Support displaying collections in outliner

Adds a new outliner display mode "Collections" which draws the active
collection. We might want to rename it to "Active Collection" if we don't
plan to support showing other collections there.
Also added the buttons for restricting visibility and selectability.

@dfelinto, code in restrictbutton_collection_hide_cb and
restrictbutton_collection_hide_select_cb is duplicated from
rna_LayerCollection_hide_update and
rna_LayerCollection_hide_select_update, maybe utility functions would be
handy for this?

source/blender/editors/space_outliner/outliner_draw.c

@@ -51,6 +51,7 @@
 #include "BKE_depsgraph.h"
 #include "BKE_fcurve.h"
 #include "BKE_global.h"
+#include "BKE_layer.h"
 #include "BKE_library.h"
 #include "BKE_main.h"
 #include "BKE_modifier.h"
@@ -247,6 +248,34 @@ static void restrictbutton_gp_layer_flag_cb(bContext *C, void *UNUSED(poin), voi
 	WM_event_add_notifier(C, NC_GPENCIL | ND_DATA | NA_EDITED, NULL);
 }
 
+static void restrictbutton_collection_hide_cb(bContext *C, void *poin, void *poin2)
+{
+	Scene *scene = poin;
+	LayerCollection *collection = poin2;
+	SceneLayer *sl = BKE_scene_layer_find_from_collection(scene, collection);
+
+	/* hide and deselect bases that are directly influenced by this LayerCollection */
+	BKE_scene_layer_base_flag_recalculate(sl);
+	BKE_scene_layer_engine_settings_collection_recalculate(sl, collection);
+	WM_event_add_notifier(C, NC_SCENE | ND_OB_SELECT, scene);
+	WM_event_add_notifier(C, NC_SCENE | ND_LAYER_CONTENT, NULL);
+}
+
+static void restrictbutton_collection_hide_select_cb(bContext *C, void *poin, void *poin2)
+{
+	Scene *scene = poin;
+	LayerCollection *collection = poin2;
+
+	if ((collection->flag & COLLECTION_SELECTABLE) == 0) {
+		SceneLayer *sl = BKE_scene_layer_find_from_collection(scene, collection);
+
+		/* deselect bases that are directly influenced by this LayerCollection */
+		BKE_scene_layer_base_flag_recalculate(sl);
+		WM_event_add_notifier(C, NC_SCENE | ND_OB_SELECT, CTX_data_scene(C));
+	}
+	WM_event_add_notifier(C, NC_SCENE | ND_LAYER_CONTENT, NULL);
+}
+
 static void restrictbutton_id_user_toggle(bContext *UNUSED(C), void *poin, void *UNUSED(poin2))
 {
 	ID *id = (ID *)poin;
@@ -537,6 +566,27 @@ static void outliner_draw_restrictbuts(uiBlock *block, Scene *scene, ARegion *ar
 				
 				/* TODO: visibility in renders */
 				
+				UI_block_emboss_set(block, UI_EMBOSS);
+			}
+			else if (tselem->type == TSE_COLLECTION) {
+				LayerCollection *collection = te->directdata;
+
+				UI_block_emboss_set(block, UI_EMBOSS_NONE);
+
+				bt = uiDefIconButBitS(block, UI_BTYPE_ICON_TOGGLE_N, COLLECTION_VISIBLE, 0, ICON_RESTRICT_VIEW_OFF,
+				                      (int)(ar->v2d.cur.xmax - OL_TOG_RESTRICT_VIEWX), te->ys, UI_UNIT_X,
+				                      UI_UNIT_Y, &collection->flag, 0, 0, 0, 0,
+				                      TIP_("Restrict/Allow 3D View visibility of objects in the collection"));
+				UI_but_func_set(bt, restrictbutton_collection_hide_cb, scene, collection);
+				UI_but_flag_enable(bt, UI_BUT_DRAG_LOCK);
+
+				bt = uiDefIconButBitS(block, UI_BTYPE_ICON_TOGGLE_N, COLLECTION_SELECTABLE, 0, ICON_RESTRICT_SELECT_OFF,
+				                      (int)(ar->v2d.cur.xmax - OL_TOG_RESTRICT_SELECTX), te->ys, UI_UNIT_X,
+				                      UI_UNIT_Y, &collection->flag, 0, 0, 0, 0,
+				                      TIP_("Restrict/Allow 3D View selection of objects in the collection"));
+				UI_but_func_set(bt, restrictbutton_collection_hide_select_cb, scene, collection);
+				UI_but_flag_enable(bt, UI_BUT_DRAG_LOCK);
+
 				UI_block_emboss_set(block, UI_EMBOSS);
 			}
 		}

source/blender/editors/space_outliner/outliner_tree.c

@@ -904,8 +904,8 @@ static TreeElement *outliner_add_element(SpaceOops *soops, ListBase *lb, void *i
 		id = TREESTORE(parent)->id;
 	}
 
-	/* One exception */
-	if (type == TSE_ID_BASE) {
+	/* exceptions */
+	if (ELEM(type, TSE_ID_BASE, TSE_COLLECTION)) {
 		/* pass */
 	}
 	else if (id == NULL) {
@@ -942,6 +942,9 @@ static TreeElement *outliner_add_element(SpaceOops *soops, ListBase *lb, void *i
 	else if (type == TSE_GP_LAYER) {
 		/* pass */
 	}
+	else if (type == TSE_COLLECTION) {
+		/* pass */
+	}
 	else if (type == TSE_ID_BASE) {
 		/* pass */
 	}
@@ -1371,6 +1374,24 @@ static void outliner_add_orphaned_datablocks(Main *mainvar, SpaceOops *soops)
 	}
 }
 
+static void outliner_add_collections_recursive(SpaceOops *soops, ListBase *tree, ListBase *layer_collections,
+                                               TreeElement *parent_ten)
+{
+	for (LayerCollection *collection = layer_collections->first; collection; collection = collection->next) {
+		TreeElement *ten = outliner_add_element(soops, tree, NULL, parent_ten, TSE_COLLECTION, 0);
+
+		ten->name = collection->scene_collection->name;
+		ten->directdata = collection;
+
+		outliner_add_collections_recursive(soops, &ten->subtree, &collection->layer_collections, ten);
+	}
+}
+
+static void outliner_add_collections(SpaceOops *soops, SceneLayer *layer)
+{
+	outliner_add_collections_recursive(soops, &soops->tree, &layer->layer_collections, NULL);
+}
+
 /* ======================================================= */
 /* Generic Tree Building helpers - order these are called is top to bottom */
 
@@ -1832,6 +1853,9 @@ void outliner_build_tree(Main *mainvar, Scene *scene, SceneLayer *sl, SpaceOops
 	else if (soops->outlinevis == SO_ID_ORPHANS) {
 		outliner_add_orphaned_datablocks(mainvar, soops);
 	}
+	else if (soops->outlinevis == SO_COLLECTIONS) {
+		outliner_add_collections(soops, BLI_findlink(&scene->render_layers, scene->active_layer));
+	}
 	else {
 		ten = outliner_add_element(soops, &soops->tree, OBACT_NEW, NULL, 0, 0);
 	}

source/blender/makesdna/DNA_outliner_types.h

@@ -99,6 +99,7 @@ enum {
 #define TSE_KEYMAP_ITEM     35  /* NO ID */
 #define TSE_ID_BASE         36  /* NO ID */
 #define TSE_GP_LAYER        37  /* NO ID */
+#define TSE_COLLECTION      38  /* NO ID */
 
 
 /* Check whether given TreeStoreElem should have a real ID in its ->id member. */

source/blender/makesdna/DNA_space_types.h

@@ -274,21 +274,22 @@ typedef enum eSpaceOutliner_Flag {
 
 /* SpaceOops->outlinevis */
 typedef enum eSpaceOutliner_Mode {
-	SO_ALL_SCENES = 0,
-	SO_CUR_SCENE = 1,
-	SO_VISIBLE = 2,
-	SO_SELECTED = 3,
-	SO_ACTIVE = 4,
-	SO_SAME_TYPE = 5,
-	SO_GROUPS = 6,
-	SO_LIBRARIES = 7,
-	/* SO_VERSE_SESSION = 8, */  /* deprecated! */
-	/* SO_VERSE_MS = 9, */       /* deprecated! */
-	SO_SEQUENCE = 10,
-	SO_DATABLOCKS = 11,
-	SO_USERDEF = 12,
-	/* SO_KEYMAP = 13, */        /* deprecated! */
-	SO_ID_ORPHANS = 14,
+	SO_ALL_SCENES     = 0,
+	SO_CUR_SCENE      = 1,
+	SO_VISIBLE        = 2,
+	SO_SELECTED       = 3,
+	SO_ACTIVE         = 4,
+	SO_SAME_TYPE      = 5,
+	SO_GROUPS         = 6,
+	SO_LIBRARIES      = 7,
+	/* SO_VERSE_SESSION  = 8, */  /* deprecated! */
+	/* SO_VERSE_MS       = 9, */  /* deprecated! */
+	SO_SEQUENCE       = 10,
+	SO_DATABLOCKS     = 11,
+	SO_USERDEF        = 12,
+	/* SO_KEYMAP      = 13, */    /* deprecated! */
+	SO_ID_ORPHANS     = 14,
+	SO_COLLECTIONS    = 15,
 } eSpaceOutliner_Mode;
 
 /* SpaceOops->storeflag */

source/blender/makesrna/intern/rna_space.c

@@ -2108,6 +2108,7 @@ static void rna_def_space_outliner(BlenderRNA *brna)
 		{SO_USERDEF, "USER_PREFERENCES", 0, "User Preferences", "Display user preference data"},
 		{SO_ID_ORPHANS, "ORPHAN_DATA", 0, "Orphan Data",
 		                "Display data-blocks which are unused and/or will be lost when the file is reloaded"},
+		{SO_COLLECTIONS, "COLLECTIONS", 0, "Collections", "Display the collections of the active render layer"},
 		{0, NULL, 0, NULL, NULL}
 	};