Image.glsl

// [2TC 15] Psychedelic Sand Dunes. Created by Reinder Nijhoff 2015
// Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
// @reindernijhoff
//
// https://www.shadertoy.com/view/MtlGWM
//

void mainImage( out vec4 f, in vec2 w ) {
    vec3 d = vec3(w.xy,1)/iResolution-.5, p=d-d, o=d;
 	
    o.z+=iDate.w*4.;
    float i=.0;
    
    for( ; i<9. && cos(p.z) - abs(sin(p.x*.7+cos(p.z))) < ++p.y; i+=.01 ) 
        p = (o += d*i*.05)*.3;

    f.xyz = mix( (3.+p.y) * vec3(.6,.3,0), d, i/9.);
}

/* or, in 218 char:

void main() {
    vec3 d = gl_fragCoord.xyw/iResolution-.5, p, c, g=d, o=d;

    for( float i=.0; i<9.; i+=.01 ) {
        p = (c = o += d*i*.05)*.3;
        if(  abs(sin(p.x+cos(p.z+iDate.w))) > p.y+2. ) {
	    	g = mix( (3.+p.y) * vec3(.6,.3,0), d, i/9.);
            break;
        }
    }
    gl_fragColor.xyz = g;
}

*/