GdkImage trouble

[David Scrève <dscreve clickteam com>]

        Hello,

        I would like to create an off-screen buffer that is a GdkDrawable,
but that allows to access to the image buffer too. GdkImage seems to be
perfect, but it does not seems to be able to create a GdkImage without any
GdkVisual that support the same depth.
        For example, I have only one Visual with depth, but I would like to
be able to create GdkImage with depth of 8 or 24 or 32.
        I know there is GdkRGB, but GdkRGB is not a GdkDrawable, forbidding
me to use standard graphic operation on it.

        Is there any workaround/solution for that ?

David