CPU Software Rasterizer

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A header-only CPU software rendering pipeline written in C++17. No OpenGL, Vulkan, or any graphics library required. Simulates a GPU programmable pipeline (vertex + fragment shaders), streams PPM frames directly to a built-in encoder (ppm2mp4) via pipe — no intermediate files on disk.

Features

• Templated pipeline Pipeline<Vertex, Varying> — shaders are user-defined lambdas
• Perspective-correct interpolation (Varying weighted by val/w)
• Sutherland-Hodgman clipping against all 6 homogeneous frustum planes
• Multithreaded rasterization (thread pool, lock-free row partitioning)
• Incremental rasterization (edge function stepping + early depth rejection)
• Trilinear mipmap sampling (generateMipmaps() + sampleLod())
• Alpha blending (src-over) with independent depth write toggle
• Wireframe rendering mode

Directory Structure

softras/
├── rasterizer/         # Core headers (header-only)
│   ├── math.h          #   vec2/vec3/vec4/mat4 + GLSL-style math
│   ├── framebuffer.h   #   Color buffer + depth buffer + PPM output
│   ├── texture.h       #   Texture2D, bilinear/trilinear sampling
│   └── pipeline.h      #   Pipeline<Vertex, Varying>
├── demo/               # Example programs
│   ├── quad.cpp        #   Fullscreen procedural shader (1920×1080)
│   ├── cube.cpp        #   Rotating cube + Blinn-Phong (960×540)
│   └── showcase.cpp    #   Feature showcase (960×540)
├── tools/              # Build tools
│   ├── ppm2mp4.cpp     #   PPM frame stream → H.264/MP4 encoder (libx264)
│   └── mp4mux.h        #   Minimal ISOBMFF/MP4 muxer (ftyp+mdat+moov)
├── media/              # MP4 output (e.g. quad-3s.mp4)
└── Makefile

Getting Started

Requirements

• C++17 compiler (GCC 7+ or Clang 5+)
• libx264 (for ppm2mp4, the built-in video encoder)

Install on Ubuntu/Debian:

sudo apt install build-essential libx264-dev

ppm2mp4

tools/ppm2mp4 is a self-contained tool built alongside the demos. It reads a raw PPM frame stream from stdin, encodes it with libx264 (H.264 baseline profile), and writes a self-contained MP4 file — no ffmpeg required.

Usage: ppm2mp4 --fps <N> -o <output.mp4> [--duration <seconds>]

  --fps <N>           Frames per second (required)
  -o <file>           Output MP4 path (required)
  --duration <secs>   Video duration; used to compute total frames for
                      progress display (optional, total = fps × duration)

The Makefile pipes demo output directly into ppm2mp4:

./build/quad 3 | ./build/ppm2mp4 --fps 60 --duration 3 -o media/quad-3s.mp4

Build & Render

make test              # Render 3 seconds (180 frames) by default
make test DURATION=5   # Custom duration
make                   # Build only
make clean             # Remove build/ (keeps videos)
make clean-media       # Remove build/ and media/

Output:

File	Resolution	Content
media/quad-3s.mp4	1920×1080 60fps	Fullscreen procedural shader
media/cube-3s.mp4	960×540 60fps	Rotating cube, Blinn-Phong
media/showcase-3s.mp4	960×540 60fps	Feature showcase

When DURATION changes, the target filename changes (e.g. quad-5s.mp4) so Make automatically rebuilds. When DURATION and source files are unchanged, rendering and encoding are skipped.

Demo

quad.mp4

Documentation

• API Reference — pipeline config, shaders, textures, blending, math reference, pipeline flow