. See also the section Computing the active duration.
f(t)
.At most one of repeatCount
or repeatDur
should be
specified. If both are specified (and the simple duration is not indefinite),
the active duration is defined as the minimum of the specified repeatDur and
the�simple duration multiplied by repeatCount. For the purposes of this
comparison, a defined value is considered to be "less than" a value of
"indefinite". If the simple duration is indefinite, and both
repeatCount
and repeatDur
are specified, the
repeatCount
will be ignored, and the repeatDur
will
be used (refer to the examples below describing repeatDur
and an
indefinite simple duration). These rules are included in the section Computing the active duration.
In the following example, the 2.5 second animation function will be repeated twice; the active duration will be 5 seconds.
<animate attributeName="top" from="0" to="10" dur="2.5s"
�������� repeatCount="2" />
In the following example, the animation function will be repeated two full times and then the first half is repeated once more; the active duration will be 7.5 seconds.
<animate attributeName="top" from="0" to="10" dur="3s"
�������� repeatCount="2.5" />
In the following example, the animation function will repeat for a total of 7 seconds. It will play fully two times, followed by a fractional part of 2 seconds. This is equivalent to a repeatCount of 2.8. The last (partial) iteration will apply values in the range "0" to "8".�
<animate attributeName="top" from="0" to="10"�dur="2.5s"
�������� repeatDur="7s" />
Note that if the simple duration is not defined (e.g. it is indefinite),
repeat behavior is not defined (but repeatDur
still defines the
active duration). In the following example the simple duration is indefinite,
and so the repeatCount
is effectively ignored. Nevertheless, this
is not considered an error: the active duration is also indefinite. The effect
of the animation is to to just use the value for
f(0)
, setting the fill color to red for the remainder of
the document duration.
<animate attributeName="fill" from="red" to="blue" repeatCount="2" />
In the following example, the simple duration is indefinite, but the
repeatDur
still determines the active duration. The effect of the
animation is to set the fill color to red for 10 seconds.
<animate attributeName="fill" from="red" to="blue" repeatDur="10s" />
In the following example, the simple duration is longer than the duration
specified by repeatDur
, and so the active duration will
effectively cut short the simple duration. However, the animation function
still interpolates using the specified simple duration. The effect of the
animation is to interpolate the value of "top" from 10 to 17, over the course
of 7 seconds.
<animate attributeName="top" from="10" to="20"�
�������� dur="10s" repeatDur="7s" />
min
attribute and restart:
The min
attribute does not prevent an
element from restarting before the minimum active duration is reached.
The author may also select whether a repeating animation should repeat the original behavior for each iteration, or whether it should build upon the previous results, accumulating with each iteration. For example, a motion path that describes an arc can repeat by moving along the same arc over and over again, or it can begin each repeat iteration where the last left off, making the animated element bounce across the window. This is called cumulative animation.
Using the path notation for a simple arc (detailed in The animateMotion element), we describe this example as:
<img ...> <animateMotion path="m 0 0 c 30 50 70 50 100 0 z" dur="5s" accumulate="sum" repeatCount="4" /> </img>
The image moves from the original position along the arc over the course of 5 seconds. As the animation repeats, it builds upon the previous value and begins the second arc where the first one ended, as illustrated in Figure 3, below. In this way, the image "bounces" across the screen. The same animation could be described as a complete path of 4 arcs, but in the general case the path description can get quite large and cumbersome to edit.
accumulate="sum"
. Each repeat iteration builds upon the
previous.Note that cumulative animation only controls how a single animation accumulates the results of the animation function as it repeats. It specifically does not control how one animation interacts with other animations to produce a presentation value. This latter behavior is described in the section Additive animation.
The cumulative behavior of repeating animations is controlled with the
accumulate
attribute:
"sum"
, each repeat iteration after the first builds upon
the last value of the previous iteration."none"
, repeat iterations are not cumulative, and simply
repeat the animation function f(t)
. This
is the default.
This attribute is ignored if the target attribute value does not support addition, or if the animation element does not repeat.
Cumulative animation is not defined for "to animation". This
attribute will be ignored if the animation function is specified with
only the to
attribute. See also Specifying function values.
Any numeric attribute that supports addition can support cumulative
animation. For example, we can define a "pulsing" animation that will grow the
"width" of an SVG <rect>
element by 100 pixels in 50
seconds.
<rect width="20px"...> <animate attributeName="width" dur="5s" values="0; 15; 10" additive="sum" accumulate="sum" repeatCount="10" /> </rect>
Each simple duration causes the rectangle width to bulge by 15 pixels and end up 10 pixels larger. The shape is 20 pixels wide at the beginning, and after 5 seconds is 30 pixels wide. The animation repeats, and builds upon the previous values. The shape will bulge to 45 pixels and then end up 40 pixels wide after 10 seconds, and will eventually end up 120 (20 + 100) pixels wide after all 10 repeats.
From-to and from-by animations also support cumulative animation, as in the following example:
<rect width="20px"...> <animate attributeName="width" dur="5s" from="10px" to="20px" accumulate="sum" repeatCount="10" /> </rect>
The rectangle will grow from 10 to 20 pixels in the first 5 seconds, and
then from 20 to 30 in the next 5 seconds, and so on up to 110 pixels after 10
repeats. Note that since the default value for additive
is
"replace", the original value is ignored. The following example makes the
animation explicitly additive:
<rect width="20px"...> <animate attributeName="width" dur="5s" from="10px" to="20px" accumulate="sum" additive="sum" repeatCount="10" /> </rect>
The results are the same as before, except that all the values are shifted up by the original value of 20. The rectangle is 30 pixels wide after 5 seconds, and 130 pixels wide after 10 repeats.
To produce the cumulative animation behavior, the animation function
f(t)
must be modified slightly. Each iteration
after the first must add in the last value of the previous iteration - this is
expressed as a multiple of the last value specified for the animation function. Note that
cumulative animation is defined in terms of the values specified for the
animation behavior, and not in terms of sampled or rendered animation values.
The latter would vary from machine to machine, and could even vary between
document views on the same machine.
Let fi(t)
represent the cumulative
animation function for a given iteration i
.
The first iteration f0(t)
is
unaffected by accumulate
, and so is the same as the original
animation function definition.
f0(t) = f(t)
Let ve
be the last value specified for the
animation function (e.g., the "to" value, the last value in a "values" list, or
the end of a "path").� Each iteration after the first adds in the computed
offset:
fi(t) = (ve * i) + f(t) ; i >=
1
SMIL Animation provides an additional control over the active duration. The
end
attribute allows the author to constrain the active duration
of the animation by specifying an end value, using a simple offset, a time
base, an event-base or DOM method calls. The end
attribute can
constrain but not extend the active duration that is
otherwise defined by dur
and any repeat behavior. The rules for
combining the attributes to compute the active duration are presented in the
section, Computing the active duration.
The end value can specify a list of times. This can be used to specify multiple "ways" or "rules" to end an element, e.g. if any one of several events is raised. A list of times can also define multiple end times that can correspond to multiple begin times, allowing the element to play more than once (this behavior can be controlled - see also Restarting animations).�
In the following example, the active duration will end at the earlier of 10 seconds or the end of the "foo" element. This is particularly useful if "foo" is defined to begin or end relative to an event.
<animate dur="2s" repeatDur="10s" end="foo.end" ... />
In the following example, the animation begins when the user clicks on the target element. The active duration will end 30 seconds after the document begins. Note that if the user has not clicked on the target element before 30 seconds elapse, the animation will never begin.
<animate begin="click" dur="2s" repeatDur="indefinite" end="30s" ... />
Using end
with an event value enables authors to end an
animation based on either an interactive event or a maximum active duration.
This is sometimes known as lazy interaction.
In this example, a presentation describes some factory processes. It uses animation to move an image around (e.g. against a background), demonstrating how an object moves from one part of a factory to another. Each step is a motion path, and set to repeat 3 times to make the point clear. Each animation can also be ended by clicking on some element "next" that allows the user to advance the presentation to the next step.
<img id="objectToMove" ... > <animateMotion id="step1" begin="0" dur="5s" repeatCount="3" end="next.click" path.../> <animateMotion id="step2" begin="step1.end" dur="5s" repeatCount="3" end="next.click" path.../> <animateMotion id="step3" begin="step2.end" dur="5s" repeatCount="3" end="next.click" path.../> <animateMotion id="step4" begin="step3.end" dur="5s" repeatCount="3" end="next.click" path.../> <animateMotion id="step5" begin="step4.end" dur="5s" repeatCount="3" end="next.click" path.../> </img>
In this case, the active end of each animation is defined to be the earlier of 15 seconds after it begins, or a click on "next". This lets the viewer sit back and watch, or advance the presentation at a faster pace.
This section is informative
The min/max attributes provide the author with a way to control the lower and upper bound of the element active duration.
This section is normative
If there is any error in the argument value syntax for
min
, the attribute will be ignored (as
though it were not specified).
The default value for min
is "0". This
does not constrain the active duration at all.
If there is any error in the argument value syntax for
max
, the attribute will be ignored (as
though it were not specified).
The default value for max
is "indefinite".
This does not constrain the active duration at all.
If the "media
" argument value is specified for either
min
or
max
on an element that does not define
media, the respective attribute
will be ignored (as though it were not specified).
If both min
and
max
attributes are specified then the
max
value must be greater than or equal
to the min
value. If this requirement
is not fulfilled then both attributes are ignored.
The rule to apply to compute the active duration of an element with
min
or
max
specified is the following: Each
time the active duration of an element is computed (i.e. for each interval
of the element if it begins more than once), this computation is made without
taking into account the min
and
max
attributes (by applying the algorithm
described in Computing the active
duration). The result of this step is checked against the
min
and
max
bounds. If the result is within
the bounds, this first computed value is correct. Otherwise two situations
may occur:
if the first computed duration is greater than the max value, the active
duration of the element is defined to be equal to the
max
value (see the first example below).
if the first computed duration is less than the
min
value, the active duration of the
element becomes equal to the min
value
and the behavior of the element is as follows :
if the repeating duration (or the simple duration if the element doesn't
repeat) of the element is greater than
min
then the element is played normally
for the (min
constrained) active duration.
(see the second and third examples below).
otherwise the element is played normally for its repeating duration (or simple
duration if the element does not repeat) and then is frozen or not shown
depending on the value of the fill
attribute (see the fourth and fifth examples below).
min
attribute and negative begin times
If an element is defined to begin before its parent (e.g. with a simple negative
offset value), the min
duration is measured
from the calculated begin time not the observed begin (see example 1 below).
This means that the min
value may have
no observed effect.
See also the section The min attribute and restart.
The table in Figure 4 shows the semantics of all possible combinations of
simple duration, repeatCount
and repeatDur
, and
end
. The following conventions are used in the table:
Additionally, the following rules must be followed in computing values:
end
is event-based or DOM-based, then an event
or method call that activates end
before the
duration specified by dur
and/or repeatCount
or
repeatDur
will cut short the active duration at the
end
activation time.end
cannot be resolved (e.g. when it is
event-based), the value is considered to be "indefinite" for the purposes
of evaluating the active duration. If and when the end value becomes
resolved, the active duration is reevaluated.Some of the rules and results that are implicit in the table, and that should be noted in particular are:
end
is specified but neither of repeatCount
or repeatDur
are specified, then the active duration is
defined as the minimum of the simple duration and the duration defined by
end
.end
and either (or both) of
repeatCount
or repeatDur
are specified, the
active duration is defined by the minimum duration defined by the
respective attributes.repeatCount
can specify).The following symbols are used in the table:
B
d
| Simple duration�d |
repeatCount |
repeatDur |
end |
Active Duration |
| defined | � | � | � | d |
| defined | defined | � | � | repeatCount *d |
| defined | � | defined | � | repeatDur |
| defined | � | � | defined | MIN(�d, end -B ) |
| defined | defined | defined | � | MIN(�repeatCount *d, repeatDur
) |
| defined | defined | � | defined | MIN(�repeatCount *d,
(�end -B�)) |
| defined | � | defined | defined | MIN(�repeatDur ,
(�end -B�)) |
| defined | defined | defined | defined | MIN(�repeatCount *d,
repeatDur , (�end -B�)) |
| indefinite | * | � | � | indefinite |
| indefinite | * | defined | � | repeatDur |
| indefinite | * | � | defined | end -B |
| indefinite | * | defined | defined | MIN(�repeatDur ,
(�end -B�)) |
| * | indefinite | � | � | indefinite |
| * | � | indefinite | � | indefinite |
| * | indefinite | indefinite | � | indefinite |
| * | indefinite | � | defined | end -B |
| * | � | indefinite | defined | end -B |
| * | indefinite | indefinite | defined | end -B |
repeatCount
and repeatDur
, and
end
.By default when an animation element ends, its effect is no longer applied to the presentation value for the target attribute. For example, if an animation moves an image and the animation element ends, the image will "jump back" to its original position.
<img top="3" ...> <animate begin="5s" dur="10s" attributeName="top" by="100"/> </img>
The image will appear stationary at the top value of "3" for 5 seconds,
then move 100 pixels down in 10 seconds. 15 seconds after the document begin,
the animation ends, the effect is no longer applied, and the image jumps back
from 103 to 3 where it started (i.e., to the underlying value of the
top
attribute).
The fill
attribute can be used to maintain the value of the
animation after the active duration of the animation element ends:
<img top="3" ...> <animate begin= "5s" dur="10s" attributeName="top" by="100" fill="freeze" /> </img>
The animation ends 15 seconds after the document begin, but the image remains at the top value of 103. The attribute freezes the last value of the animation for the remainder of the document duration.
The freeze behavior of an animation is controlled using the "fill "attribute:
fill
=
"freeze | remove"If the active duration cuts short the simple duration (including the case of partial repeats), the effect value of a frozen animation is defined by the shortened simple duration. In the following example, the animation function repeats two full times and then again for one-half of the simple duration. In this case, the value while frozen will be 15:�
<animate from="10" to="20" dur="4s" repeatCount="2.5" fill="freeze" .../>
In the following example, the dur
attribute is missing, and so
the simple duration is indefinite. The active duration is constrained by
end
to be 10 seconds. Since interpolation is not defined, the
value while frozen will be 10:
<animate from="10" to="20" end="10s" fill="freeze" .../>
SMIL Animation specifies that fill="freeze"
remains in effect
for the remainder of the document, or until the element is restarted. In the
more general SMIL timing model that allows time containers, the duration of
the freeze effect is controlled by the time container, and never extends past
the end of the time container simple duration. While this may appear to
conflict, the SMIL Animation definition of fill="freeze"
is
consistent with the SMIL timing model. It is simply the case that in SMIL
Animation, the document is the only "time container", and so the effect is as
described above.
It is frequently useful to define animation as an offset or delta to an attribute's value, rather than as absolute values. A simple "grow" animation can increase the width of an object by 10 pixels:
<rect width="20px" ...> <animate attributeName="width" from="0px" to="10px" dur="10s" additive="sum"/> </rect>
The width begins at 20 pixels, and increases to 30 pixels over the course of 10 seconds.� If the animation were declared to be non-additive, the same from and to values would make the width go from 0 to 10 pixels over 10 seconds.
In addition, many complex animations are best expressed as combinations of simpler animations. A "vibrating" path, for example, can be described as a repeating up and down motion added to any other motion:
<img ...> <animateMotion from="0,0" to="100,0" dur="10s" /> <animateMotion values="0,0; 0,5; 0,0" dur="1s" repeatDur="10s" additive="sum"/> </img>
When there are multiple animations defined for a given attribute that overlap at any moment, the two either add together or one overrides the other. Animations overlap when they are both either active or frozen at the same moment. The ordering of animations (e.g. which animation overrides which) is determined by a priority associated with each animation. The animations are prioritized according to when each begins. The animation first begun has lowest priority and the most recently begun animation has highest priority.
Higher priority animations that are not additive will override all earlier (lower priority) animations, and simply set the attribute value.� Animations that are additive apply (i.e. add to) to the result of the earlier-activated animations.�For details on how animations are combined, see The animation sandwich model.
The additive behavior of an animation is controlled by the
additive
attribute:
additive
= "replace | sum"by
and
to
, as described below.Additive animation is defined for numeric attributes and other data types for which some addition function is defined. This includes numeric attributes for concepts such as position, widths and heights, sizes, etc. This also includes color (refer to The animateColor element), and may include other data types as specified by the host language.
It is often useful to combine additive animations and fill
behavior, for example when a series of motions are defined that should build
upon one another:
<img ...> <animateMotion begin="0" dur="5s" path="[some path]" additive="sum" fill="freeze" /> <animateMotion begin="5s" dur="5s" path="[some path]" additive="sum" fill="freeze" /> <animateMotion begin="10s" dur="5s" path="[some path]" additive="sum" fill="freeze" /> </img>
The image moves along the first path, and then starts the second path from the end of the first, then follows the third path from the end of the second, and stays at the final point.
While many animations of numerical attributes will be additive, this is not always the case. As an example of an animation that is defined to be non-additive, consider a hypothetical extension animation "mouseFollow" that causes an object to track the mouse.�
<img ...> <animateMotion dur=10s repeatDur="indefinite" path="[some nice path]" /> <mouseFollow begin="mouseover" dur="5s" additive="replace" fill="remove" /> </img>
The mouse-tracking animation runs for 5 seconds every time the user mouses
over the image. It cannot be additive, or it will just offset the motion path
in some odd way. The mouseFollow
needs to override the
animateMotion
while it is active. When the
mouseFollow
completes, its effect is no longer applied and the
animateMotion
again controls the presentation value for
position.
In addition, some numeric attributes (e.g., a telephone number attribute) may not sensibly support addition - it is left to the host language to specify which attributes support additive animation. Attribute types such as strings and Booleans for which addition is not defined, cannot support additive animation.
The attribute values to
and by
, used to describe the animation function, can override the
additive
attribute in certain cases:
by
is used without
from
, (by animation) the animation
is defined to be additive (i.e., the equivalent of
additive="sum"
).to
is used without
from
, (to animation) and if the
attribute supports addition, the animation is defined to be a kind of mix
of additive and non-additive. The underlying value is used as a starting
point as with additive animation, however the ending value specified by
the to
attribute overrides the underlying
value as though the animation was non-additive.For the hybrid case of a to-animation, the animation function
f(t)
is defined in terms of the underlying
value, the specified to
value, and the current value of
t
(i.e. time) relative to the simple duration
d
.
d
t
v
curv
tof(t) =
v
cur +
((
v
to - v
cur) *
(t/d))
Note that if no other (lower priority) animations are active or frozen,
this defines simple interpolation. However if another animation is
manipulating the base value, the to-animation will add to the effect
of the lower priority, but will dominate it as it nears the end of the simple
duration, eventually overriding it completely. The value for
F(t)
when a to-animation is frozen (at
the end of the simple duration) is just the to
value. If a
to-animation is frozen anywhere within the simple duration (e.g.,
using a repeatCount of "2.5"), the value for
F(t)
when the animation is frozen is the value
computed for the end of the active duration. Even if other, lower priority
animations are active while a to-animation is frozen, the value for
F(t)
does not change.
Multiple to-animations will also combine according to these semantics. The higher-priority animation will "win", and the end result will be to set the attribute to the final value of the higher-priority to-animation.
Multiple by-animations combine according to the general rules for additive animation and the animation sandwich model.
The use of from
values does not imply either additive no
non-additive animation, and both are possible. The from
value for
an additive animation is simply added to the underlying value, just as for the
initial value is in animations specified with a values
list.
Additive behavior for from-to and from-by animations is
controlled by the additive
attribute, as in the general case.
For an example of additive to-animation, consider the following two additive animations. The first, a by-animation applies a delta to attribute "x" from 0 to -10. The second, a to-animation animates to a final value of 10.
<foo x="0" .../> <animate id="A1" attributeName="x" by="-10" dur="10s" fill="freeze" /> <animate id="A2" attributeName="x" to="10" dur="10s" fill="freeze" /> </foo>
The presentation value for "x" in the example above, over the course of the
10 seconds is presented in Figure 5 below. These values are simply computed
using the formula described above. Note that the value for
F(t)
for A2 is the presentation value for
"x".
�
| Time | F(t) for A1 |
F(t) for A2 |
| �0 | 0 | 0 |
| �1 | -1 | 0.1 |
| �2 | -2 | 0.4 |
| �3 | -3 | 0.9 |
| �4 | -4 | 1.6 |
| �5 | -5 | 2.5 |
| �6 | -6 | 3.6 |
| �7 | -7 | 4.9 |
| �8 | -8 | 6.4 |
| �9 | -9 | 8.1 |
| 10 | -10 | 10 |
The accumulate
attribute should not be confused with the�
additive
attribute. The additive
attribute defines
how an animation is combined with other animations and the base value of the
attribute.� The accumulate
attribute defines only how the
animation function interacts with itself, across repeat iterations.
Typically, authors expect cumulative animations to be additive (as in the
examples described for accumulate
above), but this is not required. The following example
is cumulative but not additive.
<img ...> <animate dur="10s" repeatDur="indefinite" attributeName="top" from="20" by="10" additive="replace" accumulate="sum" /> </img>
The animation overrides whatever original value was set for "top", and begins at the value 20. It moves down by 10 pixels to 30, then repeats. It is cumulative, so the second iteration starts at 30 and moves down by another 10 to 40. Etc.
When a cumulative animation is also defined to be additive, the two
features function normally. The accumulated effect for
F(t)
is used as the value for the animation, and
is added to the underlying value for the target attribute. Refer also to The animation sandwich model.
When an animation is defined to begin at a simple offset (e.g.
begin="5s"
), there is an unequivocal time when the element
begins. However, if an animation is defined to begin relative to an event
(e.g. begin="foo.click"
), the event can happen at any time, and
moreover can happen more than once (e.g., if the user clicks on "foo"
several times). In some cases, it is desirable to restart an
animation if a second begin event is received. In other cases, an author may
want to preclude this behavior. The restart
attribute controls
the circumstances under which an animation is restarted:
restart
= "always | whenNotActive |
never"Note that there are several ways that an animation may be restarted. The
behavior (i.e. to restart or not) in all cases is controlled by the
restart
attribute. The different restart cases are:
begin
specified as an event-value can be
restarted when the named event fires multiple times.begin
specified as a syncbase value,
where the syncbase element can restart. When an animation restarts, other
animations defined to begin relative to the begin or active end of the
restarting animation may also restart (subject to the value of
restart
on these elements).begin
specified as "indefinite" can be
restarted when the DOM methods beginElement()
or
beginElementAt()
are called repeatedly.When an animation restarts, the defining semantic is that it behaves as
though this were the first time the animation had begun, independent of any
earlier behavior. The animation effect F(t)
is
defined independent of the restart behavior. Any effect of an animation
playing earlier is no longer applied, and only the current animation effect
F(t)
is applied.
If an additive animation is restarted while it is active or frozen, the
previous effect of the animation (i.e. before the restart) is no longer
applied to the attribute. Note in particular that cumulative animation is
defined only within the active duration of an animation. When an animation
restarts, all accumulated context is discarded, and the animation effect
F(t)
begins accumulating again from the first
iteration of the restarted active duration.
When an active element restarts, the element first ends the active duration, propagates this to time dependents and raises an endEvent in the normal manner (see also Evaluation of begin and end time lists).
For details on when and how the restart
attribute is evaluated, see Evaluation
of begin and end time lists.
Note that using restart can also allow the author to define a single UI event to both begin and end an element, as follows:
<img ...> <animate id="foo" begin="click" dur="2s" repeatDur="indefinite" end="click" restart="whenNotActive" ... /> </img>
If "foo" were defined with the default restart behavior "always", a second click on the image would simply restart the animation. However, since the second click cannot restart the animation when restart is set to "whenNotActive", the click will just end the active duration and stop the animation. This is sometimes described as "toggle" activation. See also Event sensitivity and Unifying event-based and scheduled timing.
This section is normative
When an element restarts, certain state is "reset":
SMIL Animation specifies that restart="never"
precludes
restart for the remainder of the document duration. In the more general SMIL
2.0 [SMIL20] timing model that allows
time containers, the duration of the restart="never"
semantic is
defined by the time container, and only extends to the end of the time
container simple duration. While this may appear to conflict, the SMIL
Animation definition of restart="never"
is consistent with the
SMIL timing model. It is simply the case that in SMIL Animation, the document
is the only "time container", and so the effect is as described above.
The specific error handling mechanisms for each attribute are described with the individual syntax descriptions.� Some of these specifications describe the behavior of an animation with syntax errors as "having no effect".� This means that the animation will continue to behave normally with respect to timing, but will not manipulate any presentation value, and so will have no visible impact upon the presentation.�
In particular, this means that if other animation elements are defined to begin or end relative to an animation that "has no effect", the other animation elements will begin and end as though there were no syntax errors. The presentation runtime may indicate an error, but need not halt presentation or animation of the document.�
Some host languages and/or runtimes may choose to impose stricter error handling (see also Error handling semantics for a discussion of host language issues with error handling). Authoring environments may also choose to be more intrusive when errors are detected.
When an animation is running, it does not actually change the attribute values in the DOM.� The animation runtime should ideally maintain a presentation value for any target attribute, separate from the DOM, CSS, or other object model (OM) in which the target attribute is defined. The presentation value is reflected in the display form of the document. The effect of animations is to manipulate this presentation value, and not to affect the underlying DOM or CSS OM values.
The remainder of this discussion uses the generic term OM for both the XML DOM [DOM-Level-2] as well as the CSS-OM. If an implementation does not support an object model, it should ideally maintain the original value as defined by the document as well as the presentation value; for the purposes of this section, we will consider this original value to be equivalent to the value in the OM.
In some implementations of DOM, it may be difficult or impractical to main a presentation value as described. CSS values should always be supported as described, as the CSS-OM provides a mechanism to do so. In implementations that do not support separate presentation values for general XML DOM properties, the implementation must at least restore the original value when animations no longer have an effect.�
The rest of this discussion assumes the recommended approach using a separate presentation value.
The model accounting for the OM and concurrently active or frozen animations for a given attribute is described as a "sandwich", a loose analogy to the layers of meat and cheeses in a "submarine sandwich" (a long sandwich made with many pieces of meats and cheese layered along the length of the bread). In the analogy, time is associated with the length of the sandwich, and each animation has its duration represented by the length of bread that the layer covers. On the bottom of the sandwich is the base value taken from the OM. Each active (or frozen) animation is a layer above this. The layers (i.e. the animations) are placed on the sandwich both in time along the length of the bread, as well as in order according to priority, with higher priority animations placed above (i.e. on top of) lower priority animations. At any given point in time, you can take a slice of the sandwich and see how the animation layers stack up.
Note that animations manipulate the presentation value coming out of the OM in which the attribute is defined, and pass the resulting value on to the next layer of document processing. This does not replace or override any of the normal document OM processing cascade.�
Specifically, animating an attribute defined in XML will modify the presentation value before it is passed through the style sheet cascade, using the XML DOM value as its base. Animating an attribute defined in a style sheet language will modify the presentation value passed through the remainder of the cascade.�
In CSS2 and the DOM 2 CSS-OM, the terms "specified", "computed" and
"actual" are used to describe the results of evaluating the syntax, the
cascade and the presentation rendering. When animation is applied to CSS
properties of a particular element, the base value to be animated is read
using the (readonly) getComputedStyle()
method on that element.
The values produced by the animation are written into an override stylesheet
for that element, which may be obtained using the
getOverrideStyle()
method. These new values then affect the
cascade and are reflected in a new computed value (and thus, modified
presentation). This means that the effect of animation overrides all style
sheet rules, except for user rules with the !important
property.
This enables !important
user style settings to have priority over
animations, an important requirement for accessibility. Note that the
animation may have side effects upon the document layout. See also the [CSS2] specification (the terms are defined in section
6.1), and the [DOM2CSS] specification (section
5.2.1).
Within an OM, animations are prioritized according to when each begins. The animation first begun has lowest priority and the most recently begun animation has highest priority. When two animations start at the same moment in time, the activation order is resolved as follows:
Note that if an animation is restarted (see also Restarting animations), it will always move to the top of the priority list, as it becomes the most recently activated animation. That is, when an animation restarts, its layer is pulled out of the sandwich, and added back on the very top.� In contrast, when an element repeats the priority is not affected (repeat behavior is not defined as restarting).
Each additive animation adds its effect to the result of all sandwich layers below. A non-additive animation simply overrides the result of all lower sandwich layers. The end result at the top of the sandwich is the presentation value that must be reflected in the document view.
Some attributes that support additive animation have a defined legal range for values (e.g., an opacity attribute may allow values between 0 and 1). In some cases, an animation function may yield out of range values. It is recommended that implementations clamp the results to the legal range as late as possible, before applying them to the presentation value. Ideally, the effect of all the animations active or frozen at a given point should be combined, before any clamping is performed. Although individual animation functions may yield out of range values, the combination of additive animations may still be legal. Clamping only the final result and not the effect of the individual animation functions provides support for these cases. Intermediate results may be clamped when necessary although this is not optimal. The host language must define the clamping semantics for each attribute that can be animated.� As an example, this is defined for The animateColor element.�
Initially, before any animations for a given attribute are active, the presentation value will be identical to the original value specified in the document (the OM value).
When all animations for a given attribute have completed and the associated
animation effects are no longer applied, the presentation value will again be
equal to the OM value. Note that if any animation is defined with
fill="freeze"
, the effect of the animation will be applied as
long as the document is displayed, and so the presentation value will reflect
the animation effect until the document end. Refer also to the section "Freezing animations".
Some animations (e.g. animateMotion
) will implicitly
target an attribute, or possibly several attributes (e.g. the "posX" and
"posY" attributes of some layout model). These animations must be combined
with any other animations for each attribute that is affected. Thus for example, an
animateMotion
animation may be in more than one animation
sandwich (depending upon the layout model of the host language). For animation
elements that implicitly target attributes, the host language designer must
specify which attributes are implicitly targeted, and the runtime must
accordingly combine animations for the respective attributes.�
Note that any queries (via DOM interfaces) on the target attribute will reflect the OM value, and will not reflect the effect of animations. Note also that the OM value may still be changed via the OM interfaces (e.g. using script).�While it may be useful or desired to provide access to the final presentation value after all animation effects have been applied, such an interface is not provided as part of SMIL Animation. A future version may address this.
Although animation does not manipulate the OM values, the document display must reflect changes to the OM values. Host languages can support script languages that can manipulate attribute values directly in the OM. If an animation is active or frozen while a change to the OM value is made, the behavior is dependent upon whether the animation is defined to be additive or not, as follows: (see also the section Additive animation).�
Throughout this specification, animation is described as a function of "time". In particular, the animation function is described as producing a value for any "time" in the range of the simple duration. However, the simple duration can be repeated, and the animation can begin and restart in many ways.� As such, there is no direct relationship between the "time" that an animation function uses, and the real world concept of time as reflected on a clock.
When a keySplines
attribute is used to adjust the pacing
between values in an animation, the semantics can be thought of as changing
the pace of time in the given interval. An equivalent model is that
keySplines
simply changes the pace at which interpolation
progresses through the given interval. The two interpretations are
equivalent mathematically, and the significant point is that the notion of
"time" as defined for the animation function f(t)
should not be construed as real world clock time. For the
purposes of animation, "time" can behave quite differently from real world
clock time.
SMIL Animation assumes the most common model for interval timing. This describes intervals of time (i.e. durations) in which the begin time of the interval is included in the interval, but the end time is excluded from the interval. This is also referred to as end-point exclusive timing. This model makes arithmetic for intervals work correctly, and provides sensible models for sequences of intervals.
In the real world, this is equivalent to the way that seconds add up to minutes, and minutes add up to hours.� Although a minute is described as 60 seconds, a digital clock never shows more than 59 seconds. Adding one more second to "00:59" does not yield "00:60" but rather "01:00", or 1 minute and 0 seconds. The theoretical end time of 60 seconds that describes a minute interval is excluded from the actual interval.
In the world of media and timelines, the same applies: Let A be a video, a clip of audio, or an animation. Assume "A" begins at 10 and runs until 15 (in any units - it does not matter). If "B" is defined to follow "A", then it begins at 15 (and not at 15 plus some minimum interval). When an animation runtime engine actually renders out frames (or samples for audio), and must render the time "15", it should not show both a frame of "A" and a frame of "B", but rather should only show the new element "B". This is the same for audio, or for any interval on a timeline. If the model does not use endpoint-exclusive timing, it will draw overlapping frames, or have overlapping samples of audio, of sequenced animations, etc.
Note that transitions from "A" to "B" also adhere to the interval timing model. They do require that "A" not actually end at 15, and that both elements actually overlap. Nevertheless, the "A" duration is simply extended by the transition duration (e.g. 1 second). This new duration for "A" is also endpoint exclusive - at the end of this new duration, the transition will be complete, and only "B" should be rendered - "A" is no longer needed.
For animation, several results of this are important: the definition of repeat, and the value sampled during the "frozen" state.
When repeating an animation, the arithmetic follows the end-point exclusive model. Consider the example:
� <animation dur="4s" repeatCount="4" .../>
At time 0, the simple duration is sampled at 0, and the first value is applied.� This is the inclusive begin of the interval. The simple duration is sampled normally up to 4 seconds. However, the appropriate way to map time on the active duration to time on the simple duration is to use the remainder of division by the simple duration:
� simpleTime = REMAINDER( activeTime, d
)�
or
� F(t) = f( REMAINDER( t, d ) )�
where t is within the active duration
Note: REMAINDER( t, d )
is defined as t -
d*floor(t/d)
Using this, a time of 4 (or 8 or 12) maps to the time of 0 on the simple duration. The endpoint of the simple duration is excluded from (i.e. not actually sampled on) the simple duration.
This implies that the last value of an animation function
f(t)
may never actually be applied (e.g. for a
linear interpolation).� This may be true in the case of an animation that does
not repeat and does not specify fill="freeze"
.
However, in the following example, the appropriate value for the frozen state
is clearly the "to" value:
� <animation from="0" to="5" dur="4s" fill=freeze
.../>
This does not break the interval timing model, but does require an
additional qualification for the animation function
F(t)
while in the frozen state:
f(t)
.The definition of accumulate also aligns to this
model. The arithmetic is effectively inverted and values accumulate by adding
in a multiple of the last value defined for the animation function
f(t)
.
SMIL Animation describes extensions to SMIL 1.0 to support interactive timing of animation elements. These extensions allow the author to specify that an animation should begin or end in response to an event (such as a user-input event like "click"), or to a hyperlink activation, or to a DOM method call.
The syntax to describe this uses event-value specifications and the special
argument value "indefinite" for the begin
and end
attribute values. Event values describe user interface and other events. DOM
method calls to begin or end an animation require that the associated
attribute use the special value "indefinite". A hyperlink can also be targeted
at an animation element that specifies begin="indefinite"
. The
animation will begin when the hyperlink is activated (usually by the user
clicking on the anchor). It is not possible to directly control the active end
of an animation using hyperlinks.
The current model represents an evolution from earlier multimedia runtimes. These were typically either pure, static schedulers or pure event-based systems.� Scheduler models present a linear timeline that integrates both discrete and continuous media.�� Scheduler models tend to be good for storytelling, but have limited support for user-interaction. Event-based systems, on the other hand, model multimedia as a graph of event bindings.� Event-based systems provide flexible support for user-interaction, but generally have poor scheduling facilities; they are best applied to highly interactive and experiential multimedia.
The SMIL 1.0 model is primarily a scheduling model, but with some flexibility to support continuous media with unknown duration. User interaction is supported in the form of timed hyperlinking semantics, but there was no support for activating individual elements via interaction.
To integrate interactive content into SMIL timing, the SMIL 1.0 scheduler model is extended to support several new concepts: indeterminate timing, and activation of the element.
With indeterminate timing, an element has an undefined begin or
end time.� The element still exists within the constraints of the document,
but the begin or end time is determined by some external activation.
Activation may be event-based (such as by a user-input event), hyperlink based
(with a hyperlink targeted at the element), or DOM based (e.g., by a call to
the beginElement()
method).� From a scheduling perspective, the
time is described as unresolved before the activation. Once the
element begin or end has been activated, the time is resolved.
The event-activation support provides a means of associating an event with the begin or active end time for an element.� When the event is raised (e.g., when the user clicks on something), the associated time is resolved to a determinate time.� For event-based begin times, the element becomes active (begins to play) at the time that the event is raised (plus any specified offset). The element plays from the beginning of the animation function.� For event-based active end times, the element becomes inactive (stops playing) when the associated event is raised.
Note that an event based end
will not be activated until the
element has already begun. Any specified end
event is ignored
before the element begins. See also Event sensitivity.
Note that when an element restarts, any event-based end time that was resolved in the previous instance of play, will be reset to the unresolved state.
Related to event-activation is link-activation.� Hyperlinking has defined semantics in SMIL 1.0 to seek a document to a point in time. When combined with indeterminate timing, hyperlinking yields a variant on interactive content. A hyperlink can be targeted at an element that does not have a scheduled begin time. When the link is traversed, the element begins. The details of when hyperlinks activate an element, and when they seek the document timeline are presented in the next section.�
Note that hyperlink activation only applies to an element begin time, and not to the element end. Event and DOM based activation can apply to both begin and end times.
Note that elements can define the begin
or end
relative to another element, using a syncbase-value (the begin or end of another
element). If the syncbase element is in turn defined with, for example,
event-based times, the syncbase value is not resolved, and so the
begin
or end
of the current element is also
unresolved. For a begin
or end
time to be resolved,
any referenced syncbase value must also be resolved.
This section is informative
The timing model supports synchronization based upon unpredictable events such as DOM events or user interface generated events. The model for handling events is that the notification of the event is delivered to the timing element, and the timing element uses a set of rules to resolve any synchronization dependent upon the event.
This section is normative
The semantics of element sensitivity to events are described by the following set of rules:
It is important to notice that in no case is a single event occurrence used to resolve both a begin and end time on the same element.
The timing model and the user event model are largely orthogonal. While the timing model does reference user events, it does not define how these events are generated, and in particular does not define semantics of keyboard focus, mouse containment, "clickability", and related issues. Because timing can affect the presentation of elements, it may impact the rules for user event processing, however it only has an effect to the extent that the presentation of the element is affected.
Hyperlinking semantics must be specifically defined for animation in order to ensure predictable behavior. Earlier hyperlinking semantics, such as those defined by SMIL 1.0 are insufficient because they do not handle indeterminate and interactive timing. Here we extend SMIL 1.0 semantics for use in presentations that include animations with indeterminate and interactive timing.
Hyperlinking behavior is described as seeking the document. To seek in this sense means to advance the document timeline to the specified time.�
A hyperlink may be targeted at an animation element by specifying the value
of the id
attribute of an animation element in the fragment part
of the link locator. Traversing a hyperlink that refers to an animation will
behave according to the following rules:
beginElement()
method call), seek the document time (forward
or back, as needed) to the earliest resolved begin time of the target
element. Note that the begin time may be
resolved as a result of an earlier hyperlink, DOM or event activation.
Once the begin time is resolved, hyperlink traversal always seeks. begin="indefinite"
and just resolve begin time to the
current document time.Note that hyperlink activation does not introduce any restart behavior, and
is not subject to the restart
attribute semantics.
If a seek of the document presentation time is required, it may be necessary to seek either forward or backward, depending upon the resolved begin time of the element and the current time at the moment of hyperlink traversal.�
After seeking a document forward, the document should be in the same state as if the user had allowed the presentation to run normally from the current time until reaching the animation element begin time (but had otherwise not interacted with the document). In particular, seeking the presentation time forward should also cause any other animation elements that have resolved begin times between the current time and the seeked-to time to begin. These elements may have ended, or may still be active or frozen at the seeked-to time, depending upon their begin times and active durations. Also any animation elements currently active at the time of hyperlinking should "fast-forward" over the seek interval. These may end or may be still active or frozen at the seeked-to time, depending upon their active durations. The net effect is that seeking forward to a presentation time puts the document into a state identical to that as if the document presentation time advanced undisturbed to reach the seek time.
If the resolved begin time for an animation element that is the target of a hyperlink is before the current presentation time, the presentation must seek backwards. Seeking backwards will rewind any animations active during the seek interval and will turn off any animations that are resolved to begin at a time after the seeked-to time. Note that resolved begin times (e.g. a begin associated with an event) are not cleared or lost by seeking to an earlier time. Subject to the rules above for hyperlinks that target animation elements, hyperlinking to elements with resolved begin times will function normally, advancing the presentation time forward to the previously resolved time.
These hyperlinking semantics assume that a record is kept of the resolved begin time for all animation elements, and this record is available to be used for determining the correct presentation time to seek to. Once resolved, begin times are not cleared. However, they can be overwritten by subsequent resolutions driven by multiple occurrences of an event (i.e. by restarting). For example:�
<animate id="A" begin="10s" .../> <animate id="B" begin="A.begin+5s" .../> <animate id="C" begin="click" .../> <animate id="D" begin="C.begin+5s" .../> ... <a href="#D">Start the last animation</a>
The begin time of elements "A" and "B" can be immediately resolved to be at 10 and 15 seconds respectively. The begin of elements "C" and "D" are unresolved when the document starts. Therefore activating the hyperlink will have no effect upon the presentation time or upon elements "C" and "D". Now, assume that "C" is clicked at 25 seconds into the presentation. The click on "C" in turn resolves "D" to begin at 30 seconds. From this point on, traversing the hyperlink will cause the presentation time to be seeked to 30 seconds.
If at 60 seconds into the presentation, the user again clicks on "C", "D" will become re-resolved to a presentation time of 65 seconds. Subsequent activation of the hyperlink will result in the seeking the presentation to 65 seconds.
There are several cases in which times may change as the document is presented. In particular, when an animation time is defined relative to an event, the time (i.e. the animation begin or active end) is resolved when the event occurs. Another case arises with restart behavior - both the begin and active end time of an animation can change when it restarts. Since the begin and active end times of one animation can be defined relative to the begin or active end of other animations, any changes to times must be propagated throughout the document.
When an animation "foo" has a begin or active end time that specifies a syncbase element (e.g. "bar" as below):
<rect ...> <animate id="bar" end="click" .../> <animate id="foo" begin="bar.end" .../> </rect>
we say that "foo" is a time-dependent of "bar" - that is, the "foo" begin time depends upon the active end of "bar".�
An element A is a time dependent of another element B if A specifies B as a syncbase element. In addition, if element A is a time dependent of element B, and if element B is a time dependent of element C (i.e., element B defines element C as a syncbase element), then element A is an indirect time dependent of element C.
When an element begins or ends, the time dependents of the element are effectively notified of the action, and the schedule for the time dependents may be affected. Note than an element must actually begin before any of the time dependents (dependent on the begin) are affected, and that an element must actually end before any of the time dependents (dependent on the end) are affected. This impacts the definition of the priority ordering of animation elements, as discussed in The animation sandwich model.
In the example above, any changes to the active end time of "bar" must be propagated to the begin of "foo". The effect of the changes depends upon the state of "foo" when the change happens, as detailed below.
If the begin time of an element is dependent upon another element (as for "foo" in the example), the resulting behavior when the syncbase element ("bar") propagates changes is determined as follows:
restart
attribute determines the behavior: if it is "always",
then the time dependent will restart; otherwise the propagated change is
ignored.restart
attribute determines
the behavior: if it is "always" or "whenNotActive", then the time
dependent will restart; otherwise the propagated change is ignored.Note that the semantic is directly analogous to event-base timing and the
restart
attribute.
If the end time of an element is dependent upon another element, the semantic is much simpler:
Another way to think of this is that the end time is always recalculated, but it will not affect the presentation unless the element is currently active, or unless the element begins (or restarts) after the change happens.
This section is normative
The syntax specifications are defined using EBNF notation as defined in [XML10]
In the syntax specifications that follow, allowed white space is indicated as "S", defined as follows (taken from the [XML10] definition for "S"):
S ::= (#x20 | #x9 | #xD | #xA)*
This section is normative
A begin-value-list is a semi-colon separated list of timing specifiers:
begin-value-list ::= begin-value (S
";"S
begin-value-list )? begin-value ::= (offset-value | syncbase-value | event-value | repeat-value | accessKey-value | wallclock-sync-value | "indefinite" )
This section is normative
An end-value-list is a semi-colon separated list of timing specifiers:
end-value-list ::= end-value (S
";"S
end-value-list )? end-value ::= (offset-value | syncbase-value | event-value | repeat-value | accessKey-value | wallclock-sync-value | "indefinite" )
Several of the timing specification values have a
similar syntax. In addition, XML ID attributes are allowed to contain the dot '.
'
separator character. The backslash character '\'
can be used to escape the dot separator within identifier and event-name
references. To parse an individual item in a value-list, the following approach
defines the correct interpretation.
'+'
or '-'
), the value should be
parsed as an offset value.
.
' separator characters preceded by a backslash '\
'
escape character. In addition, strip any leading backslash '\
'
escape character.
.
'
separator character, then the value should be parsed as an event-value
with an unspecified (i.e. default) eventbase-element.
.begin
"
or ".end
", then the value should be parsed as a syncbase-value.
\
' escape character after the '.
'
separator character should be removed.This approach allows implementations to treat the tokens wallclock and indefinite
as reserved element IDs, and begin, end
and marker as reserved event names, while retaining
an escape mechanism so that elements and events with those names may be
referenced.
Clock values have the following syntax:
Clock-value ::= ( Full-clock-value | Partial-clock-value | Timecount-value ) Full-clock-value ::= Hours ":" Minutes ":" Seconds ("." Fraction)? Partial-clock-value ::= Minutes ":" Seconds ("." Fraction)? Timecount-value ::= Timecount ("." Fraction)? (Metric)? Metric ::= "h" | "min" | "s" | "ms" Hours ::= DIGIT+; any positive number Minutes ::= 2DIGIT; range from 00 to 59 Seconds ::= 2DIGIT; range from 00 to 59 Fraction ::= DIGIT+ Timecount ::= DIGIT+ 2DIGIT ::= DIGIT DIGIT DIGIT ::= [0-9]
For Timecount values, the default metric suffix is "s" (for seconds). No embedded white space is allowed in clock values, although leading and trailing white space characters will be ignored.
The following are examples of legal clock values:
02:30:03
= 2 hours, 30 minutes and 3 seconds 50:00:10.25
= 50 hours, 10 seconds and 250 milliseconds
02:33
= 2 minutes and 33 seconds 00:10.5
= 10.5 seconds = 10 seconds and 500 milliseconds
3.2h
= 3.2 hours = 3 hours and 12
minutes 45min
= 45 minutes 30s
= 30 seconds 5ms
= 5 milliseconds 12.467
= 12 seconds and 467 millisecondsFractional values are just (base 10) floating point
definitions of seconds. The number of digits allowed is unlimited (although
actual precision may vary among implementations).
For example:
00.5s = 500 milliseconds 00:00.005 = 5 milliseconds
Offset values are used to specify when an element should begin or end relative to its syncbase.
This section is normative
An offset value has the following syntax:
offset-value ::= (( S "+" | "-" S )? ( Clock-value )
The implicit syncbase for an offset value is the document begin.
This section is normative
ID reference values are references to the value of an "id" attribute of another element in the document.
Id-value ::= IDREF
A syncbase value starts with a Syncbase-element term defining the value of an "id" attribute of another element referred to as the syncbase element.
This section is normative
A syncbase value has the following syntax:
Syncbase-value ::= (
Syncbase-element "." Time-symbol )
( S ("+"|"-") S
Clock-value )?
Syncbase-element ::= Id-value
Time-symbol ::= "begin" |
"end"
The syncbase element is qualified with one of the following time symbols:
Examples:
begin="x.end-5s"
: Begin 5 seconds before "x" ends
begin=" x.begin "
:
Begin when "x" begins
begin="x.begin + 1m"
: End 1 minute
after "x" begins
This section is informative
An Event value starts with an Eventbase-element term that specifies the event-base element. The event-base element is the element on which the event is observed. Given DOM event bubbling, the event-base element may be either the element that raised the event, or it may be an ancestor element on which the bubbled event can be observed. Refer to [DOM2Events] for details.
This section is normative
An event value has the following syntax:
Event-value
::= ( Eventbase-element "." )? Event-symbol
( S ("+"|"-") S
Clock-value )?
Eventbase-element ::= ID
The eventbase-element must be another element contained in the host document.
If the Eventbase-element term is missing, the event-base element is defined to be the target element of the animation,
The event value must specify an Event-symbol. This term specifies the name of the event that is raised on the Event-base element. The host language designer must specify which events can be specified.
If an integrating language specifies no supported events, the event-base time value is effectively unsupported for that language.
If the host language allows dynamically created events (as supported by DOM-Level2-Events [DOM2Events]), all possible Event-symbol names cannot be specified and so unrecognized names may not be considered errors.
Unless explicitly specified by a host language, it is not considered an error to specify an event that cannot be raised on the Event-base element (such as click for audio or other non-visual elements). Since the event will never be raised on the specified element, the event-base value will never be resolved.
The last term specifies an optional offset-value that is an offset from the time of the event.
This section is informative
This module defines several events that may be included
in the supported set for a host language, including beginEvent
and endEvent
.
These should not be confused with the syncbase time values. See the section on
Events and event model.
The semantics of event-based timing are detailed in Unifying Scheduling and Interactive Timing.
Examples:
begin=" x.load "
: Begin when "load" is observed on "x"
begin="x.focus+3s"
:
Begin 3 seconds after an "focus" event on "x"
begin="x.endEvent+1.5s"
: Begin 1 and a half
seconds after an "endEvent" event on "x"
begin="x.repeat"
: Begin each time a repeat
event is observed on
"x"
Repeat values are a variant on event values that support
a qualified repeat event. The repeat
event defined in
Events and event model allows an additional suffix to qualify the event based upon
an iteration value.
A repeat value has the following syntax:
Repeat-value ::= ( Eventbase-element "." )? "repeat(" iteration ")"
( S ("+"|"-") S Clock-value )?
iteration ::= DIGIT+
If this qualified form is used, the eventbase value will only be resolved when a repeat is observed that has a iteration value that matches the specified iteration.
The qualified repeat event syntax allows an author to respond only to an individual repeat of an element.
The following example describes a qualified repeat eventbase value:
<animate id="foo" repeatCount="10" end="endAnim.click" ... /> <img id="endAnim" begin="foo.repeat(2)" .../>
The "endAnim" image will appear when the animate element "foo" repeats the second time. This example allows the user to stop the animation after it has played though at least twice.
AccessKey values allow an author to tie a begin or end time to a particular keypress, independent of focus issues. It is modeled on the HTML accessKey support. Unlike with HTML, user agents should not require that a modifier key (such as "ALT") be required to activate an access key.
An access key value has the following syntax:
AccessKey-value ::= "accessKey("
character ")"
The character is a single character from [ISO10646].
( S ("+"|"-") S
Clock-value )?
The time value is defined as the time that the access key character is input by the user.
This section is informative
Wallclock-sync values have the following syntax. The values allowed are based upon several of the "profiles" described in [DATETIME], which is based upon [ISO8601].
This section is normative
wallclock-val ::= "wallclock(" S (DateTime | WallTime) S ")" DateTime ::= Date "T" WallTime Date ::= Years "-" Months "-" Days WallTime ::= (HHMM-Time | HHMMSS-Time)(TZD)? HHMM-Time ::= Hours24 ":" Minutes HHMMSS-Time ::= Hours24 ":" Minutes ":" Seconds ("." Fraction)? Years ::= 4DIGIT; Months ::= 2DIGIT; range from 01 to 12 Days ::= 2DIGIT; range from 01 to 31 Hours24 ::= 2DIGIT; range from 00 to 23 4DIGIT ::= DIGIT DIGIT DIGIT DIGIT TZD ::= "Z" | (("+" | "-") Hours24 ":" Minutes )
This section is informative
Complete date plus hours and minutes: YYYY-MM-DDThh:mmTZD (e.g. 1997-07-16T19:20+01:00) Complete date plus hours, minutes and seconds: YYYY-MM-DDThh:mm:ssTZD (e.g. 1997-07-16T19:20:30+01:00) Complete date plus hours, minutes, seconds and a decimal fraction of a second YYYY-MM-DDThh:mm:ss.sTZD (e.g. 1997-07-16T19:20:30.45+01:00)
Note that the Minutes, Seconds, Fraction, 2DIGIT and DIGIT syntax is as defined for Clock-values. Note that white space is not allowed within the date and time specification.
This section is normative
There are three ways of handling time zone offsets:
The presentation engine must be able to convert wallclock-values to a time within the document.
This section is informative
Note that the resulting begin or end time may be before the begin, or after end of the parent time container. This is not an error, but the time container constraints still apply. In any case, the semantics of the begin and end attribute govern the interpretation of the wallclock value.
This section is informative
Animation elements can have multiple begin and end values. We need to specify the semantics associated with multiple begin and end times, and how a dynamic timegraph model works with these multiple times.
The model is based around the idea of intervals for each element. An interval is defined by a begin and an end time. As the timegraph is played, more than one interval may be created for an element with multiple begin and end times. At any given moment, there is one current interval associated with each element. Intervals are created by evaluating a list of begin times and a list of end times, each of which is based upon the conditions described in the begin and end attributes for the element.
The list of begin times and the list of end times used to calculate new intervals are referred to as lists of "instance times". Each instance time in one of the lists is associated with the specification of a begin or end condition defined in the attribute syntax. Some conditions - for example offset-values - only have a single instance in the list. Other conditions may have multiple instances if the condition can happen more than once. For example a syncbase-value can have multiple instance times if the syncbase element has played several intervals, and an event-value may have multiple instance times if the event has happened more than once.�
The instance times lists for each element are initialized when the timegraph is initialized, and exist for the entire life of the timegraph. In this version of the time model without time containers, instance times remain in the lists forever, once they have been added. For example, times associated with event-values are only added when the associated event happens, but remain in the lists thereafter. Similarly, Instance times for syncbase-values are added to the list each time a new interval is created for the syncbase element, and remain in the list.
When the timegraph is initialized, each element creates a first current interval. The begin time will generally be resolved, but the end time may often be unresolved.�If the element can restart while active, the current interval can end (early) at the next begin time. This interval will play, and then when it ends, the element will review the lists of begin and end instance times. If the element should play again, another interval will be created and this new interval becomes the current interval. The history of an element can be thought of as a set of intervals.�
Because the begin and end times may depend on other times that can change, the current interval is subject to change, over time. For example, if any of the instance times for the end changes while the current interval is playing, the current interval end will be recomputed and may change. Nevertheless, once a time has happened, it is fixed. That is, once the current interval has begun, its begin time can no longer change, and once the current interval has ended, its end time can no longer change. For an element to restart, it must end the current interval and then create a new current interval to effect the restart.
When a begin or end condition defines a time dependency to another element (e.g. with a syncbase-value), the time dependency is generally thought of as a relationship between the two elements. This level of dependency is important to the model when an element creates a new current interval. However, for the purposes of propagating changes to individual times, time dependencies are more specifically a dependency from a given interval of the syncbase element to a particular instance time in one of the dependent element's instance time lists. Since only the current interval's begin and end times can change, only the current interval will generate time-change notices and propagate these to the dependent instance times.
When this section refers to the begin and end times for an element, the times are described as being in document time (relative to the document begin). All sync-arcs, event arcs, wallclock values, etc. must be converted to this time space for easy comparison.
Cycles in the timegraph must be detected and broken to ensure reasonable functioning of the implementation. A model for how to do this in the general case is described. A mechanism to support certain useful cyclic dependencies falls out of the model.
The rest of this section details the semantics of the instance times lists, the element life cycle, and the mechanisms for handling dependency relationships and cycles.
Instance lists are associated with each element, and exist for the duration of the document (i.e., there is no life cycle for instance lists). Instance lists may change, and some times may be added and removed, but� the begin and end instance times lists are persistent.
Each element can have a begin attribute that defines one or more conditions that can begin the element. In addition, the timing model describes a set of rules for determining the end of the element, including the effects of an end attribute that can have multiple conditions. In order to calculate the times that should be used for a given interval of the element, we must convert the begin times and the end times into parent simple time, sort each list of times (independently), and then find an appropriate pair of times to define an interval.
The instance times can be resolved or unresolved. In the case of the end list, an additional special value "indefinite" is allowed. The lists are maintained in sorted order, with "indefinite" sorting after all other resolved times, and unresolved times sorting to the end.
For begin, the list interpretation is straightforward, since begin times are based only upon the conditions in the attribute or upon the default begin value if there is no attribute.� However, when a begin condition is a syncbase-value, the syncbase element may have multiple intervals, and we must account for this in the list of begin times associated with the conditions.
For end, the case is somewhat more complex, since the end conditions are only one part of the calculation of the end of the active duration. The instance times list for end are used together with the other SMIL Timing semantics to calculate the actual end time for an interval.�
If an instance time was defined as syncbase-values, the instance time will maintain a time dependency relationship to the associated interval for the syncbase element. This means that if the associated begin or end time of the syncbase current interval changes, then the dependent instance time for this element will change as well.
When an element creates a new interval, it notifies time dependents and provides the begin and end times that were calculated according to the semantics described in "Computing the active duration". Each dependent element will create a new instance time tied to (i.e., with a dependency relationship to) the new syncbase current interval.�
The translation of begin or end conditions to instance times depends upon the type of condition:
If no attribute is present, the default begin value (an offset-value of 0) must be evaluated.
If a DOM method call is made to begin or end the element
(beginElement()
, beginElementAt()
,
endElement()
or endElementAt()
), each method call creates
a single instance time (in the appropriate instance times list). These time
instances are cleared upon reset just as for event times. See Resetting element state.
When a new time instance is added to the begin list, the current interval will evaluate restart semantics and may ignore the new time or it may end the current interval (this is detailed in Interaction with restart semantics). In contrast, when an instance time in the begin list changes because the syncbase (current interval) time moves, this does not invoke restart semantics, but may change the current begin time: If the current interval has not yet begun, a change to an instance time in the begin list will cause a re-evaluation of the begin instance lists, which may cause the interval begin time to change. If the interval begin time changes, a time-change notice must be propagated to all dependents, and the current interval end must also be re-evaluated.
When a new instance time is added to the end list, or when an instance time in the end list changes, the current interval will re-evaluate its end time. If it changes, it must notify dependents.
If an element has already played all intervals, there may be no current interval. In this case, additions to either list of instance times, as well as changes to any instance time in either list cause the element to re-evaluate the lists just as it would at the end of each interval (as described in End of an interval below). This may or may not lead to the creation of a new interval for the element.
When times are added to the instance times lists, they may or may not be resolved. If they are resolved, they will be converted to document time. If an instance time changes from unresolved to resolved, it will be similarly converted.
There is a difference between an unresolved instance time, and a begin or end condition that has no associated instance. If, for example, an event value condition is specified in the end attribute, but no such event has happened, there will be no associated instance time in the end list. However, if a syncbase value condition is specified for end, and if the syncbase element has a current interval, there will be an associated instance time in the end list. Since the syncbase value condition can be relative to the end of the syncbase element, and since the end of the syncbase current interval may not be resolved, the associated instance time in the end list can be unresolved. Once the syncbase current interval actually ends, the dependent instance time in the end list will get a time-change notification for the resolved syncbase interval end. The dependent instance time will convert the newly resolved syncbase time to a resolved time in document time. If the instance lists did not include the unresolved instance times, some additional mechanism would have to be defined to add the end instance time when the syncbase element's current interval actually ended, and resolved its end time.�
The list of resolved times includes historical times defined relative to sync base elements, and so can grow over time if the sync base has many intervals. Implementations may filter the list of times as an optimization, so long as it does not affect the semantics defined herein.
The life cycle of an element can be thought of as the following basic steps:
Steps 2 to 5 can loop for as many intervals as are defined before the end of the parent simple duration. At any time during step 2, the begin time for the current interval can change, and at any time during steps 2 or 3, the end time for the current interval can change. When either happens, the changes are propagated to time dependents.
When the document and the associated timegraph are initialized, the instance lists are empty. The simple offset values and any "indefinite" value in an end attribute can be added to the respective lists as part of initialization.
When an element has played all allowed instances, it can be thought of as stuck in step 5. However any changes to the instance lists during this period cause the element to jump back to step 4 and consider the creation of a new current interval.�
An element life cycle begins with the beginning of the document. The cycle begins by computing the first current interval. This requires some special consideration of the lists of times, but is relatively straight-forward. It is similar to, but not the same as the action that applies when the element ends (this is described in End of an interval). The basic idea is to find the first interval for the element, and make that the current interval. However, the model should handle two edge cases:
Thus the strict definition of the first acceptable interval for the element is the first interval that ends after the document begins. Here is some pseudo-code to get the first interval for an element. It assumes an abstract type "Time" that supports a compare function. It can be a resolved numeric value, the special value INDEFINITE (only used with end), and it can be the special value UNRESOLVED.� Indefinite compares "greater than" all resolved values, and UNRESOLVED is "greater than" both resolved values and INDEFINITE. The code uses the instance times lists associated with the begin and end attributes, as described in the previous section.
// Utility function that returns true if the end attribute specification // includes conditions that describe event-values, repeat-values or accessKey-values. boolean endHasEventConditions();
// Calculates the first acceptable interval for an element // Returns: // Interval if there is such an interval // FAILURE if there is no such interval Interval getFirstInterval() { Time beginAfter=-INFINITY; while( TRUE ) // loop till return { Set tempBegin = the first value in the begin list that is >= beginAfter. If there is no such value // No interval return FAILURE; If there was no end attribute specified // this calculates the active end with no end constraint tempEnd = calcActiveEnd( tempBegin ); else { // We have a begin value - get an end Set tempEnd = the first value in the end list that is >= tempBegin. // Allow for non-0-duration interval that begins immediately // after a 0-duration interval. If tempEnd == tempBegin && tempEnd has already been used in an interval calculated in this method call { set tempEnd to the next value in the end list that is > tempEnd } If there is no such value { // Events leave the end open-ended. If there are other conditions // that have not yet generated instances, they must be unresolved. if endHasEventConditions() OR if the instance list is empty tempEnd = UNRESOLVED; // if all ends are before the begin, bad interval else return FAILURE; } // this calculates the active dur with an end constraint tempEnd = calcActiveEnd( tempBegin, tempEnd ); } // We have an end - is it after the parent simple begin? if( tempEnd > 0 ) return( Interval( tempBegin, tempEnd ) ); // interval is too early else if( restart == never ) // if can't restart, no good interval return FAILURE; else // Change beginAfter to find next interval, and loop beginAfter = tempEnd; } // close while loop } // close getFirstInterval
Note that while we might consider the case of restart=always
separately from restart=whenNotActive
, it would just be busy work
since we need to find an interval that begins after
tempEnd
.
If the model yields no first interval for the element, it will never begin, and so there is nothing more to do at this point. However if there is a valid interval, the element must notify all time dependents that there is a new interval of the element. This is a notice from this element to all elements that are direct time dependents. This is distinct from the propagation of a changed time.
When a dependent element gets a "new interval" notice, this includes a reference to the new interval. The new interval will generally have a resolved begin time and may have a resolved end time. An associated instance time will be added to the begin or end instance time list for the dependent element, and this new instance time will maintain a time dependency relationship to the syncbase interval.
This period only occurs if the current interval does not begin immediately when (or before) it is created. While an interval is waiting to begin, any changes to syncbase element current interval times will be propagated to the instance lists and may result in a change to the current interval.
If the element receives a "new interval" notice while it is waiting to begin, it will add the associated time (i.e., the begin or end time of the syncbase interval) to the appropriate list of resolved times.
When an instance time changes, or when a new instance time is added to one of the lists, the element will re-evaluate the begin or end time of the current interval (using the same algorithm described in the previous section).� If this re-evaluation yields a changed interval, time change notice(s) will be sent to the associated dependents.
It is possible during this stage that the begin and end times could change such that the interval would never begin (i.e., the interval end is before the interval begin). In this case, the interval must be deleted and all dependent instance times must be removed from the respective instance lists of dependent elements. These changes to the instance lists will cause re-evaluation of the dependent element current intervals, in the same manner as a changed instance time does.
This period occurs when the current interval is active (i.e., once it has begun, and until it has ended).� During this period, the end time of the interval can change, but the begin time cannot. If any of the instance times in the begin list change after the current interval has begun, the change will not affect the current interval. This is different from the case of adding a new instance time to the begin list, which can cause a restart.
If the element receives a "new interval" notice while it is active, it will add the associated time (i.e., the begin or end time of the syncbase interval) to the appropriate list of resolved times. If the new interval adds a time to the begin list, restart semantics are considered, and this may end the current interval.
If restart� is set to "always", then the current interval will end early if there is an instance time in the begin list that is before (i.e. earlier than) the defined end for the current interval. Ending in this manner will also send a changed� time notice to all time dependents for the current interval end. See also Interaction with restart semantics.
When an element ends the current interval, the element must reconsider the lists of resolved begin and end times.� If there is another legal interval defined to begin at or after the just completed end time, a new interval will be created. When a new interval is created it becomes the current interval and a new interval notice is sent to all time dependents.
The algorithm� used is very similar to that used in step 1, except that we are interested in finding an interval that begins after the most recent end.
// Calculates the next acceptable interval for an element // Returns: // Interval if there is such an interval // FAILURE if there is no such interval Interval getNextInterval() { // Note that at this point, the just ended interval is still the "current interval" Time beginAfter=currentInterval.end; Set tempBegin = the first value in the begin list that is >= beginAfter. If there is no such value // No interval return FAILURE; If there was no end attribute specified // this calculates the active end with no end constraint tempEnd = calcActiveEnd( tempBegin ); else { // We have a begin value - get an end Set tempEnd = the first value in the end list that is >= tempBegin. // Allow for non-0-duration interval that begins immediately // after a 0-duration interval. If tempEnd == currentInterval.end { set tempEnd to the next value in the end list that is > tempEnd } If there is no such value { // Events leave the end open-ended. If there are other conditions // that have not yet generated instances, they must be unresolved. if endHasEventConditions() OR if the instance list is empty tempEnd = UNRESOLVED; // if all ends are before the begin, bad interval else return FAILURE; } // this calculates the active dur with an end constraint tempEnd = calcActiveEnd( tempBegin, tempEnd ); } return( Interval( tempBegin, tempEnd ) ); } // close getNextInterval