love.graphics.getStencilTest
Gets the current stencil test configuration.

When stencil testing is enabled, the geometry of everything that is drawn afterward will be clipped / stencilled out based on a comparison between the arguments of this function and the stencil value of each pixel that the geometry touches. The stencil values of pixels are affected via love.graphics.stencil.

Each Canvas has its own per-pixel stencil values.
comparemode, comparevalue = love.graphics.getStencilTest()
comparemode CompareMode The type of comparison that is made for each pixel. Will be 'always' if stencil testing is disabled.
comparevalue number The value used when comparing with the stencil value of each pixel.