* mouse.el (mouse-drag-region): Correctly handle drags which enter

	other frames.

1 files changed, 40 insertions, 24 deletions

diff --git a/lisp/mouse.el b/lisp/mouse.el
index 100860f9fbe..592d2b79458 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -161,6 +161,7 @@ This must be bound to a button-down mouse event."
   (let* ((start-posn (event-start start-event))
          (start-point (posn-point start-posn))
          (start-window (posn-window start-posn))
+         (start-frame (window-frame start-window))
          (bounds (window-edges start-window))
          (top (nth 1 bounds))
          (bottom (if (window-minibuffer-p start-window)
@@ -176,30 +177,45 @@ This must be bound to a button-down mouse event."
     (let (event end end-point)
       (track-mouse
         (while (progn
-                 (setq event (read-event)
-                       end (event-end event)
-                       end-point (posn-point end))
-                 (mouse-movement-p event))
-          ;; Is the mouse anywhere reasonable on the frame?
-          (if (windowp (posn-window end))
-              ;; If the mouse is outside the current window, scroll it.
-              (if (or (not (eq (posn-window end) start-window))
-                      (not (integer-or-marker-p end-point)))
-                  ;; Which direction should we scroll the window?
-                  (let ((mouse-row
-                         (+ (nth 1 (window-edges (posn-window end)))
-                            (cdr (posn-col-row end)))))
-                    (cond
-                     ((< mouse-row top)
-                      (mouse-scroll-subr
-                       (- mouse-row top) mouse-drag-overlay start-point))
-                     ((and (not (eobp))
-                           (>= mouse-row bottom))
-                      (mouse-scroll-subr (1+ (- mouse-row bottom))
-                                         mouse-drag-overlay start-point))))
-                (goto-char end-point)
-                (move-overlay mouse-drag-overlay
-                              start-point (point))))))
+                 (setq event (read-event))
+                 (or (mouse-movement-p event)
+                     (eq (car-safe event) 'switch-frame)))
+
+          (if (eq (car-safe event) 'switch-frame)
+              nil
+            (setq end (event-end event)
+                  end-point (posn-point end))
+
+            (cond
+
+             ;; Ignore switch-frame events.
+             ((eq (car-safe event) 'switch-frame))
+
+             ;; Are we moving within the original window?
+             ((and (eq (posn-window end) start-window)
+                   (integer-or-marker-p end-point))
+              (goto-char end-point)
+              (move-overlay mouse-drag-overlay
+                            start-point (point)))
+
+             ;; Are we moving on a different window on the same frame?
+             ((and (windowp (posn-window end))
+                   (eq (window-frame (posn-window end)) start-frame))
+              (let ((mouse-row
+                     (+ (nth 1 (window-edges (posn-window end)))
+                        (cdr (posn-col-row end)))))
+                (cond
+                 ((< mouse-row top)
+                  (mouse-scroll-subr
+                   (- mouse-row top) mouse-drag-overlay start-point))
+                 ((and (not (eobp))
+                       (>= mouse-row bottom))
+                  (mouse-scroll-subr (1+ (- mouse-row bottom))
+                                     mouse-drag-overlay start-point)))))
+
+             ;; Otherwise, we have no idea where the mouse is.
+             (t)))))
+
       (if (and (eq (get (event-basic-type event) 'event-kind) 'mouse-click)
                (eq (posn-window (event-end event)) start-window)
                (numberp (posn-point (event-end event))))