Another one for drag and drop:

Allow dropping image files from outside blender, or image datablocks from inside blender
to the compositing node editor, to add an image node.

Also small tweak: Only set 'path' properties on drops, if the drag->path isn't empty.

source/blender/editors/space_node/node_edit.c

@@ -2030,4 +2030,86 @@ void NODE_OT_show_cyclic_dependencies(wmOperatorType *ot)
 	ot->flag= OPTYPE_REGISTER|OPTYPE_UNDO;
 }
 
+/* ****************** Add File Node Operator  ******************* */
+
+static int node_add_file_exec(bContext *C, wmOperator *op)
+{
+	Scene *scene= CTX_data_scene(C);
+	SpaceNode *snode= CTX_wm_space_node(C);
+	bNode *node;
+	Image *ima= NULL;
+	int ntype=0;
+
+	/* check input variables */
+	if (RNA_property_is_set(op->ptr, "path"))
+	{
+		char path[FILE_MAX];
+		RNA_string_get(op->ptr, "path", path);
+		ima= BKE_add_image_file(path, scene ? scene->r.cfra : 1);
+	}
+	else if(RNA_property_is_set(op->ptr, "name"))
+	{
+		char name[32];
+		RNA_string_get(op->ptr, "name", name);
+		ima= (Image *)find_id("IM", name);
+	}
+	
+	if(!ima) {
+		BKE_report(op->reports, RPT_ERROR, "Not an Image.");
+		return OPERATOR_CANCELLED;
+	}
+	
+	
+	node_deselectall(snode);
+	
+	if (snode->nodetree->type==NTREE_COMPOSIT)
+		ntype = CMP_NODE_IMAGE;
+	
+	node = node_add_node(snode, scene, ntype, snode->mx, snode->my);
+	
+	if (!node) {
+		BKE_report(op->reports, RPT_ERROR, "Could not add an image node.");
+		return OPERATOR_CANCELLED;
+	}
+	
+	node->id = (ID *)ima;
+	
+	snode_notify(C, snode);
+	
+	return OPERATOR_FINISHED;
+}
+
+static int node_add_file_invoke(bContext *C, wmOperator *op, wmEvent *event)
+{
+	ARegion *ar= CTX_wm_region(C);
+	SpaceNode *snode= CTX_wm_space_node(C);
+	
+	/* convert mouse coordinates to v2d space */
+	UI_view2d_region_to_view(&ar->v2d, event->x - ar->winrct.xmin, event->y - ar->winrct.ymin, 
+							 &snode->mx, &snode->my);
+	
+	if (RNA_property_is_set(op->ptr, "path") || RNA_property_is_set(op->ptr, "name"))
+		return node_add_file_exec(C, op);
+	else
+		return WM_operator_filesel(C, op, event);
+}
+
+void NODE_OT_add_file(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name= "Add File Node";
+	ot->description= "Add a file node to the current node editor";
+	ot->idname= "NODE_OT_add_file";
+	
+	/* callbacks */
+	ot->exec= node_add_file_exec;
+	ot->invoke= node_add_file_invoke;
+	ot->poll= ED_operator_node_active;
+	
+	/* flags */
+	ot->flag= OPTYPE_REGISTER|OPTYPE_UNDO;
+	
+	WM_operator_properties_filesel(ot, FOLDERFILE|IMAGEFILE, FILE_SPECIAL, FILE_OPENFILE);
+	RNA_def_string(ot->srna, "name", "Image", 24, "Name", "Datablock name to assign.");
+}
 

source/blender/editors/space_node/node_intern.h

@@ -108,6 +108,8 @@ void NODE_OT_read_renderlayers(struct wmOperatorType *ot);
 void NODE_OT_backimage_move(struct wmOperatorType *ot);
 void NODE_OT_backimage_zoom(struct wmOperatorType *ot);
 
+void NODE_OT_add_file(struct wmOperatorType *ot);
+
 // XXXXXX
 
 // XXX from BSE_node.h

source/blender/editors/space_node/node_ops.c

@@ -77,6 +77,8 @@ void node_operatortypes(void)
 	
 	WM_operatortype_append(NODE_OT_backimage_move);
 	WM_operatortype_append(NODE_OT_backimage_zoom);
+	
+	WM_operatortype_append(NODE_OT_add_file);
 }
 
 void ED_operatormacros_node(void)

source/blender/editors/space_node/space_node.c

@@ -53,6 +53,7 @@
 #include "WM_api.h"
 #include "WM_types.h"
 
+#include "UI_resources.h"
 #include "UI_view2d.h"
 
 #include "RNA_access.h"
@@ -263,6 +264,7 @@ static void node_buttons_area_draw(const bContext *C, ARegion *ar)
 static void node_main_area_init(wmWindowManager *wm, ARegion *ar)
 {
 	wmKeyMap *keymap;
+	ListBase *lb;
 	
 	UI_view2d_region_reinit(&ar->v2d, V2D_COMMONVIEW_CUSTOM, ar->winx, ar->winy);
 	
@@ -272,6 +274,11 @@ static void node_main_area_init(wmWindowManager *wm, ARegion *ar)
 	
 	keymap= WM_keymap_find(wm->defaultconf, "Node Editor", SPACE_NODE, 0);
 	WM_event_add_keymap_handler_bb(&ar->handlers, keymap, &ar->v2d.mask, &ar->winrct);
+	
+	/* add drop boxes */
+	lb = WM_dropboxmap_find("Node Editor", SPACE_NODE, RGN_TYPE_WINDOW);
+	
+	WM_event_add_dropbox_handler(&ar->handlers, lb);
 }
 
 static void node_main_area_draw(const bContext *C, ARegion *ar)
@@ -281,6 +288,47 @@ static void node_main_area_draw(const bContext *C, ARegion *ar)
 	drawnodespace(C, ar, v2d);
 }
 
+
+/* ************* dropboxes ************* */
+
+static int node_drop_poll(bContext *C, wmDrag *drag, wmEvent *event)
+{
+	if(drag->type==WM_DRAG_ID) {
+		ID *id= (ID *)drag->poin;
+		if( GS(id->name)==ID_IM )
+			return 1;
+	}
+	else if(drag->type==WM_DRAG_PATH){
+		if(ELEM(drag->icon, 0, ICON_FILE_IMAGE))	/* rule might not work? */
+			return 1;
+	}
+	return 0;
+}
+
+static void node_id_path_drop_copy(wmDrag *drag, wmDropBox *drop)
+{
+	ID *id= (ID *)drag->poin;
+	
+	if(id) {
+		RNA_string_set(drop->ptr, "name", id->name+2);
+	}
+	if (drag->path[0]) {
+		RNA_string_set(drop->ptr, "path", drag->path);
+	}
+}
+
+/* this region dropbox definition */
+static void node_dropboxes(void)
+{
+	ListBase *lb= WM_dropboxmap_find("Node Editor", SPACE_NODE, RGN_TYPE_WINDOW);
+	
+	WM_dropbox_add(lb, "NODE_OT_add_file", node_drop_poll, node_id_path_drop_copy);
+	
+}
+
+/* ************* end drop *********** */
+
+
 /* add handlers, stuff you only do once or on area/region changes */
 static void node_header_area_init(wmWindowManager *wm, ARegion *ar)
 {
@@ -366,6 +414,7 @@ void ED_spacetype_node(void)
 	st->listener= node_area_listener;
 	st->refresh= node_area_refresh;
 	st->context= node_context;
+	st->dropboxes = node_dropboxes;
 	
 	/* regions: main window */
 	art= MEM_callocN(sizeof(ARegionType), "spacetype node region");

source/blender/editors/space_view3d/space_view3d.c

@@ -453,7 +453,7 @@ static void view3d_id_path_drop_copy(wmDrag *drag, wmDropBox *drop)
 	
 	if(id)
 		RNA_string_set(drop->ptr, "name", id->name+2);
-	if(drag->path) 
+	if(drag->path[0]) 
 		RNA_string_set(drop->ptr, "path", drag->path);
 }