Send drop complete events when the drop leaves the window on Cocoa, Wayland, and X11

This is already done on win32, however, other platforms were left in a state of limbo if a drop operation began, then never completed due to the drop leaving the window.

src/video/cocoa/SDL_cocoawindow.m

@@ -88,6 +88,7 @@
 
 // Handle drag-and-drop of files onto the SDL window.
 - (NSDragOperation)draggingEntered:(id<NSDraggingInfo>)sender;
+- (void)draggingExited:(id<NSDraggingInfo>)sender;
 - (NSDragOperation)draggingUpdated:(id<NSDraggingInfo>)sender;
 - (BOOL)performDragOperation:(id<NSDraggingInfo>)sender;
 - (BOOL)wantsPeriodicDraggingUpdates;
@@ -174,6 +175,12 @@
     return NSDragOperationNone; // no idea what to do with this, reject it.
 }
 
+- (void)draggingExited:(id<NSDraggingInfo>)sender
+{
+    SDL_Window *sdlwindow = [self findSDLWindow];
+    SDL_SendDropComplete(sdlwindow);
+}
+
 - (NSDragOperation)draggingUpdated:(id<NSDraggingInfo>)sender
 {
     if (([sender draggingSourceOperationMask] & NSDragOperationGeneric) == NSDragOperationGeneric) {

src/video/wayland/SDL_waylandevents.c

@@ -2134,6 +2134,7 @@ static void data_device_handle_leave(void *data, struct wl_data_device *wl_data_
 
     if (data_device->drag_offer) {
         if (data_device->dnd_window) {
+            SDL_SendDropComplete(data_device->dnd_window);
             SDL_LogTrace(SDL_LOG_CATEGORY_INPUT,
                          ". In wl_data_device_listener . data_device_handle_leave on data_offer 0x%08x from window %d for serial %d\n",
                          WAYLAND_wl_proxy_get_id((struct wl_proxy *)data_device->drag_offer->offer),

src/video/x11/SDL_x11events.c

@@ -1384,7 +1384,6 @@ static void X11_DispatchEvent(SDL_VideoDevice *_this, XEvent *xevent)
         // Have we been requested to quit (or another client message?)
     case ClientMessage:
     {
-
         static int xdnd_version = 0;
 
         if (xevent->xclient.message_type == videodata->atoms.XdndEnter) {
@@ -1409,6 +1408,11 @@ static void X11_DispatchEvent(SDL_VideoDevice *_this, XEvent *xevent)
                 // pick from list of three
                 data->xdnd_req = X11_PickTargetFromAtoms(display, xevent->xclient.data.l[2], xevent->xclient.data.l[3], xevent->xclient.data.l[4]);
             }
+        } else if (xevent->xclient.message_type == videodata->atoms.XdndLeave) {
+#ifdef DEBUG_XEVENTS
+            SDL_Log("XID of source window : 0x%lx\n", xevent->xclient.data.l[0]);
+#endif
+            SDL_SendDropComplete(data->window);
         } else if (xevent->xclient.message_type == videodata->atoms.XdndPosition) {
 
 #ifdef DEBUG_XEVENTS

src/video/x11/SDL_x11video.c

@@ -391,6 +391,7 @@ static bool X11_VideoInit(SDL_VideoDevice *_this)
     GET_ATOM(SDL_FORMATS);
     GET_ATOM(XdndAware);
     GET_ATOM(XdndEnter);
+    GET_ATOM(XdndLeave);
     GET_ATOM(XdndPosition);
     GET_ATOM(XdndStatus);
     GET_ATOM(XdndTypeList);

src/video/x11/SDL_x11video.h

@@ -103,6 +103,7 @@ struct SDL_VideoData
         Atom SDL_FORMATS;
         Atom XdndAware;
         Atom XdndEnter;
+        Atom XdndLeave;
         Atom XdndPosition;
         Atom XdndStatus;
         Atom XdndTypeList;