Very Computer

I have a  Linux / X-windows draphics development question, namely in
the graphics pipline area.

How do you directly access the lookup tables (LUTs) on a graphics
card? Is there a high level function for this on the XWindows layer,
or is it graphics card driver specific?

There's a call in windows getDeviceGammaRamp(...), and I know there's
an equivalent Mac call as well...does anyone know if there's something
equivalent in linux?

Ben Guthro
ben.guthro_at_alum.rpi.edu

Use a DirectColor visual.

XFree86 offers the xgamma extension to allow for this, but the driver has
to support it.  Many of them do, at depth 24, but not all.

Are you thinking of doing palette animation of some kind?
--

  Providenza & Boekelheide, Inc.

Not palette animation...precise monitor/video card color calibration
via USB hardware.

the problem with the xgamma extension, that I can see - is that it
calculates the gamma LUT for you. I need to be able to specify the
values for all 256 red, green, and blue values.

So far, I've tried to use a DirectColor visual to do this.
I need this Colormap to be applied to the whole screen, not merely one
window.

I'm a bit new to Xwindows color, and am finding that the documentation
for it online isn't giving me the information that I'm looking for.

How do I use the Colormap returned from
colormap = XDefaultColormap(display,screen_num);
to access these RGB values in the LUT?

and once I have a pointer to those, when I update the colormap, will
the screen update automatically, or do I need to XFlush(), or
something of the like?

Ben

nevermind. I figured it out:

 XF86VidModeGetGammaRampSize(display,screen_num,&n);

  XF86VidModeGetGammaRamp(display,screen_num,n,red,green,blue);

  for(int i=0;i<256;i++){
    fprintf(stderr, "%d:[%x,%x,%x]\n",i,red[i],green[i],blue[i]);
  }

  fprintf(stderr, "n:%d",n);

  XF86VidModeSetGammaRamp(display,screen_num,n,red,green,blue);

Oh?  Are you making a USB-based colorimeter?
--

  Providenza & Boekelheide, Inc.

Well, I'm attempting to get the existing product to work under Linux - but, yes.

see http://www.sequelimaging.com

Ben

Ah, yes.  I worked with the folks at Sequel while I was part of Supermac
Technology.  We shipped one of their "hockey puck" colorimeters and their
color management software with the high-end monitor/graphics cards.

Good luck.
--

  Providenza & Boekelheide, Inc.