[Cogl] [PATCH 4/4] cogland: Try forcing an EGL context

[Neil Roberts]

Cogland works a lot better with an EGL context because then Mesa will
automatically set up the wl_drm object and it can accept DRM buffers.
However Cogland is still useful with GLX because it can gracefully
fallback to accepting only SHM buffers. This patch therefore makes it
first try creating and connecting a renderer with the EGL constraint,
but if that doesn't work it will try again without it.
---
 examples/cogland.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 54 insertions(+), 8 deletions(-)

diff --git a/examples/cogland.c b/examples/cogland.c
index eb18011..e6d31b3 100644
--- a/examples/cogland.c
+++ b/examples/cogland.c
@@ -93,7 +93,6 @@ struct _CoglandCompositor
   struct wl_display *wayland_display;
   struct wl_event_loop *wayland_loop;
 
-  CoglDisplay *cogl_display;
   CoglContext *cogl_context;
 
   int virtual_width;
@@ -1014,6 +1013,36 @@ bind_shell (struct wl_client *client,
                         &cogland_shell_interface, id, data);
 }
 
+static CoglContext *
+create_cogl_context (CoglandCompositor *compositor,
+                     CoglBool use_egl_constraint,
+                     CoglError **error)
+{
+  CoglRenderer *renderer = renderer = cogl_renderer_new ();
+  CoglDisplay *display;
+  CoglContext *context;
+
+  if (use_egl_constraint)
+    cogl_renderer_add_constraint (renderer, COGL_RENDERER_CONSTRAINT_USES_EGL);
+
+  if (!cogl_renderer_connect (renderer, error))
+    {
+      cogl_object_unref (renderer);
+      return NULL;
+    }
+
+  display = cogl_display_new (renderer, NULL);
+  cogl_wayland_display_set_compositor_display (display,
+                                               compositor->wayland_display);
+
+  context = cogl_context_new (display, error);
+
+  cogl_object_unref (renderer);
+  cogl_object_unref (display);
+
+  return context;
+}
+
 int
 main (int argc, char **argv)
 {
@@ -1057,13 +1086,30 @@ main (int argc, char **argv)
     wayland_event_source_new (compositor.wayland_display);
   g_source_attach (compositor.wayland_event_source, NULL);
 
-  compositor.cogl_display = cogl_display_new (NULL, NULL);
-  cogl_wayland_display_set_compositor_display (compositor.cogl_display,
-                                               compositor.wayland_display);
-
-  compositor.cogl_context = cogl_context_new (compositor.cogl_display, &error);
-  if (!compositor.cogl_context)
-    g_error ("Failed to create a Cogl context: %s\n", error->message);
+  /* We want Cogl to use an EGL renderer because otherwise it won't
+   * set up the wl_drm object and only SHM buffers will work. */
+  compositor.cogl_context =
+    create_cogl_context (&compositor,
+                         TRUE /* use EGL constraint */,
+                         &error);
+  if (compositor.cogl_context == NULL)
+    {
+      /* If we couldn't get an EGL context then try any type of
+       * context */
+      cogl_error_free (error);
+      error = NULL;
+
+      compositor.cogl_context =
+        create_cogl_context (&compositor,
+                             FALSE, /* don't set EGL constraint */
+                             &error);
+
+      if (compositor.cogl_context)
+        g_warning ("Failed to create context with EGL constraint, "
+                   "falling back");
+      else
+        g_error ("Failed to create a Cogl context: %s\n", error->message);
+    }
 
   compositor.virtual_width = 800;
   compositor.virtual_height = 600;
-- 
1.7.11.3.g3c3efa5