bmesh edge rotate

* improve check to see if edge rotate can be done,
  was checking if both edges verts have an edge count of 2, which is really a meaningless test since the verts can have stray edges connected and the result wont work right.
  instead check if the next verts in both faces share a vertex.

* add utility function BM_face_other_vert_loop() which gets the next loop in a face.
* add convenience function BM_edge_face_pair() which returns 2 faces for edges that have exactly 2 face users. (saves ugly e->l->radial_next ... in code) and is more readable.

source/blender/bmesh/intern/bmesh_mods.c

@@ -708,6 +708,43 @@ int BM_face_validate(BMesh *bm, BMFace *face, FILE *err)
 	return ret;
 }
 
+/**
+ * \brief Check if Rotate Edge is OK
+ *
+ * Quick check to see if we could rotate the edge,
+ * use this to avoid calling exceptions on common cases.
+ */
+int BM_edge_rotate_check(BMesh *UNUSED(bm), BMEdge *e)
+{
+	BMFace *fa, *fb;
+	if (BM_edge_face_pair(e, &fa, &fb)) {
+		BMLoop *la, *lb;
+
+		la = BM_face_other_vert_loop(e->v2, fa, e->v1);
+		lb = BM_face_other_vert_loop(e->v2, fb, e->v1);
+
+		/* check that the next vert in both faces isnt the same
+		 * (ie - the next edge doesnt sharwe the same faces).
+		 * since we can't rotate usefully in this case. */
+		if (la->v == lb->v) {
+			return FALSE;
+		}
+
+		/* mirror of the check above but in the opposite direction */
+		la = BM_face_other_vert_loop(e->v1, fa, e->v2);
+		lb = BM_face_other_vert_loop(e->v1, fb, e->v2);
+
+		if (la->v == lb->v) {
+			return FALSE;
+		}
+
+		return TRUE;
+	}
+	else {
+		return FALSE;
+	}
+}
+
 /**
  * \brief Rotate Edge
  *
@@ -727,17 +764,13 @@ BMEdge *BM_edge_rotate(BMesh *bm, BMEdge *e, int ccw)
 	BMFace *f;
 	BMIter liter;
 
+	if (!BM_edge_rotate_check(bm, e)) {
+		return NULL;
+	}
+
 	v1 = e->v1;
 	v2 = e->v2;
 
-	if (BM_edge_face_count(e) != 2)
-		return NULL;
-
-	/* If either of e's vertices has valence 2, then
-	 * dissolving the edge would leave a spur, so not allowed */
-	if (BM_vert_edge_count(e->v1) == 2 || BM_vert_edge_count(e->v2) == 2)
-		return NULL;
-
 	f = BM_faces_join_pair(bm, e->l->f, e->l->radial_next->f, e);
 
 	if (f == NULL)

source/blender/bmesh/intern/bmesh_mods.h

@@ -53,6 +53,7 @@ BMVert *BM_edge_split_n(BMesh *bm, BMEdge *e, int numcuts);
 
 int     BM_face_validate(BMesh *bm, BMFace *face, FILE *err);
 
+int     BM_edge_rotate_check(BMesh *UNUSED(bm), BMEdge *e);
 BMEdge *BM_edge_rotate(BMesh *bm, BMEdge *e, int ccw);
 
 BMVert *BM_vert_rip(BMesh *bm, BMFace *sf, BMVert *sv);

source/blender/bmesh/intern/bmesh_queries.c

@@ -65,7 +65,7 @@ int BM_vert_in_edge(BMEdge *e, BMVert *v)
 /**
  * \brief BMESH OTHER EDGE IN FACE SHARING A VERTEX
  *
- * Finds the other loop that shares 'v' with 'e's loop in 'f'.
+ * Finds the other loop that shares \a v with \a e loop in \a f.
  */
 BMLoop *BM_face_other_loop(BMEdge *e, BMFace *f, BMVert *v)
 {
@@ -83,6 +83,50 @@ BMLoop *BM_face_other_loop(BMEdge *e, BMFace *f, BMVert *v)
 	return l_iter->v == v ? l_iter->prev : l_iter->next;
 }
 
+/**
+ * \brief BMESH NEXT LOOP IN FACE SHARING A VERTEX
+ *
+ * Finds the other loop in a face.
+ *
+ * This function returns a loop in \a f that shares an edge with \v
+ * The direction is defined by \a v_prev, where the return value is
+ * the loop of what would be 'v_next'
+ *
+ * \note \a v_prev and \a v _implicitly_ define an edge.
+ */
+BMLoop *BM_face_other_vert_loop(BMVert *v_prev, BMFace *f, BMVert *v)
+{
+	BMIter liter;
+	BMLoop *l_iter;
+
+	BLI_assert(BM_edge_exists(v_prev, v) != NULL);
+
+	BM_ITER(l_iter, &liter, NULL, BM_LOOPS_OF_VERT, v) {
+		if (l_iter->f == f) {
+			break;
+		}
+	}
+
+	if (l_iter) {
+		if (l_iter->prev->v == v_prev) {
+			return l_iter->next;
+		}
+		else if (l_iter->next->v == v_prev) {
+			return l_iter->prev;
+		}
+		else {
+			/* invalid args */
+			BLI_assert(0);
+			return NULL;
+		}
+	}
+	else {
+		/* invalid args */
+		BLI_assert(0);
+		return NULL;
+	}
+}
+
 /**
  * Returns TRUE if the vertex is used in a given face.
  */
@@ -190,6 +234,31 @@ BMVert *BM_edge_other_vert(BMEdge *e, BMVert *v)
 	return bmesh_edge_other_vert_get(e, v);
 }
 
+/**
+ * Utility function, since enough times we have an edge
+ * and want to access 2 connected faces.
+ *
+ * \return TRUE when only 2 faces are found.
+ */
+int BM_edge_face_pair(BMEdge *e, BMFace **r_fa, BMFace **r_fb)
+{
+	BMLoop *la, *lb;
+
+	if ((la = e->l) &&
+	    (lb = la->radial_next) &&
+	    (lb->radial_next == la))
+	{
+		*r_fa = la->f;
+		*r_fb = lb->f;
+		return TRUE;
+	}
+	else {
+		*r_fa = NULL;
+		*r_fb = NULL;
+		return FALSE;
+	}
+}
+
 /**
  *	Returns the number of edges around this vertex.
  */

source/blender/bmesh/intern/bmesh_queries.h

@@ -37,8 +37,10 @@ int     BM_edge_in_face(BMFace *f, BMEdge *e);
 int     BM_vert_in_edge(BMEdge *e, BMVert *v);
 int     BM_verts_in_edge(BMVert *v1, BMVert *v2, BMEdge *e);
 
+int     BM_edge_face_pair(BMEdge *e, BMFace **r_fa, BMFace **r_fb);
 BMVert *BM_edge_other_vert(BMEdge *e, BMVert *v);
 BMLoop *BM_face_other_loop(BMEdge *e, BMFace *f, BMVert *v);
+BMLoop *BM_face_other_vert_loop(BMVert *v_prev, BMFace *f, BMVert *v);
 
 int     BM_vert_edge_count(BMVert *v);
 int     BM_edge_face_count(BMEdge *e);

source/blender/bmesh/operators/bmo_utils.c

@@ -125,16 +125,39 @@ void bmo_edgerotate_exec(BMesh *bm, BMOperator *op)
 	BMEdge *e, *e2;
 	int ccw = BMO_slot_bool_get(op, "ccw");
 
-	BMO_ITER(e, &siter, bm, op, "edges", BM_EDGE) {
-		if (!(e2 = BM_edge_rotate(bm, e, ccw))) {
-			BMO_error_raise(bm, op, BMERR_INVALID_SELECTION, "Could not rotate edge");
-			return;
-		}
+#define EDGE_OUT   1
+#define FACE_TAINT 1
 
-		BMO_elem_flag_enable(bm, e2, 1);
+	BMO_ITER(e, &siter, bm, op, "edges", BM_EDGE) {
+		if (BM_edge_rotate_check(bm, e)) {
+			BMFace *fa, *fb;
+			if (BM_edge_face_pair(e, &fa, &fb)) {
+
+				/* check we're untouched */
+				if (BMO_elem_flag_test(bm, fa, FACE_TAINT) == FALSE &&
+				    BMO_elem_flag_test(bm, fb, FACE_TAINT) == FALSE)
+				{
+
+					if (!(e2 = BM_edge_rotate(bm, e, ccw))) {
+						BMO_error_raise(bm, op, BMERR_INVALID_SELECTION, "Could not rotate edge");
+						return;
+					}
+
+					BMO_elem_flag_enable(bm, e2, EDGE_OUT);
+
+					/* dont touch again */
+					BMO_elem_flag_enable(bm, fa, FACE_TAINT);
+					BMO_elem_flag_enable(bm, fb, FACE_TAINT);
+				}
+			}
+		}
 	}
 
-	BMO_slot_buffer_from_flag(bm, op, "edgeout", 1, BM_EDGE);
+	BMO_slot_buffer_from_flag(bm, op, "edgeout", EDGE_OUT, BM_EDGE);
+
+#undef EDGE_OUT
+#undef FACE_TAINT
+
 }
 
 #define SEL_FLAG	1