Workspaces: Option to pin scene to a workspace

Adds a "Pin Scene" option to the workspace. When activated, the workspace will
remember the scene that was last activated in it, so that when switching back
to this workspace, the same scene will be reactivated. This is important for a
VSE workflow, so that users can switch between different workspaces displaying
a scene and thus a timeline for a specific task.

The option can be found in the Properties, Workspace tab. D11890 additionally
adds an icon for this to the scene switcher in the topbar.

The workspace data contains a pointer to the scene which is a UI to scene data
relation. When appending a workspace, the pointer is cleared.

Differential Revision: https://developer.blender.org/D9140

Reviewed by: Brecht Van Lommel, Bastien Montagne (no final accept, but was fine
with the general design earlier)

1 files changed, 75 insertions, 2 deletions

diff --git a/source/blender/editors/screen/workspace_edit.c b/source/blender/editors/screen/workspace_edit.c
index 01417650b3d..0535a270176 100644
--- a/source/blender/editors/screen/workspace_edit.c
+++ b/source/blender/editors/screen/workspace_edit.c
@@ -54,17 +54,87 @@ WorkSpace *ED_workspace_add(Main *bmain, const char *name)
   return BKE_workspace_add(bmain, name);
 }
 
+static void workspace_exit(WorkSpace *workspace, wmWindow *win)
+{
+  /* Scene pinning: Store whatever scene was active when leaving the workspace. It's reactivated
+   * when the workspace gets reactivated as well. */
+  if (workspace->flags & WORKSPACE_USE_PIN_SCENE) {
+    workspace->pin_scene = WM_window_get_active_scene(win);
+  }
+  else {
+    /* The active scene may have been changed. So also always update the unpinned scene to the
+     * latest when leaving a workspace that has no scene pinning. */
+    win->unpinned_scene = WM_window_get_active_scene(win);
+  }
+}
+
+/**
+ * State changes (old workspace to new workspace):
+ * 1) unpinned -> pinned
+ *    * Store current scene as the unpinned one (done in #workspace_exit()).
+ *    * Change the current scene to the pinned one.
+ * 2) pinned   -> pinned
+ *    * Change the current scene to the new pinned one.
+ * 3) pinned   -> unpinned
+ *    * Change current scene back to the unpinned one
+ * 4) unpinned -> unpinned
+ *    * Make sure the unpinned scene is active.
+ *
+ * Note that the pin scene must also be updated when leaving a workspace with a pinned scene.
+ * That's done separately via workspace_exit() above.
+ */
+static void workspace_scene_pinning_update(WorkSpace *workspace_new,
+                                           const WorkSpace *workspace_old,
+                                           bContext *C)
+{
+  wmWindow *win = CTX_wm_window(C);
+  Main *bmain = CTX_data_main(C);
+  Scene *active_scene = WM_window_get_active_scene(win);
+
+  const bool is_new_pinned = (workspace_new->flags & WORKSPACE_USE_PIN_SCENE);
+  const bool is_old_pinned = (workspace_old->flags & WORKSPACE_USE_PIN_SCENE);
+
+  /* State changes 1 and 2. */
+  if (is_new_pinned) {
+    if (workspace_new->pin_scene && (workspace_new->pin_scene != active_scene)) {
+      WM_window_set_active_scene(bmain, C, win, workspace_new->pin_scene);
+      workspace_new->pin_scene = NULL;
+    }
+  }
+  /* State change 3 - Changing from workspace with pinned scene to unpinned scene. */
+  else if (is_old_pinned) {
+    if (win->unpinned_scene) {
+      WM_window_set_active_scene(bmain, C, win, win->unpinned_scene);
+    }
+    else {
+      /* When leaving a workspace where the pinning was just enabled, the unpinned scene wasn't set
+       * yet. */
+      win->unpinned_scene = active_scene;
+    }
+  }
+  else {
+    /* When leaving a workspace where the pinning was just disabled, we still want to restore the
+     * unpinned scene. */
+    if (win->unpinned_scene) {
+      WM_window_set_active_scene(bmain, C, win, win->unpinned_scene);
+    }
+  }
+
+  BLI_assert(WM_window_get_active_scene(win));
+}
+
 /**
  * Changes the object mode (if needed) to the one set in \a workspace_new.
  * Object mode is still stored on object level. In future it should all be workspace level instead.
  */
 static void workspace_change_update(WorkSpace *workspace_new,
-                                    const WorkSpace *workspace_old,
+                                    WorkSpace *workspace_old,
                                     bContext *C,
                                     wmWindowManager *wm)
 {
+  workspace_scene_pinning_update(workspace_new, workspace_old, C);
   /* needs to be done before changing mode! (to ensure right context) */
-  UNUSED_VARS(workspace_old, workspace_new, C, wm);
+  UNUSED_VARS(wm);
 #if 0
   Object *ob_act = CTX_data_active_object(C) eObjectMode mode_old = workspace_old->object_mode;
   eObjectMode mode_new = workspace_new->object_mode;
@@ -113,6 +183,8 @@ bool ED_workspace_change(WorkSpace *workspace_new, bContext *C, wmWindowManager
     return false;
   }
 
+  workspace_exit(workspace_old, win);
+
   screen_change_prepare(screen_old, screen_new, bmain, C, win);
 
   if (screen_new == NULL) {
@@ -143,6 +215,7 @@ WorkSpace *ED_workspace_duplicate(WorkSpace *workspace_old, Main *bmain, wmWindo
   WorkSpace *workspace_new = ED_workspace_add(bmain, workspace_old->id.name + 2);
 
   workspace_new->flags = workspace_old->flags;
+  workspace_new->pin_scene = workspace_old->pin_scene;
   workspace_new->object_mode = workspace_old->object_mode;
   workspace_new->order = workspace_old->order;
   BLI_duplicatelist(&workspace_new->owner_ids, &workspace_old->owner_ids);