Shared frame-globals uniform buffer (projection / tint / time across all shaders)

[obiot]

Summary

Put the per-frame values that every shader needs — projection matrix, global tint, elapsed time — into a single uniform buffer bound once per frame, instead of re-uploading them per program.

Motivation

The projection matrix is pushed into each program individually today: Batcher.setProjection() is called on every batcher switch (webgl_renderer.js, setBatcher), and post-effect / blit paths save, override and restore it around their passes. Every shader that wants time or a global tint takes the same per-program uniform treatment.

With a uniform block these become frame state: written once, visible to every program that declares the block, with no per-switch upload.

Relationship to #1552

Different scope, shared machinery. #1552 moves light data into a UBO to lift MAX_LIGHTS; this one moves frame globals used by every shader. They share:

• the GLSL ES 3.00 prerequisite (uniform blocks do not exist in ES 1.00 — see Lighting: uniform buffer objects for light data (raise MAX_LIGHTS, modernize the lit shaders to GLSL ES 3.00) #1552 for the shader-migration rule established in WebGL2-only: drop WebGL1 path, adopt VAOs (per-flush attribute setup → bindVertexArray) #1509)
• the std140 packing helpers (mind vec3 padding to 16 bytes)
• the bindBufferBase / uniformBlockBinding plumbing

Whichever lands first should establish that machinery for the other. This one has the wider blast radius (all shaders, including the ShaderEffect wrapper and user-authored effect bodies), so it likely wants to follow #1552 rather than lead it.

Why this is the most WebGPU-shaped of the set

Frame globals in a uniform buffer bound once per frame is exactly the WebGPU design — conventionally bind group 0, set once per render pass, with per-material and per-object data in higher groups. Unlike #1552 (whose GLSL is rewritten in WGSL at port time anyway), the structure here survives the port: "pack frame globals once, bind once" is the same shape in both backends, and it removes the per-program projection upload that has no WebGPU equivalent.

Part of the #1184 (WebGPU renderer) groundwork.

Scope sketch

• Define a FrameGlobals uniform block (projection matrix, time, global tint; leave room for viewport size / dpi)
• Migrate the shaders that need it to #version 300 es (per the WebGL2-only: drop WebGL1 path, adopt VAOs (per-flush attribute setup → bindVertexArray) #1509 rule: migrate a shader when it needs a 3.00 feature)
• Write it once per frame; drop the per-batcher-switch setProjection upload
• Decide the story for the ShaderEffect wrapper and user effect bodies, which stay ES 1.00 — probably keep the existing uProjectionMatrix / uTime uniforms working for them, so this is opt-in for engine shaders first
• Keep the FBO / blit projection override working (it currently swaps the matrix around a pass)

Unblocked by #1509. Related: #1552, #1184, #1551.