Broken tooltips with dual-head on MS Windows

[Neil Roberts <bpeeluk@yahoo.co.uk>]

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Hi,

I found a few problems with the positioning of tooltips when more than
one monitor is used under Windows. The current code seems to only take
into account the dimensions of the primary display so that for example
if the cursor is to the right of the primary display then it will
always think the tooltip doesn't fit and it will always move it to the
left of the cursor. Also, if there is a display to the left of the
primary display then all of the coordinates on that display are
negative but Emacs won't let the tooltip be positioned at a
co-ordinate less than zero so the tooltip is placed in the wrong
display.

I've made a little patch to the compute_tip_xy function to make it use
the multi-monitor API so that it can correctly position the tooltip
within the display containing the cursor. The API is checked for
dynamically using GetProcAddress so that it can still work under
Windows 95 where it isn't available. I'm not sure if the rest of Emacs
still supports Win95 so it could be tidied up if this isn't necessary.

Regards,
- Neil

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Index: src/w32fns.c
===================================================================
RCS file: /sources/emacs/emacs/src/w32fns.c,v
retrieving revision 1.290
diff -c -r1.290 w32fns.c
*** src/w32fns.c	15 Jul 2007 01:50:54 -0000	1.290
--- src/w32fns.c	21 Jul 2007 10:02:15 -0000
***************
*** 7458,7463 ****
--- 7458,7464 ----
       int *root_x, *root_y;
  {
    Lisp_Object left, top;
+   RECT monitor_rect;
  
    /* User-specified position?  */
    left = Fcdr (Fassq (Qleft, parms));
***************
*** 7468,7508 ****
    if (!INTEGERP (left) || !INTEGERP (top))
      {
        POINT pt;
  
        BLOCK_INPUT;
        GetCursorPos (&pt);
        *root_x = pt.x;
        *root_y = pt.y;
        UNBLOCK_INPUT;
      }
  
    if (INTEGERP (top))
      *root_y = XINT (top);
!   else if (*root_y + XINT (dy) <= 0)
!     *root_y = 0; /* Can happen for negative dy */
!   else if (*root_y + XINT (dy) + height <= FRAME_W32_DISPLAY_INFO (f)->height)
      /* It fits below the pointer */
!       *root_y += XINT (dy);
!   else if (height + XINT (dy) <= *root_y)
      /* It fits above the pointer.  */
      *root_y -= height + XINT (dy);
    else
      /* Put it on the top.  */
!     *root_y = 0;
  
    if (INTEGERP (left))
      *root_x = XINT (left);
!   else if (*root_x + XINT (dx) <= 0)
!     *root_x = 0; /* Can happen for negative dx */
!   else if (*root_x + XINT (dx) + width <= FRAME_W32_DISPLAY_INFO (f)->width)
      /* It fits to the right of the pointer.  */
      *root_x += XINT (dx);
!   else if (width + XINT (dx) <= *root_x)
      /* It fits to the left of the pointer.  */
      *root_x -= width + XINT (dx);
    else
      /* Put it left justified on the screen -- it ought to fit that way.  */
!     *root_x = 0;
  }
  
  
--- 7469,7538 ----
    if (!INTEGERP (left) || !INTEGERP (top))
      {
        POINT pt;
+       HMODULE user32;
+       void *(WINAPI * monitor_from_point) (POINT, DWORD);
+       BOOL (WINAPI * get_monitor_info) (void *, void *);
  
        BLOCK_INPUT;
        GetCursorPos (&pt);
        *root_x = pt.x;
        *root_y = pt.y;
+ 
+       /* Try to get the rectangle for the monitor around the point. If
+ 	 the monitor API is not available (eg, on Windows 95) then
+ 	 just assume there is only one monitor */
+       monitor_rect.left = 0;
+       monitor_rect.right = FRAME_W32_DISPLAY_INFO (f)->width;
+       monitor_rect.top = 0;
+       monitor_rect.bottom = FRAME_W32_DISPLAY_INFO (f)->height;
+       if ((user32 = LoadLibrary ("user32")))
+ 	{
+ 	  if ((monitor_from_point = (void *(WINAPI *) (POINT, DWORD))
+ 	       GetProcAddress (user32, "MonitorFromPoint"))
+ 	      && (get_monitor_info = (BOOL (WINAPI *) (void *, void*))
+ 		  GetProcAddress (user32, "GetMonitorInfoA")))
+ 	    {
+ 	      void *monitor;
+ 	      char buf[40 /* sizeof (MONITORINFO) */];
+ 	      *(DWORD *) buf = 40; /* set cbSize */
+ 	      monitor = (* monitor_from_point) (pt, 2 /* MONITOR_DEFAULTTONEAREST */);
+ 	      if ((* get_monitor_info) (monitor, buf))
+ 		monitor_rect = *(RECT *) (buf + sizeof (DWORD));
+ 	    }
+       
+ 	  FreeLibrary (user32);
+ 	}
+ 
        UNBLOCK_INPUT;
      }
  
    if (INTEGERP (top))
      *root_y = XINT (top);
!   else if (*root_y + XINT (dy) <= monitor_rect.top)
!     *root_y = monitor_rect.top; /* Can happen for negative dy */
!   else if (*root_y + XINT (dy) + height <= monitor_rect.bottom)
      /* It fits below the pointer */
!     *root_y += XINT (dy);
!   else if (*root_y - XINT (dy) - height >= monitor_rect.top)
      /* It fits above the pointer.  */
      *root_y -= height + XINT (dy);
    else
      /* Put it on the top.  */
!     *root_y = monitor_rect.top;
  
    if (INTEGERP (left))
      *root_x = XINT (left);
!   else if (*root_x + XINT (dx) <= monitor_rect.left)
!     *root_x = monitor_rect.left; /* Can happen for negative dx */
!   else if (*root_x + XINT (dx) + width <= monitor_rect.right)
      /* It fits to the right of the pointer.  */
      *root_x += XINT (dx);
!   else if (*root_x - width - XINT (dx) >= monitor_rect.left)
      /* It fits to the left of the pointer.  */
      *root_x -= width + XINT (dx);
    else
      /* Put it left justified on the screen -- it ought to fit that way.  */
!     *root_x = monitor_rect.left;
  }
  
  

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