🚀 go-pugleaf

Benjamin M. Burack <admin@no-god.org> wrote:
>My program loads 24-bit textures and displays them with Mesa on XWindows
>with a Voodoo2 card.  I'm using double-buffering and depth buffering in RGBA
>mode (not color index).  For some reason, I am losing a lot of my colors.
>For example, if I have a texture with 8 similar shades of gray, many will
>appear as exactly the same color.  Only 2 or 3 shades will be rendered for

Remember that voodoo2 uses 16 bits for its colour information, and that it
encodes its colour information in a lossy sort of way so that the
effective number is about 22 bits. Perhaps your similar shades of grey are
too similar for this lossy algorithm. The precise details of it have not
been disclosed.

-- 
Lucian Wischik, Queens' College, Cambridge CB3 9ET. www.wischik.com/lu

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Benjamin M. Burack schrieb in Nachricht ...
>My program loads 24-bit textures and displays them with Mesa on XWindows
>with a Voodoo2 card.  I'm using double-buffering and depth buffering in
RGBA
>mode (not color index).  For some reason, I am losing a lot of my colors.
>For example, if I have a texture with 8 similar shades of gray, many will
>appear as exactly the same color.  Only 2 or 3 shades will be rendered for
>all 8.  Since my program involves subtle contrast variations, this is a
huge
>problem.  I thought I would be running in a true color mode since X is set
>to 24 or 32 bit color depth, but apparently this isn't the case.  Why does
>this happen?  How can I fix it?
>
>Posted below is some of the code, such as the colormap initialization, that
>may cause the problem.
>
>Thanks for any help, and please mail responses to rascal@tseinc.com ,
>Benjamin Burack
>
>
>
>
>
>int configuration[] = {GLX_DOUBLEBUFFER, GLX_RGBA, GLX_DEPTH_SIZE, 16,
>None};
>
>void main(int argc, char **argv)
>{
>    XVisualInfo    *vi;
>    XSetWindowAttributes swa;
>    XWMHints       *wmHints;
>    Atom            wmDeleteWindow;
>    GLXContext      cx;
>
><snip>
>
>
>    /*** find an appropriate visual and a colormap for it ***/
>    /* find an OpenGL-capable RGB visual with depth buffer */
>    if (!bDoubleBuffer) goto SingleBufferOverride;
>    vi = glXChooseVisual(pDisplay, DefaultScreen(pDisplay), configuration);
>    if (vi == NULL) {
>      SingleBufferOverride:
>        vi = glXChooseVisual(pDisplay, DefaultScreen(pDisplay),
>&configuration[1]);
>        if (vi == NULL)
>            fatal_error("no appropriate RGB visual with depth buffer");
>        bDoubleBuffer = GL_FALSE;
>    }
>    cmap = getColormap(vi);
>
><snip>
>
>    /*** create an OpenGL rendering context  ***/
>    cx = glXCreateContext(pDisplay, vi, /* no sharing of display lists */
>NULL,
>                           /* direct rendering if possible */ GL_TRUE);
>    if (cx == NULL) fatal_error("could not create rendering context");
>
><snip>
>
>}
>
>Colormap getColormap(XVisualInfo* vi)
>{
>  Status           status;
>  XStandardColormap* standardCmaps;
>  Colormap         cmap;
>  int              i, numCmaps;
>
>  status = XmuLookupStandardColormap(pDisplay, vi->screen, vi->visualid,
>vi->depth, XA_RGB_DEFAULT_MAP, FALSE, TRUE);
>
>  if (status == 1) {
>    status = XGetRGBColormaps(pDisplay, RootWindow(pDisplay, vi->screen),
>         &standardCmaps, &numCmaps, XA_RGB_DEFAULT_MAP);
>    if (status == 1)
>      for (i = 0; i < numCmaps; i++)
> if (standardCmaps[i].visualid == vi->visualid) {
>   cmap = standardCmaps[i].colormap;
>   XFree(standardCmaps);
>   return cmap;
> }
>  }
>  cmap = XCreateColormap(pDisplay, RootWindow(pDisplay, vi->screen),
>    vi->visual, AllocNone);
>  return cmap;
>}
>
>
>