A software rasterizer in Rust.

Prism draws real 3D triangles on the CPU. No GPU, no graphics crates. Just a framebuffer, a z-buffer, and barycentric math turning vertices into pixels.

What it is

A small, from-scratch 3D rendering pipeline you can read start to finish in one sitting. It takes a scene of triangles, transforms them through a model, view, and projection matrix, rasterizes each one with barycentric coordinates, resolves overlaps with a z-buffer, and shades faces with a simple directional light. The output is a binary PPM image, so there is no image codec to pull in either.

How it works

1. Vertices are moved from model space to world space to camera space to clip space by a chain of 4x4 matrices, written by hand in src/vec.rs.
2. Projection divides by w to land in normalized device coordinates, then maps to pixel coordinates on the screen.
3. Rasterization walks the bounding box of each triangle and uses barycentric coordinates to decide which pixels are inside it (src/raster.rs).
4. The z-buffer keeps, for every pixel, the depth of the nearest surface drawn so far, so triangles behind others get correctly hidden.
5. Shading is flat per triangle: a dot product between the face normal and a fixed light direction sets its brightness.
6. Output is written as PPM (P6), a plain binary format any image viewer or convert can open.

Usage

cargo run -- render -o out.ppm
cargo run -- render -o out.ppm --width 800 --height 600

This renders the built-in demo scene, a rotated, lit cube, and writes it to the given path.

Tests

cargo test

Covers triangle fill (interior pixels set, exterior pixels clear), z-buffer depth resolution (the nearer triangle wins an overlap), and PPM output (correct header and byte length for the given dimensions).

By Pavan Nallamothu.