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, 62 insertions, 71 deletions

diff --git a/intern/cycles/render/mesh_subdivision.cpp b/intern/cycles/render/mesh_subdivision.cpp
index 46c8240fb71..a5a35fc049e 100644
--- a/intern/cycles/render/mesh_subdivision.cpp
+++ b/intern/cycles/render/mesh_subdivision.cpp
@@ -24,6 +24,7 @@
 
 #include "util/util_foreach.h"
 #include "util/util_algorithm.h"
+#include "util/util_hash.h"
 
 CCL_NAMESPACE_BEGIN
 
@@ -318,6 +319,9 @@ class OsdData {
 struct OsdPatch : Patch {
   OsdData *osd_data;
 
+  OsdPatch()
+  {
+  }
   OsdPatch(OsdData *data) : osd_data(data)
   {
   }
@@ -358,11 +362,6 @@ struct OsdPatch : Patch {
       *N = (t != 0.0f) ? *N / t : make_float3(0.0f, 0.0f, 1.0f);
     }
   }
-
-  BoundBox bound()
-  {
-    return BoundBox::empty;
-  }
 };
 
 #endif
@@ -397,29 +396,62 @@ void Mesh::tessellate(DiagSplit *split)
   Attribute *attr_vN = subd_attributes.find(ATTR_STD_VERTEX_NORMAL);
   float3 *vN = attr_vN->data_float3();
 
+  /* count patches */
+  int num_patches = 0;
   for (int f = 0; f < num_faces; f++) {
     SubdFace &face = subd_faces[f];
 
     if (face.is_quad()) {
-      /* quad */
-      QuadDice::SubPatch subpatch;
+      num_patches++;
+    }
+    else {
+      num_patches += face.num_corners;
+    }
+  }
 
-      LinearQuadPatch quad_patch;
+  /* build patches from faces */
 #ifdef WITH_OPENSUBDIV
-      OsdPatch osd_patch(&osd_data);
+  if (subdivision_type == SUBDIVISION_CATMULL_CLARK) {
+    vector<OsdPatch> osd_patches(num_patches, &osd_data);
+    OsdPatch *patch = osd_patches.data();
 
-      if (subdivision_type == SUBDIVISION_CATMULL_CLARK) {
-        osd_patch.patch_index = face.ptex_offset;
+    for (int f = 0; f < num_faces; f++) {
+      SubdFace &face = subd_faces[f];
 
-        subpatch.patch = &osd_patch;
+      if (face.is_quad()) {
+        patch->patch_index = face.ptex_offset;
+        patch->from_ngon = false;
+        patch->shader = face.shader;
+        patch++;
+      }
+      else {
+        for (int corner = 0; corner < face.num_corners; corner++) {
+          patch->patch_index = face.ptex_offset + corner;
+          patch->from_ngon = true;
+          patch->shader = face.shader;
+          patch++;
+        }
       }
-      else
+    }
+
+    /* split patches */
+    split->split_patches(osd_patches.data(), sizeof(OsdPatch));
+  }
+  else
 #endif
-      {
-        float3 *hull = quad_patch.hull;
-        float3 *normals = quad_patch.normals;
+  {
+    vector<LinearQuadPatch> linear_patches(num_patches);
+    LinearQuadPatch *patch = linear_patches.data();
+
+    for (int f = 0; f < num_faces; f++) {
+      SubdFace &face = subd_faces[f];
 
-        quad_patch.patch_index = face.ptex_offset;
+      if (face.is_quad()) {
+        float3 *hull = patch->hull;
+        float3 *normals = patch->normals;
+
+        patch->patch_index = face.ptex_offset;
+        patch->from_ngon = false;
 
         for (int i = 0; i < 4; i++) {
           hull[i] = verts[subd_face_corners[face.start_corner + i]];
@@ -440,55 +472,11 @@ void Mesh::tessellate(DiagSplit *split)
         swap(hull[2], hull[3]);
         swap(normals[2], normals[3]);
 
-        subpatch.patch = &quad_patch;
+        patch->shader = face.shader;
+        patch++;
       }
-
-      subpatch.patch->shader = face.shader;
-
-      /* Quad faces need to be split at least once to line up with split ngons, we do this
-       * here in this manner because if we do it later edge factors may end up slightly off.
-       */
-      subpatch.P00 = make_float2(0.0f, 0.0f);
-      subpatch.P10 = make_float2(0.5f, 0.0f);
-      subpatch.P01 = make_float2(0.0f, 0.5f);
-      subpatch.P11 = make_float2(0.5f, 0.5f);
-      split->split_quad(subpatch.patch, &subpatch);
-
-      subpatch.P00 = make_float2(0.5f, 0.0f);
-      subpatch.P10 = make_float2(1.0f, 0.0f);
-      subpatch.P01 = make_float2(0.5f, 0.5f);
-      subpatch.P11 = make_float2(1.0f, 0.5f);
-      split->split_quad(subpatch.patch, &subpatch);
-
-      subpatch.P00 = make_float2(0.0f, 0.5f);
-      subpatch.P10 = make_float2(0.5f, 0.5f);
-      subpatch.P01 = make_float2(0.0f, 1.0f);
-      subpatch.P11 = make_float2(0.5f, 1.0f);
-      split->split_quad(subpatch.patch, &subpatch);
-
-      subpatch.P00 = make_float2(0.5f, 0.5f);
-      subpatch.P10 = make_float2(1.0f, 0.5f);
-      subpatch.P01 = make_float2(0.5f, 1.0f);
-      subpatch.P11 = make_float2(1.0f, 1.0f);
-      split->split_quad(subpatch.patch, &subpatch);
-    }
-    else {
-      /* ngon */
-#ifdef WITH_OPENSUBDIV
-      if (subdivision_type == SUBDIVISION_CATMULL_CLARK) {
-        OsdPatch patch(&osd_data);
-
-        patch.shader = face.shader;
-
-        for (int corner = 0; corner < face.num_corners; corner++) {
-          patch.patch_index = face.ptex_offset + corner;
-
-          split->split_quad(&patch);
-        }
-      }
-      else
-#endif
-      {
+      else {
+        /* ngon */
         float3 center_vert = make_float3(0.0f, 0.0f, 0.0f);
         float3 center_normal = make_float3(0.0f, 0.0f, 0.0f);
 
@@ -499,13 +487,13 @@ void Mesh::tessellate(DiagSplit *split)
         }
 
         for (int corner = 0; corner < face.num_corners; corner++) {
-          LinearQuadPatch patch;
-          float3 *hull = patch.hull;
-          float3 *normals = patch.normals;
+          float3 *hull = patch->hull;
+          float3 *normals = patch->normals;
 
-          patch.patch_index = face.ptex_offset + corner;
+          patch->patch_index = face.ptex_offset + corner;
+          patch->from_ngon = true;
 
-          patch.shader = face.shader;
+          patch->shader = face.shader;
 
           hull[0] =
               verts[subd_face_corners[face.start_corner + mod(corner + 0, face.num_corners)]];
@@ -537,10 +525,13 @@ void Mesh::tessellate(DiagSplit *split)
             }
           }
 
-          split->split_quad(&patch);
+          patch++;
         }
       }
     }
+
+    /* split patches */
+    split->split_patches(linear_patches.data(), sizeof(LinearQuadPatch));
   }
 
   /* interpolate center points for attributes */