Add VAT character crowd rendering scripts and example

[mvaligursky]

Adds vertex animation texture (VAT) support as a set of reusable ESM scripts plus an example.
Skinned animation is baked ahead of time into a texture, so a whole crowd renders as one
instanced draw call with no skeletons, bone matrices or per character animation evaluation.
There are no changes to the engine itself — only new files under scripts/esm/vat, a new
example, and four symbol registrations in the scripts TypeDoc config.

Changes:

• New scripts/esm/vat script library: a runtime script, a glb converter, generic shader
  chunks and a simple shader material
• The VAT chunks override transformCoreVS / normalCoreVS, so they work with a
  StandardMaterial as well as with a custom ShaderMaterial
• New animation/vat-characters example with single character and crowd modes, a material
  switch, and an in-browser glb converter behind a file picker
• New examples/assets/vat folder holding the converted lumberjack, its source glb and credits
• Registered ContainerResource, Scene, VertexBuffer and Scene.ambientLight in
  typedoc.scripts.config.mjs so the new JSDoc links resolve

API Changes:

New, all additive — playcanvas/scripts/esm/vat/:

• vat-characters.mjs — VatCharacters script. Attributes: url, useStandardMaterial,
  castShadows, light, ambientSky, ambientGround. Properties: capacity, count,
  animations, characterBounds, ready. Methods: load, setData, getAnimationIndex,
  setAnimation, setSpeed, setLoop, setTime, getTime, setPosition, setRotation,
  setEulerAngles, setScale, setTransform
• vat-converter.mjs — convertToVat, saveVat, VAT_MAX_TEXELS
• vat-data.mjs — parseVat, VatData, createVatTexture, createVatMesh,
  createVatAlbedoTexture, createWhiteTexture, octDecode, vatTextureSize,
  VAT_VERSION, VAT_MAGIC, VAT_TEXTURE_LIMIT
• vat-chunks.mjs — vatChunks, setupVatMaterial, VAT_FRAME_SEMANTIC,
  VAT_TRANSFORM_SEMANTICS
• vat-material.mjs — createVatShaderMaterial

File format:

The converter emits a glb-style binary container (12 byte header with a magic number and a
version, then a JSON chunk and a BIN chunk). Like a glb it is stored uncompressed and leaves
compression to the transport — brotli over the raw payload is around 40% smaller than gzip
baked into the file, and pre-compressing would leave the transport nothing to work with.

The texture is RGBA16U, one texel per vertex per sampled frame: position quantized to 16 bits
per axis over the bounds of the animation in xyz, and an octahedrally encoded normal packed
into w. One fetch therefore supplies a whole vertex. Quantizing over the bounds is also more
accurate than a half float where it matters — near the top of a character fp16 has a step of
about 1.8 mm at human scale, against 28 µm for 16 bit.

Texels are addressed by the flat index vertex * frameCount + frame, wrapped at the power of
two texture width. This decouples the vertex count from a texture dimension: the limit is the
total texel count of a 4096x4096 texture, so roughly 218k vertices at 77 frames rather than
4096. 4096 is used because every WebGL 2 and WebGPU device supports at least that, so data
loads regardless of the machine it was authored on.

Examples:

• animation/vat-characters — crowd of up to 10,000 walking characters by default, with a
  single character mode with an animation drop down, a Shader/Standard material switch, a
  shadow toggle, and a Convert GLB panel that converts and previews any skinned glb in browser

Performance:

• One instanced draw call for the crowd; 6 draw calls total for the example scene at 10,000
  characters (about 31M vertices per frame), CPU 2.1 ms
• Per instance data is 52 bytes — the three rows of the affine transform plus a fractional
  frame index. The fourth row is always (0,0,0,1) and the shader appends it
• The VAT texture is 1.8 MiB for this character and is independent of the character count
• Transforms are only rebuilt when a setter is called, so a static crowd is nearly free on
  the CPU
• Verified on WebGL 2 and WebGPU, in both material modes

crowd.mov

[github-actions]

Build size report

This PR does not change the size of the minified bundles.

Bundle	Minified	Gzip	Brotli
playcanvas.min.js	2326.5 KB —	598.5 KB —	465.5 KB —
playcanvas.min.mjs	2323.9 KB —	597.4 KB —	464.4 KB —