+
+ Still, it can be useful to know bits_per_pixel before the XImage exists.
+
+ XCreateImage calls _XGetBitsPerPixel to figure this out, but that function
+ is private to Xlib.
+
+ For some reason, _XGetBitsPerPixel tries a hard-coded list of depths if
+ it doesn't find a matching pixmap format, but I (Dave Odell) couldn't
+ find any justification for this in the X11 spec. And the XFree86 CVS
+ repository doesn't quite go back far enough to shed any light on what
+ the deal is with that.
+ http://cvsweb.xfree86.org/cvsweb/xc/lib/X11/ImUtil.c
+
+ The hard-coded list apparently was added between X11R5 and X11R6.
+ See <ftp://ftp.x.org/pub/>.