On Sun, 21 Oct 2001, Jamie Zawinski wrote:
> The XFree interface only lets me specify a gamma value, not a curve.
> It generates a curve from that number in the traditional way, and the
> curve generated does not touch fully saturated colors. So only colors
> at low-to-medium saturation levels are faded properly.
>
> Furthermore, the XFree interface doesn't let me ramp all the way down
> to black: it signals an X error if you give it a gamma less than 0.1
> (or something like that.) That means that it never fades all the way
> to black, and you see a slight jump at the very end.
>
> So, while it's nice that XFree finally gave us some control over gamma,
> they didn't give us enough control. Because of that, xscreensaver's
> fading looks kinda hokey on XFree (while it works great on SGIs, and in
> 8-bit mode.)
>
> So, please provide a gamma interface where I can specify the transfer
> map for each input value: something along the lines of, letting me give
> you an array of 255 values where I can map input intensity to output
> intensity. (The SGI interface uses three such maps, for R, G, and B.)
>
>
This already exists in 4.1.0 and newer.
#include <X11/extensions/xf86vmode.h>
Bool XF86VidModeSetGammaRamp(
Display* /* dpy */,
int /* screen */,
int /* size */,
unsigned short* /* red array */,
unsigned short* /* green array */,
unsigned short* /* blue array */
);
Bool XF86VidModeGetGammaRamp(
Display* /* dpy */,
int /* screen */,
int /* size */,
unsigned short* /* red array */,
unsigned short* /* green array */,
unsigned short* /* blue array */
);
Bool XF86VidModeGetGammaRampSize(
Display* /* dpy */,
int /* screen */,
int* /* size */
);
Pay attention to the ramp size our you'll get bitten.
All colors go from 0-65535. And you had better restore it
when you're done with it our alot of people are going to
be mad at you because you mess up their custom ramps.
Mark.
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