Raster Operations For Pen on Desktop

[MarkRobbins]

Are there any UDFs for doing pen/brush type drawing on the desk that will invert the pixels. Its been a long time since I have been in Win GDI so I forgot how this is done. By inverted pixels this means if the line is drawn twice it will be effectively erased (so long as underlying bits do not change between the draws, which would leave behind anomolies).

Speaking of those anomolies, what is the HWND_BROADCAST to invalidate the entire screen, or an HWND, forcing a repaint?

The larger goal here is to create a series of 'zoomy' rectangles to draw extra attention to an area of the screen. Like Sonar, but in reverse.

TIA