Rasterization
How real-time engines draw triangles
Also known as: Rasterizer · Rasterisation · Real-time rendering · Triangle rasterization · Scanline rendering
Definition
Rasterization is the method that real-time engines use to draw 3D scenes. Each triangle is projected onto the screen, the pixels it covers are found, and a shader colors each one. It is extremely fast and runs well on GPUs, which is why games use it, but it does not naturally simulate light, so shadows, reflections and global illumination are done with extra techniques such as shadow maps and probes. Ray tracing is the main alternative.
In production
Most of a game artist's work is for a rasterized pipeline: triangle counts, textures, materials, draw calls and overdraw. Knowing how it works explains why triangles that cover many pixels, transparency and expensive pixel shaders affect performance. Modern engines combine rasterization with ray tracing for specific effects, such as reflections, shadows and global illumination.
