#ifdef GL_ES
precision mediump float;
#endif
uniform vec2  resolution;
uniform float time;

struct Ray {
	vec3 o;
	vec3 d;
};

// dueling mandelbulbs
// @acaudwell

// http://www.fractalforums.com/mandelbulb-implementation/realtime-renderingoptimisations/

float mandelbulb(in vec3 p, float power) {

	float dr = 1.0;
	float r  = length(p);

	vec3 c = p;

	for(int i=0; i<2; i++) {

		float zo0 = asin(p.z / r);
		float zi0 = atan(p.y, p.x);
		float zr  = pow(r, power-1.0);
		float zo  = (zo0) * power;
		float zi  = (zi0) * power;
		float czo=cos(zo);

		dr = zr * dr * power + 1.0;
		zr *= r;

		p = zr * vec3(czo*cos(zi), czo*sin(zi), sin(zo));

		p += c;

		r = length(p);
	}

	return 0.5 * r * log(r) / r;
}

void main() {
	vec2 p = ((gl_FragCoord.xy / resolution.xy) * 2.0 - 1.0) * 2.5;

	float t = time;

	Ray ray1;
	ray1.o = vec3(0.0);
	ray1.d = normalize( vec3((p - 1.5*vec2(sin(t-2.0), cos(t+1.0))) * vec2(resolution.x/resolution.y, 1.0), 1.0 ) );

	Ray ray2;
	ray2.o = vec3(0.0);
	ray2.d = normalize( vec3((p - 1.5*vec2(cos(-t),sin(t))) * vec2(resolution.x/resolution.y, 1.0), 1.0 ) );

	ray1.d.xy = vec2( ray1.d.x * cos(t) - ray1.d.y * sin(t), ray1.d.x * sin(t) + ray1.d.y * cos(t));
	ray2.d.xy = vec2( ray2.d.x  *cos(t) - ray2.d.y * sin(t), ray2.d.x * sin(t) + ray2.d.y * cos(t));

	float m1 =  mandelbulb(ray1.o + ray1.d, abs(cos(t)*13.0));
	float m2 =  mandelbulb(ray2.o + ray2.d, abs(sin(t)*13.0));

	float f = pow(max(m1,m2) , abs(m1-m2));
	vec3  c = m1 > m2 ? vec3(0.0, 0.05, 0.2) : vec3(0.2, 0.05, 0.0);

	gl_FragColor = vec4(c*f, 1.0);
}