//primitive functions
float sdSphere( vec3 p )
{
  return length(p)-0.1;
}
float sdTorus( vec3 p )
{
  vec2 t = vec2 (0.45,0.04);
  vec2 q = vec2(length(p.xz)-t.x,p.y);
  return length(q)-t.y;
}
//--------------------------------------------------------
float map(vec3 p) 
{
    //Repetition
    vec3 c = vec3 (1.0,1.0,1.0);
    vec3 q = mod(p,c)-0.5*c; 
    return sdTorus (q);   
}
float trace(vec3 o, vec3 r) //raymarching function
{ 
    float t = 0.0;
    for (int i=0; i<32;i++)
    {
     vec3 p = o + r * t;    
     float d = map(p);  
     t += d*1.0;   
    }   
   return t;     
}
                            
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    //resolution/uv adjustments
    vec2 uv = fragCoord.xy / iResolution.xy;   
    uv = uv*2.0 -1.0;
    uv.x *= iResolution.x/iResolution.y;  
    vec3 r = normalize (vec3(uv,1.0));
    
    //camera
    vec3 o = vec3 (0.0, iGlobalTime/5.0,+3.0- iMouse.x/50.0);
    float t = trace(o,r);
    float fog = 1.0 / (1.0 +t *t * 0.1);
    vec3 fc = vec3(fog);
    fragColor = vec4(fc,1.0);
}