Implement tests for node animation

[bghgary]

Infrastructure

Runtime

• Add runtime layer for animation

Screenshots (later):

• Generate animated gifs

Validation:

• Add data somewhere to store the animation data
• Figure out how to validate the data

Tests

For all tests:

• Add a point of reference cube with a texture that has labels for each side

Properties (using linear interpolation):

• Translation
• Rotation
• Scale

Interpolation (using translation and rotation specifically for cubic spline):

• Translation with STEP
• Translation with CUBICSPLINE
• Rotation with CUBICSPLINE

Misc:

• Cover Make sure to cover this case when implementing animation tests #404 by creating one curve that doesn't start at zero
• One model with multiple channels (translation, rotation, and scale)
• Two different channels (one with no transforms) that have different start and end times
• Has only one key
• One animation, two channels for two nodes
• Transform the model, then apply the same target animation (constant value) to it
• Rotate the model, and then apply an translation animation to it (doesn't override rotation)
• Two animations (not channels). One translates, the other rotates. They should not interact or bleed across.

[stevk]

@bghgary To do "One animation, two channels for two nodes" we'll need a model with multiple nodes. Do we want to create something specifically for this, or duplicate the original node? Duplicating will be easier, as it probably isn't worth the effort of making another model just for this one case.

[bghgary]

Having two cubes seems fine to me.

[donmccurdy]

A suggested addition: an animation with two channels, where one channel omits node. Per spec:

When node isn't defined, channel should be ignored. Valid path names are "translation", "rotation", "scale", and "weights".

... an implementation should ignore one channel and be able to play the other.

/cc KhronosGroup/glTF#1301 (comment)

[bghgary]

A suggested addition: an animation with two channels, where one channel omits node

Sure. It might be better to open another issue for this as this issue has been merged except for the screenshots with animated gifs and the validation parts, which we might split into other issues as well.

[donmccurdy]

Thanks, done: #453