Particles: initial particle birth action

A particle action is some function that is triggered by some event.
Right now, users cannot control this. There is just a
randomize-velocity on-birth action. So the direction of spawned
particles is slightly randomized now.

This also adds a new integer attribute called "Hash" which is
useful for a number of things. Mainly for generating random numbers
for a specific particle. The ID of a particle is not necessarily a good source
of randomness.

1 files changed, 3 insertions, 2 deletions

diff --git a/source/blender/simulation/intern/particle_allocator.hh b/source/blender/simulation/intern/particle_allocator.hh
index 1e7578a75ed..1c412508fe6 100644
--- a/source/blender/simulation/intern/particle_allocator.hh
+++ b/source/blender/simulation/intern/particle_allocator.hh
@@ -70,10 +70,11 @@ class ParticleAllocator : NonCopyable, NonMovable {
  private:
   AttributesAllocator attributes_allocator_;
   std::atomic<int> next_id_;
+  uint32_t hash_seed_;
 
  public:
-  ParticleAllocator(const fn::AttributesInfo &attributes_info, int next_id)
-      : attributes_allocator_(attributes_info), next_id_(next_id)
+  ParticleAllocator(const fn::AttributesInfo &attributes_info, int next_id, uint32_t hash_seed)
+      : attributes_allocator_(attributes_info), next_id_(next_id), hash_seed_(hash_seed)
   {
   }