[gnome-shell] Don't try to use GLX if Cogl isn't using that Winsys

[Neil Roberts <nroberts src gnome org>]

commit b8a8edc513f0151d0c369a44d6a43b1378dc805b
Author: Neil Roberts <neil linux intel com>
Date:   Thu Mar 15 15:58:36 2012 +0000

    Don't try to use GLX if Cogl isn't using that Winsys
    
    Instead of directly using symbols from GLX to check for the swap event
    notification, the plugin now first verifies that the Cogl renderer is
    actually using the GLX winsys and then indirectly fetches the pointers
    for the GLX functions using cogl_get_proc_address. That way it will
    continue to work if Cogl is using an EGL winsys.
    
    Nothing in the Gnome Shell plugin now directly uses symbols from libGL
    so we don't need to link to it. This helps to avoid problems linking
    against two GL APIs when cogl is using a non-GL driver such as GLES2.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=693225

 configure.ac             |    3 +-
 src/gnome-shell-plugin.c |   58 ++++++++++++++++++++++++++++++++++-----------
 2 files changed, 45 insertions(+), 16 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 1a2b947..dd3e54a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -53,7 +53,7 @@ if $PKG_CONFIG --exists gstreamer-1.0 '>=' $GSTREAMER_MIN_VERSION ; then
    AC_MSG_RESULT(yes)
    build_recorder=true
    recorder_modules="gstreamer-1.0 gstreamer-base-1.0 x11 gtk+-3.0"
-   PKG_CHECK_MODULES(TEST_SHELL_RECORDER, $recorder_modules clutter-1.0 xfixes gl)
+   PKG_CHECK_MODULES(TEST_SHELL_RECORDER, $recorder_modules clutter-1.0 xfixes)
 else
    AC_MSG_RESULT(no)
 fi
@@ -88,7 +88,6 @@ PKG_CHECK_MODULES(GNOME_SHELL, gio-unix-2.0 >= $GIO_MIN_VERSION
 			       libgnome-menu-3.0 >= $GNOME_MENUS_REQUIRED_VERSION
                                $recorder_modules
                                gdk-x11-3.0 libsoup-2.4
-                               gl
 			       clutter-x11-1.0 >= $CLUTTER_MIN_VERSION
 			       clutter-glx-1.0 >= $CLUTTER_MIN_VERSION
                                libstartup-notification-1.0 >= $STARTUP_NOTIFICATION_MIN_VERSION
diff --git a/src/gnome-shell-plugin.c b/src/gnome-shell-plugin.c
index 46da710..3470637 100644
--- a/src/gnome-shell-plugin.c
+++ b/src/gnome-shell-plugin.c
@@ -28,10 +28,10 @@
 #include <stdlib.h>
 #include <string.h>
 
+#define CLUTTER_ENABLE_EXPERIMENTAL_API
+#define COGL_ENABLE_EXPERIMENTAL_API
 #include <clutter/clutter.h>
 #include <clutter/x11/clutter-x11.h>
-#include <GL/glx.h>
-#include <GL/glxext.h>
 #include <gjs/gjs.h>
 #include <meta/display.h>
 #include <meta/meta-plugin.h>
@@ -99,6 +99,7 @@ struct _GnomeShellPlugin
   int glx_error_base;
   int glx_event_base;
   guint have_swap_event : 1;
+  CoglContext *cogl_context;
 
   ShellGlobal *global;
 };
@@ -139,30 +140,59 @@ gnome_shell_plugin_init (GnomeShellPlugin *shell_plugin)
 {
 }
 
-static void
-gnome_shell_plugin_start (MetaPlugin *plugin)
+static gboolean
+gnome_shell_plugin_has_swap_event (GnomeShellPlugin *shell_plugin)
 {
-  GnomeShellPlugin *shell_plugin = GNOME_SHELL_PLUGIN (plugin);
+  MetaPlugin *plugin = META_PLUGIN (shell_plugin);
+  CoglDisplay *cogl_display =
+    cogl_context_get_display (shell_plugin->cogl_context);
+  CoglRenderer *renderer = cogl_display_get_renderer (cogl_display);
+  const char * (* query_extensions_string) (Display *dpy, int screen);
+  Bool (* query_extension) (Display *dpy, int *error, int *event);
   MetaScreen *screen;
   MetaDisplay *display;
   Display *xdisplay;
-  GError *error = NULL;
-  int status;
   const char *glx_extensions;
-  GjsContext *gjs_context;
+
+  /* We will only get swap events if Cogl is using GLX */
+  if (cogl_renderer_get_winsys_id (renderer) != COGL_WINSYS_ID_GLX)
+    return FALSE;
 
   screen = meta_plugin_get_screen (plugin);
   display = meta_screen_get_display (screen);
 
   xdisplay = meta_display_get_xdisplay (display);
 
-  glXQueryExtension (xdisplay,
-                     &shell_plugin->glx_error_base,
-                     &shell_plugin->glx_event_base);
+  query_extensions_string =
+    (void *) cogl_get_proc_address ("glXQueryExtensionsString");
+  query_extension =
+    (void *) cogl_get_proc_address ("glXQueryExtension");
+
+  query_extension (xdisplay,
+                   &shell_plugin->glx_error_base,
+                   &shell_plugin->glx_event_base);
+
+  glx_extensions =
+    query_extensions_string (xdisplay,
+                             meta_screen_get_screen_number (screen));
+
+  return strstr (glx_extensions, "GLX_INTEL_swap_event") != NULL;
+}
+
+static void
+gnome_shell_plugin_start (MetaPlugin *plugin)
+{
+  GnomeShellPlugin *shell_plugin = GNOME_SHELL_PLUGIN (plugin);
+  GError *error = NULL;
+  int status;
+  GjsContext *gjs_context;
+  ClutterBackend *backend;
+
+  backend = clutter_get_default_backend ();
+  shell_plugin->cogl_context = clutter_backend_get_cogl_context (backend);
 
-  glx_extensions = glXQueryExtensionsString (xdisplay,
-                                             meta_screen_get_screen_number (screen));
-  shell_plugin->have_swap_event = strstr (glx_extensions, "GLX_INTEL_swap_event") != NULL;
+  shell_plugin->have_swap_event =
+    gnome_shell_plugin_has_swap_event (shell_plugin);
 
   shell_perf_log_define_event (shell_perf_log_get_default (),
                                "glx.swapComplete",