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Dec 25th, 2010
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  1. function triangleTest(rect, vertex0, vertex1, vertex2)
  2. {
  3.     /*
  4.     This function borrowed faithfully from a wonderfl (:3) discussion on
  5.     calculating triangle collision with AABBs on the following blog:
  6.     http://sebleedelisle.com/2009/05/super-fast-trianglerectangle-intersection-test/
  7.    
  8.     This particular optimization best suits my purposes and was contributed
  9.     to the discussion by someone from http://lab9.fr/
  10.     */
  11.    
  12.     var l = rect.x;
  13.     var r = rect.w;
  14.     var t = rect.y;
  15.     var b = rect.h;
  16.    
  17.     var x0 = vertex0.x;
  18.     var y0 = vertex0.y;
  19.     var x1 = vertex1.x;
  20.     var y1 = vertex1.y;
  21.     var x2 = vertex2.x;
  22.     var y2 = vertex2.y;
  23.    
  24.     var c, m, s;
  25.    
  26.     var b0 = ((x0 > l) ? 1 : 0) | (((y0 > t) ? 1 : 0) << 1) |
  27.         (((x0 > r) ? 1 : 0) << 2) | (((y0 > b) ? 1 : 0) << 3);
  28.     if (b0 == 3) return true;
  29.    
  30.     var b1 = ((x1 > l) ? 1 : 0) | (((y1 > t) ? 1 : 0) << 1) |
  31.         (((x1 > r) ? 1 : 0) << 2) | (((y1 > b) ? 1 : 0) << 3);
  32.     if (b1 == 3) return true;
  33.    
  34.     var b2 = ((x2 > l) ? 1 : 0) | (((y2 > t) ? 1 : 0) << 1) |
  35.         (((x2 > r) ? 1 : 0) << 2) | (((y2 > b) ? 1 : 0) << 3);
  36.     if (b2 == 3) return true;
  37.    
  38.     var i0 = b0 ^ b1;
  39.     if (i0 != 0)
  40.     {
  41.         m = (y1-y0) / (x1-x0);
  42.         c = y0 -(m * x0);
  43.         if (i0 & 1) { s = m * l + c; if ( s > t && s < b) return true; }
  44.         if (i0 & 2) { s = (t - c) / m; if ( s > l && s < r) return true; }
  45.         if (i0 & 4) { s = m * r + c; if ( s > t && s < b) return true; }
  46.         if (i0 & 8) { s = (b - c) / m; if ( s > l && s < r) return true; }
  47.     }
  48.    
  49.     var i1 = b1 ^ b2;
  50.     if (i1 != 0)
  51.     {
  52.         m = (y2-y1) / (x2-x1);
  53.         c = y1 -(m * x1);
  54.         if (i1 & 1) { s = m * l + c; if ( s > t && s < b) return true; }
  55.         if (i1 & 2) { s = (t - c) / m; if ( s > l && s < r) return true; }
  56.         if (i1 & 4) { s = m * r + c; if ( s > t && s < b) return true; }
  57.         if (i1 & 8) { s = (b - c) / m; if ( s > l && s < r) return true; }
  58.     }
  59.    
  60.     var i2 = b0 ^ b2;
  61.     if (i2 != 0)
  62.     {
  63.         m = (y2-y0) / (x2-x0);
  64.         c = y0 -(m * x0);
  65.         if (i2 & 1) { s = m * l + c; if ( s > t && s < b) return true; }
  66.         if (i2 & 2) { s = (t - c) / m; if ( s > l && s < r) return true; }
  67.         if (i2 & 4) { s = m * r + c; if ( s > t && s < b) return true; }
  68.         if (i2 & 8) { s = (b - c) / m; if ( s > l && s < r) return true; }
  69.     }
  70.    
  71.     return false;
  72. }
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