[Bf-blender-cvs] [de2e80a1bfa] sybren-usd: USD: Export vertex velocities for fluid simulations

[Sybren A. Stüvel]

Commit: de2e80a1bfaf8fdd9e28f6fb345bc586cd2f5b2d
Author: Sybren A. Stüvel
Date:   Fri Jul 26 11:42:03 2019 +0200
Branches: sybren-usd
https://developer.blender.org/rBde2e80a1bfaf8fdd9e28f6fb345bc586cd2f5b2d

USD: Export vertex velocities for fluid simulations

Currently only fluid simulations have explicit vertex velocities. This
is the most important case for exporting velocities, though, as the
baked mesh changes topology all the time, and thus computing the
velocities at import time in a post-processing step is hard.

===================================================================

M	source/blender/usd/intern/usd_writer_mesh.cc
M	source/blender/usd/intern/usd_writer_mesh.h

===================================================================

diff --git a/source/blender/usd/intern/usd_writer_mesh.cc b/source/blender/usd/intern/usd_writer_mesh.cc
index 4c2994ea29d..8cd7f049a5d 100644
--- a/source/blender/usd/intern/usd_writer_mesh.cc
+++ b/source/blender/usd/intern/usd_writer_mesh.cc
@@ -14,11 +14,14 @@ extern "C" {
 #include "BKE_library.h"
 #include "BKE_material.h"
 #include "BKE_mesh.h"
+#include "BKE_modifier.h"
 
 #include "DEG_depsgraph.h"
 
 #include "DNA_mesh_types.h"
 #include "DNA_meshdata_types.h"
+#include "DNA_modifier_types.h"
+#include "DNA_object_fluidsim_types.h"
 #include "DNA_particle_types.h"
 }
 
@@ -164,6 +167,7 @@ void USDGenericMeshWriter::write_mesh(HierarchyContext &context, Mesh *mesh)
 
   write_uv_maps(mesh, usd_mesh);
   write_normals(mesh, usd_mesh);
+  write_surface_velocity(context.object, mesh, usd_mesh);
 
   // TODO(Sybren): figure out what happens when the face groups change.
   if (frame_has_been_written_) {
@@ -346,6 +350,48 @@ void USDGenericMeshWriter::write_normals(const Mesh *mesh, pxr::UsdGeomMesh usd_
   usd_mesh.SetNormalsInterpolation(pxr::UsdGeomTokens->faceVarying);
 }
 
+void USDGenericMeshWriter::write_surface_velocity(Object *object,
+                                                  const Mesh *mesh,
+                                                  pxr::UsdGeomMesh usd_mesh)
+{
+  /* Only velocities from the fluid simulation are exported. This is the most important case,
+   * though, as the baked mesh changes topology all the time, and thus computing the velocities
+   * at import time in a post-processing step is hard. */
+  ModifierData *md = modifiers_findByType(object, eModifierType_Fluidsim);
+  if (md == nullptr) {
+    return;
+  }
+
+  /* Check that the fluid sim modifier is enabled and has useful data. */
+  const bool use_render = (DEG_get_mode(depsgraph) == DAG_EVAL_RENDER);
+  const ModifierMode required_mode = use_render ? eModifierMode_Render : eModifierMode_Realtime;
+  const Scene *scene = DEG_get_evaluated_scene(depsgraph);
+  if (!modifier_isEnabled(scene, md, required_mode)) {
+    return;
+  }
+  FluidsimModifierData *fsmd = reinterpret_cast<FluidsimModifierData *>(md);
+  if (!fsmd->fss || fsmd->fss->type != OB_FLUIDSIM_DOMAIN) {
+    return;
+  }
+  FluidsimSettings *fss = fsmd->fss;
+  if (!fss->meshVelocities) {
+    return;
+  }
+
+  /* Export per-vertex velocity vectors. */
+  pxr::VtVec3fArray usd_velocities;
+  usd_velocities.reserve(mesh->totvert);
+
+  FluidVertexVelocity *mesh_velocities = fss->meshVelocities;
+  for (int vertex_idx = 0, totvert = mesh->totvert; vertex_idx < totvert;
+       ++vertex_idx, ++mesh_velocities) {
+    usd_velocities.push_back(pxr::GfVec3f(mesh_velocities->vel));
+  }
+
+  pxr::UsdTimeCode timecode = get_export_time_code();
+  usd_mesh.CreateVelocitiesAttr().Set(usd_velocities, timecode);
+}
+
 USDMeshWriter::USDMeshWriter(const USDExporterContext &ctx) : USDGenericMeshWriter(ctx)
 {
 }
diff --git a/source/blender/usd/intern/usd_writer_mesh.h b/source/blender/usd/intern/usd_writer_mesh.h
index 2eddf114bf4..76e91dea522 100644
--- a/source/blender/usd/intern/usd_writer_mesh.h
+++ b/source/blender/usd/intern/usd_writer_mesh.h
@@ -27,6 +27,7 @@ class USDGenericMeshWriter : public USDAbstractWriter {
                         const std::map<short, pxr::VtIntArray> &usd_face_groups);
   void write_uv_maps(const Mesh *mesh, pxr::UsdGeomMesh usd_mesh);
   void write_normals(const Mesh *mesh, pxr::UsdGeomMesh usd_mesh);
+  void write_surface_velocity(Object *object, const Mesh *mesh, pxr::UsdGeomMesh usd_mesh);
 };
 
 class USDMeshWriter : public USDGenericMeshWriter {