Fix problems when dragging frames with the mouse

Re-implement 'mouse-drag-frame' via two new functions -
'mouse-drag-frame-resize' and 'mouse-drag-frame-move'.  This is
needed because with some toolkits the notifications for frame
movement and resizing arrive asynchronously, breaking any
calculations using intermediate frame sizes and positions.

* lisp/mouse.el (mouse-drag-mode-line, mouse-drag-left-edge)
(mouse-drag-top-left-corner, mouse-drag-top-edge)
(mouse-drag-top-right-corner, mouse-drag-right-edge)
(mouse-drag-bottom-right-corner, mouse-drag-bottom-edge)
(mouse-drag-bottom-left-corner): Call 'mouse-drag-frame-resize'
instead of 'mouse-drag-frame'.
(mouse-drag-frame): Split into two new functions -
'mouse-drag-frame-move' and 'mouse-drag-frame-resize'.
(mouse-drag-frame-resize, mouse-drag-frame-move): New functions
to implement functionality of the removed 'mouse-drag-frame'.

1 files changed, 292 insertions, 234 deletions

diff --git a/lisp/mouse.el b/lisp/mouse.el
index e58a2e6da18..9703d957d57 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -552,7 +552,7 @@ frame instead."
              (not (eq (window-frame minibuffer-window) frame))))
       ;; Drag frame when the window is on the bottom of its frame and
       ;; there is no minibuffer window below.
-      (mouse-drag-frame start-event 'move)))))
+      (mouse-drag-frame-move start-event)))))
 
 (defun mouse-drag-header-line (start-event)
   "Change the height of a window by dragging on its header line.
@@ -569,7 +569,7 @@ the frame instead."
         (mouse-drag-line start-event 'header)
       (let ((frame (window-frame window)))
         (when (frame-parameter frame 'drag-with-header-line)
-          (mouse-drag-frame start-event 'move))))))
+          (mouse-drag-frame-move start-event))))))
 
 (defun mouse-drag-vertical-line (start-event)
   "Change the width of a window by dragging on a vertical line.
@@ -577,46 +577,7 @@ START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
   (mouse-drag-line start-event 'vertical))
 
-(defun mouse-resize-frame (frame x-diff y-diff &optional x-move y-move)
-  "Helper function for `mouse-drag-frame'."
-  (let* ((frame-x-y (frame-position frame))
-         (frame-x (car frame-x-y))
-         (frame-y (cdr frame-x-y))
-         alist)
-    (if (> x-diff 0)
-        (when x-move
-          (setq x-diff (min x-diff frame-x))
-          (setq x-move (- frame-x x-diff)))
-      (let* ((min-width (frame-windows-min-size frame t nil t))
-             (min-diff (max 0 (- (frame-inner-width frame) min-width))))
-        (setq x-diff (max x-diff (- min-diff)))
-        (when x-move
-          (setq x-move (+ frame-x (- x-diff))))))
-
-    (if (> y-diff 0)
-        (when y-move
-          (setq y-diff (min y-diff frame-y))
-          (setq y-move (- frame-y y-diff)))
-      (let* ((min-height (frame-windows-min-size frame nil nil t))
-             (min-diff (max 0 (- (frame-inner-height frame) min-height))))
-        (setq y-diff (max y-diff (- min-diff)))
-        (when y-move
-          (setq y-move (+ frame-y (- y-diff))))))
-
-    (unless (zerop x-diff)
-      (when x-move
-        (push `(left . ,x-move) alist))
-      (push `(width . (text-pixels . ,(+ (frame-text-width frame) x-diff)))
-            alist))
-    (unless (zerop y-diff)
-      (when y-move
-        (push `(top . ,y-move) alist))
-      (push `(height . (text-pixels . ,(+ (frame-text-height frame) y-diff)))
-            alist))
-    (when alist
-      (modify-frame-parameters frame alist))))
-
-(defun mouse-drag-frame (start-event part)
+(defun mouse-drag-frame-resize (start-event part)
   "Drag a frame or one of its edges with the mouse.
 START-EVENT is the starting mouse event of the drag action.  Its
 position window denotes the frame that will be dragged.
@@ -635,9 +596,144 @@ frame with the mouse."
          (frame (if (window-live-p window)
                     (window-frame window)
                   window))
-         (width (frame-native-width frame))
-         (height (frame-native-height frame))
-         ;; PARENT is the parent frame of FRAME or, if FRAME is a
+         ;; Initial "first" frame position and size.  While dragging we
+         ;; base all calculations against that size and position.
+         (first-pos (frame-position frame))
+         (first-left (car first-pos))
+         (first-top (cdr first-pos))
+         (first-width (frame-text-width frame))
+         (first-height (frame-text-height frame))
+         ;; Don't let FRAME become less large than the size needed to
+         ;; fit all of its windows.
+         (min-text-width
+          (+ (frame-windows-min-size frame t nil t)
+             (- (frame-inner-width frame) first-width)))
+         (min-text-height
+          (+ (frame-windows-min-size frame nil nil t)
+             (- (frame-inner-height frame) first-height)))
+         ;; PARENT is the parent frame of FRAME or, if FRAME is a
+         ;; top-level frame, FRAME's workarea.
+         (parent (frame-parent frame))
+         (parent-edges
+          (if parent
+              (frame-edges parent)
+            (let* ((attributes
+                    (car (display-monitor-attributes-list)))
+                   (workarea (assq 'workarea attributes)))
+              (and workarea
+                   `(,(nth 1 workarea) ,(nth 2 workarea)
+                     ,(+ (nth 1 workarea) (nth 3 workarea))
+                     ,(+ (nth 2 workarea) (nth 4 workarea)))))))
+         (parent-left (and parent-edges (nth 0 parent-edges)))
+         (parent-top (and parent-edges (nth 1 parent-edges)))
+         (parent-right (and parent-edges (nth 2 parent-edges)))
+         (parent-bottom (and parent-edges (nth 3 parent-edges)))
+         ;; Drag types.  drag-left/drag-right and drag-top/drag-bottom
+         ;; are mutually exclusive.
+         (drag-left (memq part '(bottom-left left top-left)))
+         (drag-top (memq part '(top-left top top-right)))
+         (drag-right (memq part '(top-right right bottom-right)))
+         (drag-bottom (memq part '(bottom-right bottom bottom-left)))
+         ;; Initial "first" mouse position.  While dragging we base all
+         ;; calculations against that position.
+         (first-x-y (mouse-absolute-pixel-position))
+         (first-x (car first-x-y))
+         (first-y (cdr first-x-y))
+         (exitfun nil)
+         (move
+          (lambda (event)
+            (interactive "e")
+            (when (consp event)
+              (let* ((last-x-y (mouse-absolute-pixel-position))
+                     (last-x (car last-x-y))
+                     (last-y (cdr last-x-y))
+                     (left (- last-x first-x))
+                     (top (- last-y first-y))
+                     alist)
+                ;; We never want to warp the mouse position here.  When
+                ;; moving the mouse leftward or upward, then with a wide
+                ;; border the calculated left or top position of the
+                ;; frame could drop to a value less than zero depending
+                ;; on where precisely the mouse within the border.  We
+                ;; guard against this by never allowing the frame to
+                ;; move to a position less than zero here.  No such
+                ;; precautions are used for the right and bottom borders
+                ;; so with a large internal border parts of that border
+                ;; may disappear.
+                  (when (and drag-left (>= last-x parent-left)
+                             (>= (- first-width left) min-text-width))
+                    (push `(left . ,(max (+ first-left left) 0)) alist)
+                    (push `(width . (text-pixels . ,(- first-width left)))
+                          alist))
+                  (when (and drag-top (>= last-y parent-top)
+                             (>= (- first-height top) min-text-height))
+                    (push `(top . ,(max 0 (+ first-top top))) alist)
+                    (push `(height . (text-pixels . ,(- first-height top)))
+                          alist))
+                  (when (and drag-right (<= last-x parent-right)
+                             (>= (+ first-width left) min-text-width))
+                    (push `(width . (text-pixels . ,(+ first-width left)))
+                          alist))
+                  (when (and drag-bottom (<= last-y parent-bottom)
+                             (>= (+ first-height top) min-text-height))
+                    (push `(height . (text-pixels . ,(+ first-height top)))
+                          alist))
+                  (modify-frame-parameters frame alist)))))
+         (old-track-mouse track-mouse))
+    ;; Start tracking.  The special value 'dragging' signals the
+    ;; display engine to freeze the mouse pointer shape for as long
+    ;; as we drag.
+    (setq track-mouse 'dragging)
+    ;; Loop reading events and sampling the position of the mouse.
+    (setq exitfun
+          (set-transient-map
+           (let ((map (make-sparse-keymap)))
+             (define-key map [switch-frame] #'ignore)
+             (define-key map [select-window] #'ignore)
+             (define-key map [scroll-bar-movement] #'ignore)
+             (define-key map [mouse-movement] move)
+             ;; Swallow drag-mouse-1 events to avoid selecting some other window.
+             (define-key map [drag-mouse-1]
+               (lambda () (interactive) (funcall exitfun)))
+             ;; Some of the events will of course end up looked up
+             ;; with a mode-line, header-line or vertical-line prefix ...
+             (define-key map [mode-line] map)
+             (define-key map [header-line] map)
+             (define-key map [vertical-line] map)
+             ;; ... and some maybe even with a right- or bottom-divider
+             ;; prefix.
+             (define-key map [right-divider] map)
+             (define-key map [bottom-divider] map)
+             map)
+           t (lambda () (setq track-mouse old-track-mouse))))))
+
+(defun mouse-drag-frame-move (start-event)
+  "Drag a frame or one of its edges with the mouse.
+START-EVENT is the starting mouse event of the drag action.  Its
+position window denotes the frame that will be dragged.
+
+PART specifies the part that has been dragged and must be one of
+the symbols `left', `top', `right', `bottom', `top-left',
+`top-right', `bottom-left', `bottom-right' to drag an internal
+border or edge.  If PART equals `move', this means to move the
+frame with the mouse."
+  ;; Give temporary modes such as isearch a chance to turn off.
+  (run-hooks 'mouse-leave-buffer-hook)
+  (let* ((echo-keystrokes 0)
+         (start (event-start start-event))
+         (window (posn-window start))
+         ;; FRAME is the frame to drag.
+         (frame (if (window-live-p window)
+                    (window-frame window)
+                  window))
+         (native-width (frame-native-width frame))
+         (native-height (frame-native-height frame))
+         ;; Initial "first" frame position and size.  While dragging we
+         ;; base all calculations against that size and position.
+         (first-pos (frame-position frame))
+         (first-left (car first-pos))
+         (first-top (cdr first-pos))
+         ;; PARENT is the parent frame of FRAME or, if FRAME is a
          ;; top-level frame, FRAME's workarea.
          (parent (frame-parent frame))
          (parent-edges
@@ -654,19 +750,16 @@ frame with the mouse."
          (parent-top (and parent-edges (nth 1 parent-edges)))
          (parent-right (and parent-edges (nth 2 parent-edges)))
          (parent-bottom (and parent-edges (nth 3 parent-edges)))
-         ;; `pos-x' and `pos-y' record the x- and y-coordinates of the
-         ;; last sampled mouse position.  Note that we sample absolute
-         ;; mouse positions to avoid that moving the mouse from one
-         ;; frame into another gets into our way.  `last-x' and `last-y'
-         ;; records the x- and y-coordinates of the previously sampled
-         ;; position.  The differences between `last-x' and `pos-x' as
-         ;; well as `last-y' and `pos-y' determine the amount the mouse
-         ;; has been dragged between the last two samples.
-         pos-x-y pos-x pos-y
-         (last-x-y (mouse-absolute-pixel-position))
-         (last-x (car last-x-y))
-         (last-y (cdr last-x-y))
-         ;; `snap-x' and `snap-y' record the x- and y-coordinates of the
+         ;; Initial "first" mouse position.  While dragging we base all
+         ;; calculations against that position.
+         (first-x-y (mouse-absolute-pixel-position))
+         (first-x (car first-x-y))
+         (first-y (cdr first-x-y))
+         ;; `snap-width' (maybe also a yet to be provided `snap-height')
+         ;; could become floats to handle proportionality wrt PARENT.
+         ;; We don't do any checks on this parameter so far.
+         (snap-width (frame-parameter frame 'snap-width))
+         ;; `snap-x' and `snap-y' record the x- and y-coordinates of the
          ;; mouse position when FRAME snapped.  As soon as the
          ;; difference between `pos-x' and `snap-x' (or `pos-y' and
          ;; `snap-y') exceeds the value of FRAME's `snap-width'
@@ -678,176 +771,141 @@ frame with the mouse."
           (lambda (event)
             (interactive "e")
             (when (consp event)
-              (setq pos-x-y (mouse-absolute-pixel-position))
-              (setq pos-x (car pos-x-y))
-              (setq pos-y (cdr pos-x-y))
-              (cond
-               ((eq part 'left)
-                (mouse-resize-frame frame (- last-x pos-x) 0 t))
-               ((eq part 'top)
-                (mouse-resize-frame frame 0 (- last-y pos-y) nil t))
-               ((eq part 'right)
-                (mouse-resize-frame frame (- pos-x last-x) 0))
-               ((eq part 'bottom)
-                (mouse-resize-frame frame 0 (- pos-y last-y)))
-               ((eq part 'top-left)
-                (mouse-resize-frame
-                 frame (- last-x pos-x) (- last-y pos-y) t t))
-               ((eq part 'top-right)
-                (mouse-resize-frame
-                 frame (- pos-x last-x) (- last-y pos-y) nil t))
-               ((eq part 'bottom-left)
-                (mouse-resize-frame
-                 frame (- last-x pos-x) (- pos-y last-y) t))
-               ((eq part 'bottom-right)
-                (mouse-resize-frame
-                 frame (- pos-x last-x) (- pos-y last-y)))
-               ((eq part 'move)
-                (let* ((old-position (frame-position frame))
-                       (old-left (car old-position))
-                       (old-top (cdr old-position))
-                       (left (+ old-left (- pos-x last-x)))
-                       (top (+ old-top (- pos-y last-y)))
-                       right bottom
-                       ;; `snap-width' (maybe also a yet to be provided
-                       ;; `snap-height') could become floats to handle
-                       ;; proportionality wrt PARENT.  We don't do any
-                       ;; checks on this parameter so far.
-                       (snap-width (frame-parameter frame 'snap-width)))
-                  ;; Docking and constraining.
-                  (when (and (numberp snap-width) parent-edges)
+              (let* ((last-x-y (mouse-absolute-pixel-position))
+                     (last-x (car last-x-y))
+                     (last-y (cdr last-x-y))
+                     (left (- last-x first-x))
+                     (top (- last-y first-y))
+                     right bottom)
+                (setq left (+ first-left left))
+                (setq top (+ first-top top))
+                ;; Docking and constraining.
+                (when (and (numberp snap-width) parent-edges)
+                  (cond
+                   ;; Docking at the left parent edge.
+                   ((< last-x first-x)
                     (cond
-                     ;; Docking at the left parent edge.
-                     ((< pos-x last-x)
-                      (cond
-                       ((and (> left parent-left)
-                             (<= (- left parent-left) snap-width))
-                        ;; Snap when the mouse moved leftward and
-                        ;; FRAME's left edge would end up within
-                        ;; `snap-width' pixels from PARENT's left edge.
-                        (setq snap-x pos-x)
-                        (setq left parent-left))
-                       ((and (<= left parent-left)
-                             (<= (- parent-left left) snap-width)
-                             snap-x (<= (- snap-x pos-x) snap-width))
-                        ;; Stay snapped when the mouse moved leftward
-                        ;; but not more than `snap-width' pixels from
-                        ;; the time FRAME snapped.
-                        (setq left parent-left))
-                       (t
-                        ;; Unsnap when the mouse moved more than
-                        ;; `snap-width' pixels leftward from the time
-                        ;; FRAME snapped.
-                        (setq snap-x nil))))
-                     ((> pos-x last-x)
-                      (setq right (+ left width))
-                      (cond
-                       ((and (< right parent-right)
-                             (<= (- parent-right right) snap-width))
-                        ;; Snap when the mouse moved rightward and
-                        ;; FRAME's right edge would end up within
-                        ;; `snap-width' pixels from PARENT's right edge.
-                        (setq snap-x pos-x)
-                        (setq left (- parent-right width)))
-                       ((and (>= right parent-right)
-                             (<= (- right parent-right) snap-width)
-                             snap-x (<= (- pos-x snap-x) snap-width))
-                        ;; Stay snapped when the mouse moved rightward
-                        ;; but not more more than `snap-width' pixels
-                        ;; from the time FRAME snapped.
-                        (setq left (- parent-right width)))
-                       (t
-                        ;; Unsnap when the mouse moved rightward more
-                        ;; than `snap-width' pixels from the time FRAME
-                        ;; snapped.
-                        (setq snap-x nil)))))
-
+                     ((and (> left parent-left)
+                           (<= (- left parent-left) snap-width))
+                      ;; Snap when the mouse moved leftward and FRAME's
+                      ;; left edge would end up within `snap-width'
+                      ;; pixels from PARENT's left edge.
+                      (setq snap-x last-x)
+                      (setq left parent-left))
+                     ((and (<= left parent-left)
+                           (<= (- parent-left left) snap-width)
+                           snap-x (<= (- snap-x last-x) snap-width))
+                      ;; Stay snapped when the mouse moved leftward but
+                      ;; not more than `snap-width' pixels from the time
+                      ;; FRAME snapped.
+                      (setq left parent-left))
+                     (t
+                      ;; Unsnap when the mouse moved more than
+                      ;; `snap-width' pixels leftward from the time
+                      ;; FRAME snapped.
+                      (setq snap-x nil))))
+                   ((> last-x first-x)
+                    (setq right (+ left native-width))
                     (cond
-                     ((< pos-y last-y)
-                      (cond
-                       ((and (> top parent-top)
-                             (<= (- top parent-top) snap-width))
-                        ;; Snap when the mouse moved upward and FRAME's
-                        ;; top edge would end up within `snap-width'
-                        ;; pixels from PARENT's top edge.
-                        (setq snap-y pos-y)
-                        (setq top parent-top))
-                       ((and (<= top parent-top)
-                             (<= (- parent-top top) snap-width)
-                             snap-y (<= (- snap-y pos-y) snap-width))
-                        ;; Stay snapped when the mouse moved upward but
-                        ;; not more more than `snap-width' pixels from
-                        ;; the time FRAME snapped.
-                        (setq top parent-top))
-                       (t
-                        ;; Unsnap when the mouse moved upward more than
-                        ;; `snap-width' pixels from the time FRAME
-                        ;; snapped.
-                        (setq snap-y nil))))
-                     ((> pos-y last-y)
-                      (setq bottom (+ top height))
-                      (cond
-                       ((and (< bottom parent-bottom)
-                             (<= (- parent-bottom bottom) snap-width))
-                        ;; Snap when the mouse moved downward and
-                        ;; FRAME's bottom edge would end up within
-                        ;; `snap-width' pixels from PARENT's bottom
-                        ;; edge.
-                        (setq snap-y pos-y)
-                        (setq top (- parent-bottom height)))
-                       ((and (>= bottom parent-bottom)
-                             (<= (- bottom parent-bottom) snap-width)
-                             snap-y (<= (- pos-y snap-y) snap-width))
-                        ;; Stay snapped when the mouse moved downward
-                        ;; but not more more than `snap-width' pixels
-                        ;; from the time FRAME snapped.
-                        (setq top (- parent-bottom height)))
-                       (t
-                        ;; Unsnap when the mouse moved downward more
-                        ;; than `snap-width' pixels from the time FRAME
-                        ;; snapped.
-                        (setq snap-y nil))))))
-
-                  ;; If requested, constrain FRAME's draggable areas to
-                  ;; PARENT's edges.  The `top-visible' parameter should
-                  ;; be set when FRAME has a draggable header-line.  If
-                  ;; set to a number, it ascertains that the top of
-                  ;; FRAME is always constrained to the top of PARENT
-                  ;; and that at least as many pixels of FRAME as
-                  ;; specified by that number are visible on each of the
-                  ;; three remaining sides of PARENT.
-                  ;;
-                  ;; The `bottom-visible' parameter should be set when
-                  ;; FRAME has a draggable mode-line.  If set to a
-                  ;; number, it ascertains that the bottom of FRAME is
-                  ;; always constrained to the bottom of PARENT and that
-                  ;; at least as many pixels of FRAME as specified by
-                  ;; that number are visible on each of the three
-                  ;; remaining sides of PARENT.
-                  (let ((par (frame-parameter frame 'top-visible))
-                        bottom-visible)
-                    (unless par
-                      (setq par (frame-parameter frame 'bottom-visible))
-                      (setq bottom-visible t))
-                    (when (and (numberp par) parent-edges)
-                      (setq left
-                            (max (min (- parent-right par) left)
-                                 (+ (- parent-left width) par)))
-                      (setq top
-                            (if bottom-visible
-                                (min (max top (- parent-top (- height par)))
-                                     (- parent-bottom height))
-                              (min (max top parent-top)
-                                   (- parent-bottom par))))))
-
-                  ;; Use `modify-frame-parameters' since `left' and
-                  ;; `top' may want to move FRAME out of its PARENT.
-                  (modify-frame-parameters
-                   frame
-                   `((left . (+ ,left)) (top . (+ ,top)))))))
-              (setq last-x pos-x)
-              (setq last-y pos-y))))
-         (old-track-mouse track-mouse))
+                     ((and (< right parent-right)
+                           (<= (- parent-right right) snap-width))
+                      ;; Snap when the mouse moved rightward and FRAME's
+                      ;; right edge would end up within `snap-width'
+                      ;; pixels from PARENT's right edge.
+                      (setq snap-x last-x)
+                      (setq left (- parent-right native-width)))
+                     ((and (>= right parent-right)
+                           (<= (- right parent-right) snap-width)
+                           snap-x (<= (- last-x snap-x) snap-width))
+                      ;; Stay snapped when the mouse moved rightward but
+                      ;; not more more than `snap-width' pixels from the
+                      ;; time FRAME snapped.
+                      (setq left (- parent-right native-width)))
+                     (t
+                      ;; Unsnap when the mouse moved rightward more than
+                      ;; `snap-width' pixels from the time FRAME
+                      ;; snapped.
+                      (setq snap-x nil)))))
+                  (cond
+                   ((< last-y first-y)
+                    (cond
+                     ((and (> top parent-top)
+                           (<= (- top parent-top) snap-width))
+                      ;; Snap when the mouse moved upward and FRAME's
+                      ;; top edge would end up within `snap-width'
+                      ;; pixels from PARENT's top edge.
+                      (setq snap-y last-y)
+                      (setq top parent-top))
+                     ((and (<= top parent-top)
+                           (<= (- parent-top top) snap-width)
+                           snap-y (<= (- snap-y last-y) snap-width))
+                      ;; Stay snapped when the mouse moved upward but
+                      ;; not more more than `snap-width' pixels from the
+                      ;; time FRAME snapped.
+                      (setq top parent-top))
+                     (t
+                      ;; Unsnap when the mouse moved upward more than
+                      ;; `snap-width' pixels from the time FRAME
+                      ;; snapped.
+                      (setq snap-y nil))))
+                   ((> last-y first-y)
+                    (setq bottom (+ top native-height))
+                    (cond
+                     ((and (< bottom parent-bottom)
+                           (<= (- parent-bottom bottom) snap-width))
+                      ;; Snap when the mouse moved downward and FRAME's
+                      ;; bottom edge would end up within `snap-width'
+                      ;; pixels from PARENT's bottom edge.
+                      (setq snap-y last-y)
+                      (setq top (- parent-bottom native-height)))
+                     ((and (>= bottom parent-bottom)
+                           (<= (- bottom parent-bottom) snap-width)
+                           snap-y (<= (- last-y snap-y) snap-width))
+                      ;; Stay snapped when the mouse moved downward but
+                      ;; not more more than `snap-width' pixels from the
+                      ;; time FRAME snapped.
+                      (setq top (- parent-bottom native-height)))
+                     (t
+                      ;; Unsnap when the mouse moved downward more than
+                      ;; `snap-width' pixels from the time FRAME
+                      ;; snapped.
+                      (setq snap-y nil))))))
+
+                ;; If requested, constrain FRAME's draggable areas to
+                ;; PARENT's edges.  The `top-visible' parameter should
+                ;; be set when FRAME has a draggable header-line.  If
+                ;; set to a number, it ascertains that the top of FRAME
+                ;; is always constrained to the top of PARENT and that
+                ;; at least as many pixels of FRAME as specified by that
+                ;; number are visible on each of the three remaining
+                ;; sides of PARENT.
+                ;;
+                ;; The `bottom-visible' parameter should be set when
+                ;; FRAME has a draggable mode-line.  If set to a number,
+                ;; it ascertains that the bottom of FRAME is always
+                ;; constrained to the bottom of PARENT and that at least
+                ;; as many pixels of FRAME as specified by that number
+                ;; are visible on each of the three remaining sides of
+                ;; PARENT.
+                (let ((par (frame-parameter frame 'top-visible))
+                      bottom-visible)
+                  (unless par
+                    (setq par (frame-parameter frame 'bottom-visible))
+                    (setq bottom-visible t))
+                  (when (and (numberp par) parent-edges)
+                    (setq left
+                          (max (min (- parent-right par) left)
+                               (+ (- parent-left native-width) par)))
+                    (setq top
+                          (if bottom-visible
+                              (min (max top (- parent-top (- native-height par)))
+                                   (- parent-bottom native-height))
+                            (min (max top parent-top)
+                                 (- parent-bottom par))))))
+                ;; Use `modify-frame-parameters' since `left' and `top'
+                ;; may want to move FRAME out of its PARENT.
+                (modify-frame-parameters frame `((left . (+ ,left)) (top . (+ ,top))))))))
+         (old-track-mouse track-mouse))
     ;; Start tracking.  The special value 'dragging' signals the
     ;; display engine to freeze the mouse pointer shape for as long
     ;; as we drag.
@@ -879,49 +937,49 @@ frame with the mouse."
   "Drag left edge of a frame with the mouse.
 START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
-  (mouse-drag-frame start-event 'left))
+  (mouse-drag-frame-resize start-event 'left))
 
 (defun mouse-drag-top-left-corner (start-event)
   "Drag top left corner of a frame with the mouse.
 START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
-  (mouse-drag-frame start-event 'top-left))
+  (mouse-drag-frame-resize start-event 'top-left))
 
 (defun mouse-drag-top-edge (start-event)
   "Drag top edge of a frame with the mouse.
 START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
-  (mouse-drag-frame start-event 'top))
+  (mouse-drag-frame-resize start-event 'top))
 
 (defun mouse-drag-top-right-corner (start-event)
   "Drag top right corner of a frame with the mouse.
 START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
-  (mouse-drag-frame start-event 'top-right))
+  (mouse-drag-frame-resize start-event 'top-right))
 
 (defun mouse-drag-right-edge (start-event)
   "Drag right edge of a frame with the mouse.
 START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
-  (mouse-drag-frame start-event 'right))
+  (mouse-drag-frame-resize start-event 'right))
 
 (defun mouse-drag-bottom-right-corner (start-event)
   "Drag bottom right corner of a frame with the mouse.
 START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
-  (mouse-drag-frame start-event 'bottom-right))
+  (mouse-drag-frame-resize start-event 'bottom-right))
 
 (defun mouse-drag-bottom-edge (start-event)
   "Drag bottom edge of a frame with the mouse.
 START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
-  (mouse-drag-frame start-event 'bottom))
+  (mouse-drag-frame-resize start-event 'bottom))
 
 (defun mouse-drag-bottom-left-corner (start-event)
   "Drag bottom left corner of a frame with the mouse.
 START-EVENT is the starting mouse event of the drag action."
   (interactive "e")
-  (mouse-drag-frame start-event 'bottom-left))
+  (mouse-drag-frame-resize start-event 'bottom-left))
 
 (defcustom mouse-select-region-move-to-beginning nil
   "Effect of selecting a region extending backward from double click.