Question

I need to draw a transparent plane over a User control in my DotNET 2.0 app. That much is easy at least. The hard bit is that I need some (potentially overlapping) holes in this plane. Shape and size of the holes is not known at compile-time.

I tried to approach this with Region and excluding a bunch of GraphicPaths from it. This works great except that the edges of the holes are not anti-aliased.

Any other solutions?

Please bear in mind that the User control is the main part of a window which can be maximised. Thus, it has a potentially very large surface area. The solution must be fast enough to give me at least 10 fps in a full-screen case.

Edit: Added image of what I’d like to achieve:
Image of what I'm talking about. http://en.wiki.mcneel.com/content/upload/images/HolesInTPlane.png

Answer 1

This is a way to do it: (although it doesnt sound fast, it uses pure blitfunctions so potentially it could be fast enough)

1. Create an offscreen bitmap the size of your window. (you only need to do this once, you could keep it for subsequent paints)
2. Fill it with the solid color.
3. Cookiecut holes in the offscreen bitmap with a distinct color (purple for instance)
4. bitblt the entire bitmap onto your window, half opaque and with purple as the colorkey. (so purple is not copied).