How to shift color bits in fbdev?

[Maarten Maathuis]

Several things i see.

1: you are throwing away bits in the colors
2: you should undo the mangling in the read function (the system
doesn't understand your strange layout)
3: the alpha channel is in the upper 8 bits on little endian systems
(typically) for A8R8G8B
4: read/write are used by more pixmaps than just the ones going to
your videocard, you need to check if devPrivate.ptr lies in your
fontbuffer range or you need to make a list (6 entries will be more
than enough) in wrap and check in read/write to be sure (this is
because pixman (sw rendering library) is shared between the xserver
and cairo)
5: you only support A/XRGB pixmaps (no 8 or 16 bits formats)?

Maarten.