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From: jimf@SABER.COM
Newsgroups: comp.windows.x
Subject: Re: XView questions..
Message-ID: <9005311425.AA13698@lance>
Date: 31 May 90 14:25:59 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 122

|	Does anyone know where I can get the xviewsun source.?

I'm pretty sure the xviewsun you're talking about was part of my
original xbgsun distribution.  Xloadimage was supposed to replace
xbgsun/xviewsun since there were several flaws in its color handling
and image transfer functions.

If you really want the source I still have it archived but I don't
think it'd be a good teacher.  Xloadimage is much better, although it
doesn't support TrueColor or DirectColor displays.

The apropos code for color handling is all in send.c.  There's really
not very much.  The idea is to try the following in sequence:

  * try to allocate all needed colors shareable.
  * if we can't do that and it's a dynamic visual type, create a new
    colormap.
  * allocate as many colors as we need or can allocate read/write.
  * if this fails, modify the image to fit the number of colors we
    allocated.

The code which does this, simplified somewhat, follows (this hasn't
been compiled and tested, don't be surprised if something isn't quite
right).  This doesn't do colormap reduction and assumes you want to
use the default visual.

-- cut here --
  /* code to handle allocation of color entries.  this assumes that
   * COLORMAPSIZE is the size of the colormap you want and you have
   * red[] green[] and blue[] arrays describing your colormap.  disp
   * and scrn are the X display and screen indicators.
   */

  Visual        *visual;
  unsigned long  xpixel[COLORMAPSIZE]; /* array of pixel values X gave us */
  XColor         xcolor;
  Colormap       cmap;
  int            pixel, b;

  visual= DefaultVisual(disp, scrn);
  cmap= DefaultColormap(disp, scrn);
  xcolor.flags= DoRed | DoGreen | DoBlue;

  /* these are the only visuals that this code supports
   */

  switch(visual->class) {
  case PseudoColor:
  case GrayScale:
  case StaticColor:
  case StaticGray:
    break;
  default:
    printf("sendImageToX: unsupported display visual\n");
    exit(1);
  }

  /* allocate colors shareable (if we can)
   */

  for (pixel= 0; pixel < COLORMAPSIZE; pixel++) {
    xcolor.red= red[pixel];
    xcolor.green= green[pixel];
    xcolor.blue= blue[pixel];
    if (! XAllocColor(disp, cmap, &xcolor))
      if ((visual->class == StaticColor) || (visual->class == StaticGray)) {
	printf("sendImageToX: XAllocColor failed on a static visual\n");
	exit(1);
      }
      else {

	/* shareable color allocation failed.  free allocations we had made
	 * and allocate a private colormap.
	 */

	for (b= 0; b < pixel; b++)
	  XFreeColors(disp, cmap, xpixel[b], 1, 0);
	cmap= XCreateColormap(disp, RootWindow(disp, scrn), visual,
			      AllocNone);

	/* find allocate read/write color cells and count how many we have
	 */

	for (pixel= 0; pixel < COLORMAPSIZE; pixel++)
	  if (!XAllocColorCells(disp, cmap, False, NULL, 0, &xpixel[pixel], 1))
	    break;
	
	if (pixel < COLORMAPSIZE) {
	  printf("Can't allocate enough colors!\n");
	  exit(1);
	}
	
	/* store image colors in private colormap
	 */

	for (b= 0; b < pixel; b++) {
	  xcolor.pixel= xpixel[b];
	  xcolor.red= red[b];
	  xcolor.green= green[b];
	  xcolor.blue= blue[b];
	  XStoreColor(disp, cmap, &xcolor);
	}
	break;
      }
    xpixel[pixel]= xcolor.pixel;
  }

  /* at this point cmap will be the appropriate colormap and xpixel will
   * map the current pixel values to the pixel values you should use
   * when talking to the server.
   */
-- cut here --

If you're doing image processing, you have to modify your image's
pixel values to match the new colormap.  The code to do this and to
transfer the image to a pixmap is also in send.c.

I hope this is useful,

jim frost
saber software
jimf@saber.com