#version 300 es
precision highp float;

uniform float iTime;
uniform vec2  iResolution;

uniform float rotZoom; // value=0.12, min=0, max=1, step=0.01
uniform float distStep; // value=0.005, min=0, max=0.02, step=0.0001
uniform vec3  color; // value=1, .25, .8

in  vec2 vScreen;
out vec4 fragColor;

void main() {
    float t = iTime / 4.;
    vec2 I = gl_FragCoord.xy;
    
    vec3 d = -.2 * vec3(vScreen, 1.), 
         c = vec3(0);
         
    float dist = 0.;
         
    for (int x = 0; x < 50; ++x) {
        vec3 p = c;
        
        p.z -= t + (dist += distStep);
        p.xy *= mat2( sin( (p.z *= rotZoom) + vec4(0, 11, 20, 0)) );
        
        c += length(sin(p.yx) + cos(p.xz + t)) * d;
    }
    
    fragColor.rgb = 2.5 * color / length(c);
    fragColor.a = 1.;
}