Previously when a wxBitmap had an alpha channel and you drew rects or points with a memoryDC on it these shapes would have the same alpha values as the pixels before. There was no way to change this except to set each pixel with setalpha(x,y,val);
I don't see that there are any changes or other solutions in the latest release from looking at the documentation, but havn't tried it.
Also, it seems like the white pen is an exception to this, or I am making some ind of mistake in my code. Does anyone have any tips?