For optimizization purposes, compositing window managers may
like to not draw obscured regions of windows, or turn off blending
during for these regions. With RGB windows with no transparency,
this is just the shape of the window, but with ARGB32 windows, the
compositor does not know what regions of the window are transparent
or not.
This function only works for toplevel windows.
GTK+ will automatically update this property automatically if
the window background is opaque, as we know where the opaque regions
are. If your window background is not opaque, please update this
property in your "style_updated" handler.
For optimizization purposes, compositing window managers may like to not draw obscured regions of windows, or turn off blending during for these regions. With RGB windows with no transparency, this is just the shape of the window, but with ARGB32 windows, the compositor does not know what regions of the window are transparent or not. This function only works for toplevel windows. GTK+ will automatically update this property automatically if the window background is opaque, as we know where the opaque regions are. If your window background is not opaque, please update this property in your "style_updated" handler.