Fix [#29265] Particle Instance: Create Along Paths + Children inconsistent with actual children hair particles

* Hair particle rotations weren't calculated properly for particle locations along a path and the "particle on path" calculations were not correct in many other ways too.
* Now the particle's location along a path is interpolated directly from the cached paths if it exist. These paths are always correctly calculated.
* Paths are now cached if a particle instance modifier using the particle system with the path option exists.

1 files changed, 14 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c
index 5a64da7354e..e853c0fee19 100644
--- a/source/blender/blenkernel/intern/particle_system.c
+++ b/source/blender/blenkernel/intern/particle_system.c
@@ -3407,6 +3407,7 @@ static void psys_update_path_cache(ParticleSimulationData *sim, float cfra)
 	ParticleSystem *psys = sim->psys;
 	ParticleSettings *part = psys->part;
 	ParticleEditSettings *pset = &sim->scene->toolsettings->particle;
+	Base *base;
 	int distr=0, alloc=0, skip=0;
 
 	if((psys->part->childtype && psys->totchild != get_psys_tot_child(sim->scene, psys)) || psys->recalc&PSYS_RECALC_RESET)
@@ -3449,6 +3450,19 @@ static void psys_update_path_cache(ParticleSimulationData *sim, float cfra)
 		}
 	}
 
+
+	/* particle instance modifier with "path" option need cached paths even if particle system doesn't */
+	for (base = sim->scene->base.first; base; base= base->next) {
+		ModifierData *md = modifiers_findByType(base->object, eModifierType_ParticleInstance);
+		if(md) {
+			ParticleInstanceModifierData *pimd = (ParticleInstanceModifierData *)md;
+			if(pimd->flag & eParticleInstanceFlag_Path && pimd->ob == sim->ob && pimd->psys == (psys - (ParticleSystem*)sim->ob->particlesystem.first)) {
+				skip = 0;
+				break;
+			}
+		}
+	}
+
 	if(!skip) {
 		psys_cache_paths(sim, cfra);