Add 2D Gaussian Splatting (2DGS) Rendering Support

[slimbuck]

Add 2D Gaussian Splatting (2DGS) Rendering Support

This PR adds support for rendering 2D Gaussian Splats using a new GSPLAT_2DGS shader define, similar to the existing GSPLAT_AA define.

Summary

• Add GSPLAT_2DGS conditional rendering path for 2D Gaussian Splatting
• Implement oriented quad corner calculation in model space using direct quaternion-vector rotation
• Change SplatCorner.offset from vec2 to vec3 to support both 3DGS (clip-space XY) and 2DGS (model-space XYZ)
• Extract 2DGS corner calculation into dedicated initCorner2DGS function

Technical Details

2DGS Rendering Approach:

• 2DGS splats are rendered as oriented 3D quads in model space
• Corner positions are computed by scaling the quad by 3σ (3-sigma coverage) and rotating using the splat's quaternion
• The GPU's hardware rasterizer handles perspective projection, eliminating the need for covariance-based screen-space projection

Quaternion Rotation:
Uses direct quaternion-vector rotation formula (faster than matrix conversion):

vec3 t = 2.0 * cross(rotation.xyz, v);
corner.offset = v + rotation.w * t + cross(rotation.xyz, t);

Public API Changes

New Shader Define:

• GSPLAT_2DGS - When enabled, uses the 2DGS oriented quad rendering path instead of the 3DGS covariance-based path

Struct Change:

• SplatCorner.offset: Changed from vec2/vec2f to vec3/vec3f
  • 3DGS: Uses XY for clip-space offset, Z is 0
  • 2DGS: Uses XYZ for model-space offset

Files Changed

• src/scene/shader-lib/glsl/chunks/gsplat/vert/gsplatStructs.js
• src/scene/shader-lib/glsl/chunks/gsplat/vert/gsplatCorner.js
• src/scene/shader-lib/glsl/chunks/gsplat/vert/gsplat.js
• src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatStructs.js
• src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatCorner.js
• src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplat.js

Test Plan

• Verify 3DGS rendering is unchanged (no regressions)
• Enable GSPLAT_2DGS define and verify 2DGS splats render correctly
• Test rotation correctness with various quaternion orientations
• Verify WebGL2 and WebGPU backends both work correctly

[Copilot]

Pull request overview

This PR adds support for 2D Gaussian Splatting (2DGS) rendering by introducing a new GSPLAT_2DGS shader define. The implementation renders splats as oriented 3D quads in model space using quaternion rotation, contrasting with the existing 3DGS approach which uses covariance-based screen-space projection.

Changes:

• Added GSPLAT_2DGS conditional compilation path for 2D Gaussian Splatting
• Changed SplatCorner.offset from vec2/vec2f to vec3/vec3f to accommodate both clip-space (3DGS) and model-space (2DGS) offsets
• Implemented initCorner2DGS function for computing oriented quad corners using direct quaternion-vector rotation

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatStructs.js	Updated SplatCorner.offset type from vec2f to vec3f with updated comment
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatCorner.js	Added initCorner2DGS function and updated initCornerCov to use vec3f offset
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplat.js	Added conditional 2DGS rendering path with model-space corner projection
src/scene/shader-lib/glsl/chunks/gsplat/vert/gsplatStructs.js	Updated SplatCorner.offset type from vec2 to vec3 with updated comment
src/scene/shader-lib/glsl/chunks/gsplat/vert/gsplatCorner.js	Added initCorner2DGS function and updated initCornerCov to use vec3 offset
src/scene/shader-lib/glsl/chunks/gsplat/vert/gsplat.js	Added conditional 2DGS rendering path with model-space corner projection

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.