Gdi & arbitrary point?

i suppose that using gdi renderer for GUI is less ressources consuming, am i right ?
how to use arbitrary point for “mouse is inside precise aeras” with gdi ?

here my mask is used with arbitrary point in DX9, and i m doing a pipett to find if my over the yellow color.

delimitation_zone_2009.05.14-01.51.45.jpg (53.8 kB)