Revert "clutter/stage-cogl: Remove pending_swaps counter"

This reverts commit f57ce7254d.

It causes crashes, https://gitlab.gnome.org/GNOME/mutter/issues/735, and
changes various expectations relied upon by the renderer code, and being
close to release, it's safer to revert now and reconsider how to remove
the pending swap counter at a later point.

clutter/clutter/cogl/clutter-stage-cogl.c

@@ -95,7 +95,22 @@ _clutter_stage_cogl_presented (ClutterStageCogl *stage_cogl,
                                CoglFrameEvent    frame_event,
                                ClutterFrameInfo *frame_info)
 {
-  if (frame_event == COGL_FRAME_EVENT_COMPLETE)
+
+  if (frame_event == COGL_FRAME_EVENT_SYNC)
+    {
+      /* Early versions of the swap_event implementation in Mesa
+       * deliver BufferSwapComplete event when not selected for,
+       * so if we get a swap event we aren't expecting, just ignore it.
+       *
+       * https://bugs.freedesktop.org/show_bug.cgi?id=27962
+       *
+       * FIXME: This issue can be hidden inside Cogl so we shouldn't
+       * need to care about this bug here.
+       */
+      if (stage_cogl->pending_swaps > 0)
+        stage_cogl->pending_swaps--;
+    }
+  else if (frame_event == COGL_FRAME_EVENT_COMPLETE)
     {
       gint64 presentation_time_cogl = frame_info->presentation_time;
 
@@ -228,6 +243,9 @@ clutter_stage_cogl_get_update_time (ClutterStageWindow *stage_window)
 {
   ClutterStageCogl *stage_cogl = CLUTTER_STAGE_COGL (stage_window);
 
+  if (stage_cogl->pending_swaps)
+    return -1; /* in the future, indefinite */
+
   return stage_cogl->update_time;
 }
 
@@ -436,7 +454,7 @@ paint_damage_region (ClutterStageWindow    *stage_window,
   cogl_framebuffer_pop_matrix (framebuffer);
 }
 
-static void
+static gboolean
 swap_framebuffer (ClutterStageWindow    *stage_window,
                   ClutterStageView      *view,
                   cairo_rectangle_int_t *swap_region,
@@ -474,6 +492,8 @@ swap_framebuffer (ClutterStageWindow    *stage_window,
 
           cogl_onscreen_swap_region (onscreen,
                                      damage, ndamage);
+
+          return FALSE;
         }
       else
         {
@@ -482,6 +502,8 @@ swap_framebuffer (ClutterStageWindow    *stage_window,
 
           cogl_onscreen_swap_buffers_with_damage (onscreen,
                                                   damage, ndamage);
+
+          return TRUE;
         }
     }
   else
@@ -489,6 +511,8 @@ swap_framebuffer (ClutterStageWindow    *stage_window,
       CLUTTER_NOTE (BACKEND, "cogl_framebuffer_finish (framebuffer: %p)",
                     framebuffer);
       cogl_framebuffer_finish (framebuffer);
+
+      return FALSE;
     }
 }
 
@@ -612,7 +636,7 @@ scale_and_clamp_rect (const ClutterRect     *rect,
   _clutter_util_rectangle_int_extents (&tmp, dest);
 }
 
-static void
+static gboolean
 clutter_stage_cogl_redraw_view (ClutterStageWindow *stage_window,
                                 ClutterStageView   *view)
 {
@@ -931,17 +955,22 @@ clutter_stage_cogl_redraw_view (ClutterStageWindow *stage_window,
           transform_swap_region_to_onscreen (view, &swap_region);
         }
 
-      swap_framebuffer (stage_window,
+      return swap_framebuffer (stage_window,
                                view,
                                &swap_region,
                                swap_with_damage);
     }
+  else
+    {
+      return FALSE;
+    }
 }
 
 static void
 clutter_stage_cogl_redraw (ClutterStageWindow *stage_window)
 {
   ClutterStageCogl *stage_cogl = CLUTTER_STAGE_COGL (stage_window);
+  gboolean swap_event = FALSE;
   GList *l;
 
   COGL_TRACE_BEGIN (ClutterStageCoglRedraw, "Paint (Cogl Redraw)");
@@ -950,13 +979,23 @@ clutter_stage_cogl_redraw (ClutterStageWindow *stage_window)
     {
       ClutterStageView *view = l->data;
 
-      clutter_stage_cogl_redraw_view (stage_window, view);
+      swap_event =
+        clutter_stage_cogl_redraw_view (stage_window, view) || swap_event;
     }
 
   _clutter_stage_emit_after_paint (stage_cogl->wrapper);
 
   _clutter_stage_window_finish_frame (stage_window);
 
+  if (swap_event)
+    {
+      /* If we have swap buffer events then cogl_onscreen_swap_buffers
+       * will return immediately and we need to track that there is a
+       * swap in progress... */
+      if (clutter_feature_available (CLUTTER_FEATURE_SWAP_EVENTS))
+        stage_cogl->pending_swaps++;
+    }
+
   /* reset the redraw clipping for the next paint... */
   stage_cogl->initialized_redraw_clip = FALSE;
 

clutter/clutter/cogl/clutter-stage-cogl.h

@@ -49,6 +49,7 @@ struct _ClutterStageCogl
   ClutterBackend *backend;
 
   float refresh_rate;
+  int pending_swaps;
 
   gint64 last_presentation_time;
   gint64 update_time;