#ifdef GL_ES

precision mediump float;

#endif

// Tweaked from  http://glsl.heroku.com/e#6051.0

// Posted by Trisomie21 : 2D noise experiment (pan/zoom)

//

// failed attempt at faking caustics

//

uniform mat3 outputToWorld;

uniform vec4  color;

uniform float time;

vec4 textureRND2D(vec2 uv){

	uv = floor(uv);

	float v = uv.x+uv.y*1e3;

  // Build space-specific corner values

  vec4 res = fract(1e5*sin(vec4(v*1e-2, (v+1.)*1e-2, (v+1e3)*1e-2, (v+1e3+1.)*1e-2)));

  // Add 'sawtooth-like'  wavefronts evolution

  return 2.0 * abs(fract(res + vec4(time * .03)) - 0.5);

}

float noise(vec2 p) {

  vec4 r = textureRND2D(p);                           // Noise values at cell corners

  vec2 f = fract(p);

	f = f*f*(3.0-2.0*f);                                // aka the smoothstep() builtin function

	return (mix(mix(r.x, r.y, f.x), mix(r.z, r.w, f.x), f.y));

}

float buildColor(vec2 p) {

  p += noise(p);                                      // Noising p itself first. This helps

                                                      // preventing grid-like patterns.

	float v = 1.0 - abs(pow(abs(noise(p) - 0.5), 0.75)) * 1.7;  // Lots of magical constants  o_o?

	return v;

}

const float SPEED   = .15;

void main( void ) {

	vec2 p = (outputToWorld * vec3(gl_FragCoord.xy, 1.0)).xy;

	float c1 = buildColor(p*.03 + time * SPEED);

	float c2 = buildColor(p*.03 - time * SPEED);

	float c3 = buildColor(p*.02 - time * SPEED);

	float c4 = buildColor(p*.02 + time * SPEED);

	float cf = pow(c1*c2*c3*c4+0.5,6.);                 // Yep this is bad. Explicitly

                                                      // dependent on the 4 above. Better?

	vec3 c = vec3(cf);

	gl_FragColor = vec4(c, 0.0) + color;

  gl_FragColor.rgb *= gl_FragColor.a;                 // Premultiplication

}