Cycles: Stitching of subdivided and displaced meshes

This patch stitches the vertices along patch edges so that cracks can
no longer form when applying subdivision or displacement a mesh.

Subpatches are now formed in a way that ensures vertex indices along
subpatch edges are equal for adjacent subpatches. A mapping of vertices
along patch edges is built to preform stitching. Overall performance is
roughly the same, some gains were made in splitting, but some was lost
in stitching.

This fixes:
- T49049 (cracks between patches from material and uv seams)
- T49048 (discontinuous normals with true displacement)

Reviewers: sergey, brecht

Differential Revision: https://developer.blender.org/D3692

1 files changed, 8 insertions, 0 deletions

diff --git a/intern/cycles/render/mesh.h b/intern/cycles/render/mesh.h
index 50b1f0e69f1..4a24a9c2656 100644
--- a/intern/cycles/render/mesh.h
+++ b/intern/cycles/render/mesh.h
@@ -283,6 +283,14 @@ class Mesh : public Node {
 
   size_t num_subd_verts;
 
+ private:
+  unordered_map<int, int> vert_to_stitching_key_map; /* real vert index -> stitching index */
+  unordered_multimap<int, int>
+      vert_stitching_map; /* stitching index -> multiple real vert indices */
+  friend class DiagSplit;
+  friend class MeshManager;
+
+ public:
   /* Functions */
   Mesh();
   ~Mesh();