Re: window groups

[martin rudalics]

> When a temporary window or a pop-up created by splitting the root
> of a frame is deleted *and* the user hasn't otherwise touched the
> window configuration, *then* precise sizes should be restored.
> So, if a user resizes a frame or explicitly resizes, deletes, or splits
> a window it doesn't matter as much.   But if none of those things have
> happened since the pop-up, the precise sizes should be restored.

Yes.  `set-window-configuration' frequently restores a configuration
without users noticing.

> Currently, if you delete one of the windows in (say) a horizontal
> stack, then by default the new space is allocated proportionally among
> the remaining windows.

When you delete a window its space is only given to the window above or
on the left (if no such window exists it's given to the window below or
on the right).  I once thought about changing that behavior in the way
you describe it but realized that it wouldn't make sense for temporary
windows you want to get rid off soon.

> That won't always DTRT in the case of
> pop-ups that split the root of the frame.   For example, before the
> pop-up, a stack of windows may have each had an exactly equal
> number of lines.   When the pop-up appears, the remaining lines
> might not divide evenly among the other windows in the stack -
> so they are no longer all the same size.   When the pop-up disappears,
> Emacs won't always restore them to be all the same size.

What you describe here is what happens when you delete a window and the
window above/on the left (below/on the right) is an internal window.  In
that case subwindows are resized proportionally.  Small windows that are
not fixed-size may get larger than they were before creating the window
you delete.

> That's the case I was talking about fixing and I was talking about
> fixing it only in a very narrow case: that the user hasn't done anything
> to change the window configuration other than triggering the pop-up
> window and then dismissing the pop-up window.

But that's the typical use case of `save-window-excursion'.  Or am I
missing something?

> For various reasons I found the original description really difficult
> to understand and believe in.   Other people have already pointed out
> some ways in which it "isn't lispy".   I would add that it is pretty
> complicated but only a weak rationale is given for the complexity.
> It's complicated because it adds 3 parameters (that seem hard to
> explain) to split-window.

The SAFE argument is something I need to get rid of these strange
window-min-height|width bindings you find in Elisp code.  These bindings
are misleading because people sometimes believe that they will prevent
the emanating windows from being deleted later on.  While the SAFE
parameter comes handy for resizing window groups these can happily live
without it.

The INVERT argument is used for creating the new window on the "other
side" of the original window.  I could merge it into the HORIZONTAL
parameter by providing two new values 'left and 'above in addition to
nil and t and we are left with one argument I have to add.

One additional argument would be needed anyway if you want to split the
frame root window instead of a visible one.

> It's complicated because it adds a new
> primitive concept (window groups) and that concept comes with
> non-intuitive restrictions (like the non-nesting of groups and the
> non-existence of single-window groups).

Rather, these restrictions simplify both semantics and implementation.
Try to write down the semantics of nested groups in a few sentences.
The single-window restriction can be removed (though talking about a
window group when there's only one window doesn't strike me as overly
intuitive).

> I take your word for it that, given those new features, you can implement
> something that looks a lot like certain other IDEs.   On the other hand,
> these features don't obviously have many other uses besides that - they
> aren't very "general," at least as far as I can tell from the description.

Well I use them all the time and I never use IDEs.

> Presumably you want to use the new features you're working on and then
> build higher-level application code to actually implement IDE features.
> Let's just assume that all of your higher level code (actual or planned) is
> just fine but ask: is there a simpler, more general substitute for the
> low-level
> changes?

I don't intend to implement any IDE features.  But I think that if and
when such features were integrated into Emacs it should be done in a
sane and safe way.

> Well, how about this?   Modify split-window with just one new additional
> parameter which, if that parameter is 'root, then a top-level split is
> implied.
> If that parameter is nil, current behavior is implied.   No other values
> for
> that parameter should be defined yet.
>
> I *suspect* (and its only a suspicion) that those alone are sufficient to
> accomplish everything you are trying to do with window groups, without
> even very much pain (and, perhaps with some added flexibility).

Modifying `split-window' to do what I described was straightforward.
The only twist was writing a subroutine to shift edges of subwindows
appropriately - something you have to do anyway when you split the frame
root window.

The more complicated part was cloning a configuration previously saved
by `current-window-configuration'.  People asked for such a thing
although I personally don't use it.

> Not to confuse things too much but let me also suggest how, in the future,
> the new split-window parameter that might be 'root could take on other
> values.   Every window is conceptually part of both a horizontal and

I suppose you mean "either" here not "both".

> vertical stack of windows, containing 1 or more windows. One possibility
> is that if the new split-window parameter is a window, then the pop-up
> splits off the entire horizontal or vertical stack of which that window is
> a part.   This is a sneaky way to "expose the window tree to lisp" as
> Mile's
> puts it.   (Additional sneakiness would be a function that, given a window,
> returns an ordered list of all windows in the same horizontal or vertical
> stack.)

Would be very easy to implement but hardly useful.  People don't think
in terms of "stacks of windows".  That's why I propose groups as some
sort of abstraction.

> That would have use in IDE-style interfaces.   For example, suppose that
> down the screen on the left are a series of narrow "navigation" windows
> and on the right there is an edit area, an interaction area, and a debugger
> area.    A "help window pop-up" could usefully be constrained to take
> up space just on the right of the screen.   That would be a natural
> generalization
> of using 'root and having it take up space on the whole screen.

If your edit area were split horizontally you'd be stuck.  My proposal
defines the edit area as a group and you will get your "help window"
below (or above) that group.