iconcache: Avoid xrender picture formats when creating cairo surface

If an application provides its window icon via wmhints, then mutter
loads the pixmap specified by the application into a cairo xlib surface. When
creating the surface it specifies the visual, indirectly, via an XRender
picture format.

This is suboptimal, since XRender picture formats don't have a way to specify
16bpp depth, which an application may be using.

In particular, applications are likely to use 16bpp depth pixmaps for their
icons, if the video card offers a 16bpp framebuffer/root window.

This commit drops the XRender middleman, and just tells cairo a visual to use
directly.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/715

src/x11/iconcache.c

@@ -288,34 +288,12 @@ get_pixmap_geometry (MetaX11Display *x11_display,
     *d = depth;
 }
 
-static int
-standard_pict_format_for_depth (int depth)
-{
-  switch (depth)
-    {
-    case 1:
-      return PictStandardA1;
-    case 24:
-      return PictStandardRGB24;
-    case 32:
-      return PictStandardARGB32;
-    default:
-      g_assert_not_reached ();
-    }
-  return 0;
-}
-
-static XRenderPictFormat *
-pict_format_for_depth (Display *xdisplay, int depth)
-{
-  return XRenderFindStandardFormat (xdisplay, standard_pict_format_for_depth (depth));
-}
-
 static cairo_surface_t *
 surface_from_pixmap (Display *xdisplay, Pixmap xpixmap,
                      int width, int height)
 {
   Window root_return;
+  XVisualInfo visual_info;
   int x_ret, y_ret;
   unsigned int w_ret, h_ret, bw_ret, depth_ret;
 
@@ -323,8 +301,12 @@ surface_from_pixmap (Display *xdisplay, Pixmap xpixmap,
                      &x_ret, &y_ret, &w_ret, &h_ret, &bw_ret, &depth_ret))
     return NULL;
 
-  return cairo_xlib_surface_create_with_xrender_format (xdisplay, xpixmap, DefaultScreenOfDisplay (xdisplay),
+  if (!XMatchVisualInfo (xdisplay, DefaultScreen (xdisplay),
-                                                        pict_format_for_depth (xdisplay, depth_ret), w_ret, h_ret);
+                         depth_ret, TrueColor, &visual_info))
+    return NULL;
+
+  return cairo_xlib_surface_create (xdisplay, xpixmap, visual_info.visual,
+                                    w_ret, h_ret);
 }
 
 static gboolean