Fix drag-and-drop bugs on Lucid build

Also, optimize Fx_translate_coordinates to avoid excessive calls
to _XReply.

* lisp/x-dnd.el (x-dnd-get-drop-rectangle): Return empty drop
rectangle if posn-area.
* src/xfns.c (Fx_translate_coordinates): Accept arg
`require_child'.  If not set, allow optimizations based on
cached position data.
* src/xselect.c (x_handle_dnd_message): Use
x_translate_coordinates.
* src/xterm.c (x_translate_coordinates): Export function.
(x_handle_translate_coordinates): New function.
(handle_one_xevent): Fix coding style.
* src/xterm.h: Update prototypes.

1 files changed, 27 insertions, 3 deletions

diff --git a/src/xterm.c b/src/xterm.c
index 205c948c461..b061383a2ea 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -1143,7 +1143,6 @@ static Window x_get_window_below (Display *, Window, int, int, int *, int *);
 #ifndef USE_TOOLKIT_SCROLL_BARS
 static void x_scroll_bar_redraw (struct scroll_bar *);
 #endif
-static void x_translate_coordinates (struct frame *, int, int, int *, int *);
 
 /* Global state maintained during a drag-and-drop operation.  */
 
@@ -13658,7 +13657,7 @@ x_compute_root_window_offset (struct frame *f, int root_x, int root_y,
    many cases while handling events, which would otherwise result in
    slowdowns over slow network connections.  */
 
-static void
+void
 x_translate_coordinates (struct frame *f, int root_x, int root_y,
                          int *x_out, int *y_out)
 {
@@ -13731,6 +13730,31 @@ x_translate_coordinates_to_root (struct frame *f, int x, int y,
     }
 }
 
+/* Do x-translate-coordinates, but try to avoid a roundtrip to the X
+   server at the cost of not returning `child', which most callers
+   have no reason to use.  */
+
+Lisp_Object
+x_handle_translate_coordinates (struct frame *f, Lisp_Object dest_window,
+                                int source_x, int source_y)
+{
+  if (NILP (dest_window))
+    {
+      /* We are translating coordinates from a frame to the root
+         window.  Avoid a roundtrip if possible by using cached
+         coordinates.  */
+
+      if (!FRAME_X_OUTPUT (f)->window_offset_certain_p)
+        return Qnil;
+
+      return list3 (make_fixnum (source_x + FRAME_X_OUTPUT (f)->root_x),
+                    make_fixnum (source_y + FRAME_X_OUTPUT (f)->root_y),
+                    Qnil);
+    }
+
+  return Qnil;
+}
+
 /* The same, but for an XIDeviceEvent.  */
 
 #ifdef HAVE_XINPUT2
@@ -20826,7 +20850,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                                               event->xbutton.time);
                       }
                     else if (x_dnd_last_seen_window != None
-                        && x_dnd_last_protocol_version != -1)
+                             && x_dnd_last_protocol_version != -1)
                       {
                         x_dnd_pending_finish_target = x_dnd_last_seen_toplevel;
                         x_dnd_waiting_for_finish_proto = x_dnd_last_protocol_version;