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Re: No possibility of determining image position/object from click

From: David Kastrup
Subject: Re: No possibility of determining image position/object from click
Date: 15 Jun 2002 19:10:10 +0200

"Eli Zaretskii" <address@hidden> writes:

> > From: address@hidden
> > Date: 15 Jun 2002 16:34:25 +0200
> > 
> > 
> > Emacs does not update the
> > screen while it is busy, which can easily last for a few seconds.  If
> > I click onto the screen during that time, buffer positions and
> > keymaps will be calculated corresponding to what the screen will look
> > like after the next screen update finally gets done.
> How is this different from the situation where a user types C-w in
> the middle of a lengthy calculation which will eventually change the
> text inside the region (and thus the result of C-w).
> In other words, typing ahead when Emacs is busy always runs a risk of
> doing the wrong thing.  Am I missing something?

When clicking on something, we establish a visual correlation between
the object we are clicking on and the mouse pointer, not between the
naked screen position and the mouse pointer.  That is, when we are
queing keyboard events, we are conceptually queuing
"process C-x C-w"
"process C-d" ...

With mouse clicks, we are conceptually queuing "click on object/buffer
position ...", not "click on screen pixel coordinates ...".  The
perceived discrepancy in processing is quite disconcerting.

During such busy calculations, for example tooltips are still being
processed, and they are processed taking into account the look of the
buffer _before_ redisplay (which is the only thing that makes sense
to the user, anyhow), at least that is my impression.  The tooltip in
my case then promises something like "[button-2] toggles preview",
but if you press the button, and this gets queued, and then some
other stuff gets updated in a process sentinel or wherever else
before the event gets processed, something quite different from what
the tooltip promised will happen.

David Kastrup, Kriemhildstr. 15, 44793 Bochum
Email: address@hidden

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