visual.c

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      visual = (best < out_count ? vi_out [best].visual : 0);
      XFree ((char *) vi_out);
      return visual;
    }
  else
    return 0;
}

static Visual *
pick_best_gl_visual (Screen *screen)
{
  /* The best visual for GL is a TrueColor visual that is half as deep as
     the screen.  If such a thing doesn't exist, then TrueColor is best.
     Failing that, the deepest available color visual is best.

     Compare this function to get_gl_visual() in visual-gl.c.
     This function tries to find the best GL visual using Xlib calls,
     whereas that function does the same thing using GLX calls.
   */
  Display *dpy = DisplayOfScreen (screen);
  XVisualInfo vi_in, *vi_out;
  int out_count;
  Visual *result = 0;

  int ndepths = 0;
  int *depths = XListDepths (dpy, screen_number (screen), &ndepths);
  int screen_depth = depths[ndepths];
  XFree (depths);

  vi_in.class = TrueColor;
  vi_in.screen = screen_number (screen);
  vi_in.depth = screen_depth / 2;
  vi_out = XGetVisualInfo (dpy, (VisualClassMask | VisualScreenMask |
                                 VisualDepthMask),
			   &vi_in, &out_count);
  if (out_count > 0)
    result = vi_out[0].visual;

  if (vi_out)
    XFree ((char *) vi_out);

  if (!result && screen_depth > 24)
    {
      /* If it's a 32-deep screen and we didn't find a depth-16 visual,
         see if there's a depth-12 visual. */
      vi_in.class = TrueColor;
      vi_in.screen = screen_number (screen);
      vi_in.depth = 12;
      vi_out = XGetVisualInfo (dpy, (VisualClassMask | VisualScreenMask |
                                     VisualDepthMask),
                               &vi_in, &out_count);
      if (out_count > 0)
        result = vi_out[0].visual;
    }

  if (!result)
    /* No half-depth TrueColor?  Ok, try for any TrueColor (the deepest.) */
    result = pick_best_visual_of_class (screen, TrueColor);

  if (!result)
    /* No TrueColor?  Ok, try for anything. */
    result = pick_best_visual (screen, False, False);

  return result;
}


static Visual *
id_to_visual (Screen *screen, int id)
{
  Display *dpy = DisplayOfScreen (screen);
  XVisualInfo vi_in, *vi_out;
  int out_count;
  vi_in.screen = screen_number (screen);
  vi_in.visualid = id;
  vi_out = XGetVisualInfo (dpy, (VisualScreenMask | VisualIDMask),
			   &vi_in, &out_count);
  if (vi_out)
    {
      Visual *v = vi_out[0].visual;
      XFree ((char *) vi_out);
      return v;
    }
  return 0;
}

int
visual_depth (Screen *screen, Visual *visual)
{
  Display *dpy = DisplayOfScreen (screen);
  XVisualInfo vi_in, *vi_out;
  int out_count, d;
  vi_in.screen = screen_number (screen);
  vi_in.visualid = XVisualIDFromVisual (visual);
  vi_out = XGetVisualInfo (dpy, VisualScreenMask|VisualIDMask,
			   &vi_in, &out_count);
  if (! vi_out) abort ();
  d = vi_out [0].depth;
  XFree ((char *) vi_out);
  return d;
}


#if 0
/* You very probably don't want to be using this.
   Pixmap depth doesn't refer to the depths of pixmaps, but rather, to
   the depth of protocol-level on-the-wire pixmap data, that is, XImages.
   To get this info, you should be looking at XImage->bits_per_pixel
   instead.  (And allocating the data for your XImage structures by
   multiplying ximage->bytes_per_line by ximage->height.)
 */
int
visual_pixmap_depth (Screen *screen, Visual *visual)
{
  Display *dpy = DisplayOfScreen (screen);
  int vdepth = visual_depth (screen, visual);
  int pdepth = vdepth;
  int i, pfvc = 0;
  XPixmapFormatValues *pfv = XListPixmapFormats (dpy, &pfvc);

  /* Return the first matching depth in the pixmap formats.  If there are no
     matching pixmap formats (which shouldn't be able to happen at all) then
     return the visual depth instead. */
  for (i = 0; i < pfvc; i++)
    if (pfv[i].depth == vdepth)
      {
	pdepth = pfv[i].bits_per_pixel;
	break;
      }
  if (pfv)
    XFree (pfv);
  return pdepth;
}
#endif /* 0 */


int
visual_class (Screen *screen, Visual *visual)
{
  Display *dpy = DisplayOfScreen (screen);
  XVisualInfo vi_in, *vi_out;
  int out_count, c;
  vi_in.screen = screen_number (screen);
  vi_in.visualid = XVisualIDFromVisual (visual);
  vi_out = XGetVisualInfo (dpy, VisualScreenMask|VisualIDMask,
			   &vi_in, &out_count);
  if (! vi_out) abort ();
  c = vi_out [0].class;
  XFree ((char *) vi_out);
  return c;
}

Bool
has_writable_cells (Screen *screen, Visual *visual)
{
  switch (visual_class (screen, visual))
    {
    case GrayScale:	/* Mappable grays. */
    case PseudoColor:	/* Mappable colors. */
      return True;
    case StaticGray:	/* Fixed grays. */
    case TrueColor:	/* Fixed colors. */
    case StaticColor:	/* (What's the difference again?) */
    case DirectColor:	/* DirectColor visuals are like TrueColor, but have
			   three colormaps - one for each component of RGB.
			   Screw it. */
      return False;
    default:
      abort();
      return False;
    }
}

void
describe_visual (FILE *f, Screen *screen, Visual *visual, Bool private_cmap_p)
{
  char n[10];
  Display *dpy = DisplayOfScreen (screen);
  XVisualInfo vi_in, *vi_out;
  int out_count;
  vi_in.screen = screen_number (screen);
  vi_in.visualid = XVisualIDFromVisual (visual);
  vi_out = XGetVisualInfo (dpy, (VisualScreenMask | VisualIDMask),
			   &vi_in, &out_count);
  if (! vi_out) abort ();
  if (private_cmap_p)
    sprintf(n, "%3d", vi_out->colormap_size);
  else
    strcpy(n, "default");

  fprintf (f, "0x%02x (%s depth: %2d, cmap: %s)\n",
	   (unsigned int) vi_out->visualid,
	   (vi_out->class == StaticGray  ? "StaticGray, " :
	    vi_out->class == StaticColor ? "StaticColor," :
	    vi_out->class == TrueColor   ? "TrueColor,  " :
	    vi_out->class == GrayScale   ? "GrayScale,  " :
	    vi_out->class == PseudoColor ? "PseudoColor," :
	    vi_out->class == DirectColor ? "DirectColor," :
					   "UNKNOWN:    "),
	   vi_out->depth, n);
  XFree ((char *) vi_out);
}

int
screen_number (Screen *screen)
{
  Display *dpy = DisplayOfScreen (screen);
  int i;
  for (i = 0; i < ScreenCount (dpy); i++)
    if (ScreenOfDisplay (dpy, i) == screen)
      return i;
  abort ();
  return 0;
}

int
visual_cells (Screen *screen, Visual *visual)
{
  Display *dpy = DisplayOfScreen (screen);
  XVisualInfo vi_in, *vi_out;
  int out_count, c;
  vi_in.screen = screen_number (screen);
  vi_in.visualid = XVisualIDFromVisual (visual);
  vi_out = XGetVisualInfo (dpy, VisualScreenMask|VisualIDMask,
			   &vi_in, &out_count);
  if (! vi_out) abort ();
  c = vi_out [0].colormap_size;
  XFree ((char *) vi_out);
  return c;
}

Visual *
find_similar_visual(Screen *screen, Visual *old_visual)
{
  Display *dpy = DisplayOfScreen (screen);
  XVisualInfo vi_in, *vi_out;
  Visual *result = 0;
  int out_count;

  vi_in.screen = screen_number (screen);
  vi_in.class  = visual_class (screen, old_visual);
  vi_in.depth  = visual_depth (screen, old_visual);

  /* Look for a visual of the same class and depth.
   */
  vi_out = XGetVisualInfo (dpy, (VisualScreenMask | VisualClassMask |
				 VisualDepthMask),
			   &vi_in, &out_count);
  if (vi_out && out_count > 0)
    result = vi_out[0].visual;
  if (vi_out) XFree (vi_out);
  vi_out = 0;

  /* Failing that, look for a visual of the same class.
   */
  if (!result)
    {
      vi_out = XGetVisualInfo (dpy, (VisualScreenMask | VisualClassMask),
			       &vi_in, &out_count);
      if (vi_out && out_count > 0)
	result = vi_out[0].visual;
      if (vi_out) XFree (vi_out);
      vi_out = 0;
    }

  /* Failing that, return the default visual. */
  if (!result)
    result = DefaultVisualOfScreen (screen);

  return result;
}