BMesh: select similar regions

Select operator that takes multiple selected face regions and
selects any number of matching regions (when they have distinguishing features to isolate them).

UI access next.

7 files changed, 1631 insertions, 0 deletions

diff --git a/source/blender/bmesh/CMakeLists.txt b/source/blender/bmesh/CMakeLists.txt
index a43e835f022..50d3ac30ddc 100644
--- a/source/blender/bmesh/CMakeLists.txt
+++ b/source/blender/bmesh/CMakeLists.txt
@@ -140,6 +140,8 @@ set(SRC
 	tools/bmesh_intersect.h
 	tools/bmesh_path.c
 	tools/bmesh_path.h
+	tools/bmesh_region_match.c
+	tools/bmesh_region_match.h
 	tools/bmesh_triangulate.c
 	tools/bmesh_triangulate.h
 	tools/bmesh_wireframe.c
diff --git a/source/blender/bmesh/bmesh_tools.h b/source/blender/bmesh/bmesh_tools.h
index baffeb774b6..f7f767f91bf 100644
--- a/source/blender/bmesh/bmesh_tools.h
+++ b/source/blender/bmesh/bmesh_tools.h
@@ -41,6 +41,7 @@ extern "C" {
 #include "tools/bmesh_edgenet.h"
 #include "tools/bmesh_edgesplit.h"
 #include "tools/bmesh_path.h"
+#include "tools/bmesh_region_match.h"
 #include "tools/bmesh_triangulate.h"
 
 #ifdef __cplusplus
diff --git a/source/blender/bmesh/tools/bmesh_region_match.c b/source/blender/bmesh/tools/bmesh_region_match.c
new file mode 100644
index 00000000000..26c3271f663
--- /dev/null
+++ b/source/blender/bmesh/tools/bmesh_region_match.c
@@ -0,0 +1,1501 @@
+/*
+ * ***** BEGIN GPL LICENSE BLOCK *****
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * ***** END GPL LICENSE BLOCK *****
+ */
+
+/** \file blender/bmesh/tools/bmesh_region_match.c
+ *  \ingroup bmesh
+ *
+ * Given a contiguous region of faces,
+ * find multiple matching regions (based on topology) and return them.
+ */
+
+#include <string.h>
+
+#include "MEM_guardedalloc.h"
+#include "BLI_listbase.h"
+#include "BLI_linklist.h"
+#include "BLI_alloca.h"
+#include "BLI_ghash.h"
+#include "BLI_mempool.h"
+#include "BLI_linklist_stack.h"
+
+#include "bmesh.h"
+
+#include "tools/bmesh_region_match.h"  /* own incldue */
+
+/* avoid re-creating ghash and pools for each search */
+#define USE_WALKER_REUSE
+
+/* do a first-pass id of all vertices,
+ * this avoids expensive checks on every item later on
+ * (works fine without, just slower) */
+#define USE_PIVOT_FASTMATCH
+
+/* otherwise use active element as pivot, for quick tests only */
+#define USE_PIVOT_SEARCH
+
+// #define DEBUG_TIME
+// #define DEBUG_PRINT
+
+#ifdef DEBUG_TIME
+#  include "PIL_time.h"
+#  include "PIL_time_utildefines.h"
+#endif
+
+#include "BLI_strict_flags.h"
+
+
+/* -------------------------------------------------------------------- */
+/* UUID-Walk API */
+
+/** \name Internal UUIDWalk API
+ * \{ */
+
+#define PRIME_VERT_INIT 100003
+
+typedef uintptr_t UUID_Int;
+
+typedef struct UUIDWalk {
+
+	/* List of faces we can step onto (UUIDFaceStep's) */
+	ListBase faces_step;
+
+	/* Face & Vert UUID's */
+	GHash *verts_uuid;
+	GHash *faces_uuid;
+
+	/* memory pool for LinkNode's */
+	BLI_mempool *link_pool;
+
+	/* memory pool for LinkBase's */
+	BLI_mempool *lbase_pool;
+
+	/* memory pool for UUIDFaceStep's */
+	BLI_mempool *step_pool;
+	BLI_mempool *step_pool_items;
+
+	/* Optionaly use face-tag to isolate search */
+	bool use_face_isolate;
+
+	/* Increment for each pass added */
+	UUID_Int pass;
+
+	/* runtime vars, aviod re-creating each pass */
+	struct {
+		GHash *verts_uuid;  /* BMVert -> UUID */
+		GSet  *faces_step;  /* BMFace */
+
+		GHash *faces_from_uuid;   /* UUID -> UUIDFaceStepItem */
+
+		UUID_Int    *rehash_store;
+		unsigned int rehash_store_len;
+	} cache;
+
+} UUIDWalk;
+
+/* stores a set of potential faces to step onto */
+typedef struct UUIDFaceStep {
+	struct UUIDFaceStep *next, *prev;
+
+	/* unsorted 'BMFace' */
+	LinkNode *faces;
+
+	/* faces sorted into 'UUIDFaceStepItem' */
+	ListBase items;
+} UUIDFaceStep;
+
+/* store face-lists with same uuid */
+typedef struct UUIDFaceStepItem {
+	struct UUIDFaceStepItem *next, *prev;
+	uintptr_t uuid;
+
+	LinkNode    *list;
+	unsigned int list_len;
+} UUIDFaceStepItem;
+
+BLI_INLINE bool bm_uuidwalk_face_test(
+        UUIDWalk *uuidwalk, BMFace *f)
+{
+	if (uuidwalk->use_face_isolate) {
+		return BM_elem_flag_test_bool(f, BM_ELEM_TAG);
+	}
+	else {
+		return true;
+	}
+}
+
+BLI_INLINE bool bm_uuidwalk_vert_lookup(
+        UUIDWalk *uuidwalk, BMVert *v, UUID_Int *r_uuid)
+{
+	void **ret;
+	ret = BLI_ghash_lookup_p(uuidwalk->verts_uuid, v);
+	if (ret) {
+		*r_uuid = (UUID_Int)(*ret);
+		return true;
+	}
+	else {
+		return false;
+	}
+}
+
+BLI_INLINE bool bm_uuidwalk_face_lookup(
+        UUIDWalk *uuidwalk, BMFace *f, UUID_Int *r_uuid)
+{
+	void **ret;
+	ret = BLI_ghash_lookup_p(uuidwalk->faces_uuid, f);
+	if (ret) {
+		*r_uuid = (UUID_Int)(*ret);
+		return true;
+	}
+	else {
+		return false;
+	}
+}
+
+static unsigned int ghashutil_bmelem_indexhash(const void *key)
+{
+	const BMElem *ele = key;
+	return (unsigned int)BM_elem_index_get(ele);
+}
+
+static bool ghashutil_bmelem_indexcmp(const void *a, const void *b)
+{
+	BLI_assert((a != b) == (BM_elem_index_get((BMElem *)a) != BM_elem_index_get((BMElem *)b)));
+	return (a != b);
+}
+
+static GHash *ghash_bmelem_new_ex(const char *info,
+                                  const unsigned int nentries_reserve)
+{
+	return BLI_ghash_new_ex(ghashutil_bmelem_indexhash, ghashutil_bmelem_indexcmp, info, nentries_reserve);
+}
+
+static GSet *gset_bmelem_new_ex(const char *info,
+                             const unsigned int nentries_reserve)
+{
+	return BLI_gset_new_ex(ghashutil_bmelem_indexhash, ghashutil_bmelem_indexcmp, info, nentries_reserve);
+}
+
+
+static GHash *ghash_bmelem_new(const char *info)
+{
+	return ghash_bmelem_new_ex(info, 0);
+}
+
+static GSet *gset_bmelem_new(const char *info)
+{
+	return gset_bmelem_new_ex(info, 0);
+}
+
+
+static void bm_uuidwalk_init(
+        UUIDWalk *uuidwalk,
+        const unsigned int faces_src_region_len,
+        const unsigned int verts_src_region_len)
+{
+	BLI_listbase_clear(&uuidwalk->faces_step);
+
+	uuidwalk->verts_uuid = ghash_bmelem_new_ex(__func__, verts_src_region_len);
+	uuidwalk->faces_uuid = ghash_bmelem_new_ex(__func__, faces_src_region_len);
+
+	uuidwalk->cache.verts_uuid = ghash_bmelem_new(__func__);
+	uuidwalk->cache.faces_step = gset_bmelem_new(__func__);
+
+	/* works because 'int' ghash works for intptr_t too */
+	uuidwalk->cache.faces_from_uuid = BLI_ghash_int_new(__func__);
+
+	uuidwalk->cache.rehash_store = NULL;
+	uuidwalk->cache.rehash_store_len = 0;
+
+	uuidwalk->use_face_isolate = false;
+
+	/* smaller pool's for faster clearing */
+	uuidwalk->link_pool = BLI_mempool_create(sizeof(LinkNode), 64, 64, BLI_MEMPOOL_NOP);
+	uuidwalk->step_pool = BLI_mempool_create(sizeof(UUIDFaceStep), 64, 64, BLI_MEMPOOL_NOP);
+	uuidwalk->step_pool_items = BLI_mempool_create(sizeof(UUIDFaceStepItem), 64, 64, BLI_MEMPOOL_NOP);
+
+	uuidwalk->pass = 1;
+}
+
+static void bm_uuidwalk_clear(
+        UUIDWalk *uuidwalk)
+{
+	BLI_listbase_clear(&uuidwalk->faces_step);
+
+	BLI_ghash_clear(uuidwalk->verts_uuid, NULL, NULL);
+	BLI_ghash_clear(uuidwalk->faces_uuid, NULL, NULL);
+
+	BLI_ghash_clear(uuidwalk->cache.verts_uuid, NULL, NULL);
+	BLI_gset_clear(uuidwalk->cache.faces_step, NULL);
+	BLI_ghash_clear(uuidwalk->cache.faces_from_uuid, NULL, NULL);
+
+	/* keep rehash_store as-is, for reuse */
+
+	uuidwalk->use_face_isolate = false;
+
+	BLI_mempool_clear(uuidwalk->link_pool);
+	BLI_mempool_clear(uuidwalk->step_pool);
+	BLI_mempool_clear(uuidwalk->step_pool_items);
+
+	uuidwalk->pass = 1;
+}
+
+static void bm_uuidwalk_free(
+        UUIDWalk *uuidwalk)
+{
+	/**
+	 * Handled by pools
+	 *
+	 * - uuidwalk->faces_step
+	 */
+
+	BLI_ghash_free(uuidwalk->verts_uuid, NULL, NULL);
+	BLI_ghash_free(uuidwalk->faces_uuid, NULL, NULL);
+
+	/* cache */
+	BLI_ghash_free(uuidwalk->cache.verts_uuid, NULL, NULL);
+	BLI_gset_free(uuidwalk->cache.faces_step, NULL);
+	BLI_ghash_free(uuidwalk->cache.faces_from_uuid, NULL, NULL);
+	MEM_SAFE_FREE(uuidwalk->cache.rehash_store);
+
+	BLI_mempool_destroy(uuidwalk->link_pool);
+	BLI_mempool_destroy(uuidwalk->step_pool);
+	BLI_mempool_destroy(uuidwalk->step_pool_items);
+}
+
+static UUID_Int bm_uuidwalk_calc_vert_uuid(
+        UUIDWalk *uuidwalk, BMVert *v)
+{
+#define PRIME_VERT_SMALL  7
+#define PRIME_VERT_MID    43
+#define PRIME_VERT_LARGE  1031
+
+#define PRIME_FACE_SMALL  13
+#define PRIME_FACE_MID    53
+
+	UUID_Int uuid;
+
+	uuid = uuidwalk->pass * PRIME_VERT_LARGE;
+
+	/* vert -> other */
+	{
+		unsigned int tot = 0;
+		BMIter eiter;
+		BMEdge *e;
+		BM_ITER_ELEM (e, &eiter, v, BM_EDGES_OF_VERT) {
+			BMVert *v_other = BM_edge_other_vert(e, v);
+			UUID_Int uuid_other;
+			if (bm_uuidwalk_vert_lookup(uuidwalk, v_other, &uuid_other)) {
+				uuid ^= (uuid_other * PRIME_VERT_SMALL);
+				tot += 1;
+			}
+		}
+		uuid ^= (tot * PRIME_VERT_MID);
+	}
+
+	/* faces */
+	{
+		unsigned int tot = 0;
+		BMIter iter;
+		BMFace *f;
+
+		BM_ITER_ELEM (f, &iter, v, BM_FACES_OF_VERT) {
+			UUID_Int uuid_other;
+			if (bm_uuidwalk_face_lookup(uuidwalk, f, &uuid_other)) {
+				uuid ^= (uuid_other * PRIME_FACE_SMALL);
+				tot += 1;
+			}
+		}
+		uuid ^= (tot * PRIME_FACE_MID);
+	}
+
+	return uuid;
+
+#undef PRIME_VERT_SMALL
+#undef PRIME_VERT_MID
+#undef PRIME_VERT_LARGE
+
+#undef PRIME_FACE_SMALL
+#undef PRIME_FACE_MID
+}
+
+static UUID_Int bm_uuidwalk_calc_face_uuid(
+        UUIDWalk *uuidwalk, BMFace *f)
+{
+#define PRIME_VERT_SMALL  11
+
+#define PRIME_FACE_SMALL  17
+#define PRIME_FACE_LARGE  1013
+
+	UUID_Int uuid;
+
+	uuid = uuidwalk->pass * (unsigned int)f->len * PRIME_FACE_LARGE;
+
+	/* face-verts */
+	{
+		BMLoop *l_iter, *l_first;
+
+		l_iter = l_first = BM_FACE_FIRST_LOOP(f);
+		do {
+			UUID_Int uuid_other;
+			if (bm_uuidwalk_vert_lookup(uuidwalk, l_iter->v, &uuid_other)) {
+				uuid ^= (uuid_other * PRIME_VERT_SMALL);
+			}
+		} while ((l_iter = l_iter->next) != l_first);
+	}
+
+	/* face-faces (connected by edge) */
+	{
+		BMLoop *l_iter, *l_first;
+
+		l_iter = l_first = BM_FACE_FIRST_LOOP(f);
+		do {
+			if (l_iter->radial_next != l_iter) {
+				BMLoop *l_iter_radial = l_iter->radial_next;
+				do {
+					UUID_Int uuid_other;
+					if (bm_uuidwalk_face_lookup(uuidwalk, l_iter_radial->f, &uuid_other)) {
+						uuid ^= (uuid_other * PRIME_FACE_SMALL);
+					}
+				} while ((l_iter_radial = l_iter_radial->radial_next) != l_iter);
+			}
+		} while ((l_iter = l_iter->next) != l_first);
+	}
+
+	return uuid;
+
+#undef PRIME_VERT_SMALL
+
+#undef PRIME_FACE_SMALL
+#undef PRIME_FACE_LARGE
+}
+
+static void bm_uuidwalk_rehash_reserve(
+        UUIDWalk *uuidwalk, unsigned int rehash_store_len_new)
+{
+	if (UNLIKELY(rehash_store_len_new > uuidwalk->cache.rehash_store_len)) {
+		/* avoid re-allocs */
+		rehash_store_len_new *= 2;
+		uuidwalk->cache.rehash_store =
+		        MEM_reallocN(uuidwalk->cache.rehash_store,
+		                     rehash_store_len_new * sizeof(*uuidwalk->cache.rehash_store));
+		uuidwalk->cache.rehash_store_len = rehash_store_len_new;
+	}
+}
+
+/**
+ * Re-hash all elements, delay updating so as not to create feedback loop.
+ */
+static void bm_uuidwalk_rehash(
+        UUIDWalk *uuidwalk)
+{
+	GHashIterator gh_iter;
+	UUID_Int *uuid_store;
+	unsigned int i;
+
+	unsigned int rehash_store_len_new = (unsigned int)MAX2(BLI_ghash_size(uuidwalk->verts_uuid),
+	                                                       BLI_ghash_size(uuidwalk->faces_uuid));
+
+	bm_uuidwalk_rehash_reserve(uuidwalk, rehash_store_len_new);
+	uuid_store = uuidwalk->cache.rehash_store;
+
+	/* verts */
+	i = 0;
+	GHASH_ITER (gh_iter, uuidwalk->verts_uuid) {
+		BMVert *v = BLI_ghashIterator_getKey(&gh_iter);
+		uuid_store[i++] = bm_uuidwalk_calc_vert_uuid(uuidwalk, v);
+	}
+	i = 0;
+	GHASH_ITER (gh_iter, uuidwalk->verts_uuid) {
+		void **uuid_p = BLI_ghashIterator_getValue_p(&gh_iter);
+		*((UUID_Int *)uuid_p) = uuid_store[i++];
+	}
+
+	/* faces */
+	i = 0;
+	GHASH_ITER (gh_iter, uuidwalk->faces_uuid) {
+		BMFace *f = BLI_ghashIterator_getKey(&gh_iter);
+		uuid_store[i++] = bm_uuidwalk_calc_face_uuid(uuidwalk, f);
+	}
+	i = 0;
+	GHASH_ITER (gh_iter, uuidwalk->faces_uuid) {
+		void **uuid_p = BLI_ghashIterator_getValue_p(&gh_iter);
+		*((UUID_Int *)uuid_p) = uuid_store[i++];
+	}
+}
+
+static void bm_uuidwalk_rehash_facelinks(
+        UUIDWalk *uuidwalk,
+        LinkNode *faces, const unsigned int faces_len,
+        const bool is_init)
+{
+	UUID_Int *uuid_store;
+	LinkNode *f_link;
+	unsigned int i;
+
+	bm_uuidwalk_rehash_reserve(uuidwalk, faces_len);
+	uuid_store = uuidwalk->cache.rehash_store;
+
+	i = 0;
+	for (f_link = faces; f_link; f_link = f_link->next) {
+		BMFace *f = f_link->link;
+		uuid_store[i++] = bm_uuidwalk_calc_face_uuid(uuidwalk, f);
+	}
+
+	i = 0;
+	if (is_init) {
+		for (f_link = faces; f_link; f_link = f_link->next) {
+			BMFace *f = f_link->link;
+			BLI_ghash_insert(uuidwalk->faces_uuid, f, (void *)uuid_store[i++]);
+		}
+	}
+	else {
+		for (f_link = faces; f_link; f_link = f_link->next) {
+			BMFace *f = f_link->link;
+			void **uuid_p = BLI_ghash_lookup_p(uuidwalk->faces_uuid, f);
+			*((UUID_Int *)uuid_p) = uuid_store[i++];
+		}
+	}
+}
+
+static bool bm_vert_is_uuid_connect(
+        UUIDWalk *uuidwalk, BMVert *v)
+{
+	BMIter eiter;
+	BMEdge *e;
+
+	BM_ITER_ELEM (e, &eiter, v, BM_EDGES_OF_VERT) {
+		BMVert *v_other = BM_edge_other_vert(e, v);
+		if (BLI_ghash_haskey(uuidwalk->verts_uuid, v_other)) {
+			return true;
+		}
+	}
+	return false;
+}
+
+static void bm_uuidwalk_pass_add(
+        UUIDWalk *uuidwalk, LinkNode *faces_pass, const unsigned int faces_pass_len)
+{
+	GHashIterator gh_iter;
+	GHash *verts_uuid_pass;
+	GSet  *faces_step_next;
+	LinkNode *f_link;
+
+	UUIDFaceStep *fstep;
+
+	BLI_assert(faces_pass_len == (unsigned int)BLI_linklist_length(faces_pass));
+
+	/* rehash faces now all their verts have been added */
+	bm_uuidwalk_rehash_facelinks(uuidwalk, faces_pass, faces_pass_len, true);
+
+	/* create verts_new */
+	verts_uuid_pass = uuidwalk->cache.verts_uuid;
+	faces_step_next = uuidwalk->cache.faces_step;
+
+	BLI_assert(BLI_ghash_size(verts_uuid_pass) == 0);
+	BLI_assert(BLI_gset_size(faces_step_next) == 0);
+
+	/* Add the face_step data from connected faces, creating new passes */
+	fstep = BLI_mempool_alloc(uuidwalk->step_pool);
+	BLI_addhead(&uuidwalk->faces_step, fstep);
+	fstep->faces = NULL;
+	BLI_listbase_clear(&fstep->items);
+
+	for (f_link = faces_pass; f_link; f_link = f_link->next) {
+		BMFace *f = f_link->link;
+		BMLoop *l_iter, *l_first;
+
+		l_iter = l_first = BM_FACE_FIRST_LOOP(f);
+		do {
+			/* fill verts_new */
+			if (!BLI_ghash_haskey(uuidwalk->verts_uuid, l_iter->v) &&
+			    !BLI_ghash_haskey(verts_uuid_pass,      l_iter->v) &&
+			    (bm_vert_is_uuid_connect(uuidwalk, l_iter->v) == true))
+			{
+				const UUID_Int uuid = bm_uuidwalk_calc_vert_uuid(uuidwalk, l_iter->v);
+				BLI_ghash_insert(verts_uuid_pass, l_iter->v, (void *)uuid);
+			}
+
+			/* fill faces_step_next */
+			if (l_iter->radial_next != l_iter) {
+				BMLoop *l_iter_radial = l_iter->radial_next;
+				do {
+					if (!BLI_ghash_haskey(uuidwalk->faces_uuid, l_iter_radial->f) &&
+					    !BLI_gset_haskey(faces_step_next,       l_iter_radial->f) &&
+					    (bm_uuidwalk_face_test(uuidwalk,        l_iter_radial->f)))
+					{
+						BLI_gset_insert(faces_step_next, l_iter_radial->f);
+
+						/* add to fstep */
+						BLI_linklist_prepend_pool(&fstep->faces, l_iter_radial->f, uuidwalk->link_pool);
+					}
+				} while ((l_iter_radial = l_iter_radial->radial_next) != l_iter);
+			}
+		} while ((l_iter = l_iter->next) != l_first);
+	}
+
+	/* faces_uuid.update(verts_new) */
+	GHASH_ITER (gh_iter, verts_uuid_pass) {
+		BMVert *v = BLI_ghashIterator_getKey(&gh_iter);
+		void *uuid_p = BLI_ghashIterator_getValue(&gh_iter);
+		BLI_ghash_insert(uuidwalk->verts_uuid, v, uuid_p);
+	}
+
+	/* rehash faces now all their verts have been added */
+	bm_uuidwalk_rehash_facelinks(uuidwalk, faces_pass, faces_pass_len, false);
+
+	uuidwalk->pass += 1;
+
+	BLI_ghash_clear(uuidwalk->cache.verts_uuid, NULL, NULL);
+	BLI_gset_clear(uuidwalk->cache.faces_step, NULL);
+}
+
+static int bm_face_len_cmp(const void *v1, const void *v2)
+{
+	const BMFace *f1 = v1, *f2 = v2;
+
+	if      (f1->len > f2->len) return  1;
+	else if (f1->len < f2->len) return -1;
+	else                        return  0;
+}
+
+static unsigned int bm_uuidwalk_init_from_edge(
+        UUIDWalk *uuidwalk, BMEdge *e)
+{
+	BMLoop *l_iter = e->l;
+	unsigned int f_arr_len = (unsigned int)BM_edge_face_count(e);
+	BMFace **f_arr = BLI_array_alloca(f_arr, f_arr_len);
+	unsigned int fstep_num = 0, i = 0;
+
+	do {
+		BMFace *f = l_iter->f;
+		if (bm_uuidwalk_face_test(uuidwalk, f)) {
+			f_arr[i++] = f;
+		}
+	} while ((l_iter = l_iter->radial_next) != e->l);
+	BLI_assert(i <= f_arr_len);
+	f_arr_len = i;
+
+	qsort(f_arr, f_arr_len, sizeof(*f_arr), bm_face_len_cmp);
+
+	/* start us off! */
+	{
+		const UUID_Int uuid = PRIME_VERT_INIT;
+		BLI_ghash_insert(uuidwalk->verts_uuid, e->v1, (void *)uuid);
+		BLI_ghash_insert(uuidwalk->verts_uuid, e->v2, (void *)uuid);
+	}
+
+	/* turning an array into LinkNode's seems odd,
+	 * but this is just for initialization,
+	 * elsewhere using LinkNode's makes more sense */
+	for (i = 0; i < f_arr_len; i++) {
+		LinkNode *faces_pass = NULL;
+		const int f_len = f_arr[i]->len;
+
+		do {
+			BLI_linklist_prepend_pool(&faces_pass, f_arr[i++], uuidwalk->link_pool);
+		} while (i < f_arr_len && (f_len == f_arr[i]->len));
+
+		bm_uuidwalk_pass_add(uuidwalk, faces_pass, i);
+		BLI_linklist_free_pool(faces_pass, NULL, uuidwalk->link_pool);
+		fstep_num += 1;
+	}
+
+	return fstep_num;
+}
+
+#undef PRIME_VERT_INIT
+
+/** \} */
+
+
+/** \name Internal UUIDFaceStep API
+ * \{ */
+
+static int facestep_sort(const void *a, const const void *b)
+{
+	const UUIDFaceStepItem *fstep_a = a;
+	const UUIDFaceStepItem *fstep_b = b;
+	return (fstep_a->uuid > fstep_b->uuid) ? 1 : 0;
+}
+
+/**
+ * Put faces in lists based on their uuid's,
+ * re-run for each pass since rehashing may differentiate face-groups.
+ */
+static bool bm_uuidwalk_facestep_begin(
+        UUIDWalk *uuidwalk, UUIDFaceStep *fstep)
+{
+	LinkNode *f_link, *f_link_next, **f_link_prev_p;;
+	bool ok = false;
+
+	BLI_assert(BLI_ghash_size(uuidwalk->cache.faces_from_uuid) == 0);
+	BLI_assert(BLI_countlist(&fstep->items) == 0);
+
+	f_link_prev_p = &fstep->faces;
+	for (f_link = fstep->faces; f_link; f_link = f_link_next) {
+		BMFace *f = f_link->link;
+		f_link_next = f_link->next;
+
+		/* possible another pass added this face already, free in that case */
+		if (!BLI_ghash_haskey(uuidwalk->faces_uuid, f)) {
+			const UUID_Int uuid = bm_uuidwalk_calc_face_uuid(uuidwalk, f);
+			UUIDFaceStepItem *fstep_item;
+
+			ok = true;
+
+			fstep_item = BLI_ghash_lookup(uuidwalk->cache.faces_from_uuid, (void *)uuid);
+			if (UNLIKELY(fstep_item == NULL)) {
+				fstep_item = BLI_mempool_alloc(uuidwalk->step_pool_items);
+				BLI_ghash_insert(uuidwalk->cache.faces_from_uuid, (void *)uuid, fstep_item);
+
+				/* add to start, so its handled on the next round of passes */
+				BLI_addhead(&fstep->items, fstep_item);
+				fstep_item->uuid = uuid;
+				fstep_item->list = NULL;
+				fstep_item->list_len = 0;
+			}
+
+			BLI_linklist_prepend_pool(&fstep_item->list, f, uuidwalk->link_pool);
+			fstep_item->list_len += 1;
+
+			f_link_prev_p = &f_link->next;
+		}
+		else {
+			*f_link_prev_p = f_link->next;
+			BLI_mempool_free(uuidwalk->link_pool, f_link);
+		}
+	}
+
+	BLI_ghash_clear(uuidwalk->cache.faces_from_uuid, NULL, NULL);
+
+	BLI_sortlist(&fstep->items, facestep_sort);
+
+	return ok;
+}
+
+/**
+ * Cleans up temp data from #bm_uuidwalk_facestep_begin
+ */
+static void bm_uuidwalk_facestep_end(
+        UUIDWalk *uuidwalk, UUIDFaceStep *fstep)
+{
+	UUIDFaceStepItem *fstep_item;
+
+	while ((fstep_item = BLI_pophead(&fstep->items))) {
+		BLI_mempool_free(uuidwalk->step_pool_items, fstep_item);
+	}
+}
+
+static void bm_uuidwalk_facestep_free(
+        UUIDWalk *uuidwalk, UUIDFaceStep *fstep)
+{
+	LinkNode *f_link, *f_link_next;
+
+	BLI_assert(BLI_listbase_is_empty(&fstep->items));
+
+	for (f_link = fstep->faces; f_link; f_link = f_link_next) {
+		f_link_next = f_link->next;
+		BLI_mempool_free(uuidwalk->link_pool, f_link);
+	}
+
+	BLI_remlink(&uuidwalk->faces_step, fstep);
+	BLI_mempool_free(uuidwalk->step_pool, fstep);
+}
+
+/** \} */
+
+
+/* -------------------------------------------------------------------- */
+/* Main Loop to match up regions */
+
+/**
+ * Given a face region and 2 candidate verts to begin mapping.
+ * return the matching region or NULL.
+ */
+static BMFace **bm_mesh_region_match_pair(
+#ifdef USE_WALKER_REUSE
+        UUIDWalk *w_src, UUIDWalk *w_dst,
+#endif
+        BMEdge *e_src, BMEdge *e_dst,
+        const unsigned int faces_src_region_len,
+        const unsigned int verts_src_region_len,
+        unsigned int *r_faces_result_len)
+{
+#ifndef USE_WALKER_REUSE
+	UUIDWalk w_src_, w_dst_;
+	UUIDWalk *w_src = &w_src_, *w_dst = &w_dst_;
+#endif
+	BMFace **faces_result = NULL;
+	bool found = false;
+
+	BLI_assert(e_src != e_dst);
+
+#ifndef USE_WALKER_REUSE
+	bm_uuidwalk_init(w_src, faces_src_region_len, verts_src_region_len);
+	bm_uuidwalk_init(w_dst, faces_src_region_len, verts_src_region_len);
+#endif
+
+	w_src->use_face_isolate = true;
+
+	/* setup the initial state */
+	if (UNLIKELY(bm_uuidwalk_init_from_edge(w_src, e_src) !=
+	             bm_uuidwalk_init_from_edge(w_dst, e_dst)))
+	{
+		/* should never happen, if verts passed are compatible, but to be safe... */
+		goto finally;
+	}
+
+	bm_uuidwalk_rehash_reserve(w_src, MAX2(faces_src_region_len, verts_src_region_len));
+	bm_uuidwalk_rehash_reserve(w_dst, MAX2(faces_src_region_len, verts_src_region_len));
+
+	while (true) {
+		bool ok = false;
+
+		UUIDFaceStep *fstep_src = w_src->faces_step.first;
+		UUIDFaceStep *fstep_dst = w_dst->faces_step.first;
+
+		BLI_assert(BLI_countlist(&w_src->faces_step) == BLI_countlist(&w_dst->faces_step));
+
+		while (fstep_src) {
+
+			/* even if the destination has faces,
+			 * it's not important, since the source doesn't, free and move-on. */
+			if (fstep_src->faces == NULL) {
+				UUIDFaceStep *fstep_src_next = fstep_src->next;
+				UUIDFaceStep *fstep_dst_next = fstep_dst->next;
+				bm_uuidwalk_facestep_free(w_src, fstep_src);
+				bm_uuidwalk_facestep_free(w_dst, fstep_dst);
+				fstep_src = fstep_src_next;
+				fstep_dst = fstep_dst_next;
+				continue;
+			}
+
+			if (bm_uuidwalk_facestep_begin(w_src, fstep_src) &&
+			    bm_uuidwalk_facestep_begin(w_dst, fstep_dst))
+			{
+				/* Step over face-lists with matching UUID's
+				 * both lists are sorted, so no need for lookups.
+				 * The data is created on 'begin' and cleared on 'end' */
+				UUIDFaceStepItem *fstep_item_src;
+				UUIDFaceStepItem *fstep_item_dst;
+				for (fstep_item_src = fstep_src->items.first,
+				     fstep_item_dst = fstep_dst->items.first;
+				     fstep_item_src && fstep_item_dst;
+				     fstep_item_src = fstep_item_src->next,
+				     fstep_item_dst = fstep_item_dst->next)
+				{
+					while ((fstep_item_dst != NULL) &&
+					       (fstep_item_dst->uuid < fstep_item_src->uuid))
+					{
+						fstep_item_dst = fstep_item_dst->next;
+					}
+
+					if ((fstep_item_dst == NULL) ||
+					    (fstep_item_src->uuid  != fstep_item_dst->uuid) ||
+					    (fstep_item_src->list_len > fstep_item_dst->list_len))
+					{
+						/* if the target walker has less than the source
+						 * then the islands don't match, bail early */
+						ok = false;
+						break;
+					}
+
+					if (fstep_item_src->list_len == fstep_item_dst->list_len) {
+						/* found a match */
+						bm_uuidwalk_pass_add(w_src, fstep_item_src->list, fstep_item_src->list_len);
+						bm_uuidwalk_pass_add(w_dst, fstep_item_dst->list, fstep_item_dst->list_len);
+
+						BLI_linklist_free_pool(fstep_item_src->list, NULL, w_src->link_pool);
+						BLI_linklist_free_pool(fstep_item_dst->list, NULL, w_dst->link_pool);
+
+						fstep_item_src->list = NULL;
+						fstep_item_src->list_len = 0;
+
+						fstep_item_dst->list = NULL;
+						fstep_item_dst->list_len = 0;
+
+						ok = true;
+					}
+				}
+			}
+
+			bm_uuidwalk_facestep_end(w_src, fstep_src);
+			bm_uuidwalk_facestep_end(w_dst, fstep_dst);
+
+			/* lock-step */
+			fstep_src = fstep_src->next;
+			fstep_dst = fstep_dst->next;
+		}
+
+		if (!ok) {
+			break;
+		}
+
+		found = ((unsigned int)BLI_ghash_size(w_dst->faces_uuid) == faces_src_region_len);
+		if (found) {
+			break;
+		}
+
+		/* Expensive! but some cases fails without.
+		 * (also faster in other cases since it can rule-out invalid regions) */
+		bm_uuidwalk_rehash(w_src);
+		bm_uuidwalk_rehash(w_dst);
+	}
+
+	if (found) {
+		GHashIterator gh_iter;
+		const unsigned int faces_result_len = (unsigned int)BLI_ghash_size(w_dst->faces_uuid);
+		unsigned int i;
+
+		faces_result = MEM_mallocN(sizeof(faces_result) * (faces_result_len + 1), __func__);
+		GHASH_ITER_INDEX (gh_iter, w_dst->faces_uuid, i) {
+			BMFace *f = BLI_ghashIterator_getKey(&gh_iter);
+			faces_result[i] = f;
+		}
+		faces_result[faces_result_len] = NULL;
+		*r_faces_result_len = faces_result_len;
+	}
+	else {
+		*r_faces_result_len = 0;
+	}
+
+finally:
+
+#ifdef USE_WALKER_REUSE
+	bm_uuidwalk_clear(w_src);
+	bm_uuidwalk_clear(w_dst);
+#else
+	bm_uuidwalk_free(w_src);
+	bm_uuidwalk_free(w_dst);
+#endif
+
+	return faces_result;
+}
+
+/**
+ * Tag as visited, avoid re-use.
+ */
+static void bm_face_array_visit(
+        BMFace **faces, const unsigned int faces_len,
+        unsigned int *r_verts_len,
+        bool visit_faces)
+{
+	unsigned int verts_len = 0;
+	unsigned int i;
+	for (i = 0; i < faces_len; i++) {
+		BMFace *f = faces[i];
+		BMLoop *l_iter, *l_first;
+		l_iter = l_first = BM_FACE_FIRST_LOOP(f);
+		do {
+			if (r_verts_len) {
+				if (!BM_elem_flag_test(l_iter->v, BM_ELEM_TAG)) {
+					verts_len += 1;
+				}
+			}
+
+			BM_elem_flag_enable(l_iter->e, BM_ELEM_TAG);
+			BM_elem_flag_enable(l_iter->v, BM_ELEM_TAG);
+		} while ((l_iter = l_iter->next) != l_first);
+
+		if (visit_faces) {
+			BM_elem_flag_enable(f, BM_ELEM_TAG);
+		}
+	}
+
+	if (r_verts_len) {
+		*r_verts_len = verts_len;
+	}
+}
+
+#ifdef USE_PIVOT_SEARCH
+
+/** \name Internal UUIDWalk API
+ * \{ */
+
+/* signed user id */
+typedef intptr_t SUID_Int;
+
+static bool bm_edge_is_region_boundary(BMEdge *e)
+{
+	if (e->l->radial_next != e->l) {
+		BMLoop *l_iter = e->l;
+		do {
+			if (!BM_elem_flag_test(l_iter->f, BM_ELEM_TAG)) {
+				return true;
+			}
+		} while ((l_iter = l_iter->radial_next) != e->l);
+		return false;
+	}
+	else {
+		/* boundary */
+		return true;
+	}
+}
+
+static void bm_face_region_pivot_edge_use_best(
+        GHash *gh, BMEdge *e_test,
+        BMEdge **r_e_pivot_best,
+        SUID_Int e_pivot_best_id[2])
+{
+	SUID_Int e_pivot_test_id[2];
+
+	e_pivot_test_id[0] = (SUID_Int)BLI_ghash_lookup(gh, e_test->v1);
+	e_pivot_test_id[1] = (SUID_Int)BLI_ghash_lookup(gh, e_test->v2);
+	if (e_pivot_test_id[0] > e_pivot_test_id[1]) {
+		SWAP(SUID_Int, e_pivot_test_id[0], e_pivot_test_id[1]);
+	}
+
+	if ((*r_e_pivot_best == NULL) ||
+	    ((e_pivot_best_id[0] != e_pivot_test_id[0]) ?
+	     (e_pivot_best_id[0] <  e_pivot_test_id[0]) :
+	     (e_pivot_best_id[1] <  e_pivot_test_id[1])))
+	{
+		e_pivot_best_id[0] = e_pivot_test_id[0];
+		e_pivot_best_id[1] = e_pivot_test_id[1];
+
+		/* both verts are from the same pass, record this! */
+		*r_e_pivot_best = e_test;
+	}
+}
+
+/* quick id from a boundary vertex */
+static SUID_Int bm_face_region_vert_boundary_id(BMVert *v)
+{
+#define PRIME_VERT_SMALL_A  7
+#define PRIME_VERT_SMALL_B  13
+#define PRIME_VERT_MID_A    103
+#define PRIME_VERT_MID_B    131
+
+	unsigned int tot = 0;
+	BMIter iter;
+	BMLoop *l;
+	SUID_Int id = PRIME_VERT_MID_A;
+
+	BM_ITER_ELEM (l, &iter, v, BM_LOOPS_OF_VERT) {
+		const bool is_boundary_vert = (bm_edge_is_region_boundary(l->e) || bm_edge_is_region_boundary(l->prev->e));
+		id ^= (unsigned int)l->f->len * (is_boundary_vert ? PRIME_VERT_SMALL_A : PRIME_VERT_SMALL_B);
+		tot += 1;
+	}
+
+	id ^= (tot * PRIME_VERT_MID_B);
+
+	return id ? ABS(id) : 1;
+
+#undef PRIME_VERT_SMALL_A
+#undef PRIME_VERT_SMALL_B
+#undef PRIME_VERT_MID_A
+#undef PRIME_VERT_MID_B
+}
+
+/**
+ * Accumulate id's from a previous pass (swap sign each pass)
+ */
+static SUID_Int bm_face_region_vert_pass_id(GHash *gh, BMVert *v)
+{
+	BMIter eiter;
+	BMEdge *e;
+	SUID_Int tot = 0;
+	SUID_Int v_sum_face_len = 0;
+	SUID_Int v_sum_id = 0;
+	SUID_Int id;
+	SUID_Int id_min = INTPTR_MIN + 1;
+
+#define PRIME_VERT_MID_A  23
+#define PRIME_VERT_MID_B  31
+
+	BM_ITER_ELEM (e, &eiter, v, BM_EDGES_OF_VERT) {
+		if (BM_elem_flag_test(e, BM_ELEM_TAG)) {
+			BMVert *v_other = BM_edge_other_vert(e, v);
+			if (BM_elem_flag_test(v_other, BM_ELEM_TAG)) {
+				/* non-zero values aren't allowed... so no need to check haskey */
+				SUID_Int v_other_id = (SUID_Int)BLI_ghash_lookup(gh, v_other);
+				if (v_other_id > 0) {
+					v_sum_id += v_other_id;
+					tot += 1;
+
+					/* face-count */
+					{
+						BMLoop *l_iter = e->l;
+						do {
+							if (BM_elem_flag_test(l_iter->f, BM_ELEM_TAG)) {
+								v_sum_face_len += l_iter->f->len;
+							}
+						} while ((l_iter = l_iter->radial_next) != e->l);
+					}
+				}
+			}
+		}
+	}
+
+	id  = (tot * PRIME_VERT_MID_A);
+	id ^= (v_sum_face_len * PRIME_VERT_MID_B);
+	id ^= v_sum_id;
+
+	/* disallow 0 & min (since it can't be flipped) */
+	id = (UNLIKELY(id == 0) ? 1 : UNLIKELY(id < id_min) ? id_min : id);
+
+	return ABS(id);
+
+#undef PRIME_VERT_MID_A
+#undef PRIME_VERT_MID_B
+}
+
+/**
+ * Take a face region and find the inner-most vertex.
+ * also calculate the number of connections to the boundary,
+ * and the total number unique of verts used by this face region.
+ *
+ * This is only called once on the source region (no need to be highly optimized).
+ */
+static BMEdge *bm_face_region_pivot_edge_find(
+        BMFace **faces_region, unsigned int faces_region_len,
+        unsigned int verts_region_len,
+        unsigned int *r_depth)
+{
+	/* note, keep deterministic where possible (geometry order independent)
+	 * this function assumed all visit faces & edges are tagged */
+
+	BLI_LINKSTACK_DECLARE(vert_queue_prev, BMVert *);
+	BLI_LINKSTACK_DECLARE(vert_queue_next, BMVert *);
+
+	GHash *gh = BLI_ghash_ptr_new(__func__);
+	unsigned int i;
+
+	BMEdge *e_pivot = NULL;
+	/* pick any non-boundary edge (not ideal) */
+	BMEdge *e_pivot_fallback = NULL;
+
+	SUID_Int pass = 0;
+
+	/* total verts in 'gs' we have visited - aka - not v_init_none */
+	unsigned int vert_queue_used = 0;
+
+	BLI_LINKSTACK_INIT(vert_queue_prev);
+	BLI_LINKSTACK_INIT(vert_queue_next);
+
+	/* face-verts */
+	for (i = 0; i < faces_region_len; i++) {
+		BMFace *f = faces_region[i];
+
+		BMLoop *l_iter, *l_first;
+		l_iter = l_first = BM_FACE_FIRST_LOOP(f);
+		do {
+			BMEdge *e = l_iter->e;
+			if (bm_edge_is_region_boundary(e)) {
+				unsigned int j;
+				for (j = 0; j < 2; j++) {
+					if (!BLI_ghash_haskey(gh, (&e->v1)[j])) {
+						SUID_Int v_id = bm_face_region_vert_boundary_id((&e->v1)[j]);
+						BLI_ghash_insert(gh, (&e->v1)[j], (void *)v_id);
+						BLI_LINKSTACK_PUSH(vert_queue_prev, (&e->v1)[j]);
+						vert_queue_used += 1;
+					}
+				}
+			}
+			else {
+				/* use incase (depth == 0), no interior verts */
+				e_pivot_fallback = e;
+			}
+		} while ((l_iter = l_iter->next) != l_first);
+	}
+
+	while (BLI_LINKSTACK_SIZE(vert_queue_prev)) {
+		BMVert *v;
+		while ((v = BLI_LINKSTACK_POP(vert_queue_prev))) {
+			BMIter eiter;
+			BMEdge *e;
+			BLI_assert(BLI_ghash_haskey(gh, v));
+			BLI_assert((SUID_Int)BLI_ghash_lookup(gh, v) > 0);
+			BM_ITER_ELEM (e, &eiter, v, BM_EDGES_OF_VERT) {
+				if (BM_elem_flag_test(e, BM_ELEM_TAG)) {
+					BMVert *v_other = BM_edge_other_vert(e, v);
+					if (BM_elem_flag_test(v_other, BM_ELEM_TAG)) {
+						if (!BLI_ghash_haskey(gh, v_other)) {
+							/* add as negative, so we know not to read from them this pass */
+							const SUID_Int v_id_other = -bm_face_region_vert_pass_id(gh, v_other);
+							BLI_ghash_insert(gh, v_other, (void *)v_id_other);
+							BLI_LINKSTACK_PUSH(vert_queue_next, v_other);
+							vert_queue_used += 1;
+						}
+					}
+				}
+			}
+		}
+
+		/* flip all the newly added hashes to positive */
+		{
+			LinkNode *v_link;
+			for (v_link = vert_queue_next; v_link; v_link = v_link->next) {
+				SUID_Int *v_id_p = (SUID_Int *)BLI_ghash_lookup_p(gh, v_link->link);
+				*v_id_p = -(*v_id_p);
+				BLI_assert(*v_id_p > 0);
+			}
+		}
+
+		BLI_LINKSTACK_SWAP(vert_queue_prev, vert_queue_next);
+		pass += 1;
+
+		if (vert_queue_used == verts_region_len) {
+			break;
+		}
+	}
+
+	if (BLI_LINKSTACK_SIZE(vert_queue_prev) >= 2) {
+		/* common case - we managed to find some interior verts */
+		LinkNode *v_link;
+		BMEdge *e_pivot_best = NULL;
+		SUID_Int e_pivot_best_id[2] = {0, 0};
+
+		/* temp untag, so we can quickly know what other verts are in this last pass */
+		for (v_link = vert_queue_prev; v_link; v_link = v_link->next) {
+			BMVert *v = v_link->link;
+			BM_elem_flag_disable(v, BM_ELEM_TAG);
+		}
+
+		/* restore correct tagging */
+		for (v_link = vert_queue_prev; v_link; v_link = v_link->next) {
+			BMIter eiter;
+			BMEdge *e_test;
+
+			BMVert *v = v_link->link;
+			BM_elem_flag_enable(v, BM_ELEM_TAG);
+
+			BM_ITER_ELEM (e_test, &eiter, v, BM_EDGES_OF_VERT) {
+				if (BM_elem_flag_test(e_test, BM_ELEM_TAG)) {
+					BMVert *v_other = BM_edge_other_vert(e_test, v);
+					if (BM_elem_flag_test(v_other, BM_ELEM_TAG) == false) {
+						bm_face_region_pivot_edge_use_best(gh, e_test, &e_pivot_best, e_pivot_best_id);
+					}
+				}
+			}
+		}
+
+		e_pivot = e_pivot_best;
+	}
+
+	if ((e_pivot == NULL) && BLI_LINKSTACK_SIZE(vert_queue_prev)) {
+		/* find the best single edge */
+		BMEdge *e_pivot_best = NULL;
+		SUID_Int e_pivot_best_id[2] = {0, 0};
+
+		LinkNode *v_link;
+
+		/* reduce a pass since we're having to step into a previous passes vert,
+		 * and will be closer to the boundary */
+		BLI_assert(pass != 0);
+		pass -= 1;
+
+		for (v_link = vert_queue_prev; v_link; v_link = v_link->next) {
+			BMVert *v = v_link->link;
+
+			BMIter eiter;
+			BMEdge *e_test;
+			BM_ITER_ELEM (e_test, &eiter, v, BM_EDGES_OF_VERT) {
+				if (BM_elem_flag_test(e_test, BM_ELEM_TAG)) {
+					BMVert *v_other = BM_edge_other_vert(e_test, v);
+					if (BM_elem_flag_test(v_other, BM_ELEM_TAG)) {
+						bm_face_region_pivot_edge_use_best(gh, e_test, &e_pivot_best, e_pivot_best_id);
+					}
+				}
+			}
+		}
+
+		e_pivot = e_pivot_best;
+	}
+
+	BLI_LINKSTACK_FREE(vert_queue_prev);
+	BLI_LINKSTACK_FREE(vert_queue_next);
+
+	BLI_ghash_free(gh, NULL, NULL);
+
+	if (e_pivot == NULL) {
+#ifdef DEBUG_PRINT
+		printf("%s: using fallback edge!\n", __func__);
+#endif
+		e_pivot = e_pivot_fallback;
+		pass = 0;
+	}
+
+	*r_depth = (unsigned int)pass;
+
+	return e_pivot;
+}
+/** \} */
+
+#endif  /* USE_PIVOT_SEARCH */
+
+
+/* -------------------------------------------------------------------- */
+/* Quick UUID pass - identify candidates */
+
+#ifdef USE_PIVOT_FASTMATCH
+
+/** \name Fast Match
+ * \{ */
+
+typedef uintptr_t UUIDFashMatch;
+
+static UUIDFashMatch bm_vert_fasthash_single(BMVert *v)
+{
+	BMIter eiter;
+	BMEdge *e;
+	UUIDFashMatch e_num = 0, f_num = 0, l_num = 0;
+
+#define PRIME_EDGE 7
+#define PRIME_FACE 31
+#define PRIME_LOOP 61
+
+	BM_ITER_ELEM (e, &eiter, v, BM_EDGES_OF_VERT) {
+		if (!BM_edge_is_wire(e)) {
+			BMLoop *l_iter = e->l;
+			e_num += 1;
+			do {
+				f_num += 1;
+				l_num += (unsigned int)l_iter->f->len;
+			} while ((l_iter = l_iter->radial_next) != e->l);
+		}
+	}
+
+	return ((e_num * PRIME_EDGE) ^
+	        (f_num * PRIME_FACE) *
+	        (l_num * PRIME_LOOP));
+
+#undef PRIME_EDGE
+#undef PRIME_FACE
+#undef PRIME_LOOP
+}
+
+static UUIDFashMatch *bm_vert_fasthash_create(
+        BMesh *bm, const unsigned int depth)
+{
+	UUIDFashMatch *id_prev;
+	UUIDFashMatch *id_curr;
+	unsigned int pass, i;
+	BMVert *v;
+	BMIter iter;
+
+	id_prev = MEM_mallocN(sizeof(*id_prev) * (unsigned int)bm->totvert, __func__);
+	id_curr = MEM_mallocN(sizeof(*id_curr) * (unsigned int)bm->totvert, __func__);
+
+	BM_ITER_MESH_INDEX (v, &iter, bm, BM_VERTS_OF_MESH, i) {
+		id_prev[i] = bm_vert_fasthash_single(v);
+	}
+
+	for (pass = 0; pass < depth; pass++) {
+		BMEdge *e;
+
+		memcpy(id_curr, id_prev, sizeof(*id_prev) * (unsigned int)bm->totvert);
+
+		BM_ITER_MESH (e, &iter, bm, BM_EDGES_OF_MESH) {
+			if (BM_edge_is_wire(e) == false) {
+				const int i1 = BM_elem_index_get(e->v1);
+				const int i2 = BM_elem_index_get(e->v2);
+
+				id_curr[i1] += id_prev[i2];
+				id_curr[i2] += id_prev[i1];
+			}
+		}
+	}
+	MEM_freeN(id_prev);
+
+	return id_curr;
+}
+
+static void bm_vert_fasthash_edge_order(
+        UUIDFashMatch *fm, const BMEdge *e, UUIDFashMatch e_fm[2])
+{
+	e_fm[0] = fm[BM_elem_index_get(e->v1)];
+	e_fm[1] = fm[BM_elem_index_get(e->v2)];
+
+	if (e_fm[0] > e_fm[1]) {
+		SWAP(UUIDFashMatch, e_fm[0], e_fm[1]);
+	}
+}
+
+static bool bm_vert_fasthash_edge_is_match(
+        UUIDFashMatch *fm, const BMEdge *e_a, const BMEdge *e_b)
+{
+	UUIDFashMatch e_a_fm[2];
+	UUIDFashMatch e_b_fm[2];
+
+	bm_vert_fasthash_edge_order(fm, e_a, e_a_fm);
+	bm_vert_fasthash_edge_order(fm, e_b, e_b_fm);
+
+	return ((e_a_fm[0] == e_b_fm[0]) &&
+	        (e_a_fm[1] == e_b_fm[1]));
+}
+
+static void bm_vert_fasthash_distroy(
+        UUIDFashMatch *fm)
+{
+	MEM_freeN(fm);
+}
+
+/** \} */
+
+#endif  /* USE_PIVOT_FASTMATCH */
+
+
+/**
+ * Take a face-region and return a list of matching face-regions.
+ *
+ * \param faces_region  A single, contiguous face-region.
+ * \return  A list of matching null-terminated face-region arrays.
+ */
+int BM_mesh_region_match(
+        BMesh *bm,
+        BMFace **faces_region, unsigned int faces_region_len,
+        ListBase *r_face_regions)
+{
+	BMEdge *e_src;
+	BMEdge *e_dst;
+	BMIter iter;
+	unsigned int verts_region_len = 0;
+	unsigned int faces_result_len = 0;
+	/* number of steps from e_src to a boundary vert */
+	unsigned int depth;
+
+
+#ifdef USE_WALKER_REUSE
+	UUIDWalk w_src, w_dst;
+#endif
+
+#ifdef USE_PIVOT_FASTMATCH
+	UUIDFashMatch *fm;
+#endif
+
+#ifdef DEBUG_PRINT
+	int search_num = 0;
+#endif
+
+#ifdef DEBUG_TIME
+	TIMEIT_START(region_match);
+#endif
+
+	/* initialize visited verts */
+	BM_mesh_elem_hflag_disable_all(bm, BM_VERT | BM_EDGE | BM_FACE, BM_ELEM_TAG, false);
+	bm_face_array_visit(faces_region, faces_region_len, &verts_region_len, true);
+
+	/* needed for 'ghashutil_bmelem_indexhash' */
+	BM_mesh_elem_index_ensure(bm, BM_VERT | BM_FACE);
+
+#ifdef USE_PIVOT_SEARCH
+	e_src = bm_face_region_pivot_edge_find(
+	        faces_region, faces_region_len,
+	        verts_region_len, &depth);
+
+	/* see which edge is added */
+#if 0
+	BM_select_history_clear(bm);
+	if (e_src) {
+		BM_select_history_store(bm, e_src);
+	}
+#endif
+
+#else
+	/* quick test only! */
+	e_src = BM_mesh_active_edge_get(bm);
+#endif
+
+	if (e_src == NULL) {
+#ifdef DEBUG_PRINT
+		printf("Couldn't find 'e_src'");
+#endif
+		return 0;
+	}
+
+	BLI_listbase_clear(r_face_regions);
+
+#ifdef USE_PIVOT_FASTMATCH
+	if (depth > 0) {
+		fm = bm_vert_fasthash_create(bm, depth);
+	}
+	else {
+		fm = NULL;
+	}
+#endif
+
+#ifdef USE_WALKER_REUSE
+	bm_uuidwalk_init(&w_src, faces_region_len, verts_region_len);
+	bm_uuidwalk_init(&w_dst, faces_region_len, verts_region_len);
+#endif
+
+	BM_ITER_MESH (e_dst, &iter, bm, BM_EDGES_OF_MESH) {
+		BMFace **faces_result;
+		unsigned int faces_result_len_out;
+
+		if (BM_elem_flag_test(e_dst, BM_ELEM_TAG)) {
+			continue;
+		}
+
+#ifdef USE_PIVOT_FASTMATCH
+		if (fm && !bm_vert_fasthash_edge_is_match(fm, e_src, e_dst)) {
+			continue;
+		}
+#endif
+
+#ifdef DEBUG_PRINT
+		search_num += 1;
+#endif
+
+		faces_result = bm_mesh_region_match_pair(
+#ifdef USE_WALKER_REUSE
+		        &w_src, &w_dst,
+#endif
+		        e_src, e_dst,
+		        faces_region_len,
+		        verts_region_len,
+		        &faces_result_len_out);
+
+		/* tag verts as visited */
+		if (faces_result) {
+			LinkData *link;
+
+			bm_face_array_visit(faces_result, faces_result_len_out, NULL, false);
+
+			link = BLI_genericNodeN(faces_result);
+			BLI_addtail(r_face_regions, link);
+			faces_result_len += 1;
+		}
+	}
+
+#ifdef USE_WALKER_REUSE
+	bm_uuidwalk_free(&w_src);
+	bm_uuidwalk_free(&w_dst);
+#else
+	(void)bm_uuidwalk_clear;
+#endif
+
+#ifdef USE_PIVOT_FASTMATCH
+	if (fm) {
+		bm_vert_fasthash_distroy(fm);
+	}
+#endif
+
+#ifdef DEBUG_PRINT
+	printf("%s: search: %d, found %d\n", __func__, search_num, faces_result_len);
+#endif
+
+#ifdef DEBUG_TIME
+	TIMEIT_END(region_match);
+#endif
+
+	return (int)faces_result_len;
+}
diff --git a/source/blender/bmesh/tools/bmesh_region_match.h b/source/blender/bmesh/tools/bmesh_region_match.h
new file mode 100644
index 00000000000..edf8369b070
--- /dev/null
+++ b/source/blender/bmesh/tools/bmesh_region_match.h
@@ -0,0 +1,33 @@
+/*
+ * ***** BEGIN GPL LICENSE BLOCK *****
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * ***** END GPL LICENSE BLOCK *****
+ */
+
+#ifndef __BMESH_REGION_MATCH_H__
+#define __BMESH_REGION_MATCH_H__
+
+/** \file blender/bmesh/tools/bmesh_region_match.h
+ *  \ingroup bmesh
+ */
+
+int BM_mesh_region_match(
+        BMesh *bm,
+        BMFace **faces_region, unsigned int faces_region_len,
+        ListBase *r_face_regions);
+
+#endif /* __BMESH_REGION_MATCH_H__ */
diff --git a/source/blender/editors/mesh/editmesh_select.c b/source/blender/editors/mesh/editmesh_select.c
index 9cdfb43ae15..473da4c9756 100644
--- a/source/blender/editors/mesh/editmesh_select.c
+++ b/source/blender/editors/mesh/editmesh_select.c
@@ -66,6 +66,8 @@
 
 #include "UI_resources.h"
 
+#include "bmesh_tools.h"
+
 #include "mesh_intern.h"  /* own include */
 
 /* use bmesh operator flags for a few operators */
@@ -929,6 +931,96 @@ void MESH_OT_select_similar(wmOperatorType *ot)
 }
 
 
+/* -------------------------------------------------------------------- */
+/* Select Similar Regions */
+
+static int edbm_select_similar_region_exec(bContext *C, wmOperator *op)
+{
+	Object *obedit = CTX_data_edit_object(C);
+	BMEditMesh *em = BKE_editmesh_from_object(obedit);
+	BMesh *bm = em->bm;
+	bool changed = false;
+
+	/* group vars */
+	int *groups_array;
+	int (*group_index)[2];
+	int group_tot;
+	int i;
+
+	if (bm->totfacesel < 2) {
+		BKE_report(op->reports, RPT_ERROR, "No face regions selected");
+		return OPERATOR_CANCELLED;
+	}
+
+	groups_array = MEM_mallocN(sizeof(*groups_array) * bm->totfacesel, __func__);
+	group_tot = BM_mesh_calc_face_groups(bm, groups_array, &group_index,
+	                                     NULL, NULL,
+	                                     BM_ELEM_SELECT, BM_VERT);
+
+	BM_mesh_elem_table_ensure(bm, BM_FACE);
+
+	for (i = 0; i < group_tot; i++) {
+		ListBase faces_regions;
+		int tot;
+
+		const int fg_sta = group_index[i][0];
+		const int fg_len = group_index[i][1];
+		int j;
+		BMFace **fg = MEM_mallocN(sizeof(*fg) * fg_len, __func__);
+
+
+		for (j = 0; j < fg_len; j++) {
+			fg[j] = BM_face_at_index(bm, groups_array[fg_sta + j]);
+		}
+
+		tot = BM_mesh_region_match(bm, fg, fg_len, &faces_regions);
+
+		MEM_freeN(fg);
+
+		if (tot) {
+			LinkData *link;
+			while ((link = BLI_pophead(&faces_regions))) {
+				BMFace *f, **faces = link->data;
+				unsigned int i = 0;
+				while ((f = faces[i++])) {
+					BM_face_select_set(bm, f, true);
+				}
+				MEM_freeN(faces);
+				MEM_freeN(link);
+
+				changed = true;
+			}
+		}
+	}
+
+	MEM_freeN(groups_array);
+
+	if (changed) {
+		WM_event_add_notifier(C, NC_GEOM | ND_SELECT, obedit);
+	}
+	else {
+		BKE_report(op->reports, RPT_WARNING, "No matching face regions found");
+	}
+
+	return OPERATOR_FINISHED;
+}
+
+void MESH_OT_select_similar_region(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name = "Select Similar Regions";
+	ot->idname = "MESH_OT_select_similar_region";
+	ot->description = "Select similar face regions to the current selection";
+
+	/* api callbacks */
+	ot->exec = edbm_select_similar_region_exec;
+	ot->poll = ED_operator_editmesh;
+
+	/* flags */
+	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
+}
+
+
 /* ****************  Mode Select *************** */
 
 static int edbm_select_mode_exec(bContext *C, wmOperator *op)
diff --git a/source/blender/editors/mesh/mesh_intern.h b/source/blender/editors/mesh/mesh_intern.h
index 76f6cb5ebb8..6ba91097ec4 100644
--- a/source/blender/editors/mesh/mesh_intern.h
+++ b/source/blender/editors/mesh/mesh_intern.h
@@ -137,6 +137,7 @@ void MESH_OT_rip_edge(struct wmOperatorType *ot);
 
 /* *** editmesh_select.c *** */
 void MESH_OT_select_similar(struct wmOperatorType *ot);
+void MESH_OT_select_similar_region(struct wmOperatorType *ot);
 void MESH_OT_select_mode(struct wmOperatorType *ot);
 void MESH_OT_loop_multi_select(struct wmOperatorType *ot);
 void MESH_OT_loop_select(struct wmOperatorType *ot);
diff --git a/source/blender/editors/mesh/mesh_ops.c b/source/blender/editors/mesh/mesh_ops.c
index 31653efa735..5f3af733ebd 100644
--- a/source/blender/editors/mesh/mesh_ops.c
+++ b/source/blender/editors/mesh/mesh_ops.c
@@ -130,6 +130,7 @@ void ED_operatortypes_mesh(void)
 	WM_operatortype_append(MESH_OT_edge_face_add);
 	WM_operatortype_append(MESH_OT_shortest_path_pick);
 	WM_operatortype_append(MESH_OT_select_similar);
+	WM_operatortype_append(MESH_OT_select_similar_region);
 	WM_operatortype_append(MESH_OT_select_mode);
 	WM_operatortype_append(MESH_OT_loop_multi_select);
 	WM_operatortype_append(MESH_OT_mark_seam);