INT PASCAL IntersectRect(LPRECT pDest, LPRECT pRect1, LPRECT pRect2)

  This function performs an intersection of two rectangles.

Parameters
  pDest is a pointer to the rectangle which receives the intersection.
  pRect1 and pRect2 are pointers to the two rectangles to intersect.

Returns
  TRUE if the resulting intersection is not empty, FALSE if it is empty.