Cloth simulation: share point cache between CoW copies of objects

2 files changed, 24 insertions, 5 deletions

diff --git a/source/blender/makesdna/DNA_modifier_types.h b/source/blender/makesdna/DNA_modifier_types.h
index 712958deca1..49d72eddd09 100644
--- a/source/blender/makesdna/DNA_modifier_types.h
+++ b/source/blender/makesdna/DNA_modifier_types.h
@@ -119,6 +119,8 @@ typedef struct ModifierData {
 typedef enum {
 	/* This modifier has been inserted in local override, and hence can be fully edited. */
 	eModifierFlag_StaticOverride_Local  = (1 << 0),
+	/* This modifier does not own its caches, but instead shares them with another modifier. */
+	eModifierFlag_SharedCaches          = (1 << 1),
 } ModifierFlag;
 
 typedef enum {
@@ -608,8 +610,12 @@ typedef struct ClothModifierData {
 	struct Cloth *clothObject;            /* The internal data structure for cloth. */
 	struct ClothSimSettings *sim_parms;   /* definition is in DNA_cloth_types.h */
 	struct ClothCollSettings *coll_parms; /* definition is in DNA_cloth_types.h */
+
+	/* PointCache can be shared with other instances of ClothModifierData.
+	 * Inspect (modifier.flag & eModifierFlag_SharedCaches) to find out. */
 	struct PointCache *point_cache;       /* definition is in DNA_object_force_types.h */
 	struct ListBase ptcaches;
+
 	/* XXX nasty hack, remove once hair can be separated from cloth modifier data */
 	struct ClothHairData *hairdata;
 	/* grid geometry values of hair continuum */
diff --git a/source/blender/modifiers/intern/MOD_cloth.c b/source/blender/modifiers/intern/MOD_cloth.c
index 34f571f5e30..53e71bfc1a4 100644
--- a/source/blender/modifiers/intern/MOD_cloth.c
+++ b/source/blender/modifiers/intern/MOD_cloth.c
@@ -42,6 +42,7 @@
 
 #include "MEM_guardedalloc.h"
 
+#include "BLI_listbase.h"
 #include "BLI_utildefines.h"
 
 #include "BKE_cloth.h"
@@ -155,7 +156,7 @@ static CustomDataMask requiredDataMask(Object *UNUSED(ob), ModifierData *md)
 	return dataMask;
 }
 
-static void copyData(const ModifierData *md, ModifierData *target, const int UNUSED(flag))
+static void copyData(const ModifierData *md, ModifierData *target, const int flag)
 {
 	const ClothModifierData *clmd = (const ClothModifierData *) md;
 	ClothModifierData *tclmd = (ClothModifierData *) target;
@@ -170,14 +171,21 @@ static void copyData(const ModifierData *md, ModifierData *target, const int UNU
 		MEM_freeN(tclmd->coll_parms);
 
 	BKE_ptcache_free_list(&tclmd->ptcaches);
-	tclmd->point_cache = NULL;
+	if (flag & LIB_ID_CREATE_NO_MAIN) {
+		/* Share the cache with the original object's modifier. */
+		tclmd->modifier.flag |= eModifierFlag_SharedCaches;
+		tclmd->ptcaches = clmd->ptcaches;
+		tclmd->point_cache = clmd->point_cache;
+	}
+	else {
+		tclmd->point_cache = BKE_ptcache_add(&tclmd->ptcaches);
+		tclmd->point_cache->step = 1;
+	}
 
 	tclmd->sim_parms = MEM_dupallocN(clmd->sim_parms);
 	if (clmd->sim_parms->effector_weights)
 		tclmd->sim_parms->effector_weights = MEM_dupallocN(clmd->sim_parms->effector_weights);
 	tclmd->coll_parms = MEM_dupallocN(clmd->coll_parms);
-	tclmd->point_cache = BKE_ptcache_add(&tclmd->ptcaches);
-	tclmd->point_cache->step = 1;
 	tclmd->clothObject = NULL;
 	tclmd->hairdata = NULL;
 	tclmd->solver_result = NULL;
@@ -206,7 +214,12 @@ static void freeData(ModifierData *md)
 		if (clmd->coll_parms)
 			MEM_freeN(clmd->coll_parms);
 
-		BKE_ptcache_free_list(&clmd->ptcaches);
+		if (md->flag & eModifierFlag_SharedCaches) {
+			BLI_listbase_clear(&clmd->ptcaches);
+		}
+		else {
+			BKE_ptcache_free_list(&clmd->ptcaches);
+		}
 		clmd->point_cache = NULL;
 
 		if (clmd->hairdata)