bug#5703: 23.1.92; `x-show-tip' and `tooltip-frame-parameters' do not respect `left' and `top'

[Eli Zaretskii <eliz@gnu.org>]

> From: Chong Yidong <cyd@stupidchicken.com>
> Date: Sat, 13 Mar 2010 15:15:12 -0500
> Cc: 5703@debbugs.gnu.org
> 
> "Drew Adams" <drew.adams@oracle.com> wrote:
> 
> > M-: (x-show-tip "aaaaaaaa" (selected-frame) '((left . 30) (top . 40)) 10 0 0)
> >
> > Instead of displaying the tooltip frame at the absolute
> > location specified by `left' and `top', it always displays it at the mouse
> > position plus the DX and DY (0 and 0 here).
> 
> This is reported to be a regression against Emacs 22.  Unfortunately,
> it's Windows-only, and I can't reproduce it.  Could someone with access
> to a Windows box give it a shot?

I think the small patch below fixes this.  But since this is about
pretest, I would like second opinion on that from anyone who is
familiar with this stuff (not only on MS-Windows).  In particular, I'd
like to hear from Jason.

Please also try the patched version in as many different use-cases as
you can, to make sure it doesn't break anything.

Here's what I found to be the reason of the bug:

compute_tip_xy relies on the tip frame's parameters (passed to it
through the `parms' argument) for figuring out where to display the
tooltip.  But by the time compute_tip_xy is called, the `top' and
`left' parameters were already removed from `parms'.  That's because
x_create_tip_frame, called a few lines before that, calls
x_figure_window_size, which sets up f->top_pos and f->left_pos from
`top' and `left', and as a side effect removes them from the frame's
parameters alist.

I see almost identical code in xfns.c versions of these functions, so
I'd be interested to hear how come the X version does not suffer from
the same problem.  That's because the patch below, although it does
the job, feels a bit kludgey, and I wonder if there a cleaner way.

=== modified file 'src/w32fns.c'
--- src/w32fns.c	2010-01-13 08:35:10 +0000
+++ src/w32fns.c	2010-03-30 12:57:13 +0000
@@ -5927,6 +5927,10 @@ Text larger than the specified size is c
   /* Move the tooltip window where the mouse pointer is.  Resize and
      show it.  */
   compute_tip_xy (f, parms, dx, dy, width, height, &root_x, &root_y);
+  if (f->top_pos)
+    root_y = f->top_pos;
+  if (f->left_pos)
+    root_x = f->left_pos;
 
   {
     /* Adjust Window size to take border into account.  */