thebookofshaders/12/2d-voronoise.frag

#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

// Created by inigo quilez - iq/2013
// License Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
// http://iquilezles.org/www/articles/voronoise/voronoise.htm
vec3 hash3( vec2 p ) {
    vec3 q = vec3( dot(p,vec2(127.1,311.7)), 
                   dot(p,vec2(269.5,183.3)), 
                   dot(p,vec2(419.2,371.9)) );
    return fract(sin(q)*43758.5453);
}

float iqnoise( in vec2 x, float u, float v ) {
    vec2 p = floor(x);
    vec2 f = fract(x);
        
    float k = 1.0+63.0*pow(1.0-v,4.0);
    
    float va = 0.0;
    float wt = 0.0;
    for (int j=-2; j<=2; j++) {
        for (int i=-2; i<=2; i++) {
            vec2 g = vec2(float(i),float(j));
            vec3 o = hash3(p + g)*vec3(u,u,1.0);
            vec2 r = g - f + o.xy;
            float d = dot(r,r);
            float ww = pow( 1.0-smoothstep(0.0,1.414,sqrt(d)), k );
            va += o.z*ww;
            wt += ww;
        }
    }
    
    return va/wt;
}

void main() {
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    st.x *= u_resolution.x/u_resolution.y;
    vec3 color = vec3(0.0);

    st *= 10.;
    float n = iqnoise(st, u_mouse.x/u_resolution.x, u_mouse.y/u_resolution.y);

    gl_FragColor = vec4(vec3(n),1.0);
}