Subdivision: add support for vertex creasing

This adds vertex creasing support for OpenSubDiv for modeling, rendering,
Alembic and USD I/O.

For modeling, vertex creasing follows the edge creasing implementation with an
operator accessible through the Vertex menu in Edit Mode, and some parameter in
the properties panel. The option in the Subsurf and Multires to use edge
creasing also affects vertex creasing.

The vertex crease data is stored as a CustomData layer, unlike edge creases
which for now are stored in `MEdge`, but will in the future also be moved to
a `CustomData` layer. See comments for details on the difference in behavior
for the `CD_CREASE` layer between egdes and vertices.

For Cycles this adds sockets on the Mesh node to hold data about which vertices
are creased (one socket for the indices, one for the weigths).

Viewport rendering of vertex creasing reuses the same color scheme as for edges
and creased vertices are drawn bigger than uncreased vertices.

For Alembic and USD, vertex crease support follows the edge crease
implementation, they are always read, but only exported if a `Subsurf` modifier
is present on the Mesh.

Reviewed By: brecht, fclem, sergey, sybren, campbellbarton

Differential Revision: https://developer.blender.org/D10145

3 files changed, 16 insertions, 6 deletions

diff --git a/source/blender/draw/engines/overlay/overlay_shader.c b/source/blender/draw/engines/overlay/overlay_shader.c
index 389704b3d66..9899dce5df6 100644
--- a/source/blender/draw/engines/overlay/overlay_shader.c
+++ b/source/blender/draw/engines/overlay/overlay_shader.c
@@ -323,7 +323,9 @@ GPUShader *OVERLAY_shader_edit_mesh_vert(void)
                                  datatoc_edit_mesh_common_lib_glsl,
                                  datatoc_edit_mesh_vert_glsl,
                                  NULL},
-        .frag = (const char *[]){datatoc_gpu_shader_point_varying_color_frag_glsl, NULL},
+        .frag = (const char *[]){datatoc_common_globals_lib_glsl,
+                                 datatoc_gpu_shader_point_varying_color_frag_glsl,
+                                 NULL},
         .defs = (const char *[]){sh_cfg->def, "#define VERT\n", NULL},
     });
   }
diff --git a/source/blender/draw/engines/overlay/shaders/edit_mesh_common_lib.glsl b/source/blender/draw/engines/overlay/shaders/edit_mesh_common_lib.glsl
index 195d2a5a7b7..418c7bceb63 100644
--- a/source/blender/draw/engines/overlay/shaders/edit_mesh_common_lib.glsl
+++ b/source/blender/draw/engines/overlay/shaders/edit_mesh_common_lib.glsl
@@ -36,7 +36,7 @@ vec4 EDIT_MESH_edge_vertex_color(int vertex_flag)
   return color;
 }
 
-vec4 EDIT_MESH_vertex_color(int vertex_flag)
+vec4 EDIT_MESH_vertex_color(int vertex_flag, float vertex_crease)
 {
   if ((vertex_flag & VERT_ACTIVE) != 0) {
     return vec4(colorEditMeshActive.xyz, 1.0);
@@ -45,6 +45,10 @@ vec4 EDIT_MESH_vertex_color(int vertex_flag)
     return colorVertexSelect;
   }
   else {
+    /* Full crease color if not selected nor active. */
+    if (vertex_crease > 0.0) {
+      return mix(colorVertex, colorEdgeCrease, vertex_crease);
+    }
     return colorVertex;
   }
 }
diff --git a/source/blender/draw/engines/overlay/shaders/edit_mesh_vert.glsl b/source/blender/draw/engines/overlay/shaders/edit_mesh_vert.glsl
index a3ff277b714..5cee976f9a8 100644
--- a/source/blender/draw/engines/overlay/shaders/edit_mesh_vert.glsl
+++ b/source/blender/draw/engines/overlay/shaders/edit_mesh_vert.glsl
@@ -13,6 +13,9 @@ in vec4 norAndFlag;
 #endif
 
 out vec4 finalColor;
+#ifdef VERT
+out float vertexCrease;
+#endif
 #ifdef EDGE
 out vec4 finalColorOuter;
 #endif
@@ -44,8 +47,9 @@ void main()
   ivec4 m_data = data & dataMask;
 
 #if defined(VERT)
-  finalColor = EDIT_MESH_vertex_color(m_data.y);
-  gl_PointSize = sizeVertex * 2.0;
+  vertexCrease = float(m_data.z >> 4) / 15.0;
+  finalColor = EDIT_MESH_vertex_color(m_data.y, vertexCrease);
+  gl_PointSize = sizeVertex * ((vertexCrease > 0.0) ? 3.0 : 2.0);
   /* Make selected and active vertex always on top. */
   if ((data.x & VERT_SELECTED) != 0) {
     gl_Position.z -= 5e-7 * abs(gl_Position.w);
@@ -65,9 +69,9 @@ void main()
   selectOverride = (m_data.y & EDGE_SELECTED);
 #  endif
 
-  float crease = float(m_data.z) / 255.0;
+  float edge_crease = float(m_data.z & 0xF) / 15.0;
   float bweight = float(m_data.w) / 255.0;
-  finalColorOuter = EDIT_MESH_edge_color_outer(m_data.y, m_data.x, crease, bweight);
+  finalColorOuter = EDIT_MESH_edge_color_outer(m_data.y, m_data.x, edge_crease, bweight);
 
   if (finalColorOuter.a > 0.0) {
     gl_Position.z -= 5e-7 * abs(gl_Position.w);