GLSL

GLSL, short for OpenGL Shading Language, is a high-level shading language used to write programs that run on the GPU as part of the OpenGL rendering pipeline. It is a C-like, statically typed language designed to be compiled by the graphics driver and linked into shader programs that execute on the GPU.

Shaders implement per-vertex, per-fragment, and other stages such as geometry, tessellation, and compute. A shader program links several stages and communicates via input and output variables. Vertex data is provided through inputs and interpolated across primitives; uniform variables supply read-only data from the application.

GLSL uses types such as float, int, bool and vector/matrix variants (vec2, vec3, vec4, mat4). It provides built-in variables like gl_Position (vertex stage) and gl_FragCoord (fragment stage); in modern GLSL outputs are declared as user-defined out variables. Source code begins with a #version directive, typically #version 330 core. Desktop OpenGL and OpenGL ES profiles differ and may impose precision qualifiers.

GLSL code is compiled at runtime by the OpenGL driver. The usual workflow is glCreateShader, glShaderSource, glCompileShader, glCreateProgram, glAttachShader, glLinkProgram, and glUseProgram. Portable shading often targets a common subset and uses interface blocks or in/out variables with layout qualifiers.

GLSL has evolved through versions that add features such as shader storage blocks and compute shaders. It remains the predominant shading language in OpenGL contexts, while Vulkan uses SPIR-V, with GLSL sources commonly compiled to SPIR-V via tools like glslang.