The Graphics Pipeline: From Vertices to Pixels

From Vertices to Pixels in Seven Stages

Modern GPUs render images through a multi-stage pipeline. Early GPUs used fixed-function stages; today most stages are programmable shaders, but the data flow remains the same.

The standard pipeline in order:

1. Vertex Input: vertex buffers supply position, color, normals, UVs
2. Vertex Shader: transforms each vertex to clip space, outputs varyings
3. Tessellation (optional): subdivides patches for curved surfaces
4. Geometry Shader (optional): operates on whole primitives, rarely used today
5. Rasterization: fixed-function conversion of triangles to fragments
6. Fragment Shader: per-fragment color, texture sampling, lighting
7. Output Merger: depth test, blending, framebuffer writes

The rasterizer is the bridge between the vertex-centric and fragment-centric worlds. For example, one triangle with three vertices can generate thousands of fragments on a large screen area.

Parallelism and Attribute Flow

Vertex shaders run once per vertex. Fragment shaders run once per fragment. Attributes like color and texture coordinates are interpolated across the triangle surface using barycentric coordinates during rasterization.

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Vulkan, Direct3D 12, and Metal expose this same sequence as explicit pipeline state objects. Engines from id Tech to Unreal execute billions of these stage transitions per frame.

For This Exercise

You will simulate the pipeline for a single triangle, printing what happens at each stage from vertex input through fragment output. This task asks you to trace attribute interpolation and show how three vertices become many fragments. Getting rasterizer barycentric interpolation right here is the prerequisite for the software rasterizer subtrack.