bug#38013: [PATCH] Rectangular region selection with mouse

[martin rudalics]

> I don't think so; being able to select from a menu with a single
> dragging movement is not only more ergonomic, it's the expected
> behaviour of pop-up menus.

But by doing so it usurps all combinations of the control key and
mouse-1.  So we pay a high price for such a small convenience.  And
since I have never anywhere else seen a "context" menu pop up right
after a mouse press I would not consider it the expected behavior.

> mouse.el even contains a comment to that
> effect:
>
>   ;; By binding these to down-going events, we let the user use the up-going
>   ;; event to make the selection, saving a click.

In all those 25 or more years it hasn't found its way into the Emacs
manual though.

> You can try for yourself: with the patch applied, bind M-mouse-1 to a menu:
>
>   (global-set-key [M-mouse-1] 'mouse-buffer-menu)
>
> Now a single meta-click will open the menu, and meta-drag will mark
> a rectangle. This sort of multiplexing doesn't feel right, and
> affects both uses negatively.

But the same "multiplexing" already applies for operating the mouse
without any modifiers.  And I sometimes use it in a different context:
When I prematurely press the mouse button on a browser link, I can
always bow out by slightly moving the mouse, thus avoiding the
semantics of a click.

> For example, suppose you have marked a rectangle and change your
> mind. Intuitively, you will click somewhere to make the mark go
> away, using the same modifiers. But that doesn't work, because now
> you get a pop-up menu.

The menu should pop up iff the down and up events happen at the same
location.  Can we agree that this is hard to achieve after having
marked a rectangle?

> Emacs's mouse bindings seem rather haphazard and organised mainly on
> the principle of first-come, enshrining a fair bit of historical
> baggage. For example, there are two different buffer menus (one for
> font and one for everything else). There is also the secondary
> selection, of which there seems to be much fewer actual users than
> people who just want to know how to disable it.

Most applications I know do not even distinguish mouse and meta mouse
clicks so I doubt that many users will see this as a problem.

> We could do worse than following some conventions that have become
> more or less universal, such as right-clicking (control-click on
> macOS) for a context menu.

For me mouse-3 is the preferred button to pop up a menu.  I never use
mouse-3 to extend the selection because I'm not used to switch mouse
buttons during one and the same action.

> That said, do you have any particular reason (precedence,
> ergonomics) for suggesting control-shift? I'd rather use meta and
> move secondary selection to shift-meta (say).

I suggested control-shift because it's IMHO the most convenient
combination with two modifiers (at least on my past and present
keyboards).  And I wouldn't change default key bindings that have
existed for decades.  But since I never use the secondary selection I
cannot really defend it either.

martin