[mutter] clutter/paint-volume: Use graphene for computing union of paint volumes

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit d2f8a30625e8369371dd4740886586e35797e654
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Fri Oct 16 22:58:22 2020 +0200

    clutter/paint-volume: Use graphene for computing union of paint volumes
    
    Apparently clutter_paint_volume_union() has problems building the union
    of two paint volumes in eye coordinates, that's probably because of the
    negative coordinates that come into play there.
    
    Circumvent that by making even more use of Graphene and letting it take
    care of computing the union. We do that by creating two graphene_box_t's
    from the axis-aligned paint volumes and intersecting those boxes, then
    setting our vertices to the new min and max points of the resulting box.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1507

 clutter/clutter/clutter-paint-volume.c | 90 +++++++++-------------------------
 1 file changed, 24 insertions(+), 66 deletions(-)
---
diff --git a/clutter/clutter/clutter-paint-volume.c b/clutter/clutter/clutter-paint-volume.c
index 413be47a83..97077f7d1d 100644
--- a/clutter/clutter/clutter-paint-volume.c
+++ b/clutter/clutter/clutter-paint-volume.c
@@ -533,6 +533,11 @@ clutter_paint_volume_union (ClutterPaintVolume *pv,
                             const ClutterPaintVolume *another_pv)
 {
   ClutterPaintVolume aligned_pv;
+  graphene_point3d_t min;
+  graphene_point3d_t max;
+  graphene_box_t another_box;
+  graphene_box_t union_box;
+  graphene_box_t box;
 
   g_return_if_fail (pv != NULL);
   g_return_if_fail (another_pv != NULL);
@@ -540,9 +545,6 @@ clutter_paint_volume_union (ClutterPaintVolume *pv,
   /* Both volumes have to belong to the same local coordinate space */
   g_return_if_fail (pv->actor == another_pv->actor);
 
-  /* NB: we only have to update vertices 0, 1, 3 and 4
-   * (See the ClutterPaintVolume typedef for more details) */
-
   /* We special case empty volumes because otherwise we'd end up
    * calculating a bounding box that would enclose the origin of
    * the empty volume which isn't desired.
@@ -559,78 +561,34 @@ clutter_paint_volume_union (ClutterPaintVolume *pv,
   if (!pv->is_axis_aligned)
     _clutter_paint_volume_axis_align (pv);
 
-  if (!another_pv->is_axis_aligned)
+  _clutter_paint_volume_complete (pv);
+
+  if (!another_pv->is_axis_aligned || !another_pv->is_complete)
     {
       _clutter_paint_volume_copy_static (another_pv, &aligned_pv);
       _clutter_paint_volume_axis_align (&aligned_pv);
+      _clutter_paint_volume_complete (&aligned_pv);
       another_pv = &aligned_pv;
     }
 
-  /* grow left*/
-  /* left vertices 0, 3, 4, 7 */
-  if (another_pv->vertices[0].x < pv->vertices[0].x)
-    {
-      int min_x = another_pv->vertices[0].x;
-      pv->vertices[0].x = min_x;
-      pv->vertices[3].x = min_x;
-      pv->vertices[4].x = min_x;
-      /* pv->vertices[7].x = min_x; */
-    }
-
-  /* grow right */
-  /* right vertices 1, 2, 5, 6 */
-  if (another_pv->vertices[1].x > pv->vertices[1].x)
-    {
-      int max_x = another_pv->vertices[1].x;
-      pv->vertices[1].x = max_x;
-      /* pv->vertices[2].x = max_x; */
-      /* pv->vertices[5].x = max_x; */
-      /* pv->vertices[6].x = max_x; */
-    }
-
-  /* grow up */
-  /* top vertices 0, 1, 4, 5 */
-  if (another_pv->vertices[0].y < pv->vertices[0].y)
-    {
-      int min_y = another_pv->vertices[0].y;
-      pv->vertices[0].y = min_y;
-      pv->vertices[1].y = min_y;
-      pv->vertices[4].y = min_y;
-      /* pv->vertices[5].y = min_y; */
-    }
+  if (G_LIKELY (pv->is_2d))
+    graphene_box_init_from_points (&box, 4, pv->vertices);
+  else
+    graphene_box_init_from_points (&box, 8, pv->vertices);
 
-  /* grow down */
-  /* bottom vertices 2, 3, 6, 7 */
-  if (another_pv->vertices[3].y > pv->vertices[3].y)
-    {
-      int may_y = another_pv->vertices[3].y;
-      /* pv->vertices[2].y = may_y; */
-      pv->vertices[3].y = may_y;
-      /* pv->vertices[6].y = may_y; */
-      /* pv->vertices[7].y = may_y; */
-    }
+  if (G_LIKELY (another_pv->is_2d))
+    graphene_box_init_from_points (&another_box, 4, another_pv->vertices);
+  else
+    graphene_box_init_from_points (&another_box, 8, another_pv->vertices);
 
-  /* grow forward */
-  /* front vertices 0, 1, 2, 3 */
-  if (another_pv->vertices[0].z < pv->vertices[0].z)
-    {
-      int min_z = another_pv->vertices[0].z;
-      pv->vertices[0].z = min_z;
-      pv->vertices[1].z = min_z;
-      /* pv->vertices[2].z = min_z; */
-      pv->vertices[3].z = min_z;
-    }
+  graphene_box_union (&box, &another_box, &union_box);
 
-  /* grow backward */
-  /* back vertices 4, 5, 6, 7 */
-  if (another_pv->vertices[4].z > pv->vertices[4].z)
-    {
-      int maz_z = another_pv->vertices[4].z;
-      pv->vertices[4].z = maz_z;
-      /* pv->vertices[5].z = maz_z; */
-      /* pv->vertices[6].z = maz_z; */
-      /* pv->vertices[7].z = maz_z; */
-    }
+  graphene_box_get_min (&union_box, &min);
+  graphene_box_get_max (&union_box, &max);
+  graphene_point3d_init (&pv->vertices[0], min.x, max.y, min.z);
+  graphene_point3d_init (&pv->vertices[1], max.x, max.y, min.z);
+  graphene_point3d_init (&pv->vertices[3], min.x, min.y, min.z);
+  graphene_point3d_init (&pv->vertices[4], min.x, max.y, max.z);
 
   if (pv->vertices[4].z == pv->vertices[0].z)
     pv->is_2d = TRUE;