Warren_Baird@cimmetry.com writes:
It looks to me like LPtoDP is just doing a linear transform, so the area should be preserved - the rectangle should be empty after the transform if and only if it is empty before the transform.
Or am I missing something? Is there another reason to move the IsRectEmpty check after the transform?
There can be rounding issues, if multiple logical pixels correspond to a single physical pixel. Also there are sign issues, IsRectEmpty will return TRUE for left >= right which is why it's better to check after the coordinate swap.