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precision mediump float;
      uniform float iTime;
      uniform vec2 iResolution;

      float opSmoothUnion( float d1, float d2, float k ) {
          float h = clamp( 0.5 + 0.5*(d2-d1)/k, 0.0, 1.0 );
          return mix( d2, d1, h ) - k*h*(1.0-h);
      }

      float sdSphere( vec3 p, float s ) {
        return length(p) - s;
      } 

      float map(vec3 p) {
        float d = 2.0;
        for (int i = 0; i < 6; i++) {
          float fi = float(i);
          //fast
          // float time = iTime * (fract(fi * 412.531 + 0.513) - 0.5) * 2.0;
          float time = iTime * (fract(fi * 412.531 + 0.513) - 0.5) * 0.6;
          d = opSmoothUnion(
              sdSphere(p + sin(time + fi * vec3(52.5126, 64.62744, 632.25)) * vec3(2.0, 2.0, 0.8), mix(0.5, 1.0, fract(fi * 412.531 + 0.5124))),
              d,
              0.4
          );
        }
        return d;
      }

      vec3 calcNormal( in vec3 p ) {
          const float h = 1e-5; // small offset for gradient calculation
          //1, -1
          const vec2 k = vec2(1,-1);
          return normalize( k.xyy*map( p + k.xyy*h ) + 
                            k.yyx*map( p + k.yyx*h ) + 
                            k.yxy*map( p + k.yxy*h ) + 
                            k.xxx*map( p + k.xxx*h ) );
      }

      void mainImage( out vec4 fragColor, in vec2 fragCoord ) {
          vec2 uv = fragCoord / iResolution.xy;
          // vec3 rayOri = vec3((uv - 0.5) * vec2(iResolution.x / iResolution.y, 1.0) * 6.0, 3.0);
          // vec3 rayDir = vec3(0.0, 0.0, -1.0);

          vec3 rayOri = vec3((uv - 0.5) * vec2(iResolution.x / iResolution.y, 1.0) * 2.0, 1.5);
          vec3 rayDir = vec3(0.5, 0.2, -1.0);

          
          float depth = 0.0;
          vec3 p;
          
          for(int i = 0; i < 32; i++) {
              p = rayOri + rayDir * depth;
              float dist = map(p);
              depth += dist;
              if (dist < 1e-6) {
                  break;
              }
          }
          
          depth = min(6.0, depth);
          vec3 n = calcNormal(p);
          float b = max(0.0, dot(n, vec3(0.577)));

          vec3 col = (0.5 + 0.5 * cos((b + iTime * 3.0) + uv.xyx * 2.0 + vec3(0,2,4))) * (0.85 + b * 0.35);
          col *= exp( -depth * 0.3 );

          vec3 color = vec3(0.15, b * 1.0, 1.0 );
          color *= exp( -depth * 0.3);

          vec3 baseColor = vec3(0.3647, 0.5176, 0.9255);
          vec3 shadedColor = baseColor * b;
          // shadedColor *= exp( -depth * 0.3 );

          fragColor = vec4( color , 1.0 - (depth - 0.5) / 2.0);
          
      }

      void main() {
          mainImage(gl_FragColor, gl_FragCoord.xy);
      }