PseudoColor and DirectColor visuals (was Re: Documentation?)

Patrick O'Donnell pao at
Thu Apr 9 07:48:30 PDT 2009

>Date: Thu, 9 Apr 2009 01:14:28 +0200
>From: Olivier Galibert <galibert at>
>On Wed, Apr 08, 2009 at 07:00:02PM -0400, Patrick O'Donnell wrote:
>> Speaking of which -- the applications I'm maintaining are wedded to
>> using a writable color map, which has always been PseudoColor, which,
>> as you point out, pretty much means 8-bit.  I've been toying with
>> expanding the apps' repertoire to accepting a DirectColor visual, but
>> I've noticed that not a lot of servers actually offer one.  Would I be
>> wasting my time adding in the necessary support for DirectColor?
>> (Supporting TrueColor, alas, would be a royal pain, given the design
>> of the apps.)
>You would be.  On the other hand, are you sure supporting DirectColor
>is any easier than TrueColor?  The hard part, supported >255 color
>numbers, seems to be identical, and the 3 per-color palettes don't
>allow for much in terms of color animation.

Our use of the writable color map centers on using a handful of color
planes ot layer our graphics and simplify drawing and redrawing on the
separate layers.  For that purpose, at least, it turns out that the
number of colors, pixel depth, and palettes don't complicate matters
very much -- that turns out not to be the hard part.  In fact, though
I haven't done the conversion in our main toolkit, a proof-of-concept
test app was /very/ easy to convert from PseudoColor to DirectColor.

The key for us is the writability of the colormap.  Assumptions about
that rise up into more application code than I'd care to deal with.
At least one of our applications assumes it can change the color map
to highlight different aspects of the information.  If both
PseudoColor and DirectColor die, we will be faced with a much bigger
challenge than dropping of save-under support (!).

>From: Glynn Clements <glynn at>
>Date: Thu, 9 Apr 2009 01:01:04 +0100
>So much stuff breaks with a DirectColor visual that no-one ever uses

By this, I presume you mean that many clients fail to support
DirectColor correctly, (or fail to match visuals correctly) so they
break?  Or are you referring to server support for DirectColor failing

		- Patrick

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