GaussianRenderer

A CPU software rasterizer that renders 2D Gaussian splats to a PPM image.

Multiple Gaussians

Three overlapping RGB Gaussians composited with the over operator

Single Gaussian

Saturated — α=25, σ=80
HDR alpha drives white core, red halo

Smooth — α=0.5, σ=100
Correct straight-colour composite

Bug fixes (Phase 1)

• Premultiplied write — splat() no longer bakes alpha into colour. Straight colour is stored; compositing happens explicitly in writePPM.
• Index typo — accumAlpha[i*width + i] → accumAlpha[j*width + i].
• Separate alpha buffer — renderGaussian now returns pair<color_buf, alpha_buf> so both are available at write time.
• HDR alpha clamp — Removed premature clamp(alpha, 0, 1) before the colour multiply. Alpha passes through unbounded; the clamp to display range happens at the unsigned char cast.
• File error check — writePPM now reports to stderr if the output path cannot be opened.

Timeline

1. Software Rasterizer: Render a single Gaussian via CPU. ✅
2. Extended Software Rasterizer: Render a scene with multiple Gaussians via CPU (over-composite operator). ✅
3. GPU Rasterizer: Gaussian splatting via shaders.
4. WebGPU Rasterizer: Real-time rendering in the browser via WebGPU.
5. Bonus: Radiance field rendering via CPU.