$ whois glsl

GLSL

first released in 2004 · by OpenGL Architecture Review Board

$ guessprog --inspect glsl

year: 2004
paradigm: procedural
family: c like
memory: none
binding: static
safety: strong

GLSL(7)

AUTHORS: OpenGL Architecture Review Board
HISTORY: The OpenGL Shading Language was introduced as part of OpenGL 2.0 in 2004, after years in which GPU programs had to be written in vendor-specific assembly. It was standardised by the OpenGL Architecture Review Board, building on a proposal led by 3Dlabs, and is now maintained by the Khronos Group. GLSL is a C-like language with built-in vector and matrix types, swizzling (such as color.rgb) and math functions tailored to graphics. Programs run on the GPU as vertex, fragment and other shader stages.
USAGE: GLSL is widely used wherever OpenGL or WebGL is: games, visualisation, creative coding and sites like Shadertoy. Vulkan applications often still write shaders in GLSL and compile them to SPIR-V.
SEE ALSO: GLSL on Wikipedia ↗

$ cat ring.frag

#version 330 core

in vec2 uv;
out vec4 fragColor;
uniform float time;

void main() {
    vec2 p = uv * 2.0 - 1.0;          // map to [-1, 1]
    float r = 0.5 + 0.1 * sin(time);  // pulsing radius
    float ring = 1.0 - smoothstep(0.0, 0.02, abs(length(p) - r));
    vec3 color = mix(vec3(0.1, 0.1, 0.2), vec3(1.0, 0.6, 0.2), ring);
    fragColor = vec4(color.rgb, 1.0);
}