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Re: Pixel-based display functions

From: Lars Ingebrigtsen
Subject: Re: Pixel-based display functions
Date: Sat, 07 Feb 2015 02:22:26 +1100
User-agent: Gnus/5.130012 (Ma Gnus v0.12) Emacs/25.0.50 (gnu/linux)

Eli Zaretskii <address@hidden> writes:

> When you "repeat", do you start from the part of the line that's left,
> without the part that is before the just-inserted newline, or from the
> original long one?  The time it takes vertical-motion to do its job
> will be smaller if the line is shorter.

I start from the part of the line that's left.

> Also, try invoking vertical-motion from a position that is not
> immediately after a newline, I think this might speed it up a little
> more.

Ah, right.

> Why do you need to know what width you ended up with?  Or maybe I
> don't understand "ended up with" when -- before or after
> vertical-motion did its job?  IOW, do you need window-text-pixel-size
> for measuring the long unfilled line, or the lines after filling?

I need to measure the lines after filling so that I know how wide the
column ended up being.  (This is to better use the available horizontal
space when rendering tables, which is quite important.)

>> It would be equivalent to a `window-text-pixel-size' that advances one
>> character at a time (since we'd avoid the entire `font-at' problem), and
>> returns an vector of pixel points (instead of calling move_it_to just
>> once).
> You are describing an implementation.  Please describe the API and the
> contract instead.

Well, it depends on what's realistic to implement, really.  If calling
`font-at' had been fast enough, I would have been happy sticking with
that, but it turned out not to be.

So the API kinda depends on what's feasible...

I think the ideal interface for this would be a function that returns
a vector of glyph widths in the region, possibly with one vector per

So (glyph-pixel-widths FROM TO) =>
([4 5 10 12] [4 14 1] ...)

That would allow caching the computations so that they would only be
called once per (unfilled) buffer.

> Also, as long as you use these functions, there's still a problem with
> visual vs logical order that needs to be solved.


(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

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