bug#48409: Text runs away before user can copy it

[Alan Mackenzie]

Hello, Martin.

On Thu, May 20, 2021 at 18:54:45 +0200, martin rudalics wrote:
>  > For clicks into the bottom line the attached might help.  Clicks above
>  > must be caught elsewhere.  But you don't get a drag event and no error
>  > message for them.

> The attached patch should allow clicking anywhere in the minibuffer
> window.  Its more than kludgy but this is a bug that has annoyed me
> for years.

I've been laboriously working out a patch, too, and have come up with
the one below.  It takes a surprisingly similar approach to your own
patch [snipped], but doesn't test for a minibuffer, so perhaps is more
general.  I didn't actually study your patch till my own was nearly
finished.

To detect mouse movement, my patch changes from comparing window
relative x, y to frame relative x, y.  If the code detects no movement,
but a different window, the position of the up event is changed to be
inside the window of the down event.



diff --git a/src/keyboard.c b/src/keyboard.c
index 47b5e59024..08386e0685 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -5022,6 +5022,10 @@ static short const internal_border_parts[] = {
 
 static Lisp_Object button_down_location;
 
+/* A cons recording the original frame-relative x and y coordinates of
+   the down mouse event.  */
+static Lisp_Object frame_relative_event_pos;
+
 /* Information about the most recent up-going button event:  Which
    button, what location, and what time.  */
 
@@ -5673,6 +5677,7 @@ make_lispy_event (struct input_event *event)
              double_click_count = 1;
            button_down_time = event->timestamp;
            *start_pos_ptr = Fcopy_alist (position);
+           frame_relative_event_pos = Fcons (event->x, event->y);
            ignore_mouse_drag_p = false;
          }
 
@@ -5695,20 +5700,12 @@ make_lispy_event (struct input_event *event)
              ignore_mouse_drag_p = false;
            else
              {
-               Lisp_Object new_down, down;
                intmax_t xdiff = double_click_fuzz, ydiff = double_click_fuzz;
 
-               /* The third element of every position
-                  should be the (x,y) pair.  */
-               down = Fcar (Fcdr (Fcdr (start_pos)));
-               new_down = Fcar (Fcdr (Fcdr (position)));
-
-               if (CONSP (down)
-                   && FIXNUMP (XCAR (down)) && FIXNUMP (XCDR (down)))
-                 {
-                   xdiff = XFIXNUM (XCAR (new_down)) - XFIXNUM (XCAR (down));
-                   ydiff = XFIXNUM (XCDR (new_down)) - XFIXNUM (XCDR (down));
-                 }
+               xdiff = XFIXNUM (event->x)
+                 - XFIXNUM (XCAR (frame_relative_event_pos));
+               ydiff = XFIXNUM (event->y)
+                 - XFIXNUM (XCDR (frame_relative_event_pos));
 
                if (! (0 < double_click_fuzz
                       && - double_click_fuzz < xdiff
@@ -5725,12 +5722,51 @@ make_lispy_event (struct input_event *event)
                          a click.  But mouse-drag-region completely ignores
                          this case and it hasn't caused any real problem, so
                          it's probably OK to ignore it as well.  */
-                      && EQ (Fcar (Fcdr (start_pos)), Fcar (Fcdr (position)))))
+                      && (EQ (Fcar (Fcdr (start_pos)),
+                              Fcar (Fcdr (position))) /* Same buffer pos */
+                          || !EQ (Fcar (start_pos),
+                                  Fcar (position))))) /* Different window */
                  {
                    /* Mouse has moved enough.  */
                    button_down_time = 0;
                    click_or_drag_modifier = drag_modifier;
                  }
+               else if (((!EQ (Fcar (start_pos), Fcar (position)))
+                         || (!EQ (Fcar (Fcdr (start_pos)),
+                                  Fcar (Fcdr (position)))))
+                        /* Was the down event in a window body? */
+                        && FIXNUMP (Fcar (Fcdr (start_pos)))
+                        && WINDOW_LIVE_P (Fcar (start_pos))
+                        && Ffboundp (Qwindow_edges))
+                 /* If the window (etc.) at the mouse position has
+                    changed between the down event and the up event,
+                    we assume there's been a redisplay between the
+                    two events, and we pretend the mouse is still in
+                    the old window to prevent a spurious drag event
+                    being generated.  */
+                 {
+                   Lisp_Object edges
+                     = call4 (Qwindow_edges, Fcar (start_pos), Qt, Qnil, Qt);
+                   int new_x = XFIXNUM (Fcar (frame_relative_event_pos));
+                   int new_y = XFIXNUM (Fcdr (frame_relative_event_pos));
+
+                   /* If the up-event is outside the down-event's
+                      window, use coordinates that are within it.  */
+                   if (new_x < XFIXNUM (Fcar (edges)))
+                     new_x = XFIXNUM (Fcar (edges));
+                   else if (new_x >= XFIXNUM (Fcar (Fcdr (Fcdr (edges)))))
+                     new_x = XFIXNUM (Fcar (Fcdr (Fcdr (edges)))) - 1;
+                   if (new_y < XFIXNUM (Fcar (Fcdr (edges))))
+                     new_y = XFIXNUM (Fcar (Fcdr (edges)));
+                   else if (new_y
+                            >= XFIXNUM (Fcar (Fcdr (Fcdr (Fcdr (edges))))))
+                     new_y = XFIXNUM (Fcar (Fcdr (Fcdr (Fcdr (edges))))) - 1;
+
+                   position = make_lispy_position
+                     (XFRAME (event->frame_or_window),
+                      make_fixnum (new_x), make_fixnum (new_y),
+                      event->timestamp);
+                 }
              }
 
            /* Don't check is_double; treat this as multiple if the
@@ -11649,6 +11685,7 @@ syms_of_keyboard (void)
   DEFSYM (Qmake_frame_visible, "make-frame-visible");
   DEFSYM (Qselect_window, "select-window");
   DEFSYM (Qselection_request, "selection-request");
+  DEFSYM (Qwindow_edges, "window-edges");
   {
     int i;
 
@@ -11665,6 +11702,7 @@ syms_of_keyboard (void)
 
   button_down_location = make_nil_vector (5);
   staticpro (&button_down_location);
+  staticpro (&frame_relative_event_pos);
   mouse_syms = make_nil_vector (5);
   staticpro (&mouse_syms);
   wheel_syms = make_nil_vector (ARRAYELTS (lispy_wheel_names));


> martin

-- 
Alan Mackenzie (Nuremberg, Germany).