// Rotated Rectangles Collision Detection Routine// Written by Oren Becker, 2001// email: skatman AT ragestorm DOT net// website: http://qsoft.ragestorm.netstruct _Vector2D{ float x, y;};struct _RotRect{ _Vector2D C; _Vector2D S; float ang;};inline void AddVectors2D(_Vector2D * v1, _Vector2D * v2){ v1->x += v2->x; v1->y += v2->y; }inline void SubVectors2D(_Vector2D * v1, _Vector2D * v2){ v1->x -= v2->x; v1->y -= v2->y; }inline void RotateVector2DClockwise(_Vector2D * v, float ang){ float t,       cosa = cos(ang),       sina = sin(ang); t = v->x; v->x = t*cosa + v->y*sina; v->y = -t*sina + v->y*cosa;}// Rotated Rectangle Collision Detection, Oren Becker, 2001int CDRotRects(_RotRect * rr1, _RotRect * rr2){ _Vector2D A, B,   // verteces of the rotated           C,      // center of rr2           BL, TR; // verteces of rr2 (bottom-left, top-right) float ang = rr1->ang - rr2->ang, // orientation of rotated rr1       cosa = cos(ang),           // precalculated trigonometic -       sina = sin(ang);           // - values for repeated use float t, x, a;      // temporary variables for various uses float dx;           // deltaX for linear equations float vert1, vert2; // min/max vertical values // move rr2 to make rr1 cannonic C = rr2->C; SubVectors2D(&C, &rr1->C); // rotate rr2 clockwise by rr2->ang to make rr2 axis-aligned RotateVector2DClockwise(&C, rr2->ang); // calculate vertices of (moved and axis-aligned := 'ma') rr2 BL = TR = C; SubVectors2D(&BL, &rr2->S); AddVectors2D(&TR, &rr2->S); // calculate vertices of (rotated := 'r') rr1 A.x = -rr1->S.y*sina; B.x = A.x; t = rr1->S.x*cosa; A.x += t; B.x -= t; A.y =  rr1->S.y*cosa; B.y = A.y; t = rr1->S.x*sina; A.y += t; B.y -= t; t = sina*cosa; // verify that A is vertical min/max, B is horizontal min/max if (t < 0) {  t = A.x; A.x = B.x; B.x = t;  t = A.y; A.y = B.y; B.y = t; } // verify that B is horizontal minimum (leftest-vertex) if (sina < 0) { B.x = -B.x; B.y = -B.y; } // if rr2(ma) isn't in the horizontal range of // colliding with rr1(r), collision is impossible if (B.x > TR.x || B.x > -BL.x) return 0; // if rr1(r) is axis-aligned, vertical min/max are easy to get if (t == 0) {vert1 = A.y; vert2 = -vert1; } // else, find vertical min/max in the range [BL.x, TR.x] else {  x = BL.x-A.x; a = TR.x-A.x;  vert1 = A.y;  // if the first vertical min/max isn't in (BL.x, TR.x), then  // find the vertical min/max on BL.x or on TR.x  if (a*x > 0)  {   dx = A.x;   if (x < 0) { dx -= B.x; vert1 -= B.y; x = a; }   else       { dx += B.x; vert1 += B.y; }   vert1 *= x; vert1 /= dx; vert1 += A.y;  }    x = BL.x+A.x; a = TR.x+A.x;  vert2 = -A.y;  // if the second vertical min/max isn't in (BL.x, TR.x), then  // find the local vertical min/max on BL.x or on TR.x  if (a*x > 0)  {   dx = -A.x;   if (x < 0) { dx -= B.x; vert2 -= B.y; x = a; }   else       { dx += B.x; vert2 += B.y; }   vert2 *= x; vert2 /= dx; vert2 -= A.y;  } } // check whether rr2(ma) is in the vertical range of colliding with rr1(r) // (for the horizontal range of rr2) return !((vert1 < BL.y && vert2 < BL.y) ||          (vert1 > TR.y && vert2 > TR.y));}