.GLSL

Introduction

GLSL, the OpenGL Shading Language, is the Khronos Group’s C-like language for shaders, the small programs that run on the graphics card. It is used by OpenGL, OpenGL ES and WebGL, which compile it in the graphics driver while the program runs, and by Vulkan, which takes it compiled ahead of time to SPIR-V.

There is no single official extension. Files are named .glsl, or after the shader stage: .vert for vertex shaders, .frag for fragment shaders, and .geom, .comp, .tesc and .tese for geometry, compute and tessellation shaders, the names the glslang compiler recognises.

Structure

A GLSL file is plain text. It starts with a #version line naming the language version, such as 450 for desktop OpenGL 4.5 or 300 es for OpenGL ES 3.0. Then come declarations of the shader’s inputs, outputs and uniforms (values set by the program), often with layout qualifiers giving their locations, then functions. Execution starts at void main(). The language has built-in vector and matrix types such as vec4 and mat4.

#version 450

layout(location = 0) in vec3 colour;
layout(location = 0) out vec4 fragColour;

void main() {
    fragColour = vec4(colour, 1.0);
}

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