Re: GS Back xlib on 8Bit display

[Sebastian Reitenbach]

Hi,

On Wednesday, June 13, 2012 09:42 CEST, Andreas Schik 
<andreas.schik@googlemail.com> wrote:

> Hello Sebastian,
>
> On 09.06.2012 12:25, Sebastian Reitenbach wrote:
> > Hi,
> >
> > I got GNUstep up and running on a Tadpole Sparcbook 3GX under OpenBSD ;)
> > Riccardo recommended me to use the xlib graphics backend.
> >
> > Generally it seems to be all fine, besides a little bit slow. Since its 
> > only 8
> > Bit display, colors sometimes look a bit weirdo ;)
> >
> > When applications are starting, I see the following warning on the console:
> >
> > WARNING - XGServer is unable to use the fast algorithm for writing to an 
> > 8-bit
> > display on this host - the most likely reason being the StandardColormap
> > RGB_BEST_MAP has not been installed.
> >
> > My hope is when I can get rid of the warning, then colors may look a bit 
> > better,
> > and maybe if it then uses the "fast algorithm" things may feel faster on 
> > that
> > box.
> >
> > Googling for the RGB_BEST_MAP, I found its related to xlib, but what 
> > exactly,
> > and how to install it, its not clear to me.
> > I hope someone has a cluestick and can point me into the right direction.
>
> I am not too deep into X11 programming, but will try to explain at least
> a bit. RGB_BEST_MAP is the name of an X11 atom pointing to the "best"
> color map for the current screen. This map is needed to quickly map
> floating point RGB values into 8-bit RGB for your display. If it is not
> present, this "fast" alogorithm cannot be used. The question is, where
> to get the color map.
> For this purpose, you usually have a tool called xstdcmap, that can be
> run during startup (e.g. from .xsession) and which sets up the standard
> color maps. Obviously this is not the case on your system. Either this
> tool does not exist on SPARC or it simply is not run.

I wasn't aware of the xstdcmap tool. It's available on OpenBSD too, but
I just don't run it on login. I'll try it later today.

> Another option would be to make the xlib backend create the color map if
> it is not already defined. in back/x11/context.c you find the code, that
> tries to detect the color maps. In this part, the "best" map could be
> created if there cannot be found a proper one.
> If you really want to do that, I suggest you grab yourself a copy of an
> Xlib programming manual. I usually study the book by A. Nye ("Xlib
> Programming Manual"). This book can be found online as PDF and contains
> a rather detailed example of how to do that. It is a bit old, though,
> but not many basic things (if any) have changed since then.

Due to time constraints, I hope the xstdcmap tool will do fine, and that
I do not need to investigate that route ;)

Sebastian

>
>
> --
> Grüße / Cheers
>
> Andreas Schik
>