Fix missing duplicates in the subdiv_ccg neighbors function

Duplicates of a grid corner adjacent to an edge which are on the
adjacent grid of the same face were not added when requested.

Needed for D8356 to work, it may also fix some other bug in Multires.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8385

1 files changed, 36 insertions, 3 deletions

diff --git a/source/blender/blenkernel/intern/subdiv_ccg.c b/source/blender/blenkernel/intern/subdiv_ccg.c
index 22649a2af07..11d5df4f672 100644
--- a/source/blender/blenkernel/intern/subdiv_ccg.c
+++ b/source/blender/blenkernel/intern/subdiv_ccg.c
@@ -1618,6 +1618,18 @@ static int prev_adjacent_edge_point_index(const SubdivCCG *subdiv_ccg, const int
   return point_index - 1;
 }
 
+/* When the point index corresponds to a grid corner, returs the point index which corresponds to
+ * the corner of the adjacent grid, as the adjacent edge has two separate points for each grid
+ * corner at the middle of the edge. */
+static int adjacent_grid_corner_point_index_on_edge(const SubdivCCG *subdiv_ccg,
+                                                    const int point_index)
+{
+  if (point_index == subdiv_ccg->grid_size) {
+    return point_index - 1;
+  }
+  return point_index + 1;
+}
+
 /* Common implementation of neighbor calculation when input coordinate is at the edge between two
  * coarse faces, but is not at the coarse vertex. */
 static void neighbor_coords_edge_get(const SubdivCCG *subdiv_ccg,
@@ -1626,6 +1638,7 @@ static void neighbor_coords_edge_get(const SubdivCCG *subdiv_ccg,
                                      SubdivCCGNeighbors *r_neighbors)
 
 {
+  const bool is_corner = is_corner_grid_coord(subdiv_ccg, coord);
   const int adjacent_edge_index = adjacent_edge_index_from_coord(subdiv_ccg, coord);
   BLI_assert(adjacent_edge_index >= 0);
   BLI_assert(adjacent_edge_index < subdiv_ccg->num_adjacent_edges);
@@ -1633,15 +1646,27 @@ static void neighbor_coords_edge_get(const SubdivCCG *subdiv_ccg,
 
   /* 2 neighbor points along the edge, plus one inner point per every adjacent grid. */
   const int num_adjacent_faces = adjacent_edge->num_adjacent_faces;
-  subdiv_ccg_neighbors_init(
-      r_neighbors, num_adjacent_faces + 2, (include_duplicates) ? num_adjacent_faces - 1 : 0);
+  int num_duplicates = 0;
+  if (include_duplicates) {
+    num_duplicates += num_adjacent_faces - 1;
+    if (is_corner) {
+      /* When the coord is a grid corner, add an extra duplicate per adajacent grid in all adjacent
+       * faces to the edge. */
+      num_duplicates += num_adjacent_faces;
+    }
+  }
+  subdiv_ccg_neighbors_init(r_neighbors, num_adjacent_faces + 2, num_duplicates);
 
   const int point_index = adjacent_edge_point_index_from_coord(
       subdiv_ccg, coord, adjacent_edge_index);
+  const int point_index_duplicate = adjacent_grid_corner_point_index_on_edge(subdiv_ccg,
+                                                                             point_index);
+
   const int next_point_index = next_adjacent_edge_point_index(subdiv_ccg, point_index);
   const int prev_point_index = prev_adjacent_edge_point_index(subdiv_ccg, point_index);
 
-  for (int i = 0, duplicate_i = num_adjacent_faces; i < num_adjacent_faces; ++i) {
+  int duplicate_i = num_adjacent_faces;
+  for (int i = 0; i < num_adjacent_faces; ++i) {
     SubdivCCGCoord *boundary_coords = adjacent_edge->boundary_coords[i];
     /* One step into the grid from the edge for each adjacent face. */
     SubdivCCGCoord grid_coord = boundary_coords[point_index];
@@ -1657,7 +1682,15 @@ static void neighbor_coords_edge_get(const SubdivCCG *subdiv_ccg,
       r_neighbors->coords[duplicate_i + 2] = grid_coord;
       duplicate_i++;
     }
+
+    /* When it is a corner, add the duplicate of the adjacent grid in the same face. */
+    if (include_duplicates && is_corner) {
+      SubdivCCGCoord duplicate_corner_grid_coord = boundary_coords[point_index_duplicate];
+      r_neighbors->coords[duplicate_i + 2] = duplicate_corner_grid_coord;
+      duplicate_i++;
+    }
   }
+  BLI_assert(duplicate_i - num_adjacent_faces == num_duplicates);
 }
 
 /* The corner is at the middle of edge between faces. */