_SetToWindowCorner
_SetToWindowCorner(fLeftTopCrossing->RightBottomCorner());
_SetToWindowCorner(fRightTopCrossing->LeftBottomCorner());
_SetToWindowCorner(fLeftBottomCrossing->RightTopCorner());
_SetToWindowCorner(fRightBottomCrossing->LeftTopCorner());
inline void _SetToWindowCorner(Corner* corner);