Re: Scrollbar thumbs

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

>>>>> On Wed, 04 Nov 2009 15:57:06 -0500, Stefan Monnier <monnier@iro.umontreal.ca> said:

> In any case, given how widespread the problem is, it's clear that we
> can't expect the toolkit to adapt to Emacs.  And since nobody has
> found a way yet to make Emacs DTRT, all we can do is provide various
> workarounds, which is what we've done until now.

The Carbon port and its descendants don't let the toolkit scrollbar
process the mouse events: we can't do that (without nontrivial changes
for multithreading of the GUI part) in the first place because the
toolkit scrollbar on Mac processes them in its own modal loop (i.e.,
we can't go back to the Lisp event loop during the mouse tracking, and
that is not compatible with the current scrollbar handling in Emacs.).

What the Carbon port (and its descendants) does is to process the
whole mouse events at the Emacs side.  It includes timer processing
for repeated scrolling (e.g, pressing an arrow button for a while.)
The toolkit is used only for displaying the scrollbar with
highlighting, detecting which part of the bar is pressed, and getting
the rectangle for a specified part of the bar.

The result is like a sort of mixture of native and toolkit scrollbars
on X11: it generates Lisp events and looks like the toolkit one, but
the size of the thumb usually changes during dragging and also
overscrolling at the bottom works as in the native one.

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp