Shader

A shader is a small program executed on the GPU that controls a specific stage of the rendering pipeline. Shaders replace fixed-function graphics hardware with programmable logic, enabling custom lighting models, geometric deformation, and post-processing effects. The most common types are vertex shaders (which transform geometry into screen space), fragment shaders (which compute the final color of each pixel), and compute shaders (which perform general-purpose parallel computation outside the graphics pipeline).

Because shaders execute once per vertex or pixel, a single expensive operation can destroy the frame budget of an entire scene. Shader programming is therefore an exercise in constraint: expressing visual complexity through data texture and arithmetic, not through control-flow complexity. The GPU executes shader code across thousands of threads simultaneously, and any thread divergence — when different pixels require different computational paths — collapses throughput. The shader is the atomic unit of GPU computation, and the art of real-time graphics is largely the art of writing shaders that lie convincingly within the perceptual tolerance of the viewer.