Particles: initial object socket and emitter node support

Object sockets work now, but only the new Object Transforms and the
Particle Mesh Emitter node use it. The emitter does not actually
use the mesh surface yet. Instead, new particles are just emitted around
the origin of the object.

Internally, handles to object data blocks are passed around in the network,
instead of raw object pointers. Using handles has a couple of benefits:
* The caller of the function has control over which handles can be resolved
  and therefore limit access to specific data. The set of data blocks that
  is accessed by a node tree should be known statically. This is necessary
  for a proper integration with the dependency graph.
* When the pointer to an object changes (e.g. after restarting Blender),
  all handles are still valid.
* When an object is deleted, the handle is invalidated without causing crashes.
* The handle is just an integer that can be stored per particle and can be cached easily.

The mapping between handles and their corresponding data blocks is
stored in the Simulation data block.

1 files changed, 12 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_simulation_types.h b/source/blender/makesdna/DNA_simulation_types.h
index c4ff51a107e..f7a7f94da53 100644
--- a/source/blender/makesdna/DNA_simulation_types.h
+++ b/source/blender/makesdna/DNA_simulation_types.h
@@ -37,6 +37,9 @@ typedef struct Simulation {
 
   /** List containing SimulationState objects. */
   struct ListBase states;
+
+  /** List containing PersistentDataHandleItem objects. */
+  struct ListBase persistent_data_handles;
 } Simulation;
 
 typedef struct SimulationState {
@@ -64,6 +67,15 @@ typedef struct ParticleSimulationState {
   struct ListBase ptcaches;
 } ParticleSimulationState;
 
+/** Stores a mapping between an integer handle and a corresponding ID data block. */
+typedef struct PersistentDataHandleItem {
+  struct PersistentDataHandleItem *next;
+  struct PersistentDataHandleItem *prev;
+  struct ID *id;
+  int handle;
+  char _pad[4];
+} PersistentDataHandleItem;
+
 /* Simulation.flag */
 enum {
   SIM_DS_EXPAND = (1 << 0),