Re: Coordinates and Windows

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 16 Jul 2015 09:14:25 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: emacs-devel@gnu.org
> 
> >> Currently we confuse the user.
> >
> > My suggestion attempts to remove that confusion, I think.
> 
> We'd expect users (like we currently do on Windows, Lucid and Motif) to
> care about tool bar dimensions when talking about window and frame
> coordinates.  Asking Gtk users to do the same would certainly not be met
> with great enthusiasm (once such a change had been installed).

I don't see why.  Having the top-left corner of the frame as the
reference point sounds simpler and more clear to me, and allows one to
use it in the same way in all the builds.  No?

> >> I'm not sure yet.  Coordinates on TTY frames are a separate issue,
> >> functions like `window-pixel-edges' don't make too much sense there.
> >
> > They still should work, to avoid complications in applications.
> 
> Actually, I started to look into this when I detected that it's
> virtually impossible to position a tooltip frame via `x-show-tip' at a
> window position obtained via `pos-visible-in-window-p' consistently on
> all platforms.
> 
> To illustrate how little care has been applied to this so far, consider
> the function `window-absolute-pixel-edges'.  With a maximized frame on
> Windows XP this function returns (-4 -4 1676 964) here.

I get (-8 28 1912 984) on Windows 7 and (-4 32 1916 1022) on XP, so at
least the Y coordinate seems OK.

> Apparently, this was designed for Gtk users, never really tested on
> other platforms.  But this also implies that changing things for Gtk
> might not be a good idea.

I don't follow the logic, can you elaborate why this implies what you
think it implies?  Are you saying that on GTK a maximized frame has
some of its GTK decorations off-screen?

> >>   > And don't forget that some modes, like gdb-mi, simulate the tool bar
> >>   > below the menu bar on TTY frames -- what about those?
> >>
> >> But if I'm not mistaken neither of these are windows.
> >
> > No, but their glyph rows still have coordinates.
> 
> Which implies that in order to build a glyph matrix we don't necessarily
> need a window.  So couldn't we do away with those pseudo-windows needed
> for tool and menu bars?

Not on GUI frames, no.  On text-mode frames we have per-frame glyph
matrices (and actually the glyph matrices of the windows are just
slices of their frame's matrix).  But on GUI frames, there's no frame
glyph matrix, so you need a window to be able to draw anything.

(And they are not pseudo-windows, btw; they are full-fledged windows,
they just display stuff that comes from strings generated by the
display engine, not from some buffer.)

> >> So usually the root window top line must be rounded which I dislike
> >> profoundly.  With a toolbar on the left I would then have to round the
> >> value of (window-left-column) on GTK as well.
> >
> > Why do we have to round, now that we have pixel-wise accuracy in
> > resizing windows and frames?
> 
> Because most programmers think (and applications work) in terms of rows
> and columns.  `window-edges' is still quite in use although it's bound
> to provide inaccurate results in many occasions now.

I'm afraid I still don't see why this requires rounding, especially if
the results are already inaccurate.  E.g., can we consider the menu
bar a single line, and the tool bar another N lines (N is usually 1,
but doesn't have to be).  IOW, can we treat each "row" of display in
these windows as a single line, for the purposes of counting rows?  If
not, why not?

> >> And then we would have still the problem that while for most builds we
> >> do not include the menu bar, we would have to include it when we draw it
> >> ourselves.  So the problem would be only partly solved.
> >
> > The only cases I know of are the TTY and non-toolkit X.  Are there any
> > others?  If not, these are special anyway, and could be handled
> > separately.
> 
> The non-toolkit X code is rather intertwingled with the non-GTK code so
> we'd certainly had to provide lots more of special casing than we do
> now.

Most special casing will be hidden behind macros and small functions,
so I see no particular problems here.  Of course, I might be missing
something.

> To coherently apply your proposal we would have to put the origin
> at the left upper corner of the menu bar - toolkit or not.

Yes, that's the idea.