On Mon, 1 Nov 2004, Bussoletti, John E wrote:
>
> At Boeing we have a number of graphics applications that have been
> developed in-house, originally for various SGI platforms. These
> applications are used for engineering visualization They work well on
> the native hardware and even display well across the network using third
> party applications under Windows like Hummingbird's ExCeed 3D. However,
> under Linux, the fail to work properly, either natively or via remote
> display with the original SGI hardware acting as server, due to
> omissions in the available Pseudocolor Visuals.
Most PC graphics hardware does not support overlays and therefore
doesn't really support simultaneous PseudoColor and TrueColor visuals.
Some PC hardware can, for instance, some Matrox cards and some NVIDIA
Quadro cards and some others. You'll need to research that pretty
carefully because while some hardware may support it, the drivers
may not. Hummingbird does PseudoColor emulation in software, probably
by rendering PseudoColor windows offscreen and then translating
into TrueColor windows during PseudoColor window updates and palette
changes. XFree86 doesn't support this because nobody has cared enough
about it to write support for it. I don't expect that to change.
>
> Examination of the output of xdpyinfo in the SGI machines shows that the
> SGI X drivers support Pseudocolor visuals at both 8 bit planes and 12
> bit planes. Similar output under Linux shows support for Pseudocolor
> Visuals at only 8 bit planes. These applications were built to take
> advantage of the 12 bit plane Pseudocolor Visual under the SGI X
> drivers.
No PC hardware supports palettes with more than 2^8 entries.
A 2^12 entry palette could be implemented only by emultation (rendering
offscreen and then translating to TrueColor windows).
>
> To allow use of these graphics applications within a Linux environment,
> we're contemplating a port of the applications to Directcolor Visuals.
> But prior to initiating such an activity, I've been asked to ask whether
> new developments or releases of the XFree86 X drivers might be in the
> pipeline for future release that might offer a wider variety of
> Pseudocolor Visuals. Hence this note.
Porting to depth 24 DirectColor will increase the number of
cards that your application will run on. Most XFree86 drivers
support simultaneous depth 24 DirectColor and TrueColor visuals,
although there will be color flashing when changing window focus
because PC hardware only supports a single hardware palette.
But if your application requires 12 bit plane palettes, I don't
see how depth 24 (8 plane palettes) will help your situation.
>
> Is there any support for 12 bit plane Pseudocolor Visuals within at
> least one video card and the XFree86 drivers? Will there be support for
> such features in the future? If so, is there an anticipated release
> date?
No PC hardware supports 12 bit plane PseudoColor. No drivers
emulate this in software. I know of no plans to implement this
and expect adding such a feature to be unlikely.
My recommendation is that you get away from PseudoColor entirely.
Most people stuck in your position have legacy apps for which they
do not have source code and have no choice. I recommend doing everything
in TrueColor, and depending on the application, you might want to
consider using OpenGL. This problem will likely get worse for you
in the future. Some hardware support 8 bit PseudoColor overlays now
but I expect this to go the way of the dodo. My impression is that
a future Microsoft operating system will not support 8 bit PseudoColor
modes nor will it support overlays so eventually these will disappear
from the hardware, leaving emulation as the only solution.
Mark
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