uniform float time;         // time in seconds  (also: iTime, iGlobalTime)
uniform vec2  resolution;   // viewport size (width, height)  (also: iResolution.xy)
uniform vec4  mouse;        // mouse position (x,y) current, (z,w) click. Shadertoy style. (also: iMouse)
uniform float fxrand;       // random seed (fxhash)
uniform float BPM;          // global BPM control
uniform vec2  pointers[32];  // multi-user mouse positions (only while pressed)
uniform int   pointersCount; // number of users currently pressing
uniform sampler2D iChannel0;
uniform sampler2D iChannel1;
uniform sampler2D iChannel2;
uniform sampler2D iChannel3;

// Shadertoy aliases (auto-injected as #defines):
// iTime        = time
// iResolution  = vec3(resolution, 1.0)
// iMouse       = mouse
// iGlobalTime  = time

void mainImage( out vec4 fragColor, in vec2 fragCoord ) {
    vec2 uv = fragCoord / iResolution.xy;
    fragColor = vec4(uv, 0.0, 1.0);
}

// Sample iChannel0 (buffer output or texture)
vec4 col = texture2D(iChannel0, uv);

// Sample with tiling
vec4 col = texture2D(iChannel0, fract(uv * 2.0));