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Re: Selection threshold with mouse

From: Stefan Monnier
Subject: Re: Selection threshold with mouse
Date: Sun, 20 Jul 2014 12:44:22 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4.50 (gnu/linux)

>> Hmm... but don't the display matrices contain the needed info (i.e. the
>> "left-pixel boundary position"), since it's needed to react to an
>> expose event?
> Not sure I follow (what does an expose event have to do with the issue
> at hand?).

An expose event comes with pixel coordinates and we need to respond by
drawing chars at the proper pixel positions, so we clearly need to be
able to find the chars placed at those pixel positions as well as their
pixel boundaries.

> In any case, we cannot rely on glyph matrices alone,
> because that would severely limit the usefulness of such an API.

Ah, I see.

> E.g., you will be unable to use it in a function that is called
> several times in a row, like via a numeric argument or from a keyboard
> macro.

We could make it update glyph matrices if/when needed.

> For these reasons, posn-at-x-y etc. do not rely on glyph matrices, but
> instead simulate display.

Then I don't understand why the precise pixel position is not available.

> I think hyperlinks are the odd one out, and not directly related to
> the issue here, which is where to put point given a click, especially
> in the context of highlighting the region.

I don't know which one is the rule and which one is the exception.
I just know that the behavior should be decided on a case by case basis.


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