Simple mistake - I also needed to set Qt::WA_NoSystemBackground
to false so Qt would actually draw the window...
So, the procedure to turn off an extended frame is:
- Call DwmExtendFrameIntoClientArea (misleading, right?) with all margins set to 0
- Set WA_TranslucentBackground = false on the window (or non-Qt equivalent)
- Set WA_NoSystemBackground = false on the window (or non-Qt equivalent)