ParticleSystem:setEmissionArea
Sets area-based spawn parameters for the particles. Newly created particles will spawn in an area around the emitter based on the parameters to this function.
ParticleSystem:setEmissionArea( distribution, dx, dy, angle, directionRelativeToCenter )
distribution AreaSpreadDistribution The type of distribution for new particles.
dx number The maximum spawn distance from the emitter along the x-axis for uniform distribution, or the standard deviation along the x-axis for normal distribution.
dy number The maximum spawn distance from the emitter along the y-axis for uniform distribution, or the standard deviation along the y-axis for normal distribution.
angle (0) number The angle in radians of the emission area.
directionRelativeToCenter (false) boolean True if newly spawned particles will be oriented relative to the center of the emission area, false otherwise.