Bug 10931 – WebCore needs a separate AnimationCompositor class for animation calculations

• Status: RESOLVED
• Resolution: FIXED
• Component: SVG

[Eric Seidel (no email)]

WebCore needs a separate AnimationCompositor class for animation calculations

KSVG2 had a hackish animation model in which a single class (KSVGTimeScheduler) held all of the logic necessary for animation (in a single function with a large switch statement).

A bette model for animation would involve at least:
1. a separate timer scheduling class
2. separate classes containing animation application logic for each of the basic animation elements
3. a animation compositor class, to orchestrate the application of animation

This bug covers implementing #3, the compositor.

The SMIL animation composition model (aka "AnimationSandwichModel") is pretty well spelled out in:
http://www.w3.org/TR/2005/REC-SMIL2-20051213/animation.html#animationNS-AnimationSandwichModel

1. individual animation elements will need to know their priority (a monotonically increasing number based on parse order, or a override value manually specified on the element)
2. when the "applyAnimations()" method is called on the compositor, a specific target will be passed
3. animation elements targeting the passed element will be grabbed out of a hash and sorted into priority order.
4. the compositor will walk backwards through that priority list until either hitting the beginning or an animation with additive="replace".
5.  the compositor can then walk forwards to generate the new value from the original baseValue or replaced value.

This is a very rough sketch.

This bug covers breaking the existing KSVGTimeScheduler composition logic out into its own class, and wiring things up enough to at least confirm that simple animations work.

[Nikolas Zimmermann]

This is long done.