shader

A shader is a small program that runs on the graphics processing unit (GPU) to determine how to render graphics. Shaders are part of a programmable graphics pipeline, replacing fixed-function stages with configurable code that can implement vertex transformations, lighting calculations, texture sampling, color output, and post-processing effects. They are designed to run in parallel across many lightweight threads to handle large numbers of vertices or pixels efficiently.

Common shader types include vertex shaders, fragment (pixel) shaders, geometry shaders, tessellation shaders, and compute shaders. A vertex shader processes each vertex, outputting its position in clip space and optionally data for later stages. A fragment shader computes the color of each pixel or sample, determining the final image color. Geometry shaders can generate new primitives from input geometry, while tessellation shaders refine geometry for smoother surfaces. Compute shaders perform general-purpose computations not directly tied to a specific rendering pass, enabling tasks such as physics, simulations, and image processing.

Shaders are written in shading languages such as GLSL (OpenGL Shading Language), HLSL (High-Level Shading Language for DirectX), and Metal Shading Language for Apple platforms. These are compiled by graphics drivers into GPU-specific code or bytecode, often using an intermediate representation like SPIR-V. Modern graphics engines use shaders to implement lighting models, including physically based rendering (PBR), texture mapping, shadows, and various post-processing effects.

Historically, shaders emerged with programmable GPUs in the late 1990s, enabling more flexible and realistic rendering. Today, shader programs are fundamental to real-time rendering, enabling visually rich, dynamic, and scalable graphics across platforms.