- add knife project to toolbar.

- when running knife project, disable vertex selection since it may select areas between the newly cut regions.
  add EDBM_selectmode_disable() function since loopcut does this too.
- (optimization) avoid looping over all geometry when flushing and no selection exists.

release/scripts/startup/bl_ui/space_view3d_toolbar.py

@@ -180,6 +180,7 @@ class VIEW3D_PT_tools_meshedit(View3DPanel, Panel):
         props = row.operator("mesh.knife_tool", text="Select")
         props.use_occlude_geometry = False
         props.only_selected = True
+        col.operator("mesh.knife_project")
 
         col = layout.column(align=True)
         col.label(text="Remove:")

source/blender/editors/include/ED_mesh.h

@@ -161,6 +161,9 @@ void EDBM_selectmode_convert(struct BMEditMesh *em, const short selectmode_old,
 bool EDBM_selectmode_toggle(struct bContext *C, const short selectmode_new,
                             const int action, const bool use_extend, const bool use_expand);
 
+bool EDBM_selectmode_disable(struct Scene *scene, struct BMEditMesh *em,
+                             const short selectmode_disable,
+                             const short selectmode_fallback);
 
 void EDBM_deselect_by_material(struct BMEditMesh *em, const short index, const short select);
 

source/blender/editors/mesh/editmesh_knife_project.c

@@ -51,6 +51,7 @@
 
 #include "WM_types.h"
 
+#include "ED_mesh.h"
 #include "ED_screen.h"
 #include "ED_view3d.h"
 
@@ -137,6 +138,12 @@ static int knifeproject_exec(bContext *C, wmOperator *op)
 
 		/* select only tagged faces */
 		BM_mesh_elem_hflag_disable_all(em->bm, BM_VERT | BM_EDGE | BM_FACE, BM_ELEM_SELECT, false);
+
+		/* note essential, but switch out of vertex mode since the
+		 * selected regions wont be nicely isolated after flushing.
+		 * note: call after de-select to avoid selection flushing */
+		EDBM_selectmode_disable(scene, em, SCE_SELECT_VERTEX, SCE_SELECT_EDGE);
+
 		BM_mesh_elem_hflag_enable_test(em->bm, BM_FACE, BM_ELEM_SELECT, true, BM_ELEM_TAG);
 
 		BM_mesh_select_mode_flush(em->bm);
@@ -165,4 +172,3 @@ void MESH_OT_knife_project(wmOperatorType *ot)
 	/* flags */
 	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_BLOCKING;
 }
-

source/blender/editors/mesh/editmesh_loopcut.c

@@ -300,17 +300,11 @@ static void ringsel_finish(bContext *C, wmOperator *op)
 			EDBM_update_generic(em, false, true);
 
 			/* force edge slide to edge select mode in in face select mode */
-			if (em->selectmode & SCE_SELECT_FACE) {
-				if (em->selectmode == SCE_SELECT_FACE)
-					em->selectmode = SCE_SELECT_EDGE;
-				else
-					em->selectmode &= ~SCE_SELECT_FACE;
-				CTX_data_tool_settings(C)->selectmode = em->selectmode;
-				EDBM_selectmode_set(em);
-
-				WM_event_add_notifier(C, NC_SCENE | ND_TOOLSETTINGS, CTX_data_scene(C));
+			if (EDBM_selectmode_disable(lcd->vc.scene, em, SCE_SELECT_FACE, SCE_SELECT_EDGE)) {
+				/* pass, the change will flush selection */
 			}
 			else {
+				/* else flush explicitly */
 				EDBM_selectmode_flush(lcd->em);
 			}
 		}

source/blender/editors/mesh/editmesh_select.c

@@ -1946,38 +1946,57 @@ void EDBM_selectmode_set(BMEditMesh *em)
 
 	edbm_strip_selections(em); /* strip BMEditSelections from em->selected that are not relevant to new mode */
 	
+	if (em->bm->totvertsel == 0 &&
+	    em->bm->totedgesel == 0 &&
+	    em->bm->totfacesel == 0)
+	{
+		return;
+	}
+
 	if (em->selectmode & SCE_SELECT_VERTEX) {
-		EDBM_select_flush(em);
+		if (em->bm->totvertsel) {
+			EDBM_select_flush(em);
+		}
 	}
 	else if (em->selectmode & SCE_SELECT_EDGE) {
 		/* deselect vertices, and select again based on edge select */
-		eve = BM_iter_new(&iter, em->bm, BM_VERTS_OF_MESH, NULL);
-		for (; eve; eve = BM_iter_step(&iter)) BM_vert_select_set(em->bm, eve, false);
-		
-		eed = BM_iter_new(&iter, em->bm, BM_EDGES_OF_MESH, NULL);
-		for (; eed; eed = BM_iter_step(&iter)) {
-			if (BM_elem_flag_test(eed, BM_ELEM_SELECT)) {
-				BM_edge_select_set(em->bm, eed, true);
-			}
+		BM_ITER_MESH (eve, &iter, em->bm, BM_VERTS_OF_MESH) {
+			BM_vert_select_set(em->bm, eve, false);
+		}
+
+		if (em->bm->totedgesel) {
+			BM_ITER_MESH (eed, &iter, em->bm, BM_EDGES_OF_MESH) {
+				if (BM_elem_flag_test(eed, BM_ELEM_SELECT)) {
+					BM_edge_select_set(em->bm, eed, true);
+				}
+			}
+
+			/* selects faces based on edge status */
+			EDBM_selectmode_flush(em);
 		}
-		
-		/* selects faces based on edge status */
-		EDBM_selectmode_flush(em);
 	}
 	else if (em->selectmode & SCE_SELECT_FACE) {
 		/* deselect eges, and select again based on face select */
-		eed = BM_iter_new(&iter, em->bm, BM_EDGES_OF_MESH, NULL);
-		for (; eed; eed = BM_iter_step(&iter)) BM_edge_select_set(em->bm, eed, false);
-		
-		efa = BM_iter_new(&iter, em->bm, BM_FACES_OF_MESH, NULL);
-		for (; efa; efa = BM_iter_step(&iter)) {
-			if (BM_elem_flag_test(efa, BM_ELEM_SELECT)) {
-				BM_face_select_set(em->bm, efa, true);
+		BM_ITER_MESH (eed, &iter, em->bm, BM_EDGES_OF_MESH) {
+			BM_edge_select_set(em->bm, eed, false);
+		}
+
+		if (em->bm->totfacesel) {
+			efa = BM_iter_new(&iter, em->bm, BM_FACES_OF_MESH, NULL);
+			for (; efa; efa = BM_iter_step(&iter)) {
+				if (BM_elem_flag_test(efa, BM_ELEM_SELECT)) {
+					BM_face_select_set(em->bm, efa, true);
+				}
 			}
 		}
 	}
 }
 
+/**
+ * Flush the selection up:
+ * - vert -> edge
+ * - edge -> face
+ */
 void EDBM_selectmode_convert(BMEditMesh *em, const short selectmode_old, const short selectmode_new)
 {
 	BMEdge *eed;
@@ -1988,7 +2007,10 @@ void EDBM_selectmode_convert(BMEditMesh *em, const short selectmode_old, const s
 
 	/* have to find out what the selectionmode was previously */
 	if (selectmode_old == SCE_SELECT_VERTEX) {
-		if (selectmode_new == SCE_SELECT_EDGE) {
+		if (em->bm->totvertsel == 0) {
+			/* pass */
+		}
+		else if (selectmode_new == SCE_SELECT_EDGE) {
 			/* select all edges associated with every selected vert */
 			BM_ITER_MESH (eed, &iter, em->bm, BM_EDGES_OF_MESH) {
 				BM_elem_flag_set(eed, BM_ELEM_TAG, BM_edge_is_any_vert_flag_test(eed, BM_ELEM_SELECT));
@@ -2014,7 +2036,10 @@ void EDBM_selectmode_convert(BMEditMesh *em, const short selectmode_old, const s
 		}
 	}
 	else if (selectmode_old == SCE_SELECT_EDGE) {
-		if (selectmode_new == SCE_SELECT_FACE) {
+		if (em->bm->totedgesel == 0) {
+			/* pass */
+		}
+		else if (selectmode_new == SCE_SELECT_FACE) {
 			/* select all faces associated with every selected edge */
 			BM_ITER_MESH (efa, &iter, em->bm, BM_FACES_OF_MESH) {
 				BM_elem_flag_set(efa, BM_ELEM_TAG, BM_face_is_any_edge_flag_test(efa, BM_ELEM_SELECT));
@@ -2125,6 +2150,37 @@ bool EDBM_selectmode_toggle(bContext *C, const short selectmode_new,
 	return ret;
 }
 
+/**
+ * Use to disable a selectmode if its enabled, Using another mode as a fallback
+ * if the disabled mode is the only mode set.
+ *
+ * \return true if the mode is changed.
+ */
+bool EDBM_selectmode_disable(Scene *scene, BMEditMesh *em,
+                             const short selectmode_disable,
+                             const short selectmode_fallback)
+{
+	/* note essential, but switch out of vertex mode since the
+	 * selected regions wont be nicely isolated after flushing */
+	if (em->selectmode & selectmode_disable) {
+		if (em->selectmode == selectmode_disable) {
+			em->selectmode = selectmode_fallback;
+		}
+		else {
+			em->selectmode &= ~selectmode_disable;
+		}
+		scene->toolsettings->selectmode = em->selectmode;
+		EDBM_selectmode_set(em);
+
+		WM_main_add_notifier(NC_SCENE | ND_TOOLSETTINGS, scene);
+
+		return true;
+	}
+	else {
+		return false;
+	}
+}
+
 void EDBM_deselect_by_material(BMEditMesh *em, const short index, const short select)
 {
 	BMIter iter;