On Thu, 27 Dec 2001 [EMAIL PROTECTED] wrote:
> Dear Sirs,
>
> I am trying to understand the implimemtation of Pseudocolors.
>
> I am told that the Matrox G400 supports one psuedocolor, two 24 bit
> truecolor and one monochrome visuals.
There is only one hardware palette. Matrox cards and some other
cards using TI or IBM ramdacs have a special mode where you can,
in 32bpp, have two framebuffers: one with 8 bits in the top byte of
each 32bit pixel and another in the 3 bottom bytes. The 8 bits can
go through a palette lookup, the bottom 3 just hold 8:8:8 RGB data
and cannot. This lets you offer a TrueColor visual (without
gamma correction) and you implement PseudoColor and GrayScale
with the 8bits that go through the palette. Actually you can
emulate all visuals through an 8 bit palette, but only
PseudoColor and GrayScale are offered because those are the
only read-write visuals. They have to be read-write because
you need to preallocate the colorkey which determines which
framebuffer the ramdac reads out, so there's really only 255
usable pixels + a transparent one. 256 colormap entries are
advertised, but one is preallocated.
>
>
> How does Xfree86 know this?
The driver knows this.
>
>
> I take it that when I program in C++/Motif with Xwindows commands that the
> instructions are translated in to calls to the graphics card through the
> GUI. Is there a way that one of the 24bit visuals could be used as a second
> pseudocolor?
No, the 24 bit portion doesn't have a palette.
>
>
> does the NVidia GForce 2 or the ATI Radeon 850 support multiple pseudocolor
> support?
I'm not aware of any PC graphics hardware that has more than one
hardware palette.
Mark.
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