Particles: Support changing modifiers during particle edit mode

The idea is to only use pointers to particles in original object when
creating an edit structure. The derived mesh we get from evaluated
object.

The rest of the commit is just keeping pointers in sync.

3 files changed, 35 insertions, 8 deletions

diff --git a/source/blender/blenkernel/BKE_pointcache.h b/source/blender/blenkernel/BKE_pointcache.h
index 8daef0348b9..21673213db1 100644
--- a/source/blender/blenkernel/BKE_pointcache.h
+++ b/source/blender/blenkernel/BKE_pointcache.h
@@ -246,13 +246,25 @@ typedef struct PTCacheUndo {
 	size_t undo_size;
 } PTCacheUndo;
 
+enum {
+	/* Modifier stack got evaluated during particle edit mode, need to copy
+	 * new evaluated particles to the edit struct.
+	 */
+	PT_CACHE_EDIT_UPDATE_PARTICLE_FROM_EVAL = (1 << 0),
+};
+
 typedef struct PTCacheEdit {
+	int flags;
+
 	PTCacheEditPoint *points;
 
 	struct PTCacheID pid;
 
 	/* particles stuff */
 	struct ParticleSystem *psys;
+	struct ParticleSystem *psys_eval;
+	struct ParticleSystemModifierData *psmd;
+	struct ParticleSystemModifierData *psmd_eval;
 	struct KDTree *emitter_field;
 	float *emitter_cosnos; /* localspace face centers and normals (average of its verts), from the derived mesh */
 	int *mirror_cache;
diff --git a/source/blender/blenkernel/intern/particle.c b/source/blender/blenkernel/intern/particle.c
index 9461b0a21a5..693d6ac587e 100644
--- a/source/blender/blenkernel/intern/particle.c
+++ b/source/blender/blenkernel/intern/particle.c
@@ -2824,7 +2824,6 @@ void psys_cache_edit_paths(Depsgraph *depsgraph, Scene *scene, Object *ob, PTCac
 	ParticleEditSettings *pset = &scene->toolsettings->particle;
 
 	ParticleSystem *psys = edit->psys;
-	ParticleSystemModifierData *psmd = psys_get_modifier(ob, psys);
 
 	ParticleData *pa = psys ? psys->particles : NULL;
 
@@ -2851,7 +2850,7 @@ void psys_cache_edit_paths(Depsgraph *depsgraph, Scene *scene, Object *ob, PTCac
 	CacheEditrPathsIterData iter_data;
 	iter_data.object = ob;
 	iter_data.edit = edit;
-	iter_data.psmd = psmd;
+	iter_data.psmd = edit->psmd_eval;
 	iter_data.pa = pa;
 	iter_data.segments = segments;
 	iter_data.use_weight = use_weight;
@@ -2881,7 +2880,7 @@ void psys_cache_edit_paths(Depsgraph *depsgraph, Scene *scene, Object *ob, PTCac
 		sim.scene = scene;
 		sim.ob = ob;
 		sim.psys = psys;
-		sim.psmd = psys_get_modifier(ob, psys);
+		sim.psmd = edit->psmd_eval;
 
 		psys_cache_child_paths(&sim, cfra, true, use_render_params);
 	}
diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c
index 9c6c30143cc..314a58647a9 100644
--- a/source/blender/blenkernel/intern/particle_system.c
+++ b/source/blender/blenkernel/intern/particle_system.c
@@ -4211,7 +4211,9 @@ void particle_system_update(struct Depsgraph *depsgraph, Scene *scene, Object *o
 {
 	ParticleSimulationData sim= {0};
 	ParticleSettings *part = psys->part;
+	ParticleSystem *psys_orig = psys_orig_get(psys);
 	float cfra;
+	ParticleSystemModifierData *psmd = psys_get_modifier(ob, psys);
 
 	/* drawdata is outdated after ANY change */
 	if (psys->pdd) psys->pdd->flag &= ~PARTICLE_DRAW_DATA_UPDATED;
@@ -4219,13 +4221,23 @@ void particle_system_update(struct Depsgraph *depsgraph, Scene *scene, Object *o
 	if (!psys_check_enabled(ob, psys, use_render_params))
 		return;
 
+	if (DEG_is_active(depsgraph)) {
+		if (psys->orig_psys != NULL &&
+		    psys->orig_psys->edit != NULL &&
+		    psys->orig_psys->edit->psys == psys_orig_get(psys))
+		{
+			psys->orig_psys->edit->psys_eval = psys;
+			psys->orig_psys->edit->psmd_eval = psmd;
+		}
+	}
+
 	cfra = DEG_get_ctime(depsgraph);
 
 	sim.depsgraph = depsgraph;
 	sim.scene = scene;
 	sim.ob = ob;
 	sim.psys = psys;
-	sim.psmd = psys_get_modifier(ob, psys);
+	sim.psmd = psmd;
 
 	/* system was already updated from modifier stack */
 	if (sim.psmd->flag & eParticleSystemFlag_psys_updated) {
@@ -4270,10 +4282,10 @@ void particle_system_update(struct Depsgraph *depsgraph, Scene *scene, Object *o
 
 				free_hair(ob, psys, 0);
 
-				if (psys->edit && psys->free_edit) {
-					psys->free_edit(psys->edit);
-					psys->edit = NULL;
-					psys->free_edit = NULL;
+				if (psys_orig->edit && psys_orig->free_edit) {
+					psys_orig->free_edit(psys_orig->edit);
+					psys_orig->edit = NULL;
+					psys_orig->free_edit = NULL;
 				}
 
 				/* first step is negative so particles get killed and reset */
@@ -4369,6 +4381,10 @@ void particle_system_update(struct Depsgraph *depsgraph, Scene *scene, Object *o
 		psys->flag &= ~PSYS_OB_ANIM_RESTORE;
 	}
 
+	if (psys_orig->edit) {
+		psys_orig->edit->flags |= PT_CACHE_EDIT_UPDATE_PARTICLE_FROM_EVAL;
+	}
+
 	psys->cfra = cfra;
 	psys->recalc = 0;