[backend] Update the viewport when updating the GL context

Bug 1442 - multistage, same-window resize events invalidate stage

When ensuring that the GL context is attached to the correct
ClutterStage we need to set the SYNC_MATRICES flag on the stage
itself. This is needed in case the size of the new stage does
not match the size of the old -- thus requiring a call to
glViewport() when the paint cycle starts.

diff --git a/clutter/clutter-backend.c b/clutter/clutter-backend.c
index 2c94c02..36dbfad 100644 (file)
--- a/clutter/clutter-backend.c
+++ b/clutter/clutter-backend.c
@@ -310,6 +310,17 @@ _clutter_backend_ensure_context (ClutterBackend *backend,
        * potential issue of GL calls with no context)
        */
       current_context_stage = stage;
+
+      /* if the new stage has a different size than the previous one
+       * we need to update the viewport; we do it by simply setting the
+       * SYNC_MATRICES flag and letting the next redraw cycle take care
+       * of calling glViewport()
+       */
+      if (current_context_stage)
+        {
+          CLUTTER_SET_PRIVATE_FLAGS (current_context_stage,
+                                     CLUTTER_ACTOR_SYNC_MATRICES);
+        }
     }
   else
     CLUTTER_NOTE (MULTISTAGE, "Stage is the same");