NativeEngine: divisor-driven per-instance vertex attributes

[bkaradzic-microsoft]

Problem

Consumer-declared per-instance vertex attributes were routed to per-vertex shader slots, so their data was read incorrectly at draw time. The ShaderCompiler only recognized the built-in instanced names (world0-3, instanceColor, splatIndex); any other attribute backed by an instance buffer (divisor > 0) — e.g. GPU-particle position/color/angle/size, or a custom instanced color buffer — was assigned a per-vertex location.

Fix

Drive instancing purely from the vertex-buffer divisor instead of a fixed name list:

• ShaderCompiler traversers (D3D, OpenGL, Metal) now take a map<name, target-location> of instanced attributes and route each declared attribute to an explicit bgfx i_data slot (TEXCOORD7..TEXCOORD3 = i_data0..i_data4). Built-in instanced names keep their existing reverse-count assignment.
• Program caches lazily-compiled instanced shader variants keyed by the instanced-attribute map; the base program is used when nothing is instanced.
• NativeEngine computes the instanced-attribute set at draw time from the bound vertex array's per-attribute divisors and submits the matching variant. No JS-side hint is required.

This generalizes the instancing path so it works for any divisor-driven attribute, not just the hardcoded names, and supersedes the prior name-list approach.

Test enablement

Re-enables 18 previously-excluded Playground validation tests that failed under the old name-list instancing (most were marked as follow-ups to the #1691 instance-data stride fix). These are the GPU-particle suite plus the instanced color-buffer test:

Particles, Instances with color buffer, Prepass SSAO + particles, halo-particle-system, particle-system-with-custom-nme-shader, and Particles - Basic Properties / Change / Emitters / Attractors variants.

Each was confirmed to actually exercise the fixed path (it compiles a per-instance shader variant) and now matches its reference image.

Verification

• D3D11: all 18 enabled tests pass in default automatic mode (ran=18 passed=18 failed=0); no regression in existing instanced tests (Gaussian Splatting, mesh instancing).
• OpenGL / Metal: use the identical explicit-slot routing and are compile-checked; runtime coverage is via CI.

[Copilot]

Pull request overview

This PR fixes incorrect routing of consumer-declared per-instance vertex attributes that previously ended up bound to per-vertex shader inputs unless they matched a hardcoded instanced-name list. The solution makes instancing behavior depend on the vertex-buffer divisor by compiling and selecting shader variants that explicitly route divisor-driven attributes into bgfx’s i_data slots.

Changes:

• Extend shader compilation (D3D/OpenGL/Metal/Vulkan paths) to accept an instancedAttributes map (name -> i_data target location) and route those attributes to explicit i_data0..4 slots.
• Add lazy, per-program caching of instanced shader variants keyed by the instanced-attribute map, and select the correct variant at draw time.
• Re-enable previously excluded Playground validation tests by removing excludeFromAutomaticTesting entries for the affected particle/instancing scenarios.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Plugins/ShaderCompiler/Source/ShaderCompilerVulkan.cpp	Passes instanced-attribute routing info into the traverser for Vulkan compilation.
Plugins/ShaderCompiler/Source/ShaderCompilerTraversers.h	Adds instancedAttributes parameter (with docs) to varying-location assigners; includes needed headers.
Plugins/ShaderCompiler/Source/ShaderCompilerTraversers.cpp	Implements generic instanced-attribute routing to explicit i_data slots across D3D/OpenGL/Metal traversers.
Plugins/ShaderCompiler/Source/ShaderCompilerOpenGL.cpp	Threads instancedAttributes into OpenGL shader compilation.
Plugins/ShaderCompiler/Source/ShaderCompilerMetal.cpp	Threads instancedAttributes into Metal shader compilation.
Plugins/ShaderCompiler/Source/ShaderCompilerDXIL.cpp	Threads instancedAttributes into DXIL shader compilation.
Plugins/ShaderCompiler/Source/ShaderCompilerDXBC.cpp	Threads instancedAttributes into DXBC shader compilation.
Plugins/ShaderCompiler/InternalInclude/Babylon/Plugins/ShaderCompiler.h	Updates public compiler API to accept instanced-attribute routing map (default empty).
Plugins/NativeEngine/Source/VertexArray.h	Exposes recorded instance-attribute bindings for draw-time variant selection.
Plugins/NativeEngine/Source/ShaderProvider.h	Updates shader-provider API to accept instanced-attribute routing map.
Plugins/NativeEngine/Source/ShaderProvider.cpp	Bypasses source-only shader cache for instanced variants and compiles with routing map.
Plugins/NativeEngine/Source/Program.h	Stores sources and adds instanced-variant caching keyed by the instanced-attribute map.
Plugins/NativeEngine/Source/Program.cpp	Implements lazy instanced-variant compilation and destroys cached variant program handles on dispose.
Plugins/NativeEngine/Source/NativeEngine.cpp	Computes divisor-driven instanced attribute routing from bound vertex array and submits the matching program variant.
Apps/Playground/Scripts/config.json	Re-enables excluded tests by removing excludeFromAutomaticTesting flags for impacted cases.

[bkaradzic-microsoft]

Pushed an update addressing CI + review feedback:

CI fix (Linux GL): Prepass SSAO + particles aborted the OpenGL run, but the failure is unrelated to instancing — it's the SSAO2 blur post-process fragment shader, whose samples uniform (declared vec4) is used as an int loop bound, which desktop GL (GLSL ES 3.0) rejects:

mediump int _42 = -samples.x;                 // float -> int
for (mediump int i = _42; i < samples.x; ...) // int < float

That test's original exclusion reason was "crashes or hangs" (not the instancing follow-up), so it has been re-excluded. The genuinely instancing-attributable particle tests are confirmed passing on OpenGL (e.g. Particles, same per-instance attributes, validates on the Linux GL build). Net enablement is now 17 tests.

Copilot review nits (all addressed):

• Removed the now-unused <set> include from NativeEngine.cpp (replaced with <map>).
• Removed the unused instanceInfo structured binding in the draw-time loop.
• The invalid-i_data-slot error now includes the attribute name and computed location/slot (all three traverser paths).