Cleanup: move most outliner drag & drop code into one file.

6 files changed, 1131 insertions, 1078 deletions

diff --git a/source/blender/editors/space_outliner/CMakeLists.txt b/source/blender/editors/space_outliner/CMakeLists.txt
index 96d27c6fd89..796e8732fca 100644
--- a/source/blender/editors/space_outliner/CMakeLists.txt
+++ b/source/blender/editors/space_outliner/CMakeLists.txt
@@ -39,6 +39,7 @@ set(INC_SYS
 
 set(SRC
 	outliner_collections.c
+	outliner_dragdrop.c
 	outliner_draw.c
 	outliner_edit.c
 	outliner_ops.c
diff --git a/source/blender/editors/space_outliner/outliner_dragdrop.c b/source/blender/editors/space_outliner/outliner_dragdrop.c
new file mode 100644
index 00000000000..f37cd7fa5e4
--- /dev/null
+++ b/source/blender/editors/space_outliner/outliner_dragdrop.c
@@ -0,0 +1,1115 @@
+/*
+ * ***** BEGIN GPL LICENSE BLOCK *****
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2004 Blender Foundation.
+ * All rights reserved.
+ *
+ * The Original Code is: all of this file.
+ *
+ * Contributor(s): Joshua Leung
+ *
+ * ***** END GPL LICENSE BLOCK *****
+ */
+
+/** \file blender/editors/space_outliner/outliner_dragdrop.c
+ *  \ingroup spoutliner
+ */
+
+#include <string.h>
+
+#include "MEM_guardedalloc.h"
+
+#include "DNA_group_types.h"
+#include "DNA_material_types.h"
+#include "DNA_object_types.h"
+#include "DNA_space_types.h"
+
+#include "BLI_listbase.h"
+
+#include "BLT_translation.h"
+
+#include "BKE_collection.h"
+#include "BKE_context.h"
+#include "BKE_layer.h"
+#include "BKE_main.h"
+#include "BKE_material.h"
+#include "BKE_report.h"
+#include "BKE_scene.h"
+
+#include "DEG_depsgraph.h"
+#include "DEG_depsgraph_build.h"
+
+#include "ED_object.h"
+#include "ED_outliner.h"
+#include "ED_screen.h"
+
+#include "UI_interface.h"
+#include "UI_resources.h"
+#include "UI_view2d.h"
+
+#include "GPU_state.h"
+
+#include "RNA_access.h"
+#include "RNA_define.h"
+#include "RNA_enum_types.h"
+
+#include "WM_api.h"
+#include "WM_types.h"
+
+#include "outliner_intern.h"
+
+/* ******************** Drop Target Find *********************** */
+
+static TreeElement *outliner_dropzone_element(TreeElement *te, const float fmval[2], const bool children)
+{
+	if ((fmval[1] > te->ys) && (fmval[1] < (te->ys + UI_UNIT_Y))) {
+		/* name and first icon */
+		if ((fmval[0] > te->xs + UI_UNIT_X) && (fmval[0] < te->xend))
+			return te;
+	}
+	/* Not it.  Let's look at its children. */
+	if (children && (TREESTORE(te)->flag & TSE_CLOSED) == 0 && (te->subtree.first)) {
+		for (te = te->subtree.first; te; te = te->next) {
+			TreeElement *te_valid = outliner_dropzone_element(te, fmval, children);
+			if (te_valid)
+				return te_valid;
+		}
+	}
+	return NULL;
+}
+
+/* Find tree element to drop into. */
+static TreeElement *outliner_dropzone_find(const SpaceOops *soops, const float fmval[2], const bool children)
+{
+	TreeElement *te;
+
+	for (te = soops->tree.first; te; te = te->next) {
+		TreeElement *te_valid = outliner_dropzone_element(te, fmval, children);
+		if (te_valid)
+			return te_valid;
+	}
+	return NULL;
+}
+
+/* ******************** Parent Drop Operator *********************** */
+
+static bool parent_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
+{
+	ARegion *ar = CTX_wm_region(C);
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	float fmval[2];
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	if (drag->type == WM_DRAG_ID) {
+		ID *id = drag->poin;
+		if (GS(id->name) == ID_OB) {
+			/* Ensure item under cursor is valid drop target */
+			TreeElement *te = outliner_dropzone_find(soops, fmval, true);
+			TreeStoreElem *tselem = te ? TREESTORE(te) : NULL;
+
+			if (!te) {
+				/* pass */
+			}
+			else if (te->idcode == ID_OB && tselem->type == 0) {
+				Scene *scene;
+				ID *te_id = tselem->id;
+
+				/* check if dropping self or parent */
+				if (te_id == id || (Object *)te_id == ((Object *)id)->parent)
+					return 0;
+
+				/* check that parent/child are both in the same scene */
+				scene = (Scene *)outliner_search_back(soops, te, ID_SCE);
+
+				/* currently outliner organized in a way that if there's no parent scene
+				 * element for object it means that all displayed objects belong to
+				 * active scene and parenting them is allowed (sergey)
+				 */
+				if (!scene) {
+					return 1;
+				}
+				else {
+					for (ViewLayer *view_layer = scene->view_layers.first;
+					     view_layer;
+					     view_layer = view_layer->next)
+					{
+						if (BKE_view_layer_base_find(view_layer, (Object *)id)) {
+							return 1;
+						}
+					}
+				}
+			}
+		}
+	}
+	return 0;
+}
+
+static void parent_drop_copy(wmDrag *drag, wmDropBox *drop)
+{
+	ID *id = drag->poin;
+
+	RNA_string_set(drop->ptr, "child", id->name + 2);
+}
+
+static int parent_drop_exec(bContext *C, wmOperator *op)
+{
+	Object *par = NULL, *ob = NULL;
+	Main *bmain = CTX_data_main(C);
+	Scene *scene = CTX_data_scene(C);
+	int partype = -1;
+	char parname[MAX_ID_NAME], childname[MAX_ID_NAME];
+
+	partype = RNA_enum_get(op->ptr, "type");
+	RNA_string_get(op->ptr, "parent", parname);
+	par = (Object *)BKE_libblock_find_name(bmain, ID_OB, parname);
+	RNA_string_get(op->ptr, "child", childname);
+	ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, childname);
+
+	if (ID_IS_LINKED(ob)) {
+		BKE_report(op->reports, RPT_INFO, "Can't edit library linked object");
+		return OPERATOR_CANCELLED;
+	}
+
+	ED_object_parent_set(op->reports, C, scene, ob, par, partype, false, false, NULL);
+
+	DEG_relations_tag_update(bmain);
+	WM_event_add_notifier(C, NC_OBJECT | ND_TRANSFORM, NULL);
+	WM_event_add_notifier(C, NC_OBJECT | ND_PARENT, NULL);
+
+	return OPERATOR_FINISHED;
+}
+
+static int parent_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	Object *par = NULL;
+	Object *ob = NULL;
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	ARegion *ar = CTX_wm_region(C);
+	Main *bmain = CTX_data_main(C);
+	Scene *scene = NULL;
+	TreeElement *te = NULL;
+	char childname[MAX_ID_NAME];
+	char parname[MAX_ID_NAME];
+	int partype = 0;
+	float fmval[2];
+
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	/* Find object hovered over */
+	te = outliner_dropzone_find(soops, fmval, true);
+
+	if (te) {
+		RNA_string_set(op->ptr, "parent", te->name);
+		/* Identify parent and child */
+		RNA_string_get(op->ptr, "child", childname);
+		ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, childname);
+		RNA_string_get(op->ptr, "parent", parname);
+		par = (Object *)BKE_libblock_find_name(bmain, ID_OB, parname);
+
+		if (ELEM(NULL, ob, par)) {
+			if (par == NULL) printf("par==NULL\n");
+			return OPERATOR_CANCELLED;
+		}
+		if (ob == par) {
+			return OPERATOR_CANCELLED;
+		}
+		if (ID_IS_LINKED(ob)) {
+			BKE_report(op->reports, RPT_INFO, "Can't edit library linked object");
+			return OPERATOR_CANCELLED;
+		}
+
+		scene = (Scene *)outliner_search_back(soops, te, ID_SCE);
+
+		if (scene == NULL) {
+			/* currently outlier organized in a way, that if there's no parent scene
+			 * element for object it means that all displayed objects belong to
+			 * active scene and parenting them is allowed (sergey)
+			 */
+
+			scene = CTX_data_scene(C);
+		}
+
+		if ((par->type != OB_ARMATURE) && (par->type != OB_CURVE) && (par->type != OB_LATTICE)) {
+			if (ED_object_parent_set(op->reports, C, scene, ob, par, partype, false, false, NULL)) {
+				DEG_relations_tag_update(bmain);
+				WM_event_add_notifier(C, NC_OBJECT | ND_TRANSFORM, NULL);
+				WM_event_add_notifier(C, NC_OBJECT | ND_PARENT, NULL);
+			}
+		}
+		else {
+			/* Menu creation */
+			wmOperatorType *ot = WM_operatortype_find("OUTLINER_OT_parent_drop", false);
+			uiPopupMenu *pup = UI_popup_menu_begin(C, IFACE_("Set Parent To"), ICON_NONE);
+			uiLayout *layout = UI_popup_menu_layout(pup);
+			PointerRNA ptr;
+
+			/* Cannot use uiItemEnumO()... have multiple properties to set. */
+			uiItemFullO_ptr(layout, ot, IFACE_("Object"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+			RNA_string_set(&ptr, "parent", parname);
+			RNA_string_set(&ptr, "child", childname);
+			RNA_enum_set(&ptr, "type", PAR_OBJECT);
+
+			/* par becomes parent, make the associated menus */
+			if (par->type == OB_ARMATURE) {
+				uiItemFullO_ptr(layout, ot, IFACE_("Armature Deform"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_ARMATURE);
+
+				uiItemFullO_ptr(layout, ot, IFACE_("   With Empty Groups"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_ARMATURE_NAME);
+
+				uiItemFullO_ptr(layout, ot, IFACE_("   With Envelope Weights"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_ARMATURE_ENVELOPE);
+
+				uiItemFullO_ptr(layout, ot, IFACE_("   With Automatic Weights"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_ARMATURE_AUTO);
+
+				uiItemFullO_ptr(layout, ot, IFACE_("Bone"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_BONE);
+			}
+			else if (par->type == OB_CURVE) {
+				uiItemFullO_ptr(layout, ot, IFACE_("Curve Deform"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_CURVE);
+
+				uiItemFullO_ptr(layout, ot, IFACE_("Follow Path"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_FOLLOW);
+
+				uiItemFullO_ptr(layout, ot, IFACE_("Path Constraint"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_PATH_CONST);
+			}
+			else if (par->type == OB_LATTICE) {
+				uiItemFullO_ptr(layout, ot, IFACE_("Lattice Deform"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
+				RNA_string_set(&ptr, "parent", parname);
+				RNA_string_set(&ptr, "child", childname);
+				RNA_enum_set(&ptr, "type", PAR_LATTICE);
+			}
+
+			UI_popup_menu_end(C, pup);
+
+			return OPERATOR_INTERFACE;
+		}
+	}
+	else {
+		return OPERATOR_CANCELLED;
+	}
+
+	return OPERATOR_FINISHED;
+}
+
+void OUTLINER_OT_parent_drop(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name = "Drop to Set Parent";
+	ot->description = "Drag to parent in Outliner";
+	ot->idname = "OUTLINER_OT_parent_drop";
+
+	/* api callbacks */
+	ot->invoke = parent_drop_invoke;
+	ot->exec = parent_drop_exec;
+
+	ot->poll = ED_operator_outliner_active;
+
+	/* flags */
+	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+
+	/* properties */
+	RNA_def_string(ot->srna, "child", "Object", MAX_ID_NAME, "Child", "Child Object");
+	RNA_def_string(ot->srna, "parent", "Object", MAX_ID_NAME, "Parent", "Parent Object");
+	RNA_def_enum(ot->srna, "type", prop_make_parent_types, 0, "Type", "");
+}
+
+static bool parenting_poll(bContext *C)
+{
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+
+	if (soops) {
+		if (soops->outlinevis == SO_SCENES) {
+			return true;
+		}
+		else if ((soops->outlinevis == SO_VIEW_LAYER) &&
+		         (soops->filter & SO_FILTER_NO_COLLECTION))
+		{
+			return true;
+		}
+	}
+
+	return false;
+}
+
+/* ******************** Parent Clear Operator *********************** */
+
+static bool parent_clear_poll(bContext *C, wmDrag *drag, const wmEvent *event)
+{
+	ARegion *ar = CTX_wm_region(C);
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	TreeElement *te = NULL;
+	float fmval[2];
+
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	if (!ELEM(soops->outlinevis, SO_VIEW_LAYER)) {
+		return false;
+	}
+
+	if (drag->type == WM_DRAG_ID) {
+		ID *id = drag->poin;
+		if (GS(id->name) == ID_OB) {
+			if (((Object *)id)->parent) {
+				if ((te = outliner_dropzone_find(soops, fmval, true))) {
+					TreeStoreElem *tselem = TREESTORE(te);
+
+					switch (te->idcode) {
+						case ID_SCE:
+							return (ELEM(tselem->type, TSE_R_LAYER_BASE, TSE_R_LAYER));
+						case ID_OB:
+							return (ELEM(tselem->type, TSE_MODIFIER_BASE, TSE_CONSTRAINT_BASE));
+						/* Other codes to ignore? */
+					}
+				}
+				return (te == NULL);
+			}
+		}
+	}
+	return 0;
+}
+
+static void parent_clear_copy(wmDrag *drag, wmDropBox *drop)
+{
+	ID *id = drag->poin;
+	RNA_string_set(drop->ptr, "dragged_obj", id->name + 2);
+
+	/* Set to simple parent clear type. Avoid menus for drag and drop if possible.
+	 * If desired, user can toggle the different "Clear Parent" types in the operator
+	 * menu on tool shelf. */
+	RNA_enum_set(drop->ptr, "type", 0);
+}
+
+static int parent_clear_invoke(bContext *C, wmOperator *op, const wmEvent *UNUSED(event))
+{
+	Main *bmain = CTX_data_main(C);
+	Object *ob = NULL;
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	char obname[MAX_ID_NAME];
+
+	RNA_string_get(op->ptr, "dragged_obj", obname);
+	ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, obname);
+
+	/* search forwards to find the object */
+	outliner_find_id(soops, &soops->tree, (ID *)ob);
+
+	ED_object_parent_clear(ob, RNA_enum_get(op->ptr, "type"));
+
+	DEG_relations_tag_update(bmain);
+	WM_event_add_notifier(C, NC_OBJECT | ND_TRANSFORM, NULL);
+	WM_event_add_notifier(C, NC_OBJECT | ND_PARENT, NULL);
+	return OPERATOR_FINISHED;
+}
+
+void OUTLINER_OT_parent_clear(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name = "Drop to Clear Parent";
+	ot->description = "Drag to clear parent in Outliner";
+	ot->idname = "OUTLINER_OT_parent_clear";
+
+	/* api callbacks */
+	ot->invoke = parent_clear_invoke;
+
+	ot->poll = parenting_poll;
+
+	/* flags */
+	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+
+	/* properties */
+	RNA_def_string(ot->srna, "dragged_obj", "Object", MAX_ID_NAME, "Child", "Child Object");
+	RNA_def_enum(ot->srna, "type", prop_clear_parent_types, 0, "Type", "");
+}
+
+/* ******************** Scene Drop Operator *********************** */
+
+static bool scene_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
+{
+	ARegion *ar = CTX_wm_region(C);
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	float fmval[2];
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	if (drag->type == WM_DRAG_ID) {
+		ID *id = drag->poin;
+		if (GS(id->name) == ID_OB) {
+			/* Ensure item under cursor is valid drop target */
+			TreeElement *te = outliner_dropzone_find(soops, fmval, false);
+			return (te && te->idcode == ID_SCE && TREESTORE(te)->type == 0);
+		}
+	}
+	return 0;
+}
+
+static void scene_drop_copy(wmDrag *drag, wmDropBox *drop)
+{
+	ID *id = drag->poin;
+
+	RNA_string_set(drop->ptr, "object", id->name + 2);
+}
+
+static int scene_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	Scene *scene = NULL;
+	Object *ob = NULL;
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	ARegion *ar = CTX_wm_region(C);
+	Main *bmain = CTX_data_main(C);
+	TreeElement *te = NULL;
+	char obname[MAX_ID_NAME];
+	float fmval[2];
+
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	/* Find object hovered over */
+	te = outliner_dropzone_find(soops, fmval, false);
+
+	if (te) {
+		RNA_string_set(op->ptr, "scene", te->name);
+		scene = (Scene *)BKE_libblock_find_name(bmain, ID_SCE, te->name);
+
+		RNA_string_get(op->ptr, "object", obname);
+		ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, obname);
+
+		if (ELEM(NULL, ob, scene) || ID_IS_LINKED(scene)) {
+			return OPERATOR_CANCELLED;
+		}
+
+		if (BKE_scene_has_object(scene, ob)) {
+			return OPERATOR_CANCELLED;
+		}
+
+		Collection *collection;
+		if (scene != CTX_data_scene(C)) {
+			/* when linking to an inactive scene link to the master collection */
+			collection = BKE_collection_master(scene);
+		}
+		else {
+			collection = CTX_data_collection(C);
+		}
+
+		BKE_collection_object_add(bmain, collection, ob);
+
+		for (ViewLayer *view_layer = scene->view_layers.first; view_layer; view_layer = view_layer->next) {
+			Base *base = BKE_view_layer_base_find(view_layer, ob);
+			if (base) {
+				ED_object_base_select(base, BA_SELECT);
+			}
+		}
+
+		DEG_relations_tag_update(bmain);
+
+		DEG_id_tag_update(&scene->id, DEG_TAG_SELECT_UPDATE);
+		WM_main_add_notifier(NC_SCENE | ND_OB_SELECT, scene);
+
+		return OPERATOR_FINISHED;
+	}
+
+	return OPERATOR_CANCELLED;
+}
+
+void OUTLINER_OT_scene_drop(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name = "Drop Object to Scene";
+	ot->description = "Drag object to scene in Outliner";
+	ot->idname = "OUTLINER_OT_scene_drop";
+
+	/* api callbacks */
+	ot->invoke = scene_drop_invoke;
+
+	ot->poll = ED_operator_outliner_active;
+
+	/* flags */
+	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+
+	/* properties */
+	RNA_def_string(ot->srna, "object", "Object", MAX_ID_NAME, "Object", "Target Object");
+	RNA_def_string(ot->srna, "scene", "Scene", MAX_ID_NAME, "Scene", "Target Scene");
+}
+
+/* ******************** Material Drop Operator *********************** */
+
+static bool material_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
+{
+	ARegion *ar = CTX_wm_region(C);
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	float fmval[2];
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	if (drag->type == WM_DRAG_ID) {
+		ID *id = drag->poin;
+		if (GS(id->name) == ID_MA) {
+			/* Ensure item under cursor is valid drop target */
+			TreeElement *te = outliner_dropzone_find(soops, fmval, true);
+			return (te && te->idcode == ID_OB && TREESTORE(te)->type == 0);
+		}
+	}
+	return 0;
+}
+
+static void material_drop_copy(wmDrag *drag, wmDropBox *drop)
+{
+	ID *id = drag->poin;
+
+	RNA_string_set(drop->ptr, "material", id->name + 2);
+}
+
+static int material_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	Material *ma = NULL;
+	Object *ob = NULL;
+	Main *bmain = CTX_data_main(C);
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	ARegion *ar = CTX_wm_region(C);
+	TreeElement *te = NULL;
+	char mat_name[MAX_ID_NAME - 2];
+	float fmval[2];
+
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	/* Find object hovered over */
+	te = outliner_dropzone_find(soops, fmval, true);
+
+	if (te) {
+		RNA_string_set(op->ptr, "object", te->name);
+		ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, te->name);
+
+		RNA_string_get(op->ptr, "material", mat_name);
+		ma = (Material *)BKE_libblock_find_name(bmain, ID_MA, mat_name);
+
+		if (ELEM(NULL, ob, ma)) {
+			return OPERATOR_CANCELLED;
+		}
+
+		assign_material(bmain, ob, ma, ob->totcol + 1, BKE_MAT_ASSIGN_USERPREF);
+
+		WM_event_add_notifier(C, NC_SPACE | ND_SPACE_VIEW3D, CTX_wm_view3d(C));
+		WM_event_add_notifier(C, NC_MATERIAL | ND_SHADING_LINKS, ma);
+
+		return OPERATOR_FINISHED;
+	}
+
+	return OPERATOR_CANCELLED;
+}
+
+void OUTLINER_OT_material_drop(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name = "Drop Material on Object";
+	ot->description = "Drag material to object in Outliner";
+	ot->idname = "OUTLINER_OT_material_drop";
+
+	/* api callbacks */
+	ot->invoke = material_drop_invoke;
+
+	ot->poll = ED_operator_outliner_active;
+
+	/* flags */
+	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+
+	/* properties */
+	RNA_def_string(ot->srna, "object", "Object", MAX_ID_NAME, "Object", "Target Object");
+	RNA_def_string(ot->srna, "material", "Material", MAX_ID_NAME, "Material", "Target Material");
+}
+
+/* ******************** Collection Drop Operator *********************** */
+
+static bool collection_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
+{
+	ARegion *ar = CTX_wm_region(C);
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	float fmval[2];
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	if (drag->type == WM_DRAG_ID) {
+		ID *id = drag->poin;
+		if (ELEM(GS(id->name), ID_OB, ID_GR)) {
+			/* Ensure item under cursor is valid drop target */
+			TreeElement *te = outliner_dropzone_find(soops, fmval, true);
+			return (te && outliner_is_collection_tree_element(te));
+		}
+	}
+	return 0;
+}
+
+static void collection_drop_copy(wmDrag *drag, wmDropBox *drop)
+{
+	ID *id = drag->poin;
+	RNA_string_set(drop->ptr, "child", id->name + 2);
+}
+
+static int collection_drop_exec(bContext *UNUSED(C), wmOperator *UNUSED(op))
+{
+	/* TODO: implement */
+#if 0
+	Object *par = NULL, *ob = NULL;
+	Main *bmain = CTX_data_main(C);
+	Scene *scene = CTX_data_scene(C);
+	int partype = -1;
+	char parname[MAX_ID_NAME], childname[MAX_ID_NAME];
+
+	RNA_string_get(op->ptr, "parent", parname);
+	par = (Object *)BKE_libblock_find_name(ID_OB, parname);
+	RNA_string_get(op->ptr, "child", childname);
+	ob = (Object *)BKE_libblock_find_name(ID_OB, childname);
+
+	if (ID_IS_LINKED(ob)) {
+		BKE_report(op->reports, RPT_INFO, "Can't edit library linked object");
+		return OPERATOR_CANCELLED;
+	}
+
+	ED_object_parent_set(op->reports, C, scene, ob, par, partype, false, false, NULL);
+
+	DEG_relations_tag_update(bmain);
+	WM_event_add_notifier(C, NC_OBJECT | ND_TRANSFORM, NULL);
+	WM_event_add_notifier(C, NC_OBJECT | ND_PARENT, NULL);
+#endif
+
+	return OPERATOR_FINISHED;
+}
+
+static int collection_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	ARegion *ar = CTX_wm_region(C);
+	Main *bmain = CTX_data_main(C);
+	char childname[MAX_ID_NAME];
+	float fmval[2];
+
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
+
+	/* Find object hovered over */
+	TreeElement *te = outliner_dropzone_find(soops, fmval, true);
+
+	if (!te || !outliner_is_collection_tree_element(te)) {
+		return OPERATOR_CANCELLED;
+	}
+
+	Collection *collection = outliner_collection_from_tree_element(te);
+
+	// TODO: don't use scene, makes no sense anymore
+	// TODO: move rather than link, change hover text
+	Scene *scene = BKE_scene_find_from_collection(bmain, collection);
+	BLI_assert(scene);
+	RNA_string_get(op->ptr, "child", childname);
+	Object *ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, childname);
+	BKE_collection_object_add(bmain, collection, ob);
+
+	DEG_id_tag_update(&collection->id, DEG_TAG_COPY_ON_WRITE);
+	DEG_relations_tag_update(bmain);
+	WM_event_add_notifier(C, NC_SCENE | ND_LAYER, scene);
+
+	return OPERATOR_FINISHED;
+}
+
+void OUTLINER_OT_collection_drop(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name = "Link to Collection"; // TODO: rename to move?
+	ot->description = "Drag to move to collection in Outliner";
+	ot->idname = "OUTLINER_OT_collection_drop";
+
+	/* api callbacks */
+	ot->invoke = collection_drop_invoke;
+	ot->exec = collection_drop_exec;
+
+	ot->poll = ED_operator_outliner_active;
+
+	/* flags */
+	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+
+	/* properties */
+	RNA_def_string(ot->srna, "child", "Object", MAX_ID_NAME, "Child", "Child Object");
+	RNA_def_string(ot->srna, "parent", "Collection", MAX_ID_NAME, "Parent", "Parent Collection");
+}
+
+/* ********************* Outliner Drag Operator ******************** */
+
+typedef struct OutlinerDragDropTooltip {
+	TreeElement *te;
+	void *handle;
+} OutlinerDragDropTooltip;
+
+static bool outliner_item_drag_drop_poll(bContext *C)
+{
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	return ED_operator_outliner_active(C) &&
+	       /* Only collection display modes supported for now. Others need more design work */
+	       ELEM(soops->outlinevis, SO_VIEW_LAYER, SO_LIBRARIES);
+}
+
+static TreeElement *outliner_item_drag_element_find(SpaceOops *soops, ARegion *ar, const wmEvent *event)
+{
+	/* note: using EVT_TWEAK_ events to trigger dragging is fine,
+	 * it sends coordinates from where dragging was started */
+	const float my = UI_view2d_region_to_view_y(&ar->v2d, event->mval[1]);
+	return outliner_find_item_at_y(soops, &soops->tree, my);
+}
+
+static void outliner_item_drag_end(wmWindow *win, OutlinerDragDropTooltip *data)
+{
+	MEM_SAFE_FREE(data->te->drag_data);
+
+	if (data->handle) {
+		WM_draw_cb_exit(win, data->handle);
+	}
+
+	MEM_SAFE_FREE(data);
+}
+
+static void outliner_item_drag_get_insert_data(
+        const SpaceOops *soops, ARegion *ar, const wmEvent *event, TreeElement *te_dragged,
+        TreeElement **r_te_insert_handle, TreeElementInsertType *r_insert_type)
+{
+	TreeElement *te_hovered;
+	float view_mval[2];
+
+	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &view_mval[0], &view_mval[1]);
+	te_hovered = outliner_find_item_at_y(soops, &soops->tree, view_mval[1]);
+
+	if (te_hovered) {
+		/* mouse hovers an element (ignoring x-axis), now find out how to insert the dragged item exactly */
+
+		if (te_hovered == te_dragged) {
+			*r_te_insert_handle = te_dragged;
+		}
+		else if (te_hovered != te_dragged) {
+			const float margin = UI_UNIT_Y * (1.0f / 4);
+
+			*r_te_insert_handle = te_hovered;
+			if (view_mval[1] < (te_hovered->ys + margin)) {
+				if (TSELEM_OPEN(TREESTORE(te_hovered), soops)) {
+					/* inserting after a open item means we insert into it, but as first child */
+					if (BLI_listbase_is_empty(&te_hovered->subtree)) {
+						*r_insert_type = TE_INSERT_INTO;
+					}
+					else {
+						*r_insert_type = TE_INSERT_BEFORE;
+						*r_te_insert_handle = te_hovered->subtree.first;
+					}
+				}
+				else {
+					*r_insert_type = TE_INSERT_AFTER;
+				}
+			}
+			else if (view_mval[1] > (te_hovered->ys + (3 * margin))) {
+				*r_insert_type = TE_INSERT_BEFORE;
+			}
+			else {
+				*r_insert_type = TE_INSERT_INTO;
+			}
+		}
+	}
+	else {
+		/* mouse doesn't hover any item (ignoring x-axis), so it's either above list bounds or below. */
+
+		TreeElement *first = soops->tree.first;
+		TreeElement *last = soops->tree.last;
+
+		if (view_mval[1] < last->ys) {
+			*r_te_insert_handle = last;
+			*r_insert_type = TE_INSERT_AFTER;
+		}
+		else if (view_mval[1] > (first->ys + UI_UNIT_Y)) {
+			*r_te_insert_handle = first;
+			*r_insert_type = TE_INSERT_BEFORE;
+		}
+		else {
+			BLI_assert(0);
+		}
+	}
+}
+
+static void outliner_item_drag_handle(
+        SpaceOops *soops, ARegion *ar, const wmEvent *event, TreeElement *te_dragged)
+{
+	TreeElement *te_insert_handle;
+	TreeElementInsertType insert_type;
+
+	outliner_item_drag_get_insert_data(soops, ar, event, te_dragged, &te_insert_handle, &insert_type);
+
+	if (!te_dragged->reinsert_poll &&
+	    /* there is no reinsert_poll, so we do some generic checks (same types and reinsert callback is available) */
+	    (TREESTORE(te_dragged)->type == TREESTORE(te_insert_handle)->type) &&
+	    te_dragged->reinsert)
+	{
+		/* pass */
+	}
+	else if (te_dragged == te_insert_handle) {
+		/* nothing will happen anyway, no need to do poll check */
+	}
+	else if (!te_dragged->reinsert_poll ||
+	         !te_dragged->reinsert_poll(te_dragged, &te_insert_handle, &insert_type))
+	{
+		te_insert_handle = NULL;
+	}
+	te_dragged->drag_data->insert_type = insert_type;
+	te_dragged->drag_data->insert_handle = te_insert_handle;
+}
+
+/**
+ * Returns true if it is a collection and empty.
+ */
+static bool is_empty_collection(TreeElement *te)
+{
+	Collection *collection = outliner_collection_from_tree_element(te);
+
+	if (!collection) {
+		return false;
+	}
+
+	return BLI_listbase_is_empty(&collection->gobject) &&
+	       BLI_listbase_is_empty(&collection->children);
+}
+
+static bool outliner_item_drag_drop_apply(
+        Main *bmain,
+        Scene *scene,
+        SpaceOops *soops,
+        OutlinerDragDropTooltip *data,
+        const wmEvent *event)
+{
+	TreeElement *dragged_te = data->te;
+	TreeElement *insert_handle = dragged_te->drag_data->insert_handle;
+	TreeElementInsertType insert_type = dragged_te->drag_data->insert_type;
+
+	if ((insert_handle == dragged_te) || !insert_handle) {
+		/* No need to do anything */
+	}
+	else if (dragged_te->reinsert) {
+		BLI_assert(!dragged_te->reinsert_poll || dragged_te->reinsert_poll(dragged_te, &insert_handle,
+		                                                                   &insert_type));
+		/* call of assert above should not have changed insert_handle and insert_type at this point */
+		BLI_assert(dragged_te->drag_data->insert_handle == insert_handle &&
+		           dragged_te->drag_data->insert_type == insert_type);
+
+		/* If the collection was just created and you moved objects/collections inside it,
+		 * it is strange to have it closed and we not see the newly dragged elements. */
+		const bool should_open_collection = (insert_type == TE_INSERT_INTO) && is_empty_collection(insert_handle);
+
+		dragged_te->reinsert(bmain, scene, soops, dragged_te, insert_handle, insert_type, event);
+
+		if (should_open_collection && !is_empty_collection(insert_handle)) {
+			TREESTORE(insert_handle)->flag &= ~TSE_CLOSED;
+		}
+		return true;
+	}
+
+	return false;
+}
+
+static int outliner_item_drag_drop_modal(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	Main *bmain = CTX_data_main(C);
+	Scene *scene = CTX_data_scene(C);
+	ARegion *ar = CTX_wm_region(C);
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	OutlinerDragDropTooltip *data = op->customdata;
+	TreeElement *te_dragged = data->te;
+	int retval = OPERATOR_RUNNING_MODAL;
+	bool redraw = false;
+	bool skip_rebuild = true;
+
+	switch (event->type) {
+		case EVT_MODAL_MAP:
+			if (event->val == OUTLINER_ITEM_DRAG_CONFIRM) {
+				if (outliner_item_drag_drop_apply(bmain, scene, soops, data, event)) {
+					skip_rebuild = false;
+				}
+				retval = OPERATOR_FINISHED;
+			}
+			else if (event->val == OUTLINER_ITEM_DRAG_CANCEL) {
+				retval = OPERATOR_CANCELLED;
+			}
+			else {
+				BLI_assert(0);
+			}
+			WM_event_add_mousemove(C); /* update highlight */
+			outliner_item_drag_end(CTX_wm_window(C), data);
+			redraw = true;
+			break;
+		case MOUSEMOVE:
+			outliner_item_drag_handle(soops, ar, event, te_dragged);
+			redraw = true;
+			break;
+	}
+
+	if (redraw) {
+		if (skip_rebuild) {
+			ED_region_tag_redraw_no_rebuild(ar);
+		}
+		else {
+			ED_region_tag_redraw(ar);
+		}
+	}
+
+	return retval;
+}
+
+static const char *outliner_drag_drop_tooltip_get(
+        const TreeElement *te_float)
+{
+	const char *name = NULL;
+
+	const TreeElement *te_insert = te_float->drag_data->insert_handle;
+	if (te_float && outliner_is_collection_tree_element(te_float)) {
+		if (te_insert == NULL) {
+			name = TIP_("Move collection");
+		}
+		else {
+			switch (te_float->drag_data->insert_type) {
+				case TE_INSERT_BEFORE:
+					if (te_insert->prev && outliner_is_collection_tree_element(te_insert->prev)) {
+						name = TIP_("Move between collections");
+					}
+					else {
+						name = TIP_("Move before collection");
+					}
+					break;
+				case TE_INSERT_AFTER:
+					if (te_insert->next && outliner_is_collection_tree_element(te_insert->next)) {
+						name = TIP_("Move between collections");
+					}
+					else {
+						name = TIP_("Move after collection");
+					}
+					break;
+				case TE_INSERT_INTO:
+					name = TIP_("Move inside collection");
+					break;
+			}
+		}
+	}
+	else if ((TREESTORE(te_float)->type == 0) && (te_float->idcode == ID_OB)) {
+		name = TIP_("Move to collection (Ctrl to link)");
+	}
+
+	return name;
+}
+
+static void outliner_drag_drop_tooltip_cb(const wmWindow *win, void *vdata)
+{
+	OutlinerDragDropTooltip *data = vdata;
+	const char *tooltip;
+
+	int cursorx, cursory;
+	int x, y;
+
+	tooltip = outliner_drag_drop_tooltip_get(data->te);
+	if (tooltip == NULL) {
+		return;
+	}
+
+	cursorx = win->eventstate->x;
+	cursory = win->eventstate->y;
+
+	x = cursorx + U.widget_unit;
+	y = cursory - U.widget_unit;
+
+	/* Drawing. */
+	const uiFontStyle *fstyle = UI_FSTYLE_WIDGET;
+
+	const float col_fg[4] = {1.0f, 1.0f, 1.0f, 1.0f};
+	const float col_bg[4] = {0.0f, 0.0f, 0.0f, 0.2f};
+
+	GPU_blend(true);
+	UI_fontstyle_draw_simple_backdrop(fstyle, x, y, tooltip, col_fg, col_bg);
+	GPU_blend(false);
+}
+
+static int outliner_item_drag_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+	ARegion *ar = CTX_wm_region(C);
+	SpaceOops *soops = CTX_wm_space_outliner(C);
+	TreeElement *te_dragged = outliner_item_drag_element_find(soops, ar, event);
+
+	if (!te_dragged) {
+		return (OPERATOR_FINISHED | OPERATOR_PASS_THROUGH);
+	}
+
+	OutlinerDragDropTooltip *data = MEM_mallocN(sizeof(OutlinerDragDropTooltip), __func__);
+	data->te = te_dragged;
+
+	op->customdata = data;
+	te_dragged->drag_data = MEM_callocN(sizeof(*te_dragged->drag_data), __func__);
+	/* by default we don't change the item position */
+	te_dragged->drag_data->insert_handle = te_dragged;
+	/* unset highlighted tree element, dragged one will be highlighted instead */
+	outliner_flag_set(&soops->tree, TSE_HIGHLIGHTED, false);
+
+	ED_region_tag_redraw_no_rebuild(ar);
+
+	WM_event_add_modal_handler(C, op);
+
+	data->handle = WM_draw_cb_activate(CTX_wm_window(C), outliner_drag_drop_tooltip_cb, data);
+
+	return OPERATOR_RUNNING_MODAL;
+}
+
+/**
+ * Notes about Outliner Item Drag 'n Drop:
+ * Right now only collections display mode is supported. But ideally all/most modes would support this. There are
+ * just some open design questions that have to be answered: do we want to allow mixing order of different data types
+ * (like render-layers and objects)? Would that be a purely visual change or would that have any other effect? ...
+ */
+void OUTLINER_OT_item_drag_drop(wmOperatorType *ot)
+{
+	ot->name = "Drag and Drop";
+	ot->idname = "OUTLINER_OT_item_drag_drop";
+	ot->description = "Change the hierarchical position of an item by repositioning it using drag and drop";
+
+	ot->invoke = outliner_item_drag_drop_invoke;
+	ot->modal = outliner_item_drag_drop_modal;
+
+	ot->poll = outliner_item_drag_drop_poll;
+
+	ot->flag = OPTYPE_UNDO;
+}
+
+/* *************************** Drop Boxes ************************** */
+
+/* region dropbox definition */
+void outliner_dropboxes(void)
+{
+	ListBase *lb = WM_dropboxmap_find("Outliner", SPACE_OUTLINER, RGN_TYPE_WINDOW);
+
+	WM_dropbox_add(lb, "OUTLINER_OT_parent_drop", parent_drop_poll, parent_drop_copy);
+	WM_dropbox_add(lb, "OUTLINER_OT_parent_clear", parent_clear_poll, parent_clear_copy);
+	WM_dropbox_add(lb, "OUTLINER_OT_scene_drop", scene_drop_poll, scene_drop_copy);
+	WM_dropbox_add(lb, "OUTLINER_OT_material_drop", material_drop_poll, material_drop_copy);
+	WM_dropbox_add(lb, "OUTLINER_OT_collection_drop", collection_drop_poll, collection_drop_copy);
+}
diff --git a/source/blender/editors/space_outliner/outliner_edit.c b/source/blender/editors/space_outliner/outliner_edit.c
index d9bcf05fa29..6316b65fefb 100644
--- a/source/blender/editors/space_outliner/outliner_edit.c
+++ b/source/blender/editors/space_outliner/outliner_edit.c
@@ -90,68 +90,6 @@
 #include "outliner_intern.h"
 
 /* ************************************************************** */
-/* Unused Utilities */
-// XXX: where to place these?
-
-/* This is not used anywhere at the moment */
-#if 0
-static void outliner_open_reveal(SpaceOops *soops, ListBase *lb, TreeElement *teFind, int *found)
-{
-	TreeElement *te;
-	TreeStoreElem *tselem;
-
-	for (te = lb->first; te; te = te->next) {
-		/* check if this tree-element was the one we're seeking */
-		if (te == teFind) {
-			*found = 1;
-			return;
-		}
-
-		/* try to see if sub-tree contains it then */
-		outliner_open_reveal(soops, &te->subtree, teFind, found);
-		if (*found) {
-			tselem = TREESTORE(te);
-			if (tselem->flag & TSE_CLOSED)
-				tselem->flag &= ~TSE_CLOSED;
-			return;
-		}
-	}
-}
-#endif
-
-static TreeElement *outliner_dropzone_element(TreeElement *te, const float fmval[2], const bool children)
-{
-	if ((fmval[1] > te->ys) && (fmval[1] < (te->ys + UI_UNIT_Y))) {
-		/* name and first icon */
-		if ((fmval[0] > te->xs + UI_UNIT_X) && (fmval[0] < te->xend))
-			return te;
-	}
-	/* Not it.  Let's look at its children. */
-	if (children && (TREESTORE(te)->flag & TSE_CLOSED) == 0 && (te->subtree.first)) {
-		for (te = te->subtree.first; te; te = te->next) {
-			TreeElement *te_valid = outliner_dropzone_element(te, fmval, children);
-			if (te_valid)
-				return te_valid;
-		}
-	}
-	return NULL;
-}
-
-/* Used for drag and drop parenting */
-TreeElement *outliner_dropzone_find(const SpaceOops *soops, const float fmval[2], const bool children)
-{
-	TreeElement *te;
-
-	for (te = soops->tree.first; te; te = te->next) {
-		TreeElement *te_valid = outliner_dropzone_element(te, fmval, children);
-		if (te_valid)
-			return te_valid;
-	}
-	return NULL;
-}
-
-
-/* ************************************************************** */
 
 /* Highlight --------------------------------------------------- */
 
@@ -1951,474 +1889,3 @@ void OUTLINER_OT_orphans_purge(wmOperatorType *ot)
 	/* flags */
 	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
 }
-
-/* ************************************************************** */
-/* DRAG AND DROP OPERATORS */
-
-/* ******************** Parent Drop Operator *********************** */
-
-static int parent_drop_exec(bContext *C, wmOperator *op)
-{
-	Object *par = NULL, *ob = NULL;
-	Main *bmain = CTX_data_main(C);
-	Scene *scene = CTX_data_scene(C);
-	int partype = -1;
-	char parname[MAX_ID_NAME], childname[MAX_ID_NAME];
-
-	partype = RNA_enum_get(op->ptr, "type");
-	RNA_string_get(op->ptr, "parent", parname);
-	par = (Object *)BKE_libblock_find_name(bmain, ID_OB, parname);
-	RNA_string_get(op->ptr, "child", childname);
-	ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, childname);
-
-	if (ID_IS_LINKED(ob)) {
-		BKE_report(op->reports, RPT_INFO, "Can't edit library linked object");
-		return OPERATOR_CANCELLED;
-	}
-
-	ED_object_parent_set(op->reports, C, scene, ob, par, partype, false, false, NULL);
-
-	DEG_relations_tag_update(bmain);
-	WM_event_add_notifier(C, NC_OBJECT | ND_TRANSFORM, NULL);
-	WM_event_add_notifier(C, NC_OBJECT | ND_PARENT, NULL);
-
-	return OPERATOR_FINISHED;
-}
-
-static int parent_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
-{
-	Object *par = NULL;
-	Object *ob = NULL;
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	ARegion *ar = CTX_wm_region(C);
-	Main *bmain = CTX_data_main(C);
-	Scene *scene = NULL;
-	TreeElement *te = NULL;
-	char childname[MAX_ID_NAME];
-	char parname[MAX_ID_NAME];
-	int partype = 0;
-	float fmval[2];
-
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	/* Find object hovered over */
-	te = outliner_dropzone_find(soops, fmval, true);
-
-	if (te) {
-		RNA_string_set(op->ptr, "parent", te->name);
-		/* Identify parent and child */
-		RNA_string_get(op->ptr, "child", childname);
-		ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, childname);
-		RNA_string_get(op->ptr, "parent", parname);
-		par = (Object *)BKE_libblock_find_name(bmain, ID_OB, parname);
-
-		if (ELEM(NULL, ob, par)) {
-			if (par == NULL) printf("par==NULL\n");
-			return OPERATOR_CANCELLED;
-		}
-		if (ob == par) {
-			return OPERATOR_CANCELLED;
-		}
-		if (ID_IS_LINKED(ob)) {
-			BKE_report(op->reports, RPT_INFO, "Can't edit library linked object");
-			return OPERATOR_CANCELLED;
-		}
-
-		scene = (Scene *)outliner_search_back(soops, te, ID_SCE);
-
-		if (scene == NULL) {
-			/* currently outlier organized in a way, that if there's no parent scene
-			 * element for object it means that all displayed objects belong to
-			 * active scene and parenting them is allowed (sergey)
-			 */
-
-			scene = CTX_data_scene(C);
-		}
-
-		if ((par->type != OB_ARMATURE) && (par->type != OB_CURVE) && (par->type != OB_LATTICE)) {
-			if (ED_object_parent_set(op->reports, C, scene, ob, par, partype, false, false, NULL)) {
-				DEG_relations_tag_update(bmain);
-				WM_event_add_notifier(C, NC_OBJECT | ND_TRANSFORM, NULL);
-				WM_event_add_notifier(C, NC_OBJECT | ND_PARENT, NULL);
-			}
-		}
-		else {
-			/* Menu creation */
-			wmOperatorType *ot = WM_operatortype_find("OUTLINER_OT_parent_drop", false);
-			uiPopupMenu *pup = UI_popup_menu_begin(C, IFACE_("Set Parent To"), ICON_NONE);
-			uiLayout *layout = UI_popup_menu_layout(pup);
-			PointerRNA ptr;
-
-			/* Cannot use uiItemEnumO()... have multiple properties to set. */
-			uiItemFullO_ptr(layout, ot, IFACE_("Object"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-			RNA_string_set(&ptr, "parent", parname);
-			RNA_string_set(&ptr, "child", childname);
-			RNA_enum_set(&ptr, "type", PAR_OBJECT);
-
-			/* par becomes parent, make the associated menus */
-			if (par->type == OB_ARMATURE) {
-				uiItemFullO_ptr(layout, ot, IFACE_("Armature Deform"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_ARMATURE);
-
-				uiItemFullO_ptr(layout, ot, IFACE_("   With Empty Groups"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_ARMATURE_NAME);
-
-				uiItemFullO_ptr(layout, ot, IFACE_("   With Envelope Weights"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_ARMATURE_ENVELOPE);
-
-				uiItemFullO_ptr(layout, ot, IFACE_("   With Automatic Weights"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_ARMATURE_AUTO);
-
-				uiItemFullO_ptr(layout, ot, IFACE_("Bone"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_BONE);
-			}
-			else if (par->type == OB_CURVE) {
-				uiItemFullO_ptr(layout, ot, IFACE_("Curve Deform"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_CURVE);
-
-				uiItemFullO_ptr(layout, ot, IFACE_("Follow Path"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_FOLLOW);
-
-				uiItemFullO_ptr(layout, ot, IFACE_("Path Constraint"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_PATH_CONST);
-			}
-			else if (par->type == OB_LATTICE) {
-				uiItemFullO_ptr(layout, ot, IFACE_("Lattice Deform"), 0, NULL, WM_OP_EXEC_DEFAULT, 0, &ptr);
-				RNA_string_set(&ptr, "parent", parname);
-				RNA_string_set(&ptr, "child", childname);
-				RNA_enum_set(&ptr, "type", PAR_LATTICE);
-			}
-
-			UI_popup_menu_end(C, pup);
-
-			return OPERATOR_INTERFACE;
-		}
-	}
-	else {
-		return OPERATOR_CANCELLED;
-	}
-
-	return OPERATOR_FINISHED;
-}
-
-void OUTLINER_OT_parent_drop(wmOperatorType *ot)
-{
-	/* identifiers */
-	ot->name = "Drop to Set Parent";
-	ot->description = "Drag to parent in Outliner";
-	ot->idname = "OUTLINER_OT_parent_drop";
-
-	/* api callbacks */
-	ot->invoke = parent_drop_invoke;
-	ot->exec = parent_drop_exec;
-
-	ot->poll = ED_operator_outliner_active;
-
-	/* flags */
-	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
-
-	/* properties */
-	RNA_def_string(ot->srna, "child", "Object", MAX_ID_NAME, "Child", "Child Object");
-	RNA_def_string(ot->srna, "parent", "Object", MAX_ID_NAME, "Parent", "Parent Object");
-	RNA_def_enum(ot->srna, "type", prop_make_parent_types, 0, "Type", "");
-}
-
-static bool outliner_parenting_poll(bContext *C)
-{
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-
-	if (soops) {
-		if (soops->outlinevis == SO_SCENES) {
-			return true;
-		}
-		else if ((soops->outlinevis == SO_VIEW_LAYER) &&
-		         (soops->filter & SO_FILTER_NO_COLLECTION))
-		{
-			return true;
-		}
-	}
-
-	return false;
-}
-
-static int parent_clear_invoke(bContext *C, wmOperator *op, const wmEvent *UNUSED(event))
-{
-	Main *bmain = CTX_data_main(C);
-	Object *ob = NULL;
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	char obname[MAX_ID_NAME];
-
-	RNA_string_get(op->ptr, "dragged_obj", obname);
-	ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, obname);
-
-	/* search forwards to find the object */
-	outliner_find_id(soops, &soops->tree, (ID *)ob);
-
-	ED_object_parent_clear(ob, RNA_enum_get(op->ptr, "type"));
-
-	DEG_relations_tag_update(bmain);
-	WM_event_add_notifier(C, NC_OBJECT | ND_TRANSFORM, NULL);
-	WM_event_add_notifier(C, NC_OBJECT | ND_PARENT, NULL);
-	return OPERATOR_FINISHED;
-}
-
-void OUTLINER_OT_parent_clear(wmOperatorType *ot)
-{
-	/* identifiers */
-	ot->name = "Drop to Clear Parent";
-	ot->description = "Drag to clear parent in Outliner";
-	ot->idname = "OUTLINER_OT_parent_clear";
-
-	/* api callbacks */
-	ot->invoke = parent_clear_invoke;
-
-	ot->poll = outliner_parenting_poll;
-
-	/* flags */
-	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
-
-	/* properties */
-	RNA_def_string(ot->srna, "dragged_obj", "Object", MAX_ID_NAME, "Child", "Child Object");
-	RNA_def_enum(ot->srna, "type", prop_clear_parent_types, 0, "Type", "");
-}
-
-static int scene_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
-{
-	Scene *scene = NULL;
-	Object *ob = NULL;
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	ARegion *ar = CTX_wm_region(C);
-	Main *bmain = CTX_data_main(C);
-	TreeElement *te = NULL;
-	char obname[MAX_ID_NAME];
-	float fmval[2];
-
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	/* Find object hovered over */
-	te = outliner_dropzone_find(soops, fmval, false);
-
-	if (te) {
-		RNA_string_set(op->ptr, "scene", te->name);
-		scene = (Scene *)BKE_libblock_find_name(bmain, ID_SCE, te->name);
-
-		RNA_string_get(op->ptr, "object", obname);
-		ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, obname);
-
-		if (ELEM(NULL, ob, scene) || ID_IS_LINKED(scene)) {
-			return OPERATOR_CANCELLED;
-		}
-
-		if (BKE_scene_has_object(scene, ob)) {
-			return OPERATOR_CANCELLED;
-		}
-
-		Collection *collection;
-		if (scene != CTX_data_scene(C)) {
-			/* when linking to an inactive scene link to the master collection */
-			collection = BKE_collection_master(scene);
-		}
-		else {
-			collection = CTX_data_collection(C);
-		}
-
-		BKE_collection_object_add(bmain, collection, ob);
-
-		for (ViewLayer *view_layer = scene->view_layers.first; view_layer; view_layer = view_layer->next) {
-			Base *base = BKE_view_layer_base_find(view_layer, ob);
-			if (base) {
-				ED_object_base_select(base, BA_SELECT);
-			}
-		}
-
-		DEG_relations_tag_update(bmain);
-
-		DEG_id_tag_update(&scene->id, DEG_TAG_SELECT_UPDATE);
-		WM_main_add_notifier(NC_SCENE | ND_OB_SELECT, scene);
-
-		return OPERATOR_FINISHED;
-	}
-
-	return OPERATOR_CANCELLED;
-}
-
-void OUTLINER_OT_scene_drop(wmOperatorType *ot)
-{
-	/* identifiers */
-	ot->name = "Drop Object to Scene";
-	ot->description = "Drag object to scene in Outliner";
-	ot->idname = "OUTLINER_OT_scene_drop";
-
-	/* api callbacks */
-	ot->invoke = scene_drop_invoke;
-
-	ot->poll = ED_operator_outliner_active;
-
-	/* flags */
-	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
-
-	/* properties */
-	RNA_def_string(ot->srna, "object", "Object", MAX_ID_NAME, "Object", "Target Object");
-	RNA_def_string(ot->srna, "scene", "Scene", MAX_ID_NAME, "Scene", "Target Scene");
-}
-
-static int material_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
-{
-	Material *ma = NULL;
-	Object *ob = NULL;
-	Main *bmain = CTX_data_main(C);
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	ARegion *ar = CTX_wm_region(C);
-	TreeElement *te = NULL;
-	char mat_name[MAX_ID_NAME - 2];
-	float fmval[2];
-
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	/* Find object hovered over */
-	te = outliner_dropzone_find(soops, fmval, true);
-
-	if (te) {
-		RNA_string_set(op->ptr, "object", te->name);
-		ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, te->name);
-
-		RNA_string_get(op->ptr, "material", mat_name);
-		ma = (Material *)BKE_libblock_find_name(bmain, ID_MA, mat_name);
-
-		if (ELEM(NULL, ob, ma)) {
-			return OPERATOR_CANCELLED;
-		}
-
-		assign_material(bmain, ob, ma, ob->totcol + 1, BKE_MAT_ASSIGN_USERPREF);
-
-		WM_event_add_notifier(C, NC_SPACE | ND_SPACE_VIEW3D, CTX_wm_view3d(C));
-		WM_event_add_notifier(C, NC_MATERIAL | ND_SHADING_LINKS, ma);
-
-		return OPERATOR_FINISHED;
-	}
-
-	return OPERATOR_CANCELLED;
-}
-
-void OUTLINER_OT_material_drop(wmOperatorType *ot)
-{
-	/* identifiers */
-	ot->name = "Drop Material on Object";
-	ot->description = "Drag material to object in Outliner";
-	ot->idname = "OUTLINER_OT_material_drop";
-
-	/* api callbacks */
-	ot->invoke = material_drop_invoke;
-
-	ot->poll = ED_operator_outliner_active;
-
-	/* flags */
-	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
-
-	/* properties */
-	RNA_def_string(ot->srna, "object", "Object", MAX_ID_NAME, "Object", "Target Object");
-	RNA_def_string(ot->srna, "material", "Material", MAX_ID_NAME, "Material", "Target Material");
-}
-
-/* ******************** Collection Drop Operator *********************** */
-
-static int collection_drop_exec(bContext *UNUSED(C), wmOperator *UNUSED(op))
-{
-	/* TODO: implement */
-#if 0
-	Object *par = NULL, *ob = NULL;
-	Main *bmain = CTX_data_main(C);
-	Scene *scene = CTX_data_scene(C);
-	int partype = -1;
-	char parname[MAX_ID_NAME], childname[MAX_ID_NAME];
-
-	RNA_string_get(op->ptr, "parent", parname);
-	par = (Object *)BKE_libblock_find_name(ID_OB, parname);
-	RNA_string_get(op->ptr, "child", childname);
-	ob = (Object *)BKE_libblock_find_name(ID_OB, childname);
-
-	if (ID_IS_LINKED(ob)) {
-		BKE_report(op->reports, RPT_INFO, "Can't edit library linked object");
-		return OPERATOR_CANCELLED;
-	}
-
-	ED_object_parent_set(op->reports, C, scene, ob, par, partype, false, false, NULL);
-
-	DEG_relations_tag_update(bmain);
-	WM_event_add_notifier(C, NC_OBJECT | ND_TRANSFORM, NULL);
-	WM_event_add_notifier(C, NC_OBJECT | ND_PARENT, NULL);
-#endif
-
-	return OPERATOR_FINISHED;
-}
-
-static int collection_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
-{
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	ARegion *ar = CTX_wm_region(C);
-	Main *bmain = CTX_data_main(C);
-	char childname[MAX_ID_NAME];
-	float fmval[2];
-
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	/* Find object hovered over */
-	TreeElement *te = outliner_dropzone_find(soops, fmval, true);
-
-	if (!te || !outliner_is_collection_tree_element(te)) {
-		return OPERATOR_CANCELLED;
-	}
-
-	Collection *collection = outliner_collection_from_tree_element(te);
-
-	// TODO: don't use scene, makes no sense anymore
-	// TODO: move rather than link, change hover text
-	Scene *scene = BKE_scene_find_from_collection(bmain, collection);
-	BLI_assert(scene);
-	RNA_string_get(op->ptr, "child", childname);
-	Object *ob = (Object *)BKE_libblock_find_name(bmain, ID_OB, childname);
-	BKE_collection_object_add(bmain, collection, ob);
-
-	DEG_id_tag_update(&collection->id, DEG_TAG_COPY_ON_WRITE);
-	DEG_relations_tag_update(bmain);
-	WM_event_add_notifier(C, NC_SCENE | ND_LAYER, scene);
-
-	return OPERATOR_FINISHED;
-}
-
-void OUTLINER_OT_collection_drop(wmOperatorType *ot)
-{
-	/* identifiers */
-	ot->name = "Link to Collection"; // TODO: rename to move?
-	ot->description = "Drag to move to collection in Outliner";
-	ot->idname = "OUTLINER_OT_collection_drop";
-
-	/* api callbacks */
-	ot->invoke = collection_drop_invoke;
-	ot->exec = collection_drop_exec;
-
-	ot->poll = ED_operator_outliner_active;
-
-	/* flags */
-	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
-
-	/* properties */
-	RNA_def_string(ot->srna, "child", "Object", MAX_ID_NAME, "Child", "Child Object");
-	RNA_def_string(ot->srna, "parent", "Collection", MAX_ID_NAME, "Parent", "Parent Collection");
-}
diff --git a/source/blender/editors/space_outliner/outliner_intern.h b/source/blender/editors/space_outliner/outliner_intern.h
index 461d4bd7c56..ecc092358d6 100644
--- a/source/blender/editors/space_outliner/outliner_intern.h
+++ b/source/blender/editors/space_outliner/outliner_intern.h
@@ -284,10 +284,23 @@ void item_object_mode_exit_cb(
         struct bContext *C, struct ReportList *reports, struct Scene *scene,
         TreeElement *te, struct TreeStoreElem *tsep, struct TreeStoreElem *tselem, void *user_data);
 
-TreeElement *outliner_dropzone_find(const struct SpaceOops *soops, const float fmval[2], const bool children);
-
 void outliner_set_coordinates(struct ARegion *ar, struct SpaceOops *soops);
 
+/* outliner_dragdrop.c */
+enum {
+	OUTLINER_ITEM_DRAG_CANCEL,
+	OUTLINER_ITEM_DRAG_CONFIRM,
+};
+
+void outliner_dropboxes(void);
+
+void OUTLINER_OT_item_drag_drop(struct wmOperatorType *ot);
+void OUTLINER_OT_parent_drop(struct wmOperatorType *ot);
+void OUTLINER_OT_parent_clear(struct wmOperatorType *ot);
+void OUTLINER_OT_scene_drop(struct wmOperatorType *ot);
+void OUTLINER_OT_material_drop(struct wmOperatorType *ot);
+void OUTLINER_OT_collection_drop(struct wmOperatorType *ot);
+
 /* ...................................................... */
 
 void OUTLINER_OT_highlight_update(struct wmOperatorType *ot);
@@ -319,12 +332,6 @@ void OUTLINER_OT_drivers_delete_selected(struct wmOperatorType *ot);
 
 void OUTLINER_OT_orphans_purge(struct wmOperatorType *ot);
 
-void OUTLINER_OT_parent_drop(struct wmOperatorType *ot);
-void OUTLINER_OT_parent_clear(struct wmOperatorType *ot);
-void OUTLINER_OT_scene_drop(struct wmOperatorType *ot);
-void OUTLINER_OT_material_drop(struct wmOperatorType *ot);
-void OUTLINER_OT_collection_drop(struct wmOperatorType *ot);
-
 /* outliner_tools.c ---------------------------------------------- */
 
 void OUTLINER_OT_operation(struct wmOperatorType *ot);
diff --git a/source/blender/editors/space_outliner/outliner_ops.c b/source/blender/editors/space_outliner/outliner_ops.c
index 576038979d3..a4aad11a821 100644
--- a/source/blender/editors/space_outliner/outliner_ops.c
+++ b/source/blender/editors/space_outliner/outliner_ops.c
@@ -55,353 +55,6 @@
 
 #include "outliner_intern.h"
 
-typedef struct OutlinerDragDropTooltip {
-	TreeElement *te;
-	void *handle;
-} OutlinerDragDropTooltip;
-
-enum {
-	OUTLINER_ITEM_DRAG_CANCEL,
-	OUTLINER_ITEM_DRAG_CONFIRM,
-};
-
-static bool outliner_item_drag_drop_poll(bContext *C)
-{
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	return ED_operator_outliner_active(C) &&
-	       /* Only collection display modes supported for now. Others need more design work */
-	       ELEM(soops->outlinevis, SO_VIEW_LAYER, SO_LIBRARIES);
-}
-
-static TreeElement *outliner_item_drag_element_find(SpaceOops *soops, ARegion *ar, const wmEvent *event)
-{
-	/* note: using EVT_TWEAK_ events to trigger dragging is fine,
-	 * it sends coordinates from where dragging was started */
-	const float my = UI_view2d_region_to_view_y(&ar->v2d, event->mval[1]);
-	return outliner_find_item_at_y(soops, &soops->tree, my);
-}
-
-static void outliner_item_drag_end(wmWindow *win, OutlinerDragDropTooltip *data)
-{
-	MEM_SAFE_FREE(data->te->drag_data);
-
-	if (data->handle) {
-		WM_draw_cb_exit(win, data->handle);
-	}
-
-	MEM_SAFE_FREE(data);
-}
-
-static void outliner_item_drag_get_insert_data(
-        const SpaceOops *soops, ARegion *ar, const wmEvent *event, TreeElement *te_dragged,
-        TreeElement **r_te_insert_handle, TreeElementInsertType *r_insert_type)
-{
-	TreeElement *te_hovered;
-	float view_mval[2];
-
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &view_mval[0], &view_mval[1]);
-	te_hovered = outliner_find_item_at_y(soops, &soops->tree, view_mval[1]);
-
-	if (te_hovered) {
-		/* mouse hovers an element (ignoring x-axis), now find out how to insert the dragged item exactly */
-
-		if (te_hovered == te_dragged) {
-			*r_te_insert_handle = te_dragged;
-		}
-		else if (te_hovered != te_dragged) {
-			const float margin = UI_UNIT_Y * (1.0f / 4);
-
-			*r_te_insert_handle = te_hovered;
-			if (view_mval[1] < (te_hovered->ys + margin)) {
-				if (TSELEM_OPEN(TREESTORE(te_hovered), soops)) {
-					/* inserting after a open item means we insert into it, but as first child */
-					if (BLI_listbase_is_empty(&te_hovered->subtree)) {
-						*r_insert_type = TE_INSERT_INTO;
-					}
-					else {
-						*r_insert_type = TE_INSERT_BEFORE;
-						*r_te_insert_handle = te_hovered->subtree.first;
-					}
-				}
-				else {
-					*r_insert_type = TE_INSERT_AFTER;
-				}
-			}
-			else if (view_mval[1] > (te_hovered->ys + (3 * margin))) {
-				*r_insert_type = TE_INSERT_BEFORE;
-			}
-			else {
-				*r_insert_type = TE_INSERT_INTO;
-			}
-		}
-	}
-	else {
-		/* mouse doesn't hover any item (ignoring x-axis), so it's either above list bounds or below. */
-
-		TreeElement *first = soops->tree.first;
-		TreeElement *last = soops->tree.last;
-
-		if (view_mval[1] < last->ys) {
-			*r_te_insert_handle = last;
-			*r_insert_type = TE_INSERT_AFTER;
-		}
-		else if (view_mval[1] > (first->ys + UI_UNIT_Y)) {
-			*r_te_insert_handle = first;
-			*r_insert_type = TE_INSERT_BEFORE;
-		}
-		else {
-			BLI_assert(0);
-		}
-	}
-}
-
-static void outliner_item_drag_handle(
-        SpaceOops *soops, ARegion *ar, const wmEvent *event, TreeElement *te_dragged)
-{
-	TreeElement *te_insert_handle;
-	TreeElementInsertType insert_type;
-
-	outliner_item_drag_get_insert_data(soops, ar, event, te_dragged, &te_insert_handle, &insert_type);
-
-	if (!te_dragged->reinsert_poll &&
-	    /* there is no reinsert_poll, so we do some generic checks (same types and reinsert callback is available) */
-	    (TREESTORE(te_dragged)->type == TREESTORE(te_insert_handle)->type) &&
-	    te_dragged->reinsert)
-	{
-		/* pass */
-	}
-	else if (te_dragged == te_insert_handle) {
-		/* nothing will happen anyway, no need to do poll check */
-	}
-	else if (!te_dragged->reinsert_poll ||
-	         !te_dragged->reinsert_poll(te_dragged, &te_insert_handle, &insert_type))
-	{
-		te_insert_handle = NULL;
-	}
-	te_dragged->drag_data->insert_type = insert_type;
-	te_dragged->drag_data->insert_handle = te_insert_handle;
-}
-
-/**
- * Returns true if it is a collection and empty.
- */
-static bool is_empty_collection(TreeElement *te)
-{
-	Collection *collection = outliner_collection_from_tree_element(te);
-
-	if (!collection) {
-		return false;
-	}
-
-	return BLI_listbase_is_empty(&collection->gobject) &&
-	       BLI_listbase_is_empty(&collection->children);
-}
-
-static bool outliner_item_drag_drop_apply(
-        Main *bmain,
-        Scene *scene,
-        SpaceOops *soops,
-        OutlinerDragDropTooltip *data,
-        const wmEvent *event)
-{
-	TreeElement *dragged_te = data->te;
-	TreeElement *insert_handle = dragged_te->drag_data->insert_handle;
-	TreeElementInsertType insert_type = dragged_te->drag_data->insert_type;
-
-	if ((insert_handle == dragged_te) || !insert_handle) {
-		/* No need to do anything */
-	}
-	else if (dragged_te->reinsert) {
-		BLI_assert(!dragged_te->reinsert_poll || dragged_te->reinsert_poll(dragged_te, &insert_handle,
-		                                                                   &insert_type));
-		/* call of assert above should not have changed insert_handle and insert_type at this point */
-		BLI_assert(dragged_te->drag_data->insert_handle == insert_handle &&
-		           dragged_te->drag_data->insert_type == insert_type);
-
-		/* If the collection was just created and you moved objects/collections inside it,
-		 * it is strange to have it closed and we not see the newly dragged elements. */
-		const bool should_open_collection = (insert_type == TE_INSERT_INTO) && is_empty_collection(insert_handle);
-
-		dragged_te->reinsert(bmain, scene, soops, dragged_te, insert_handle, insert_type, event);
-
-		if (should_open_collection && !is_empty_collection(insert_handle)) {
-			TREESTORE(insert_handle)->flag &= ~TSE_CLOSED;
-		}
-		return true;
-	}
-
-	return false;
-}
-
-static int outliner_item_drag_drop_modal(bContext *C, wmOperator *op, const wmEvent *event)
-{
-	Main *bmain = CTX_data_main(C);
-	Scene *scene = CTX_data_scene(C);
-	ARegion *ar = CTX_wm_region(C);
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	OutlinerDragDropTooltip *data = op->customdata;
-	TreeElement *te_dragged = data->te;
-	int retval = OPERATOR_RUNNING_MODAL;
-	bool redraw = false;
-	bool skip_rebuild = true;
-
-	switch (event->type) {
-		case EVT_MODAL_MAP:
-			if (event->val == OUTLINER_ITEM_DRAG_CONFIRM) {
-				if (outliner_item_drag_drop_apply(bmain, scene, soops, data, event)) {
-					skip_rebuild = false;
-				}
-				retval = OPERATOR_FINISHED;
-			}
-			else if (event->val == OUTLINER_ITEM_DRAG_CANCEL) {
-				retval = OPERATOR_CANCELLED;
-			}
-			else {
-				BLI_assert(0);
-			}
-			WM_event_add_mousemove(C); /* update highlight */
-			outliner_item_drag_end(CTX_wm_window(C), data);
-			redraw = true;
-			break;
-		case MOUSEMOVE:
-			outliner_item_drag_handle(soops, ar, event, te_dragged);
-			redraw = true;
-			break;
-	}
-
-	if (redraw) {
-		if (skip_rebuild) {
-			ED_region_tag_redraw_no_rebuild(ar);
-		}
-		else {
-			ED_region_tag_redraw(ar);
-		}
-	}
-
-	return retval;
-}
-
-static const char *outliner_drag_drop_tooltip_get(
-        const TreeElement *te_float)
-{
-	const char *name = NULL;
-
-	const TreeElement *te_insert = te_float->drag_data->insert_handle;
-	if (te_float && outliner_is_collection_tree_element(te_float)) {
-		if (te_insert == NULL) {
-			name = TIP_("Move collection");
-		}
-		else {
-			switch (te_float->drag_data->insert_type) {
-				case TE_INSERT_BEFORE:
-					if (te_insert->prev && outliner_is_collection_tree_element(te_insert->prev)) {
-						name = TIP_("Move between collections");
-					}
-					else {
-						name = TIP_("Move before collection");
-					}
-					break;
-				case TE_INSERT_AFTER:
-					if (te_insert->next && outliner_is_collection_tree_element(te_insert->next)) {
-						name = TIP_("Move between collections");
-					}
-					else {
-						name = TIP_("Move after collection");
-					}
-					break;
-				case TE_INSERT_INTO:
-					name = TIP_("Move inside collection");
-					break;
-			}
-		}
-	}
-	else if ((TREESTORE(te_float)->type == 0) && (te_float->idcode == ID_OB)) {
-		name = TIP_("Move to collection (Ctrl to link)");
-	}
-
-	return name;
-}
-
-static void outliner_drag_drop_tooltip_cb(const wmWindow *win, void *vdata)
-{
-	OutlinerDragDropTooltip *data = vdata;
-	const char *tooltip;
-
-	int cursorx, cursory;
-	int x, y;
-
-	tooltip = outliner_drag_drop_tooltip_get(data->te);
-	if (tooltip == NULL) {
-		return;
-	}
-
-	cursorx = win->eventstate->x;
-	cursory = win->eventstate->y;
-
-	x = cursorx + U.widget_unit;
-	y = cursory - U.widget_unit;
-
-	/* Drawing. */
-	const uiFontStyle *fstyle = UI_FSTYLE_WIDGET;
-
-	const float col_fg[4] = {1.0f, 1.0f, 1.0f, 1.0f};
-	const float col_bg[4] = {0.0f, 0.0f, 0.0f, 0.2f};
-
-	GPU_blend(true);
-	UI_fontstyle_draw_simple_backdrop(fstyle, x, y, tooltip, col_fg, col_bg);
-	GPU_blend(false);
-}
-
-static int outliner_item_drag_drop_invoke(bContext *C, wmOperator *op, const wmEvent *event)
-{
-	ARegion *ar = CTX_wm_region(C);
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	TreeElement *te_dragged = outliner_item_drag_element_find(soops, ar, event);
-
-	if (!te_dragged) {
-		return (OPERATOR_FINISHED | OPERATOR_PASS_THROUGH);
-	}
-
-	OutlinerDragDropTooltip *data = MEM_mallocN(sizeof(OutlinerDragDropTooltip), __func__);
-	data->te = te_dragged;
-
-	op->customdata = data;
-	te_dragged->drag_data = MEM_callocN(sizeof(*te_dragged->drag_data), __func__);
-	/* by default we don't change the item position */
-	te_dragged->drag_data->insert_handle = te_dragged;
-	/* unset highlighted tree element, dragged one will be highlighted instead */
-	outliner_flag_set(&soops->tree, TSE_HIGHLIGHTED, false);
-
-	ED_region_tag_redraw_no_rebuild(ar);
-
-	WM_event_add_modal_handler(C, op);
-
-	data->handle = WM_draw_cb_activate(CTX_wm_window(C), outliner_drag_drop_tooltip_cb, data);
-
-	return OPERATOR_RUNNING_MODAL;
-}
-
-/**
- * Notes about Outliner Item Drag 'n Drop:
- * Right now only collections display mode is supported. But ideally all/most modes would support this. There are
- * just some open design questions that have to be answered: do we want to allow mixing order of different data types
- * (like render-layers and objects)? Would that be a purely visual change or would that have any other effect? ...
- */
-static void OUTLINER_OT_item_drag_drop(wmOperatorType *ot)
-{
-	ot->name = "Drag and Drop";
-	ot->idname = "OUTLINER_OT_item_drag_drop";
-	ot->description = "Change the hierarchical position of an item by repositioning it using drag and drop";
-
-	ot->invoke = outliner_item_drag_drop_invoke;
-	ot->modal = outliner_item_drag_drop_modal;
-
-	ot->poll = outliner_item_drag_drop_poll;
-
-	ot->flag = OPTYPE_UNDO;
-}
-
-
 /* ************************** registration **********************************/
 
 void outliner_operatortypes(void)
diff --git a/source/blender/editors/space_outliner/space_outliner.c b/source/blender/editors/space_outliner/space_outliner.c
index e4e99f88bf4..b0d63aee7c0 100644
--- a/source/blender/editors/space_outliner/space_outliner.c
+++ b/source/blender/editors/space_outliner/space_outliner.c
@@ -93,196 +93,6 @@ static void outliner_main_region_init(wmWindowManager *wm, ARegion *ar)
 	WM_event_add_dropbox_handler(&ar->handlers, lb);
 }
 
-static bool outliner_parent_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
-{
-	ARegion *ar = CTX_wm_region(C);
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	float fmval[2];
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	if (drag->type == WM_DRAG_ID) {
-		ID *id = drag->poin;
-		if (GS(id->name) == ID_OB) {
-			/* Ensure item under cursor is valid drop target */
-			TreeElement *te = outliner_dropzone_find(soops, fmval, true);
-			TreeStoreElem *tselem = te ? TREESTORE(te) : NULL;
-
-			if (!te) {
-				/* pass */
-			}
-			else if (te->idcode == ID_OB && tselem->type == 0) {
-				Scene *scene;
-				ID *te_id = tselem->id;
-
-				/* check if dropping self or parent */
-				if (te_id == id || (Object *)te_id == ((Object *)id)->parent)
-					return 0;
-
-				/* check that parent/child are both in the same scene */
-				scene = (Scene *)outliner_search_back(soops, te, ID_SCE);
-
-				/* currently outliner organized in a way that if there's no parent scene
-				 * element for object it means that all displayed objects belong to
-				 * active scene and parenting them is allowed (sergey)
-				 */
-				if (!scene) {
-					return 1;
-				}
-				else {
-					for (ViewLayer *view_layer = scene->view_layers.first;
-					     view_layer;
-					     view_layer = view_layer->next)
-					{
-						if (BKE_view_layer_base_find(view_layer, (Object *)id)) {
-							return 1;
-						}
-					}
-				}
-			}
-		}
-	}
-	return 0;
-}
-
-static void outliner_parent_drop_copy(wmDrag *drag, wmDropBox *drop)
-{
-	ID *id = drag->poin;
-
-	RNA_string_set(drop->ptr, "child", id->name + 2);
-}
-
-static bool outliner_parent_clear_poll(bContext *C, wmDrag *drag, const wmEvent *event)
-{
-	ARegion *ar = CTX_wm_region(C);
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	TreeElement *te = NULL;
-	float fmval[2];
-
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	if (!ELEM(soops->outlinevis, SO_VIEW_LAYER)) {
-		return false;
-	}
-
-	if (drag->type == WM_DRAG_ID) {
-		ID *id = drag->poin;
-		if (GS(id->name) == ID_OB) {
-			if (((Object *)id)->parent) {
-				if ((te = outliner_dropzone_find(soops, fmval, true))) {
-					TreeStoreElem *tselem = TREESTORE(te);
-
-					switch (te->idcode) {
-						case ID_SCE:
-							return (ELEM(tselem->type, TSE_R_LAYER_BASE, TSE_R_LAYER));
-						case ID_OB:
-							return (ELEM(tselem->type, TSE_MODIFIER_BASE, TSE_CONSTRAINT_BASE));
-						/* Other codes to ignore? */
-					}
-				}
-				return (te == NULL);
-			}
-		}
-	}
-	return 0;
-}
-
-static void outliner_parent_clear_copy(wmDrag *drag, wmDropBox *drop)
-{
-	ID *id = drag->poin;
-	RNA_string_set(drop->ptr, "dragged_obj", id->name + 2);
-
-	/* Set to simple parent clear type. Avoid menus for drag and drop if possible.
-	 * If desired, user can toggle the different "Clear Parent" types in the operator
-	 * menu on tool shelf. */
-	RNA_enum_set(drop->ptr, "type", 0);
-}
-
-static bool outliner_scene_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
-{
-	ARegion *ar = CTX_wm_region(C);
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	float fmval[2];
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	if (drag->type == WM_DRAG_ID) {
-		ID *id = drag->poin;
-		if (GS(id->name) == ID_OB) {
-			/* Ensure item under cursor is valid drop target */
-			TreeElement *te = outliner_dropzone_find(soops, fmval, false);
-			return (te && te->idcode == ID_SCE && TREESTORE(te)->type == 0);
-		}
-	}
-	return 0;
-}
-
-static void outliner_scene_drop_copy(wmDrag *drag, wmDropBox *drop)
-{
-	ID *id = drag->poin;
-
-	RNA_string_set(drop->ptr, "object", id->name + 2);
-}
-
-static bool outliner_material_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
-{
-	ARegion *ar = CTX_wm_region(C);
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	float fmval[2];
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	if (drag->type == WM_DRAG_ID) {
-		ID *id = drag->poin;
-		if (GS(id->name) == ID_MA) {
-			/* Ensure item under cursor is valid drop target */
-			TreeElement *te = outliner_dropzone_find(soops, fmval, true);
-			return (te && te->idcode == ID_OB && TREESTORE(te)->type == 0);
-		}
-	}
-	return 0;
-}
-
-static void outliner_material_drop_copy(wmDrag *drag, wmDropBox *drop)
-{
-	ID *id = drag->poin;
-
-	RNA_string_set(drop->ptr, "material", id->name + 2);
-}
-
-static bool outliner_collection_drop_poll(bContext *C, wmDrag *drag, const wmEvent *event)
-{
-	ARegion *ar = CTX_wm_region(C);
-	SpaceOops *soops = CTX_wm_space_outliner(C);
-	float fmval[2];
-	UI_view2d_region_to_view(&ar->v2d, event->mval[0], event->mval[1], &fmval[0], &fmval[1]);
-
-	if (drag->type == WM_DRAG_ID) {
-		ID *id = drag->poin;
-		if (ELEM(GS(id->name), ID_OB, ID_GR)) {
-			/* Ensure item under cursor is valid drop target */
-			TreeElement *te = outliner_dropzone_find(soops, fmval, true);
-			return (te && outliner_is_collection_tree_element(te));
-		}
-	}
-	return 0;
-}
-
-static void outliner_collection_drop_copy(wmDrag *drag, wmDropBox *drop)
-{
-	ID *id = drag->poin;
-	RNA_string_set(drop->ptr, "child", id->name + 2);
-}
-
-/* region dropbox definition */
-static void outliner_dropboxes(void)
-{
-	ListBase *lb = WM_dropboxmap_find("Outliner", SPACE_OUTLINER, RGN_TYPE_WINDOW);
-
-	WM_dropbox_add(lb, "OUTLINER_OT_parent_drop", outliner_parent_drop_poll, outliner_parent_drop_copy);
-	WM_dropbox_add(lb, "OUTLINER_OT_parent_clear", outliner_parent_clear_poll, outliner_parent_clear_copy);
-	WM_dropbox_add(lb, "OUTLINER_OT_scene_drop", outliner_scene_drop_poll, outliner_scene_drop_copy);
-	WM_dropbox_add(lb, "OUTLINER_OT_material_drop", outliner_material_drop_poll, outliner_material_drop_copy);
-	WM_dropbox_add(lb, "OUTLINER_OT_collection_drop", outliner_collection_drop_poll, outliner_collection_drop_copy);
-}
-
 static void outliner_main_region_draw(const bContext *C, ARegion *ar)
 {
 	View2D *v2d = &ar->v2d;