Workspaces: add main and child windows.

* Main windows show a topbar and statusbar, and select a workspace and
  scene. They are created with Window > New Main Window.

* Child windows do not show a topbar or statusbar. These follow the
  workspace and scene of their parent main window. Created with Window >
  New Window or View > Duplicate Area into New Window.

* The purpose of this change is to support multi monitor setups where you
  just want to put more editors on the other monitors. Without multiple
  topbars and statusbars, working within a single workspace and scene.
  Creating multiple main windows is intended to be a concious choice to
  do different tasks in different workspaces and scenes.

* Note these changes do not currently affect how the operating system
  treats the windows.

* When changing the workspace, the layout in all child windows changes.
  This makes sense if we consider child windows to be just a way to
  extend the main window across more monitors. In some case it may be
  useful to keep the same layout though, we can add an option for this
  depending on user feedback.

20 files changed, 203 insertions, 135 deletions

diff --git a/source/blender/blenkernel/intern/scene.c b/source/blender/blenkernel/intern/scene.c
index a38384f8f2b..1b309d76f61 100644
--- a/source/blender/blenkernel/intern/scene.c
+++ b/source/blender/blenkernel/intern/scene.c
@@ -906,7 +906,7 @@ Object *BKE_scene_object_find_by_name(Scene *scene, const char *name)
 /**
  * Sets the active scene, mainly used when running in background mode (``--scene`` command line argument).
  * This is also called to set the scene directly, bypassing windowing code.
- * Otherwise #WM_window_change_active_scene is used when changing scenes by the user.
+ * Otherwise #WM_window_set_active_scene is used when changing scenes by the user.
  */
 void BKE_scene_set_background(Main *bmain, Scene *scene)
 {
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 2a48bf8fc5a..4fa897bb689 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -6926,9 +6926,11 @@ static void direct_link_windowmanager(FileData *fd, wmWindowManager *wm)
 	link_list(fd, &wm->windows);
 
 	for (win = wm->windows.first; win; win = win->next) {
-		WorkSpaceInstanceHook *hook = win->workspace_hook;
+		win->parent = newdataadr(fd, win->parent);
 
+		WorkSpaceInstanceHook *hook = win->workspace_hook;
 		win->workspace_hook = newdataadr(fd, hook);
+
 		/* we need to restore a pointer to this later when reading workspaces, so store in global oldnew-map */
 		oldnewmap_insert(fd->globmap, hook, win->workspace_hook, 0);
 
diff --git a/source/blender/editors/include/ED_scene.h b/source/blender/editors/include/ED_scene.h
index 9b48187e541..116d9bd24fc 100644
--- a/source/blender/editors/include/ED_scene.h
+++ b/source/blender/editors/include/ED_scene.h
@@ -31,10 +31,7 @@ enum eSceneCopyMethod;
 
 struct Scene *ED_scene_add(struct Main *bmain, struct bContext *C, struct wmWindow *win, enum eSceneCopyMethod method) ATTR_NONNULL();
 bool ED_scene_delete(struct bContext *C, struct Main *bmain, struct wmWindow *win, struct Scene *scene) ATTR_NONNULL();
-void ED_scene_change_update(
-        struct Main *bmain, struct bContext *C,
-        struct wmWindow *win, const struct bScreen *screen,
-        struct Scene *scene_old, struct Scene *scene_new) ATTR_NONNULL();
+void ED_scene_change_update(struct Main *bmain, struct Scene *scene, struct ViewLayer *layer) ATTR_NONNULL();
 bool ED_scene_view_layer_delete(
         struct Main *bmain, struct Scene *scene, struct ViewLayer *layer,
         struct ReportList *reports) ATTR_NONNULL(1, 2, 3);
diff --git a/source/blender/editors/include/ED_screen.h b/source/blender/editors/include/ED_screen.h
index 1fdbd46bacf..cc80108e20c 100644
--- a/source/blender/editors/include/ED_screen.h
+++ b/source/blender/editors/include/ED_screen.h
@@ -184,10 +184,7 @@ void    ED_screen_refresh(struct wmWindowManager *wm, struct wmWindow *win);
 void    ED_screen_ensure_updated(struct wmWindowManager *wm, struct wmWindow *win, struct bScreen *screen);
 void    ED_screen_do_listen(struct bContext *C, struct wmNotifier *note);
 bool    ED_screen_change(struct bContext *C, struct bScreen *sc);
-void    ED_screen_update_after_scene_change(
-        const struct bScreen *screen,
-        struct Scene *scene_new,
-        struct ViewLayer *view_layer);
+void    ED_screen_scene_change(struct bContext *C, struct wmWindow *win, struct Scene *scene);
 void    ED_screen_set_active_region(struct bContext *C, struct wmWindow *win, const int xy[2]);
 void    ED_screen_exit(struct bContext *C, struct wmWindow *window, struct bScreen *screen);
 void    ED_screen_animation_timer(struct bContext *C, int redraws, int refresh, int sync, int enable);
diff --git a/source/blender/editors/scene/scene_edit.c b/source/blender/editors/scene/scene_edit.c
index 677fc0a068e..0ebbd770c9f 100644
--- a/source/blender/editors/scene/scene_edit.c
+++ b/source/blender/editors/scene/scene_edit.c
@@ -80,7 +80,7 @@ Scene *ED_scene_add(Main *bmain, bContext *C, wmWindow *win, eSceneCopyMethod me
 		}
 	}
 
-	WM_window_change_active_scene(bmain, C, win, scene_new);
+	WM_window_set_active_scene(bmain, C, win, scene_new);
 
 	WM_event_add_notifier(C, NC_SCENE | ND_SCENEBROWSE, scene_new);
 
@@ -102,7 +102,7 @@ bool ED_scene_delete(bContext *C, Main *bmain, wmWindow *win, Scene *scene)
 	else
 		return false;
 
-	WM_window_change_active_scene(bmain, C, win, scene_new);
+	WM_window_set_active_scene(bmain, C, win, scene_new);
 
 	BKE_libblock_remap(bmain, scene, scene_new, ID_REMAP_SKIP_INDIRECT_USAGE | ID_REMAP_SKIP_NEVER_NULL_USAGE);
 
@@ -114,43 +114,17 @@ bool ED_scene_delete(bContext *C, Main *bmain, wmWindow *win, Scene *scene)
 	return true;
 }
 
-static ViewLayer *scene_change_get_new_view_layer(const WorkSpace *workspace, const Scene *scene_new)
+/* Depsgraph updates after scene becomes active in a window. */
+void ED_scene_change_update(Main *bmain, Scene *scene, ViewLayer *layer)
 {
-	ViewLayer *layer_new = BKE_workspace_view_layer_exists(workspace, scene_new);
-	return layer_new ? layer_new : BKE_view_layer_default_view(scene_new);
-}
+	Depsgraph *depsgraph = BKE_scene_get_depsgraph(scene, layer, true);
 
-void ED_scene_change_update(
-        Main *bmain, bContext *C,
-        wmWindow *win, const bScreen *screen, Scene *UNUSED(scene_old), Scene *scene_new)
-{
-	WorkSpace *workspace = CTX_wm_workspace(C);
-	ViewLayer *layer_new = scene_change_get_new_view_layer(workspace, scene_new);
-	Depsgraph *depsgraph = BKE_scene_get_depsgraph(scene_new, layer_new, true);
-	Object *obact_new = OBACT(layer_new);
-	UNUSED_VARS(obact_new);
-
-#if 0
-	/* mode syncing */
-	eObjectMode object_mode_old = workspace->object_mode;
-	ViewLayer *layer_old = BKE_view_layer_from_workspace_get(scene_old, workspace);
-	Object *obact_old = OBACT(layer_old);
-	UNUSED_VARS(obact_old, object_mode_old);
-#endif
-
-	win->scene = scene_new;
-	CTX_data_scene_set(C, scene_new);
-	BKE_workspace_view_layer_set(workspace, layer_new, scene_new);
-	BKE_scene_set_background(bmain, scene_new);
-	DEG_graph_relations_update(depsgraph, bmain, scene_new, layer_new);
+	BKE_scene_set_background(bmain, scene);
+	DEG_graph_relations_update(depsgraph, bmain, scene, layer);
 	DEG_on_visible_update(bmain, false);
 
-	ED_screen_update_after_scene_change(screen, scene_new, layer_new);
 	ED_render_engine_changed(bmain);
 	ED_update_for_newframe(bmain, depsgraph);
-
-	/* complete redraw */
-	WM_event_add_notifier(C, NC_WINDOW, NULL);
 }
 
 static bool view_layer_remove_poll(
diff --git a/source/blender/editors/screen/screen_edit.c b/source/blender/editors/screen/screen_edit.c
index 6bc8a6c10cf..50609815168 100644
--- a/source/blender/editors/screen/screen_edit.c
+++ b/source/blender/editors/screen/screen_edit.c
@@ -477,8 +477,8 @@ void ED_screens_initialize(Main *bmain, wmWindowManager *wm)
 	wmWindow *win;
 
 	for (win = wm->windows.first; win; win = win->next) {
-		if (WM_window_get_active_workspace(win) == NULL) {
-			WM_window_set_active_workspace(win, bmain->workspaces.first);
+		if (BKE_workspace_active_get(win->workspace_hook) == NULL) {
+			BKE_workspace_active_set(win->workspace_hook, bmain->workspaces.first);
 		}
 
 		if (BLI_listbase_is_empty(&win->global_areas.areabase)) {
@@ -792,11 +792,19 @@ static void screen_global_statusbar_area_create(wmWindow *win)
 
 void ED_screen_global_areas_create(wmWindow *win)
 {
+	/* Don't create global areas for child windows. */
+	if (win->parent) {
+		return;
+	}
+
+	/* Don't create global area for temporary windows. */
 	bScreen *screen = BKE_workspace_active_screen_get(win->workspace_hook);
-	if (screen->temp == 0) {
-		screen_global_topbar_area_create(win);
-		screen_global_statusbar_area_create(win);
+	if (screen->temp) {
+		return;
 	}
+
+	screen_global_topbar_area_create(win);
+	screen_global_statusbar_area_create(win);
 }
 
 
@@ -936,13 +944,40 @@ static void screen_set_3dview_camera(Scene *scene, ViewLayer *view_layer, ScrAre
 	}
 }
 
-void ED_screen_update_after_scene_change(const bScreen *screen, Scene *scene_new, ViewLayer *view_layer)
+static ViewLayer *scene_change_get_new_view_layer(const WorkSpace *workspace, const Scene *scene_new)
+{
+	ViewLayer *layer_new = BKE_workspace_view_layer_exists(workspace, scene_new);
+	return layer_new ? layer_new : BKE_view_layer_default_view(scene_new);
+}
+
+void ED_screen_scene_change(bContext *C, wmWindow *win, Scene *scene)
 {
+	const bScreen *screen = WM_window_get_active_screen(win);
+	WorkSpace *workspace = CTX_wm_workspace(C);
+	ViewLayer *view_layer = scene_change_get_new_view_layer(workspace, scene);
+
+#if 0
+	/* mode syncing */
+	Object *obact_new = OBACT(view_layer);
+	UNUSED_VARS(obact_new);
+	eObjectMode object_mode_old = workspace->object_mode;
+	ViewLayer *layer_old = BKE_view_layer_from_workspace_get(scene_old, workspace);
+	Object *obact_old = OBACT(layer_old);
+	UNUSED_VARS(obact_old, object_mode_old);
+#endif
+
+	BKE_workspace_view_layer_set(workspace, view_layer, scene);
+
+	win->scene = scene;
+	if (CTX_wm_window(C) == win) {
+		CTX_data_scene_set(C, scene);
+	}
+
 	for (ScrArea *sa = screen->areabase.first; sa; sa = sa->next) {
 		for (SpaceLink *sl = sa->spacedata.first; sl; sl = sl->next) {
 			if (sl->spacetype == SPACE_VIEW3D) {
 				View3D *v3d = (View3D *)sl;
-				screen_set_3dview_camera(scene_new, view_layer, sa, v3d);
+				screen_set_3dview_camera(scene, view_layer, sa, v3d);
 			}
 		}
 	}
diff --git a/source/blender/editors/screen/screen_ops.c b/source/blender/editors/screen/screen_ops.c
index a0e8357b8f3..ab0fbfacf93 100644
--- a/source/blender/editors/screen/screen_ops.c
+++ b/source/blender/editors/screen/screen_ops.c
@@ -1130,7 +1130,7 @@ static int area_dupli_invoke(bContext *C, wmOperator *op, const wmEvent *event)
 
 	newwin->scene = scene;
 
-	WM_window_set_active_workspace(newwin, workspace);
+	BKE_workspace_active_set(newwin->workspace_hook, workspace);
 	/* allocs new screen and adds to newly created window, using window size */
 	layout_new = ED_workspace_layout_add(bmain, workspace, newwin, BKE_workspace_layout_name_get(layout_old));
 	newsc = BKE_workspace_layout_screen_get(layout_new);
diff --git a/source/blender/editors/screen/workspace_edit.c b/source/blender/editors/screen/workspace_edit.c
index 9d329355500..9ba9b70a6e8 100644
--- a/source/blender/editors/screen/workspace_edit.c
+++ b/source/blender/editors/screen/workspace_edit.c
@@ -191,8 +191,8 @@ bool ED_workspace_change(
 	BLI_assert(BKE_workspace_layout_screen_get(layout_new) == screen_new);
 
 	if (screen_new) {
-		WM_window_set_active_layout(win, workspace_new, layout_new);
-		WM_window_set_active_workspace(win, workspace_new);
+		BKE_workspace_hook_layout_for_workspace_set(win->workspace_hook, workspace_new, layout_new);
+		BKE_workspace_active_set(win->workspace_hook, workspace_new);
 
 		/* update screen *after* changing workspace - which also causes the
 		 * actual screen change and updates context (including CTX_wm_workspace) */
diff --git a/source/blender/editors/space_outliner/outliner_select.c b/source/blender/editors/space_outliner/outliner_select.c
index 6668ea1faeb..8a5df196c7b 100644
--- a/source/blender/editors/space_outliner/outliner_select.c
+++ b/source/blender/editors/space_outliner/outliner_select.c
@@ -262,7 +262,7 @@ static eOLDrawState tree_element_set_active_object(
 
 	sce = (Scene *)outliner_search_back(soops, te, ID_SCE);
 	if (sce && scene != sce) {
-		WM_window_change_active_scene(CTX_data_main(C), C, CTX_wm_window(C), sce);
+		WM_window_set_active_scene(CTX_data_main(C), C, CTX_wm_window(C), sce);
 		scene = sce;
 	}
 
@@ -431,7 +431,7 @@ static eOLDrawState tree_element_active_world(
 	if (set != OL_SETSEL_NONE) {
 		/* make new scene active */
 		if (sce && scene != sce) {
-			WM_window_change_active_scene(CTX_data_main(C), C, CTX_wm_window(C), sce);
+			WM_window_set_active_scene(CTX_data_main(C), C, CTX_wm_window(C), sce);
 		}
 	}
 
@@ -950,7 +950,7 @@ static void do_outliner_item_activate_tree_element(
 		/* editmode? */
 		if (te->idcode == ID_SCE) {
 			if (scene != (Scene *)tselem->id) {
-				WM_window_change_active_scene(CTX_data_main(C), C, CTX_wm_window(C), (Scene *)tselem->id);
+				WM_window_set_active_scene(CTX_data_main(C), C, CTX_wm_window(C), (Scene *)tselem->id);
 			}
 		}
 		else if (te->idcode == ID_GR) {
diff --git a/source/blender/editors/space_outliner/outliner_tools.c b/source/blender/editors/space_outliner/outliner_tools.c
index 9952db5e652..b23ea8e4dae 100644
--- a/source/blender/editors/space_outliner/outliner_tools.c
+++ b/source/blender/editors/space_outliner/outliner_tools.c
@@ -580,7 +580,7 @@ void outliner_do_object_operation_ex(
 				// when objects selected in other scenes... dunno if that should be allowed
 				Scene *scene_owner = (Scene *)outliner_search_back(soops, te, ID_SCE);
 				if (scene_owner && scene_act != scene_owner) {
-					WM_window_change_active_scene(CTX_data_main(C), C, CTX_wm_window(C), scene_owner);
+					WM_window_set_active_scene(CTX_data_main(C), C, CTX_wm_window(C), scene_owner);
 				}
 				/* important to use 'scene_owner' not scene_act else deleting objects can crash.
 				 * only use 'scene_act' when 'scene_owner' is NULL, which can happen when the
@@ -956,7 +956,7 @@ static int outliner_object_operation_exec(bContext *C, wmOperator *op)
 		Scene *sce = scene;  // to be able to delete, scenes are set...
 		outliner_do_object_operation(C, op->reports, scene, soops, &soops->tree, object_select_cb);
 		if (scene != sce) {
-			WM_window_change_active_scene(bmain, C, win, sce);
+			WM_window_set_active_scene(bmain, C, win, sce);
 		}
 
 		str = "Select Objects";
@@ -967,7 +967,7 @@ static int outliner_object_operation_exec(bContext *C, wmOperator *op)
 		Scene *sce = scene;  // to be able to delete, scenes are set...
 		outliner_do_object_operation_ex(C, op->reports, scene, soops, &soops->tree, object_select_hierarchy_cb, false);
 		if (scene != sce) {
-			WM_window_change_active_scene(bmain, C, win, sce);
+			WM_window_set_active_scene(bmain, C, win, sce);
 		}
 		str = "Select Object Hierarchy";
 		DEG_id_tag_update(&scene->id, DEG_TAG_SELECT_UPDATE);
diff --git a/source/blender/makesdna/DNA_windowmanager_types.h b/source/blender/makesdna/DNA_windowmanager_types.h
index c6ad1470561..0ef9e9b134a 100644
--- a/source/blender/makesdna/DNA_windowmanager_types.h
+++ b/source/blender/makesdna/DNA_windowmanager_types.h
@@ -186,8 +186,10 @@ typedef struct wmWindow {
 	void *ghostwin;             /* don't want to include ghost.h stuff */
 	void *gwnctx;               /* don't want to include gawin stuff */
 
-	struct Scene *scene;     /* The scene displayed in this window. */
-	struct Scene *new_scene; /* temporary when switching */
+	struct wmWindow *parent;    /* Parent window */
+
+	struct Scene *scene;        /* The scene displayed in this window. */
+	struct Scene *new_scene;    /* temporary when switching */
 
 	struct WorkSpaceInstanceHook *workspace_hook;
 
diff --git a/source/blender/makesrna/intern/rna_main_api.c b/source/blender/makesrna/intern/rna_main_api.c
index fff53aafcc7..5fca91064b6 100644
--- a/source/blender/makesrna/intern/rna_main_api.c
+++ b/source/blender/makesrna/intern/rna_main_api.c
@@ -185,7 +185,7 @@ static void rna_Main_scenes_remove(Main *bmain, bContext *C, ReportList *reports
 				BPy_BEGIN_ALLOW_THREADS;
 #endif
 
-				WM_window_change_active_scene(bmain, C, win, scene_new);
+				WM_window_set_active_scene(bmain, C, win, scene_new);
 
 #ifdef WITH_PYTHON
 				BPy_END_ALLOW_THREADS;
diff --git a/source/blender/makesrna/intern/rna_wm.c b/source/blender/makesrna/intern/rna_wm.c
index 1c94582c57e..569bc20d435 100644
--- a/source/blender/makesrna/intern/rna_wm.c
+++ b/source/blender/makesrna/intern/rna_wm.c
@@ -675,7 +675,7 @@ static void rna_Window_scene_update(bContext *C, PointerRNA *ptr)
 		BPy_BEGIN_ALLOW_THREADS;
 #endif
 
-		WM_window_change_active_scene(bmain, C, win, win->new_scene);
+		WM_window_set_active_scene(bmain, C, win, win->new_scene);
 
 #ifdef WITH_PYTHON
 		BPy_END_ALLOW_THREADS;
@@ -2041,6 +2041,9 @@ static void rna_def_window(BlenderRNA *brna)
 	RNA_def_struct_ui_text(srna, "Window", "Open window");
 	RNA_def_struct_sdna(srna, "wmWindow");
 
+	prop = RNA_def_property(srna, "parent", PROP_POINTER, PROP_NONE);
+	RNA_def_property_ui_text(prop, "Parent Window", "Active workspace and scene follow this window");
+
 	rna_def_window_stereo3d(brna);
 
 	prop = RNA_def_property(srna, "scene", PROP_POINTER, PROP_NONE);
diff --git a/source/blender/windowmanager/WM_api.h b/source/blender/windowmanager/WM_api.h
index 3d1ee273108..0ed23a8fb20 100644
--- a/source/blender/windowmanager/WM_api.h
+++ b/source/blender/windowmanager/WM_api.h
@@ -111,10 +111,10 @@ struct Scene *WM_windows_scene_get_from_screen(const struct wmWindowManager *wm,
 struct WorkSpace *WM_windows_workspace_get_from_screen(const wmWindowManager *wm, const struct bScreen *screen) ATTR_NONNULL() ATTR_WARN_UNUSED_RESULT;
 
 struct Scene *WM_window_get_active_scene(const struct wmWindow *win) ATTR_NONNULL() ATTR_WARN_UNUSED_RESULT;
-void          WM_window_change_active_scene(struct Main *bmain, struct bContext *C, struct wmWindow *win,
+void          WM_window_set_active_scene(struct Main *bmain, struct bContext *C, struct wmWindow *win,
                                             struct Scene *scene_new) ATTR_NONNULL();
 struct WorkSpace *WM_window_get_active_workspace(const struct wmWindow *win) ATTR_NONNULL() ATTR_WARN_UNUSED_RESULT;
-void              WM_window_set_active_workspace(struct wmWindow *win, struct WorkSpace *workspace) ATTR_NONNULL(1);
+void              WM_window_set_active_workspace(struct bContext *C, struct wmWindow *win, struct WorkSpace *workspace) ATTR_NONNULL(1);
 struct WorkSpaceLayout *WM_window_get_active_layout(const struct wmWindow *win) ATTR_NONNULL() ATTR_WARN_UNUSED_RESULT;
 void                    WM_window_set_active_layout(
         struct wmWindow *win, struct WorkSpace *workspace, struct WorkSpaceLayout *layout) ATTR_NONNULL(1);
diff --git a/source/blender/windowmanager/intern/wm.c b/source/blender/windowmanager/intern/wm.c
index 701ad49b520..9ef0883cbbf 100644
--- a/source/blender/windowmanager/intern/wm.c
+++ b/source/blender/windowmanager/intern/wm.c
@@ -461,10 +461,10 @@ void wm_add_default(Main *bmain, bContext *C)
 	WorkSpaceLayout *layout = BKE_workspace_layout_find_global(bmain, screen, &workspace);
 
 	CTX_wm_manager_set(C, wm);
-	win = wm_window_new(C);
+	win = wm_window_new(C, NULL);
 	win->scene = CTX_data_scene(C);
-	WM_window_set_active_workspace(win, workspace);
-	WM_window_set_active_layout(win, workspace, layout);
+	BKE_workspace_active_set(win->workspace_hook, workspace);
+	BKE_workspace_hook_layout_for_workspace_set(win->workspace_hook, workspace, layout);
 	screen->winid = win->winid;
 
 	wm->winactive = win;
@@ -484,7 +484,8 @@ void wm_close_and_free(bContext *C, wmWindowManager *wm)
 		wm_autosave_timer_ended(wm);
 
 	while ((win = BLI_pophead(&wm->windows))) {
-		WM_window_set_active_workspace(win, NULL); /* prevent draw clear to use screen */
+		/* prevent draw clear to use screen */
+		BKE_workspace_active_set(win->workspace_hook, NULL);
 		wm_window_free(C, wm, win);
 	}
 
diff --git a/source/blender/windowmanager/intern/wm_event_system.c b/source/blender/windowmanager/intern/wm_event_system.c
index 6fd23dc6b08..3aee57d5801 100644
--- a/source/blender/windowmanager/intern/wm_event_system.c
+++ b/source/blender/windowmanager/intern/wm_event_system.c
@@ -384,7 +384,7 @@ void wm_event_do_notifiers(bContext *C)
 
 						UI_popup_handlers_remove_all(C, &win->modalhandlers);
 
-						ED_workspace_change(ref_ws, C, wm, win);
+						WM_window_set_active_workspace(C, win, ref_ws);
 						if (G.debug & G_DEBUG_EVENTS)
 							printf("%s: Workspace set %p\n", __func__, note->reference);
 					}
diff --git a/source/blender/windowmanager/intern/wm_operators.c b/source/blender/windowmanager/intern/wm_operators.c
index 5628d39e5f8..1983c0e6b84 100644
--- a/source/blender/windowmanager/intern/wm_operators.c
+++ b/source/blender/windowmanager/intern/wm_operators.c
@@ -2298,7 +2298,7 @@ static void WM_OT_window_close(wmOperatorType *ot)
 {
 	ot->name = "Close Window";
 	ot->idname = "WM_OT_window_close";
-	ot->description = "Close the current Blender window";
+	ot->description = "Close the current window";
 
 	ot->exec = wm_window_close_exec;
 	ot->poll = WM_operator_winactive;
@@ -2308,12 +2308,22 @@ static void WM_OT_window_new(wmOperatorType *ot)
 {
 	ot->name = "New Window";
 	ot->idname = "WM_OT_window_new";
-	ot->description = "Create a new Blender window";
+	ot->description = "Create a new window";
 
 	ot->exec = wm_window_new_exec;
 	ot->poll = wm_operator_winactive_normal;
 }
 
+static void WM_OT_window_new_main(wmOperatorType *ot)
+{
+	ot->name = "New Main Window";
+	ot->idname = "WM_OT_window_new_main";
+	ot->description = "Create a new main window with its own workspace and scene selection";
+
+	ot->exec = wm_window_new_main_exec;
+	ot->poll = wm_operator_winactive_normal;
+}
+
 static void WM_OT_window_fullscreen_toggle(wmOperatorType *ot)
 {
 	ot->name = "Toggle Window Fullscreen";
@@ -3703,6 +3713,7 @@ void wm_operatortype_init(void)
 
 	WM_operatortype_append(WM_OT_window_close);
 	WM_operatortype_append(WM_OT_window_new);
+	WM_operatortype_append(WM_OT_window_new_main);
 	WM_operatortype_append(WM_OT_read_history);
 	WM_operatortype_append(WM_OT_read_homefile);
 	WM_operatortype_append(WM_OT_read_factory_settings);
diff --git a/source/blender/windowmanager/intern/wm_stereo.c b/source/blender/windowmanager/intern/wm_stereo.c
index 4450d18a5df..2c779ba9c7c 100644
--- a/source/blender/windowmanager/intern/wm_stereo.c
+++ b/source/blender/windowmanager/intern/wm_stereo.c
@@ -404,7 +404,7 @@ int wm_stereo3d_set_exec(bContext *C, wmOperator *op)
 	    prev_display_mode != win_src->stereo3d_format->display_mode)
 	{
 		/* in case the hardward supports pageflip but not the display */
-		if ((win_dst = wm_window_copy_test(C, win_src, false))) {
+		if ((win_dst = wm_window_copy_test(C, win_src, false, false))) {
 			/* pass */
 		}
 		else {
@@ -423,7 +423,7 @@ int wm_stereo3d_set_exec(bContext *C, wmOperator *op)
 			ok = false;
 		}
 		/* pageflip requires a new window to be created with the proper OS flags */
-		else if ((win_dst = wm_window_copy_test(C, win_src, false))) {
+		else if ((win_dst = wm_window_copy_test(C, win_src, false, false))) {
 			if (wm_stereo3d_quadbuffer_supported()) {
 				BKE_report(op->reports, RPT_INFO, "Quad-buffer window successfully created");
 			}
diff --git a/source/blender/windowmanager/intern/wm_window.c b/source/blender/windowmanager/intern/wm_window.c
index 43231855162..d28d2c6b001 100644
--- a/source/blender/windowmanager/intern/wm_window.c
+++ b/source/blender/windowmanager/intern/wm_window.c
@@ -256,7 +256,7 @@ static int find_free_winid(wmWindowManager *wm)
 }
 
 /* don't change context itself */
-wmWindow *wm_window_new(bContext *C)
+wmWindow *wm_window_new(bContext *C, wmWindow *parent)
 {
 	Main *bmain = CTX_data_main(C);
 	wmWindowManager *wm = CTX_wm_manager(C);
@@ -265,6 +265,7 @@ wmWindow *wm_window_new(bContext *C)
 	BLI_addtail(&wm->windows, win);
 	win->winid = find_free_winid(wm);
 
+	win->parent = (parent && parent->parent) ? parent->parent : parent;
 	win->stereo3d_format = MEM_callocN(sizeof(Stereo3dFormat), "Stereo 3D Format (window)");
 	win->workspace_hook = BKE_workspace_instance_hook_create(bmain);
 
@@ -272,10 +273,11 @@ wmWindow *wm_window_new(bContext *C)
 }
 
 /* part of wm_window.c api */
-wmWindow *wm_window_copy(bContext *C, wmWindow *win_src, const bool duplicate_layout)
+wmWindow *wm_window_copy(bContext *C, wmWindow *win_src, const bool duplicate_layout, const bool child)
 {
 	Main *bmain = CTX_data_main(C);
-	wmWindow *win_dst = wm_window_new(C);
+	wmWindow *win_parent = (child) ? win_src : win_src->parent;
+	wmWindow *win_dst = wm_window_new(C, win_parent);
 	WorkSpace *workspace = WM_window_get_active_workspace(win_src);
 	WorkSpaceLayout *layout_old = WM_window_get_active_layout(win_src);
 	Scene *scene = WM_window_get_active_scene(win_src);
@@ -287,9 +289,9 @@ wmWindow *wm_window_copy(bContext *C, wmWindow *win_src, const bool duplicate_la
 	win_dst->sizey = win_src->sizey;
 
 	win_dst->scene = scene;
-	WM_window_set_active_workspace(win_dst, workspace);
+	BKE_workspace_active_set(win_dst->workspace_hook, workspace);
 	layout_new = duplicate_layout ? ED_workspace_layout_duplicate(bmain, workspace, layout_old, win_dst) : layout_old;
-	WM_window_set_active_layout(win_dst, workspace, layout_new);
+	BKE_workspace_hook_layout_for_workspace_set(win_dst->workspace_hook, workspace, layout_new);
 
 	*win_dst->stereo3d_format = *win_src->stereo3d_format;
 
@@ -300,12 +302,12 @@ wmWindow *wm_window_copy(bContext *C, wmWindow *win_src, const bool duplicate_la
  * A higher level version of copy that tests the new window can be added.
  * (called from the operator directly)
  */
-wmWindow *wm_window_copy_test(bContext *C, wmWindow *win_src, const bool duplicate_layout)
+wmWindow *wm_window_copy_test(bContext *C, wmWindow *win_src, const bool duplicate_layout, const bool child)
 {
 	wmWindowManager *wm = CTX_wm_manager(C);
 	wmWindow *win_dst;
 
-	win_dst = wm_window_copy(C, win_src, duplicate_layout);
+	win_dst = wm_window_copy(C, win_src, duplicate_layout, child);
 
 	WM_check(C);
 
@@ -473,56 +475,67 @@ void wm_window_close(bContext *C, wmWindowManager *wm, wmWindow *win)
 {
 	wmWindow *tmpwin;
 
-	/* first check if we have to quit (there are non-temp remaining windows) */
-	for (tmpwin = wm->windows.first; tmpwin; tmpwin = tmpwin->next) {
-		if (tmpwin == win)
-			continue;
-		if (WM_window_is_temp_screen(tmpwin) == false)
-			break;
+	/* first check if we have to quit (there are non-temp and non-child windows remaining) */
+	if (win->parent == NULL) {
+		for (tmpwin = wm->windows.first; tmpwin; tmpwin = tmpwin->next) {
+			if (tmpwin == win)
+				continue;
+			if (tmpwin->parent == NULL)
+				break;
+			if (WM_window_is_temp_screen(tmpwin) == false)
+				break;
+		}
+
+		if (tmpwin == NULL) {
+			wm_quit_with_optional_confirmation_prompt(C, win);
+			return;
+		}
 	}
 
-	if (tmpwin == NULL) {
-		wm_quit_with_optional_confirmation_prompt(C, win);
+	/* close child windows */
+	for (tmpwin = wm->windows.first; tmpwin; tmpwin = tmpwin->next) {
+		if (tmpwin->parent == win) {
+			wm_window_close(C, wm, tmpwin);
+		}
 	}
-	else {
-		bScreen *screen = WM_window_get_active_screen(win);
-		WorkSpace *workspace = WM_window_get_active_workspace(win);
-		WorkSpaceLayout *layout = BKE_workspace_active_layout_get(win->workspace_hook);
 
-		BLI_remlink(&wm->windows, win);
+	bScreen *screen = WM_window_get_active_screen(win);
+	WorkSpace *workspace = WM_window_get_active_workspace(win);
+	WorkSpaceLayout *layout = BKE_workspace_active_layout_get(win->workspace_hook);
 
-		CTX_wm_window_set(C, win);  /* needed by handlers */
-		WM_event_remove_handlers(C, &win->handlers);
-		WM_event_remove_handlers(C, &win->modalhandlers);
+	BLI_remlink(&wm->windows, win);
 
-		/* for regular use this will _never_ be NULL,
-		 * however we may be freeing an improperly initialized window. */
-		if (screen) {
-			ED_screen_exit(C, win, screen);
-		}
+	CTX_wm_window_set(C, win);  /* needed by handlers */
+	WM_event_remove_handlers(C, &win->handlers);
+	WM_event_remove_handlers(C, &win->modalhandlers);
 
-		if (tmpwin) {
-			BLF_batch_reset();
-			gpu_batch_presets_reset();
-			immDeactivate();
-		}
+	/* for regular use this will _never_ be NULL,
+	 * however we may be freeing an improperly initialized window. */
+	if (screen) {
+		ED_screen_exit(C, win, screen);
+	}
 
-		wm_window_free(C, wm, win);
+	if (tmpwin) {
+		BLF_batch_reset();
+		gpu_batch_presets_reset();
+		immDeactivate();
+	}
 
-		/* keep imediatemode active before the next `wm_window_make_drawable` call */
-		if (tmpwin) {
-			GHOST_ActivateWindowDrawingContext(tmpwin->ghostwin);
-			GWN_context_active_set(tmpwin->gwnctx);
-			immActivate();
-		}
+	wm_window_free(C, wm, win);
+
+	/* keep imediatemode active before the next `wm_window_make_drawable` call */
+	if (tmpwin) {
+		GHOST_ActivateWindowDrawingContext(tmpwin->ghostwin);
+		GWN_context_active_set(tmpwin->gwnctx);
+		immActivate();
+	}
 
-		/* if temp screen, delete it after window free (it stops jobs that can access it) */
-		if (screen && screen->temp) {
-			Main *bmain = CTX_data_main(C);
+	/* if temp screen, delete it after window free (it stops jobs that can access it) */
+	if (screen && screen->temp) {
+		Main *bmain = CTX_data_main(C);
 
-			BLI_assert(BKE_workspace_layout_screen_get(layout) == screen);
-			BKE_workspace_layout_remove(bmain, workspace, layout);
-		}
+		BLI_assert(BKE_workspace_layout_screen_get(layout) == screen);
+		BKE_workspace_layout_remove(bmain, workspace, layout);
 	}
 }
 
@@ -809,7 +822,7 @@ void wm_window_ghostwindows_remove_invalid(bContext *C, wmWindowManager *wm)
 wmWindow *WM_window_open(bContext *C, const rcti *rect)
 {
 	wmWindow *win_prev = CTX_wm_window(C);
-	wmWindow *win = wm_window_new(C);
+	wmWindow *win = wm_window_new(C, win_prev);
 
 	win->posx = rect->xmin;
 	win->posy = rect->ymin;
@@ -869,7 +882,7 @@ wmWindow *WM_window_open_temp(bContext *C, int x, int y, int sizex, int sizey, i
 
 	/* add new window? */
 	if (win == NULL) {
-		win = wm_window_new(C);
+		win = wm_window_new(C, win_prev);
 
 		win->posx = rect.xmin;
 		win->posy = rect.ymin;
@@ -887,7 +900,7 @@ wmWindow *WM_window_open_temp(bContext *C, int x, int y, int sizex, int sizey, i
 
 	if (WM_window_get_active_workspace(win) == NULL) {
 		WorkSpace *workspace = WM_window_get_active_workspace(win_prev);
-		WM_window_set_active_workspace(win, workspace);
+		BKE_workspace_active_set(win->workspace_hook, workspace);
 	}
 
 	if (screen == NULL) {
@@ -904,7 +917,7 @@ wmWindow *WM_window_open_temp(bContext *C, int x, int y, int sizex, int sizey, i
 	}
 	/* In case we reuse an already existing temp window (see win lookup above). */
 	else if (WM_window_get_active_scene(win) != scene) {
-		WM_window_change_active_scene(bmain, C, win, scene);
+		WM_window_set_active_scene(bmain, C, win, scene);
 	}
 
 	screen->temp = 1;
@@ -976,17 +989,25 @@ int wm_window_close_exec(bContext *C, wmOperator *UNUSED(op))
 	return OPERATOR_FINISHED;
 }
 
-/* operator callback */
 int wm_window_new_exec(bContext *C, wmOperator *UNUSED(op))
 {
 	wmWindow *win_src = CTX_wm_window(C);
 	bool ok;
 
-	ok = (wm_window_copy_test(C, win_src, true) != NULL);
+	ok = (wm_window_copy_test(C, win_src, true, true) != NULL);
 
 	return ok ? OPERATOR_FINISHED : OPERATOR_CANCELLED;
 }
 
+int wm_window_new_main_exec(bContext *C, wmOperator *UNUSED(op))
+{
+	wmWindow *win_src = CTX_wm_window(C);
+	bool ok;
+
+	ok = (wm_window_copy_test(C, win_src, true, false) != NULL);
+
+	return ok ? OPERATOR_FINISHED : OPERATOR_CANCELLED;
+}
 
 /* fullscreen operator callback */
 int wm_window_fullscreen_toggle_exec(bContext *C, wmOperator *UNUSED(op))
@@ -2103,21 +2124,45 @@ Scene *WM_window_get_active_scene(const wmWindow *win)
 /**
  * \warning Only call outside of area/region loops
  */
-void WM_window_change_active_scene(Main *bmain, bContext *C, wmWindow *win, Scene *scene_new)
+void WM_window_set_active_scene(Main *bmain, bContext *C, wmWindow *win, Scene *scene)
 {
-	const bScreen *screen = WM_window_get_active_screen(win);
-	Scene *scene_old = win->scene;
+	wmWindowManager *wm = CTX_wm_manager(C);
+	wmWindow *win_parent = (win->parent) ? win->parent : win;
 
-	ED_scene_change_update(bmain, C, win, screen, scene_old, scene_new);
+	/* Set scene in parent and its child windows. */
+	ED_screen_scene_change(C, win_parent, scene);
+
+	for (wmWindow *win_child = wm->windows.first; win_child; win_child = win_child->next) {
+		if (win_child->parent == win_parent) {
+			ED_screen_scene_change(C, win_child, scene);
+		}
+	}
+
+	/* Update depsgraph and renderers for scene change. */
+	ViewLayer *view_layer = WM_window_get_active_view_layer(win_parent);
+	ED_scene_change_update(bmain, scene, view_layer);
+
+	/* Complete redraw. */
+	WM_event_add_notifier(C, NC_WINDOW, NULL);
 }
 
 WorkSpace *WM_window_get_active_workspace(const wmWindow *win)
 {
 	return BKE_workspace_active_get(win->workspace_hook);
 }
-void WM_window_set_active_workspace(wmWindow *win, WorkSpace *workspace)
+
+void WM_window_set_active_workspace(bContext *C, wmWindow *win, WorkSpace *workspace)
 {
-	BKE_workspace_active_set(win->workspace_hook, workspace);
+	wmWindowManager *wm = CTX_wm_manager(C);
+	wmWindow *win_parent = (win->parent) ? win->parent : win;
+
+	ED_workspace_change(workspace, C, wm, win);
+
+	for (wmWindow *win_child = wm->windows.first; win_child; win_child = win_child->next) {
+		if (win_child->parent == win_parent) {
+			ED_workspace_change(workspace, C, wm, win_child);
+		}
+	}
 }
 
 WorkSpaceLayout *WM_window_get_active_layout(const wmWindow *win)
diff --git a/source/blender/windowmanager/wm_window.h b/source/blender/windowmanager/wm_window.h
index 952ffe5c117..385d61217ad 100644
--- a/source/blender/windowmanager/wm_window.h
+++ b/source/blender/windowmanager/wm_window.h
@@ -45,9 +45,9 @@ void		wm_ghost_exit(void);
 void wm_get_screensize(int *r_width, int *r_height);
 void wm_get_desktopsize(int *r_width, int *r_height);
 
-wmWindow	*wm_window_new			(bContext *C);
-wmWindow	*wm_window_copy			(bContext *C, wmWindow *win_src, const bool duplicate_layout);
-wmWindow	*wm_window_copy_test	(bContext *C, wmWindow *win_src, const bool duplicate_layout);
+wmWindow	*wm_window_new			(bContext *C, wmWindow *parent);
+wmWindow	*wm_window_copy			(bContext *C, wmWindow *win_src, const bool duplicate_layout, const bool child);
+wmWindow	*wm_window_copy_test	(bContext *C, wmWindow *win_src, const bool duplicate_layout, const bool child);
 void		wm_window_free			(bContext *C, wmWindowManager *wm, wmWindow *win);
 void		wm_window_close			(bContext *C, wmWindowManager *wm, wmWindow *win);
 
@@ -85,6 +85,7 @@ int			wm_window_fullscreen_toggle_exec(bContext *C, struct wmOperator *op);
 void		wm_quit_with_optional_confirmation_prompt(bContext *C, wmWindow *win) ATTR_NONNULL();
 
 int			wm_window_new_exec(bContext *C, struct wmOperator *op);
+int			wm_window_new_main_exec(bContext *C, struct wmOperator *op);
 
 /* Initial (unmaximized) size to start with for
  * systems that can't find it for themselves (X11).