WebGL2: Implement gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT)

[Copilot]

gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT) returns undefined instead of the platform-specific alignment value (typically 256/512/1024). This breaks WebGL2 conformance tests and libraries using uniform buffer objects.

Changes

Backend (renderer)

• Query GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT via glGetIntegerv() during WebGL2 context initialization
• Pass value to client through WebGL2ContextInitCommandBufferResponse

Client (context)

• Store alignment value in WebGL2Context::uniformBufferOffsetAlignment
• Add kUniformBufferOffsetAlignment to WebGL2IntegerParameterName enum
• Return stored value in getParameterV2() when requested

The constant was already exported to JavaScript bindings; only the query/storage path was missing.

Example Usage

const gl = canvas.getContext('webgl2');
const alignment = gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT);
// Before: undefined
// After:  256 (or platform-specific value)

// Use for uniform buffer alignment
const offset = Math.ceil(size / alignment) * alignment;

Original prompt

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This section details on the original issue you should resolve

<issue_title>WebGL2: gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT) returns undefined instead of expected alignment value</issue_title>
<issue_description>## Background
When running the following test in JSAR Runtime (from Khronos or EndlessJour9527/WebGL's conformance suite):

var offset = gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT);
// offset is expected to be a non-zero number, e.g. 256
// instead, JSAR returns 'undefined'.

This causes failures in conformance tests such as:

• conformance-suites/2.0.0/conformance2/buffers/bound-buffer-size-change-test.html
• Any test or library code requiring uniform buffer alignment (Three.js, Babylon.js, etc.)

Expected Behavior

According to WebGL 2.0 Spec §5.14.4 getParameter, and browser implementations (see Chromium/WebKit/Gecko), gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT) must return the minimum required alignment for uniform buffer offsets. Typical values are 256, 512, or 1024 depending on platform and GL driver.

References:

• Spec: WebGL2 getParameter (gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT)
• Chromium implementation: WebGL2RenderingContextBase::getParameter
• Gecko implementation: WebGLContext::GetParameter
• Example value: MDN Documentation

Root Cause

• The JSAR binding or backend does not implement the correct mapping for UNIFORM_BUFFER_OFFSET_ALIGNMENT, so getParameter returns undefined.
• Native backend (C/C++) code likely missing or incorrectly implements querying the GL constant GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT via glGetIntegerv.
• The value must be queried from GL on context init and exposed to JS correctly.

Acceptance Criteria

• gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT) returns a correct, non-zero integer value as per the platform/driver
• Affects WebGL2 contexts only
• Conformance tests using uniform buffer alignment (see above) pass

Implementation Guidance (C++)

• Bind the constant UNIFORM_BUFFER_OFFSET_ALIGNMENT in JS
• In native code:

// On WebGL2 context creation:
GLint alignment = 0;
glGetIntegerv(GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT, &alignment);
// Store alignment value in context
// On getParameter call:
if (pname == GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT) {
    return JS::Number(alignment);
}

• Test output for getParameter

Relevant locations to update

• src/client/builtin_scene/webgl_rendering_context.cpp

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Supporting this constant is required for WebGL2 native uniform buffer API compatibility and test suite coverage.</issue_description>

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

• Fixes WebGL2: gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT) returns undefined instead of expected alignment value #409

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Pull Request Overview

This PR implements support for gl.getParameter(gl.UNIFORM_BUFFER_OFFSET_ALIGNMENT) in WebGL2 contexts, fixing a conformance issue where the method previously returned undefined instead of the platform-specific alignment value.

• Queries the GL implementation for GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT during context initialization
• Stores and returns the value through the existing parameter query infrastructure
• Follows the established pattern used by other WebGL2 context parameters

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/renderer/render_api_opengles.cpp	Added glGetIntegerv query for GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT during WebGL2 context initialization
src/common/command_buffers/details/webgl_context_init.hpp	Added uniformBufferOffsetAlignment field to copy constructor and response structure
src/client/graphics/webgl_context.hpp	Added enum entry kUniformBufferOffsetAlignment and member variable declaration
src/client/graphics/webgl_context.cpp	Added initialization from response and return logic in getParameterV2()
src/client/script_bindings/webgl/webgl_rendering_context.cpp	Added case handler for WEBGL2_UNIFORM_BUFFER_OFFSET_ALIGNMENT in parameter retrieval