thebookofshaders/12/cellnoise-01.frag

// Author: @patriciogv
// Title: CellularNoise

#ifdef GL_ES
precision mediump float;
#endif

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

vec2 random2( vec2 p ) {
    return fract(sin(vec2(dot(p,vec2(127.1,311.7)),dot(p,vec2(269.5,183.3))))*43758.5453);
}

void main() {
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    st.x *= u_resolution.x/u_resolution.y;
    vec3 color = vec3(.0);
    
    // Scale 
    st *= 3.;
    
    // Tile the space
    vec2 i_st = floor(st);
    vec2 f_st = fract(st);

    vec2 point = random2(i_st);
    vec2 diff = point - f_st;
    
    float dist = length(diff);

    // Draw the min distance (distance field)
    color += dist;

    // Draw cell center
    color += 1.-step(.02, dist);
    
    // Draw grid
    color.r += step(.98, f_st.x) + step(.98, f_st.y);
    
    // Show isolines
    // color -= step(.7,abs(sin(27.0*dist)))*.5;
    
    gl_FragColor = vec4(color,1.0);
}