Modifiers: export motion blur velocity through attribute

Previously fluid simulation and Alembic modifiers had a dedicated function
to query the velocity for motion blur. Now use a more generic system where
those modifiers output a velocity attribute.

Advantages:
* Geometry and particle nodes can output velocity through the same mechanism,
  or read the attribute coming from earlier modifiers.
* The velocity can be preserved through modifiers like subdivision surface or
  auto smooth.
* USD and Alembic previously only output velocity from fluid simulation, now
  they work with velocity from other sources too.
* Simplifies the code for renderers like Cycles and exporters like
  Alembic and USD.

This breaks compatibility:
* External renderers and exporters accessing these velocities through the
  Python API now need to use the attribute instead.
* Existing modifier node setups that create an attribute named "velocity"
  will render differently with motion blur.

Differential Revision: https://developer.blender.org/D12305

1 files changed, 0 insertions, 24 deletions

diff --git a/source/blender/makesrna/intern/rna_fluid.c b/source/blender/makesrna/intern/rna_fluid.c
index 10e899b7ee3..90e77406f23 100644
--- a/source/blender/makesrna/intern/rna_fluid.c
+++ b/source/blender/makesrna/intern/rna_fluid.c
@@ -1242,22 +1242,6 @@ static void rna_Fluid_flowtype_set(struct PointerRNA *ptr, int value)
 
 #else
 
-static void rna_def_fluid_mesh_vertices(BlenderRNA *brna)
-{
-  StructRNA *srna;
-  PropertyRNA *prop;
-
-  srna = RNA_def_struct(brna, "FluidDomainVertexVelocity", NULL);
-  RNA_def_struct_ui_text(srna, "Fluid Mesh Velocity", "Velocity of a simulated fluid 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_fluid_domain_settings(BlenderRNA *brna)
 {
   StructRNA *srna;
@@ -2019,14 +2003,6 @@ static void rna_def_fluid_domain_settings(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Mesh generator", "Which particle level set generator to use");
   RNA_def_property_update(prop, NC_OBJECT | ND_DRAW, "rna_Fluid_update");
 
-  prop = RNA_def_property(srna, "mesh_vertices", PROP_COLLECTION, PROP_NONE);
-  RNA_def_property_collection_sdna(prop, NULL, "mesh_velocities", "totvert");
-  RNA_def_property_struct_type(prop, "FluidDomainVertexVelocity");
-  RNA_def_property_ui_text(
-      prop, "Fluid Mesh Vertices", "Vertices of the fluid mesh generated by simulation");
-
-  rna_def_fluid_mesh_vertices(brna);
-
   prop = RNA_def_property(srna, "use_mesh", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "flags", FLUID_DOMAIN_USE_MESH);
   RNA_def_property_ui_text(prop, "Use Mesh", "Enable fluid mesh (using amplification)");