Implement WebGL2 framebufferTextureLayer for layered texture rendering

[Copilot]

WebGL2 contexts were throwing TypeError: gl.framebufferTextureLayer is not a function due to missing implementation. This blocked rendering to texture array layers and 3D texture slices, breaking WebGL2 conformance.

Changes

Command buffer infrastructure

• Added FRAMEBUFFER_TEXTURE_LAYER request type to command buffer macros
• Implemented FramebufferTextureLayerCommandBufferRequest class (target, attachment, texture, level, layer)

Backend implementation

• Replaced NOT_IMPLEMENTED() stub in WebGL2Context::framebufferTextureLayer
• Routes to OpenGL via command buffer: glFramebufferTextureLayer(target, attachment, texture, level, layer)

JavaScript bindings

• Exposed framebufferTextureLayer method on WebGL2RenderingContext
• Validates 5 arguments: target (GLenum), attachment (GLenum), texture (WebGLTexture|null), level (GLint), layer (GLint)

Usage

const gl = canvas.getContext('webgl2');
const texture = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D_ARRAY, texture);
gl.texStorage3D(gl.TEXTURE_2D_ARRAY, 1, gl.RGBA8, 256, 256, 8);

// Attach layer 3 to framebuffer
gl.framebufferTextureLayer(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, texture, 0, 3);

Enables rendering to GL_TEXTURE_2D_ARRAY and GL_TEXTURE_3D layers per WebGL 2.0 §5.19.8.
case

Original prompt

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This section details on the original issue you should resolve

<issue_title>WebGL2: gl.framebufferTextureLayer is not implemented (TypeError)</issue_title>
<issue_description>## Bug Description
When running WebGL2 content or Khronos/WebGL2 conformance tests in JSAR Runtime, the following error is triggered:

Uncaught TypeError: gl.framebufferTextureLayer is not a function

This occurs on calls like:

gl.framebufferTextureLayer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, texture, level, layer);

Spec Reference

• WebGL 2.0 Spec §5.19.8 framebufferTextureLayer
• MDN - WebGL2RenderingContext.framebufferTextureLayer
• OpenGL Spec - glFramebufferTextureLayer
• Chromium Implementation

Expected Behavior

gl.framebufferTextureLayer() should be present and correctly bind a specific layer of a 3D/array texture to the framebuffer in all WebGL2 contexts.

• Required for rendering to texture arrays and 3D textures (GL_TEXTURE_2D_ARRAY/GL_TEXTURE_3D)

Root Cause

• JSAR does not currently implement the framebufferTextureLayer function in its WebGL2RenderingContext binding.
• Calls to this function yield a TypeError, breaking WebGL2 applications and test suites.

Acceptance Criteria

• gl.framebufferTextureLayer must exist and be callable on all WebGL2 contexts
• The function should bind the specified texture layer and produce correct OpenGL calls
• Should pass Khronos/WebGL2 conformance tests that use layered rendering

Implementation Guidance (C++)

Implement the binding for framebufferTextureLayer:

void WebGL2RenderingContext::framebufferTextureLayer(GLenum target, GLenum attachment, WebGLTexture* texture, GLint level, GLint layer) {
    glFramebufferTextureLayer(target, attachment, texture ? texture->glObject() : 0, level, layer);
}

• Add argument validation per WebGL2 spec
• Update JS-to-native binding so this function is exposed
• Ensure proper GL error handling and spec compliance

Impact

• Required for compatibility with WebGL2 content using layered rendering
• Required for Khronos/WebGL2 conformance suite coverage
• Breaks apps/libraries that depend on array/3D texture rendering

---

Please prioritize as this blocks WebGL2 specification compliance and advanced rendering support.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes WebGL2: gl.framebufferTextureLayer is not implemented (TypeError) #414

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Pull Request Overview

This PR implements the missing WebGL2 framebufferTextureLayer API, which allows rendering to specific layers of 3D textures and texture arrays. The implementation follows established patterns in the codebase and correctly threads the functionality from JavaScript bindings through the command buffer system to the OpenGL backend.

• Adds command buffer infrastructure for FRAMEBUFFER_TEXTURE_LAYER requests
• Implements JavaScript binding with proper argument validation for all 5 parameters
• Routes calls to OpenGL via glFramebufferTextureLayer in the rendering backend

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/common/command_buffers/shared.hpp	Adds COMMAND_BUFFER_FRAMEBUFFER_TEXTURE_LAYER_REQ enum constant for the new command type
src/common/command_buffers/macros.hpp	Registers the FRAMEBUFFER_TEXTURE_LAYER command buffer macro with class name and debug label
src/common/command_buffers/details/buffer.hpp	Defines FramebufferTextureLayerCommandBufferRequest class with 5 parameters (target, attachment, texture, level, layer)
src/renderer/render_api_opengles.cpp	Implements OnFramebufferTextureLayer handler that extracts texture ID from object manager and calls glFramebufferTextureLayer
src/client/script_bindings/webgl/webgl2_rendering_context.hpp	Declares FramebufferTextureLayer method in WebGL2RenderingContext class
src/client/script_bindings/webgl/webgl2_rendering_context.cpp	Implements JavaScript binding with comprehensive argument validation and WebGLTexture null handling
src/client/graphics/webgl_context.cpp	Creates and sends command buffer request, replacing NOT_IMPLEMENTED() stub