Cycles: add support for rendering deformation motion blur from Alembic caches.

This patch adds the ability to render motion blur from Alembic caches.
The motion blur data is derived from a velocity attribute whose name has
to be defined by the user through the MeshSequenceCache modifier, with a
default value of ".velocities", which is the standard name in Alembic
for the velocity property, although other software may ignore it and
write velocity with their own naming convention (e.g. "v" in Houdini).

Furthermore, a property was added to define how the velocity vectors
are interpreted with regard to time : frame or second. "Frame"
means that the velocity is already scaled by the time step and we do not
need to modify it for it to look proper. "Second" means that the unit
the velocity was measured in is in seconds and so has to be scaled by
some time step computed here as being the time between two frames (1 /
FPS, which would be typical for a simulation). This appears to be
common, and is the default behavior.

Another property was added to control the scale of the velocity to
further modify the look of the motion blur.

Reviewed By: brecht, sybren

Differential Revision: https://developer.blender.org/D2388

1 files changed, 91 insertions, 1 deletions

diff --git a/source/blender/makesrna/intern/rna_modifier.c b/source/blender/makesrna/intern/rna_modifier.c
index d4b1009df4d..ea33307060c 100644
--- a/source/blender/makesrna/intern/rna_modifier.c
+++ b/source/blender/makesrna/intern/rna_modifier.c
@@ -113,7 +113,7 @@ const EnumPropertyItem rna_enum_object_modifier_type_items[] = {
     {0, "", 0, N_("Generate"), ""},
     {eModifierType_Array,
      "ARRAY",
-     ICON_MOD_ARRAY,
+  ICON_MOD_ARRAY,
      "Array",
      "Create copies of the shape with offsets"},
     {eModifierType_Bevel,
@@ -1699,6 +1699,51 @@ static bool rna_Modifier_show_expanded_get(PointerRNA *ptr)
   return md->ui_expand_flag & (1 << 0);
 }
 
+static int rna_MeshSequenceCacheModifier_has_velocity_get(PointerRNA *ptr)
+{
+#  ifdef WITH_ALEMBIC
+  MeshSeqCacheModifierData *mcmd = (MeshSeqCacheModifierData *)ptr->data;
+  return ABC_has_vec3_array_property_named(mcmd->reader, mcmd->cache_file->velocity_name);
+#  else
+  return false;
+  UNUSED_VARS(ptr);
+#  endif
+}
+
+static int rna_MeshSequenceCacheModifier_read_velocity_get(PointerRNA *ptr)
+{
+#  ifdef WITH_ALEMBIC
+  MeshSeqCacheModifierData *mcmd = (MeshSeqCacheModifierData *)ptr->data;
+
+  if (mcmd->num_vertices == 0) {
+    return 0;
+  }
+
+  if (mcmd->vertex_velocities) {
+    MEM_freeN(mcmd->vertex_velocities);
+  }
+
+  mcmd->vertex_velocities = MEM_mallocN(sizeof(MeshCacheVertexVelocity) * mcmd->num_vertices,
+                                        "Mesh Cache Velocities");
+
+  int num_read = ABC_read_velocity_cache(mcmd->reader,
+                                         mcmd->cache_file->velocity_name,
+                                         mcmd->last_lookup_time,
+                                         mcmd->velocity_scale * mcmd->velocity_delta,
+                                         mcmd->num_vertices,
+                                         (float *)mcmd->vertex_velocities);
+
+  if (num_read == -1 || num_read != mcmd->num_vertices) {
+    return false;
+  }
+
+  return true;
+#  else
+  return false;
+  UNUSED_VARS(ptr);
+#  endif
+}
+
 #else
 
 /* NOTE: *MUST* return subdivision_type property. */
@@ -6066,6 +6111,22 @@ static void rna_def_modifier_meshcache(BlenderRNA *brna)
   RNA_define_lib_overridable(false);
 }
 
+static void rna_def_mesh_cache_velocities(BlenderRNA *brna)
+{
+  StructRNA *srna;
+  PropertyRNA *prop;
+
+  srna = RNA_def_struct(brna, "MeshCacheVertexVelocity", NULL);
+  RNA_def_struct_ui_text(srna, "Mesh Cache Velocity", "Velocity attribute of an Alembic mesh");
+  RNA_def_struct_ui_icon(srna, ICON_VERTEXSEL);
+
+  prop = RNA_def_property(srna, "velocity", PROP_FLOAT, PROP_VELOCITY);
+  RNA_def_property_array(prop, 3);
+  RNA_def_property_float_sdna(prop, NULL, "vel");
+  RNA_def_property_ui_text(prop, "Velocity", "");
+  RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+}
+
 static void rna_def_modifier_meshseqcache(BlenderRNA *brna)
 {
   StructRNA *srna;
@@ -6108,6 +6169,35 @@ static void rna_def_modifier_meshseqcache(BlenderRNA *brna)
 
   RNA_def_property_update(prop, 0, "rna_Modifier_update");
 
+  prop = RNA_def_property(srna, "velocity_scale", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_float_sdna(prop, NULL, "velocity_scale");
+  RNA_def_property_range(prop, 0.0f, FLT_MAX);
+  RNA_def_property_ui_text(
+      prop,
+      "Velocity Scale",
+      "Multiplier used to control the magnitude of the velocity vectors for time effects");
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  /* -------------------------- Velocity Vectors -------------------------- */
+
+  prop = RNA_def_property(srna, "vertex_velocities", PROP_COLLECTION, PROP_NONE);
+  RNA_def_property_collection_sdna(prop, NULL, "vertex_velocities", "num_vertices");
+  RNA_def_property_struct_type(prop, "MeshCacheVertexVelocity");
+  RNA_def_property_ui_text(
+      prop, "Fluid Mesh Vertices", "Vertices of the fluid mesh generated by simulation");
+
+  rna_def_mesh_cache_velocities(brna);
+
+  prop = RNA_def_property(srna, "has_velocity", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_ui_text(prop, "Has Velocity Cache", "");
+  RNA_def_property_boolean_funcs(prop, "rna_MeshSequenceCacheModifier_has_velocity_get", NULL);
+  RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+
+  prop = RNA_def_property(srna, "read_velocity", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_ui_text(prop, "Read Velocity Cache", "");
+  RNA_def_property_boolean_funcs(prop, "rna_MeshSequenceCacheModifier_read_velocity_get", NULL);
+  RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+
   RNA_define_lib_overridable(false);
 }