thebookofshaders/03/SUMMARY.md

Learn how to use Uniform variables. Uniform variables, or simply uniforms are the variables that carry information equally accessible from all of the threads of your shader. The GSLS editor has three uniforms set up for you.

uniform vec2 u_resolution; // Canvas size (width,height)
uniform vec2 u_mouse;      // mouse position in screen pixels
uniform float u_time;	  // Time in seconds since load