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, 23 deletions

diff --git a/source/blender/makesdna/DNA_modifier_types.h b/source/blender/makesdna/DNA_modifier_types.h
index 8520786a030..31daa778b03 100644
--- a/source/blender/makesdna/DNA_modifier_types.h
+++ b/source/blender/makesdna/DNA_modifier_types.h
@@ -2144,10 +2144,6 @@ enum {
   MOD_NORMALEDIT_MIX_MUL = 3,
 };
 
-typedef struct MeshCacheVertexVelocity {
-  float vel[3];
-} MeshCacheVertexVelocity;
-
 typedef struct MeshSeqCacheModifierData {
   ModifierData modifier;
 
@@ -2163,25 +2159,6 @@ typedef struct MeshSeqCacheModifierData {
   /* Runtime. */
   struct CacheReader *reader;
   char reader_object_path[1024];
-
-  /* Vertex velocities read from the cache. The velocities are not automatically read during
-   * modifier execution, and therefore have to manually be read when needed. This is only used
-   * through the RNA for now. */
-  struct MeshCacheVertexVelocity *vertex_velocities;
-
-  /* The number of vertices of the Alembic mesh, set when the modifier is executed. */
-  int num_vertices;
-
-  /* Time (in frames or seconds) between two velocity samples. Automatically computed to
-   * scale the velocity vectors at render time for generating proper motion blur data. */
-  float velocity_delta;
-
-  /* Caches the scene time (in seconds) used to lookup data in the Alembic archive when the
-   * modifier was last executed. Used to access Alembic samples through the RNA. */
-  float last_lookup_time;
-
-  int _pad1;
-  void *_pad2;
 } MeshSeqCacheModifierData;
 
 /* MeshSeqCacheModifierData.read_flag */