PixelShader

A pixel shader is a programmable stage in modern graphics pipelines that computes the final color and other per-pixel attributes for fragments produced by rasterization. It executes after the vertex shader and after texture coordinates and other interpolated data have been prepared, and before the final color is written to the framebuffer. Each pixel that overlaps a primitive is processed by the pixel shader.

Pixel shaders perform per-pixel lighting and shading, texture sampling, and various visual effects. They can implement diffuse and specular lighting, normal mapping, parallax mapping, ambient occlusion, reflections, refractions, and fog. They may output the primary color and, in many APIs, additional render targets or data used by later stages.

Common shading languages include HLSL for DirectX, GLSL for OpenGL and OpenGL ES, and Metal Shading Language for Apple platforms; in practice, the pixel shader is the fragment shader in OpenGL terminology. The concept exists across APIs such as DirectX, OpenGL/Vulkan, and Metal, with differences in syntax and resource binding but a shared role of per-fragment computation.

Historically, programmable pixel shading emerged to replace fixed-function pipelines, enabling more complex lighting and texturing. With modern GPUs, pixel shaders run in highly parallel fashion on many shader units and are complemented by vertex and geometry shaders in the programmable pipeline. Optimization considerations include branch divergence, texture fetch costs, and instruction limits.