bug#25818: 25.2; frame moved off display does not return (OS X)

[martin rudalics <rudalics@gmx.at>]

 > No, I did not; thanks for the reminder.  In 24.3, with a second monitor
 > plugged in, (display-pixel-width) returns 1280, i.e. the width only of
 > my primary monitor.  In 24.4, in the same situation,
 > (display-pixel-width) returns 2330 = (+ 1280 1050).  Second monitor is
 > 1050 pixels wide.

So the problem occurs only with the second monitor plugged in?

 > In both the case of 24.3 and 24.4 with no external monitor attached,
 > (display-pixel-width) returns 1280.

And there is no problem in this case with 24.4?

 > So it seems that the code for `display-pixel-width' (or code that it
 > calls) was changed between those releases, maybe to support multiple
 > monitors.

The code was changed in two tranches

2013-05-20  YAMAMOTO Mitsuharu  <mituharu@math.s.chiba-u.ac.jp>

2013-07-04  YAMAMOTO Mitsuharu  <mituharu@math.s.chiba-u.ac.jp>

I'll CC him - maybe he can help us solving this issue in a more general
way.

 > I notice now that when running the test form on 24.3, the created frame
 > never actually leaves the visible portion of the screen.  For example,
 > when the code calls (sleep-for 1) with the frame supposedly being
 > offscreen according to its frame parameters (right before step 2), the
 > frame is in reality maybe 50 pixels left of the screen's right edge.
 > This is with just one monitor.  When I run the example with two
 > monitors, the frame just spills into the second monitor but does not go
 > further (since 24.3 does not seem to give correct values for
 > `display-pixel-width' with multiple monitors).

Do you mean that the value is already wrong for the primary monitor or
that the value simply does not account for the second monitor?

 > So it seems like there used to be code in Emacs that prevented a frame
 > from programmatically leaving the screen area in OS X.  For example, in
 > 24.3, if I call (modify-frame-parameters nil '((left . 10000))), the
 > frame is put, as above, about 50 pixels left of the screen's right edge.

In any case we have to change ediff-wind.el in order to fix the issue at
hand.

martin