#version 300 es

precision highp float;

uniform float time;
uniform vec2 offset;

in vec2 fragCoord;

// shader: https://www.shadertoy.com/view/tsXBzS

vec3 palette(float d){
	return mix(vec3(0.2,0.0,0.0),vec3(.5,0.,0.),d);
}

vec2 rotate(vec2 p,float a){
	float c = cos(a);
    float s = sin(a);
    return p*mat2(c,s,-s,c);
}

float map(vec3 p){
    for( int i = 0; i<8; ++i){
        float t = time*0.2;
        p.xz =rotate(p.xz,t);
        p.xy =rotate(p.xy,t*1.89);
        p.xz = abs(p.xz);
        p.xz-=.5;
	}
	return dot(sign(p),p)/5.;
}

vec4 rm (vec3 ro, vec3 rd){
    float t = 0.;
    vec3 col = vec3(0.);
    float d;
    for(float i =0.; i<64.; i++){
		vec3 p = ro + rd*t;
        d = map(p)*.5;
        if(d<0.02){
            break;
        }
        if(d>100.){
        	break;
        }
        //col+=vec3(0.6,0.8,0.8)/(400.*(d));
        col+=palette(length(p)*.1)/(400.*(d));
        t+=d;
    }
    return vec4(col,1./(d*100.));
}
void main()
{
    vec2 uv = fragCoord / 5.0;
	vec3 ro = vec3(0.,0.,-50.);
    ro.xz = rotate(ro.xz,time);
    vec3 cf = normalize(-ro);
    vec3 cs = normalize(cross(cf,vec3(0.,1.,0.)));
    vec3 cu = normalize(cross(cf,cs));
    
    vec3 uuv = ro+cf*3. + uv.x*cs + uv.y*cu;
    
    vec3 rd = normalize(uuv-ro);
    
    vec4 col = rm(ro,rd);
    
    
    gl_FragColor = col;
}