feat: Composable Shaders

[hmans]

As is:

As of now, the library uses two monolithic shader chunks that are injected into the built-in materials of Three.js through three-custom-shader-material. All animation input is passed to this shader code by way of vertex attributes attached to the material.

This approach has a couple of limitations:

• The same shader code needs to support all possible effects, which is bound to make it more complex than we'd want it to be.
• Since the only way to configure it is through uniforms and attribute buffers, we will quickly run into their respective limits.
• All animations are currently implemented using linear interpolation; supporting easing functions would need additional uniforms/buffers; see above.

To be:

For these reasons (and, admittedly, because it feels like a fun challenge), one of the goals for this library has always been to change this into a system that generates per-effect shader code. Basically, each effect would declaratively build a pipeline of operations that would then be compiled to shader code. The individual steps might be:

• Billboarding
• Velocity + Acceleration/Damping (with or without easing)
• Animating Opacity
• Animating Color
• etc.

[hmans]

Closing this, as we now have a "starting version" of this thanks to #32.