nanogui: Images and palette
Subject:
Re: [nanogui] Images and palette
From:
"Greg Haerr" ####@####.####
Date:
29 May 2002 16:01:30 -0000
Message-Id: <029601c20728$444a4700$3aba46a6@xmission.com>
: Yes, the simple algorithm it uses is terrible, and it doesn't force a
: redraw either after it messes with the palette. The symptom I was seeing
: was that displaying an image with a lot of colours "stole" a lot of the
: colours which other things on the screen were already using,
The current algorithm was designed so that a single complex
image could be displayed using the exact colors it requested.
When multiple images are displayed, the algorithm doesn't do
too well. Looking at the code in engine/devdraw.c, there's a
global gr_firstuserpalentry. This is normally set a value that divides
the programmer-supplied palette into two: values below this value
will be used for all system-shared images, borders, title bars, etc.
Values above will be used to custom-allocate colors when
an image requests it. By default, a three-part palette is
supplied: engine/devpal8.c. The first 16 colors are std EGA
colors. The second 32 are basic windows colors. The final
216 colors are a uniform palette, used to display most images
in a basic fashion. To turn off any palette optimization for
images, just set gr_firstuserpalentry to 256.
The reason Microwindows doesn't force a redraw when
values above gr_firstuserpalentry are first used is that it doesn't
track palette multiple uses of palette entries. I originally decided
to keep the color model simple. To correct this, instead of
merely using entries above a marker, each palette entry needs
to be assigned a use count, and this needs to be tracked per
application.
Regards,
Greg
and then it
: doesn't even force a redraw so all the colours are messed up until you
: wave a window around the screen forcing it to redraw everything. I got
: much better results simply fixing the palette so the colours never get
: automatically redefined.
:
: > I would like to have a fixed palette, that only the user changes, how can i
: > do that?
:
: In my tree you can change FIXEDPALETTE to 1 in device.h to disable the
: dynamic palette stuff (actually I think I left that as default). You
: should be able to set the palette yourself with GrSetSystemPalette().
:
: http://www.linuxhacker.org/pub/cvs-snapshots/microwin-aph/
:
: --
: ------------ Alex Holden - http://www.linuxhacker.org ------------
: If it doesn't work, you're not hitting it with a big enough hammer
:
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