clutter/stage: Use graphene_frustum_t for clipping

Instead of 4 planes, use a graphene_frustum_t to store the clipping
planes.

The cautious reviewer might noticed that we are now setting up 6
planes: the 4 planes we were doing before, plus 2 extra planes in
the Z axis. These extra planes simulate an "infinite" Z far, and
an "on-camera" Z near.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1489

clutter/clutter/clutter-actor.c

@@ -3444,7 +3444,7 @@ cull_actor (ClutterActor        *self,
 {
   ClutterActorPrivate *priv = self->priv;
   ClutterStage *stage;
-  const graphene_plane_t *stage_clip;
+  const graphene_frustum_t *clip_frustum;
 
   if (!priv->last_paint_volume_valid)
     {
@@ -3466,10 +3466,10 @@ cull_actor (ClutterActor        *self,
     }
 
   stage = (ClutterStage *) _clutter_actor_get_stage_internal (self);
-  stage_clip = _clutter_stage_get_clip (stage);
+  clip_frustum = _clutter_stage_get_clip (stage);
 
   *result_out =
-    _clutter_paint_volume_cull (&priv->last_paint_volume, stage_clip);
+    _clutter_paint_volume_cull (&priv->last_paint_volume, clip_frustum);
 
   if (*result_out != CLUTTER_CULL_RESULT_OUT)
     {

clutter/clutter/clutter-paint-volume-private.h

@@ -124,7 +124,7 @@ void                _clutter_paint_volume_set_reference_actor  (ClutterPaintVolu
                                                                 ClutterActor *actor);
 
 ClutterCullResult   _clutter_paint_volume_cull                 (ClutterPaintVolume       *pv,
-                                                                const graphene_plane_t *planes);
+                                                                const graphene_frustum_t *frustum);
 
 void                _clutter_paint_volume_get_stage_paint_box  (ClutterPaintVolume *pv,
                                                                 ClutterStage *stage,

clutter/clutter/clutter-paint-volume.c

@@ -1072,13 +1072,10 @@ _clutter_paint_volume_set_reference_actor (ClutterPaintVolume *pv,
 
 ClutterCullResult
 _clutter_paint_volume_cull (ClutterPaintVolume       *pv,
-                            const graphene_plane_t *planes)
+                            const graphene_frustum_t *frustum)
 {
   int vertex_count;
-  graphene_point3d_t *vertices = pv->vertices;
+  graphene_box_t box;
-  gboolean partial = FALSE;
-  int i;
-  int j;
 
   if (pv->is_empty)
     return CLUTTER_CULL_RESULT_OUT;
@@ -1095,26 +1092,12 @@ _clutter_paint_volume_cull (ClutterPaintVolume     *pv,
   else
     vertex_count = 8;
 
-  for (i = 0; i < 4; i++)
+  graphene_box_init_from_points (&box, vertex_count, pv->vertices);
-    {
-      const graphene_plane_t *plane = &planes[i];
-      int out = 0;
-      for (j = 0; j < vertex_count; j++)
-        {
-          if (graphene_plane_distance (plane, &vertices[j]) < 0)
-            out++;
-        }
 
-      if (out == vertex_count)
+  if (graphene_frustum_intersects_box (frustum, &box))
-        return CLUTTER_CULL_RESULT_OUT;
-      else if (out != 0)
-        partial = TRUE;
-    }
-
-  if (partial)
-    return CLUTTER_CULL_RESULT_PARTIAL;
-  else
     return CLUTTER_CULL_RESULT_IN;
+  else
+    return CLUTTER_CULL_RESULT_OUT;
 }
 
 void

clutter/clutter/clutter-stage-private.h

@@ -98,7 +98,7 @@ ClutterActor *_clutter_stage_do_pick (ClutterStage    *stage,
 ClutterPaintVolume *_clutter_stage_paint_volume_stack_allocate (ClutterStage *stage);
 void                _clutter_stage_paint_volume_stack_free_all (ClutterStage *stage);
 
-const graphene_plane_t *_clutter_stage_get_clip (ClutterStage *stage);
+const graphene_frustum_t *_clutter_stage_get_clip (ClutterStage *stage);
 
 ClutterStageQueueRedrawEntry *_clutter_stage_queue_actor_redraw            (ClutterStage                 *stage,
                                                                             ClutterStageQueueRedrawEntry *entry,

clutter/clutter/clutter-stage.c

@@ -115,7 +115,7 @@ struct _ClutterStagePrivate
 
   GArray *paint_volume_stack;
 
-  graphene_plane_t current_clip_planes[4];
+  graphene_frustum_t clip_frustum;
 
   GSList *pending_relayouts;
   GList *pending_queue_redraws;
@@ -664,8 +664,11 @@ _cogl_util_get_eye_planes_for_screen_poly (float                   *polygon,
                                            float                    *viewport,
                                            const graphene_matrix_t  *projection,
                                            const graphene_matrix_t  *inverse_project,
-                                           graphene_plane_t        *planes)
+                                           const ClutterPerspective *perspective,
+                                           graphene_frustum_t       *frustum)
 {
+  graphene_plane_t planes[6];
+  graphene_vec4_t v;
   float Wc;
   Vector4 *tmp_poly;
   int i;
@@ -749,6 +752,18 @@ _cogl_util_get_eye_planes_for_screen_poly (float                   *polygon,
 
       graphene_plane_init_from_points (&planes[i], &p[0], &p[1], &p[2]);
     }
+
+  graphene_plane_init_from_vec4 (&planes[4],
+                                 graphene_vec4_init (&v, 0.f, 0.f, -1.f,
+                                                     perspective->z_near));
+  graphene_plane_init_from_vec4 (&planes[5],
+                                 graphene_vec4_init (&v, 0.f, 0.f, 1.f,
+                                                     perspective->z_far));
+
+  graphene_frustum_init (frustum,
+                         &planes[0], &planes[1],
+                         &planes[2], &planes[3],
+                         &planes[4], &planes[5]);
 }
 
 /* XXX: Instead of having a toplevel 2D clip region, it might be
@@ -809,7 +824,8 @@ setup_view_for_pick_or_paint (ClutterStage                *stage,
                                              viewport,
                                              &priv->projection,
                                              &priv->inverse_projection,
-                                             priv->current_clip_planes);
+                                             &priv->perspective,
+                                             &priv->clip_frustum);
 
   _clutter_stage_paint_volume_stack_free_all (stage);
 }
@@ -3075,10 +3091,10 @@ _clutter_stage_paint_volume_stack_free_all (ClutterStage *stage)
 
 /* The is an out-of-band parameter available while painting that
  * can be used to cull actors. */
-const graphene_plane_t *
+const graphene_frustum_t *
 _clutter_stage_get_clip (ClutterStage *stage)
 {
-  return stage->priv->current_clip_planes;
+  return &stage->priv->clip_frustum;
 }
 
 /* When an actor queues a redraw we add it to a list on the stage that