Cache default gdk visuals in the GDK_VISUALS property on the root window

This means we don't have to try to initialize opengl in every gtk
instance that is stated. It will only happen for the first one.

https://bugzilla.gnome.org/show_bug.cgi?id=738670

gdk/x11/gdkdisplay-x11.c

@@ -165,7 +165,8 @@ static const char *const precache_atoms[] = {
   "_NET_WM_USER_TIME_WINDOW",
   "_NET_VIRTUAL_ROOTS",
   "GDK_SELECTION",
-  "_NET_WM_STATE_FOCUSED"
+  "_NET_WM_STATE_FOCUSED",
+  "GDK_VISUALS"
 };
 
 static char *gdk_sm_client_id;

gdk/x11/gdkglcontext-x11.c

@@ -30,6 +30,8 @@
 #include "gdkx11window.h"
 #include "gdkx11visual.h"
 #include "gdkvisualprivate.h"
+#include "gdkx11property.h"
+#include <X11/Xatom.h>
 
 #include "gdkinternals.h"
 
@@ -817,6 +819,66 @@ pick_better_visual_for_gl (GdkX11Screen *x11_screen,
   return compatible;
 }
 
+static gboolean
+get_cached_gl_visuals (GdkDisplay *display, int *system, int *rgba)
+{
+  gboolean found;
+  Atom type_return;
+  gint format_return;
+  gulong nitems_return;
+  gulong bytes_after_return;
+  guchar *data = NULL;
+  Display *dpy;
+
+  dpy = gdk_x11_display_get_xdisplay (display);
+
+  found = FALSE;
+
+  gdk_x11_display_error_trap_push (display);
+  if (XGetWindowProperty (dpy, DefaultRootWindow (dpy),
+                          gdk_x11_get_xatom_by_name_for_display (display, "GDK_VISUALS"),
+                          0, 2, False, XA_INTEGER, &type_return,
+                          &format_return, &nitems_return,
+                          &bytes_after_return, &data) == Success)
+    {
+      if (type_return == XA_INTEGER &&
+          format_return == 32 &&
+          nitems_return == 2 &&
+          data != NULL)
+        {
+          long *visuals = (long *) data;
+
+          *system = (int)visuals[0];
+          *rgba = (int)visuals[1];
+          found = TRUE;
+        }
+    }
+  gdk_x11_display_error_trap_pop_ignored (display);
+
+  if (data)
+    XFree (data);
+
+  return found;
+}
+
+static void
+save_cached_gl_visuals (GdkDisplay *display, int system, int rgba)
+{
+  long visualdata[2];
+  Display *dpy;
+
+  dpy = gdk_x11_display_get_xdisplay (display);
+
+  visualdata[0] = system;
+  visualdata[1] = rgba;
+
+  gdk_x11_display_error_trap_push (display);
+  XChangeProperty(dpy, DefaultRootWindow (dpy), gdk_x11_get_xatom_by_name_for_display (display, "GDK_VISUALS"),
+                  XA_INTEGER, 32, PropModeReplace, (unsigned char *)visualdata, 2);
+  gdk_x11_display_error_trap_pop_ignored (display);
+}
+
+
 void
 _gdk_x11_screen_update_visuals_for_gl (GdkScreen *screen)
 {
@@ -826,16 +888,34 @@ _gdk_x11_screen_update_visuals_for_gl (GdkScreen *screen)
   Display *dpy;
   struct glvisualinfo *gl_info;
   int i;
+  int system_visual_id, rgba_visual_id;
 
   x11_screen = GDK_X11_SCREEN (screen);
   display = x11_screen->display;
   display_x11 = GDK_X11_DISPLAY (display);
+  dpy = gdk_x11_display_get_xdisplay (display);
+
+  /* We save the default visuals as a property on the root window to avoid
+     having to initialize GL each time, as it may not be used later. */
+  if (get_cached_gl_visuals (display, &system_visual_id, &rgba_visual_id))
+    {
+      for (i = 0; i < x11_screen->nvisuals; i++)
+        {
+          GdkVisual *visual = x11_screen->visuals[i];
+          int visual_id = gdk_x11_visual_get_xvisual (visual)->visualid;
+
+          if (visual_id == system_visual_id)
+            x11_screen->system_visual = visual;
+          if (visual_id == rgba_visual_id)
+            x11_screen->rgba_visual = visual;
+        }
+
+      return;
+    }
 
   if (!gdk_x11_screen_init_gl (screen))
     return;
 
-  dpy = gdk_x11_display_get_xdisplay (display);
-
   gl_info = g_new0 (struct glvisualinfo, x11_screen->nvisuals);
 
   for (i = 0; i < x11_screen->nvisuals; i++)
@@ -872,6 +952,10 @@ _gdk_x11_screen_update_visuals_for_gl (GdkScreen *screen)
   x11_screen->system_visual = pick_better_visual_for_gl (x11_screen, gl_info, x11_screen->system_visual);
   if (x11_screen->rgba_visual)
     x11_screen->rgba_visual = pick_better_visual_for_gl (x11_screen, gl_info, x11_screen->rgba_visual);
+
+  save_cached_gl_visuals (display,
+                          gdk_x11_visual_get_xvisual (x11_screen->system_visual)->visualid,
+                          x11_screen->rgba_visual ? gdk_x11_visual_get_xvisual (x11_screen->rgba_visual)->visualid : 0);
 }