// using the base ray-marcher of Trisomie21: https://www.shadertoy.com/view/4tfGRB#

#define T iTime
#define r(v,t) { float a = (t)*T, c=cos(a),s=sin(a); v*=mat2(c,s,-s,c); }
#define SQRT3_2  1.26
#define SQRT2_3  1.732
#define smin(a,b) (1./(1./(a)+1./(b)))

void mainImage( out vec4 f, vec2 w ) {
    vec4 p = vec4(w,0,1)/iResolution.yyxy-.5, d,c; p.x-=.4; // init ray
    r(p.xz,.13); r(p.yz,.2); r(p.xy,.1);   // camera rotations
    d = p;                                 // ray dir = ray0-vec3(0)
    p.z += 5. *T;
    vec2 mouse = iMouse.xy/iResolution.xy;
    float closest = 999.0;
    f = vec4(0);

    for (float i=1.; i>0.; i-=.01)  {

        vec4 u = floor(p/8.), t = mod(p, 8.)-4., ta; // objects id + local frame
        // vec4 u=floor(p/18.+3.5), t = p, ta,v;
        // r(t.xy,u.x); r(t.xz,u.y); r(t.yz,1.);    // objects rotations
        u = sin(78.*(u+u.yzxw));                    // randomize ids
        // t -= u;                                  // jitter positions
        c = p/p*1.2; // *vec4(1,0,0,0);

        float x1,x2,x3,x=1e9, t4 = clamp(cos(T/4.),0.,1.), t8 = clamp(cos(T/8.),0.,1.);
        // r(t.xy,u.x); r(t.xz,u.y); r(t.yz,u.z);
        // t -= 2.*u;
        ta = abs(t);
        x2 = smin(length(t.xy),smin(length(t.yz),length(t.xz))) -.7;
        // ta = abs(mod(p, .25)); x1 = min(ta.x,min(ta.y,ta.z))-.05; x = sqrt(x1*x1+x*x)-.0; // max(-x1,x);
        // ta = abs(mod(p, 1.)); x1 = min(ta.x,min(ta.y,ta.z))-.4; x = sqrt(x1*x1+x2*x2)-.0; // x = max(-x1,x);
        ta = abs(mod(p, 1.)-.2); x1 = min(ta.x,min(ta.y,ta.z)); x1 = sqrt(x1*x1+x2*x2)-.0; // x = max(-x1,x);
        ta = abs(mod(p, 1.)+.2); x3 = min(ta.x,min(ta.y,ta.z)); x3 = sqrt(x3*x3+x2*x2)-.0; // x = max(-x1,x);
     	x = min(x1,x3);
        x3 = min(length(t.xy),min(length(t.yz),length(t.xz))) -.0; //x = min(x,x3);
        f += .7*vec4(1,1,0,0) * exp(-10.*x3)*clamp(dot(.3+.7*sin(3.*(p+8.*T+u)),vec4(1,1,1,0)),0.,1.)*t8*t4;
        // x3 = min(x3, closest);
        // if (x==x3) c=vec4(1,1,0,0);

        if(x2<.01) f += .01*vec4(1.5,.3,.3,0)*t4; //*texture(iChannel0, t.xyz-3.)*2.;

        if(x<.01) // hit !
            { f += i*c*1.; break;  }  // color texture + black fog

        p -= d*x;           // march ray
     }
    //f += vec4(1,1,0,0) * exp(-closest); // *(.5+.5*cos(T/2.)); // thanks kuvkar !
}