Re: Simplification to mouse-avoidance-mode (patch) + redisplay bug?

[Kim F. Storm]

Jan Djärv <address@hidden> writes:

> Kim F. Storm skrev:
>
>> I've debugged this far -- and need an X-pert (Jan?) to take over:
>>
>>
>> mouse-avoidance-mode 'animate uses set-mouse-position to move
>> the mouse cursor in ~10 steps to reach its end position.
>>
>> If I type very slowly, approaching the window cursor to the mouse
>> cursor -- and don't type anything while the mouse cursor is moving,
>> everything works, i.e. the mouse cursor shape at the final destination
>> is ok.
>>
>> If I type more quickly, the mouse cursor still moves in steps, but
>> it may end up with any of the cursor shapes it had along the path.
>>
>> I put some trace output into xterm.c, and it seems that (in the first
>> case) for each call to x_set_mouse_position (which calls
>> XWarpPointer), the event loop receives a MotionNotify event
>> (event.type = 6) with the new mouse cursor position.
>>
>> .. unless I hit a key while the mouse is moving (the second case).
>>
>> As soon as emacs gets the key event (event.type = 2), no further
>> MotionNotify events are delivered for the remaining mouse positions
>> along the path.
>>
>> This looks like an X bug.  This is the Xfree server from redhat 9.0.
>
> Are you sure x_set_mouse_position is called?

I put trace output int x_set_mouse_position, and it definitely gets
called (several times).

>                                               When I hold down a key
> and let it repeat, mouse avoidance is not working at all
> (i.e. x_set_mouse_position is not called).  I suspect event processing
> takes all time so mouse avoidance does not get time to check where the
> cursor is.

mouse-avoidance-mode runs via the idle timer, so if your keyboard
repeats too fast, emacs probably never runs the timer.

>
> Another thing is that X is not guaranteed to deliver MotionNotify for
> every pixel the mouse moves through.

Sure -- but it should deliver events for the (discrete) positions
set via XWarpPointer (according to the docs).

>                                       It is actually undefined how
> many MotionNotify you will get when moiving the mouse, but you are
> guaranteed to get one MotionNotify when the mouse movement stops.

The problem is that the MotionNotify event that you get is not the
final mouse position.

>
> A third thing to check is if the XWarpPointer requests are queued or
> not.  You can add a call to XFlush after XWarpPointer and see if that
> improves the situation.

It actually makes the situation worse -- now the final mouse shape
is wrong also when I type slowly, i.e. when I don't hit a key after
the mouse cursor starts moving.

>
> I tried, but could not reproduce the situation where the cursor shape
> is wrong.  I'm sure it is timing related, i.e. events not sent or
> received when expected to.

So, it is probably a bug in the (old) version of Xfree that I'm using,
and it looks like the bug is fixed in later versions.


I tried to add an explicit call to note_mouse_highlight after the
call to XWarpPointer, and it definitely has a positive effect,
but even with that change, the pointer shape ends up wrong in
some cases.

I'm not sure how important it is to fix this, but there is 
a patch which works for me -- of course a similar change
is probably needed in x_set_mouse_pixel_position.

*** xterm.c     10 May 2006 16:58:38 +0200      1.910
--- xterm.c     11 May 2006 11:52:27 +0200      
***************
*** 226,231 ****
--- 226,233 ----
  
  static unsigned long ignore_next_mouse_click_timeout;
  
+ static int ignore_next_motion_event;
+ 
  /* Mouse movement.
  
     Formerly, we used PointerMotionHintMask (in standard_event_mask)
***************
*** 6543,6548 ****
--- 6545,6556 ----
  
      case MotionNotify:
        {
+       if (ignore_next_motion_event)
+         {
+           ignore_next_motion_event = 0;
+           goto OTHER;
+         }
+ 
          previous_help_echo_string = help_echo_string;
          help_echo_string = Qnil;
  
***************
*** 8453,8458 ****
--- 8461,8471 ----
  
    XWarpPointer (FRAME_X_DISPLAY (f), None, FRAME_X_WINDOW (f),
                0, 0, 0, 0, pix_x, pix_y);
+ 
+   last_mouse_motion_event.x = pix_x;
+   last_mouse_motion_event.y = pix_y;
+   note_mouse_movement (f, &last_mouse_motion_event);
+   ignore_next_motion_event = 1;
    UNBLOCK_INPUT;
  }
  
***************
*** 10795,10800 ****
--- 10808,10814 ----
    last_tool_bar_item = -1;
    any_help_event_p = 0;
    ignore_next_mouse_click_timeout = 0;
+   ignore_next_motion_event = 0;
  #ifdef HAVE_X_SM
    x_session_initialized = 0;
  #endif

--
Kim F. Storm <address@hidden> http://www.cua.dk