xorg.conf and bpp in KDE

fransex gmail fransex at gmail.com
Tue Jun 5 03:33:27 UTC 2007

>From the xorg.conf manual (man xorg.conf):

Depth  depth
 This entry specifies what colour depth the Display subsection is to be used
for. This entry is usually specified, but it may be omitted to  create  a
match-all Display subsection or when wishing to match only against the FbBpp
parameter. The range of depth values that are allowed depends on the
driver.  Most drivers support 8, 15, 16 and 24. Some also support 1 and/or
4, and some may support  other values (like 30). Note: depth means the
number of bits in a pixel that are actually used to determine the pixel
colour. 32 is not a valid depth value. Most hardware that uses 32 bits per
pixel only uses 24 of them to hold the colour information, which means that
the colour depth is 24, not 32.

FbBpp  bpp
 This  entry specifies the framebuffer format this Display subsection is to
be used for. This entry is only needed when providing depth 24
configurations that allow a choice between a 24 bpp packed framebuffer
format and a 32bpp sparse framebuffer format. In most  cases this entry
should not be used.

DefaultFbBpp  bpp
 specifies  which  framebuffer  layout  to use by default.  The -fbbpp
command line option can be used to override this.  In most cases the driver
will chose the best default value for this.  The only case where there is
even a choice in this value is for depth 24,  where  some hardware supports
both a packed 24 bit framebuffer layout and a sparse 32 bit framebuffer

Option "Pixmap"  "bpp"
 This sets the pixmap format to use for depth 24.  Allowed values for bpp
are 24 and 32.  Default: 32 unless driver constraints don't allow this
(which is rare).  Note: some clients don't behave well when this value is
set to 24.

2007/6/5, Robert Tilley <tilleyrw at cfl.rr.com>:
> Thanks for the advice and now a further question.
> I added a Display subsection under the Screen section.  The depth is 32
> and
> the mode is 1280x1024.  The default depth for the screen was 16.  This is
> where the problem begins.
> I changed the default of 16 to 32 and restarted X.  X would not restart.
> After rebooting into recovery mode (console) and changing the default
> depth
> to 24, X would start with no difficulty.  Both the 16, 24, and 32 depths
> have
> a mode entry of 1280x1024.
> I want to see 32-bit depth, but apparently X or my video card can't handle
> it.
> I am running on a Dell Dimension 2350 with an Intel 82845G (i810) video
> card.
> Can anyone help me?
> Thanks, Bob
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