Re: Pixel-based display functions

[Eli Zaretskii <eliz@gnu.org>]

> From: Thien-Thi Nguyen <ttn@gnu.org>
> Date: Wed, 28 Jan 2015 08:16:46 +0100
> 
>    1) A pixel equivalent of `current-column'

As I wrote elsewhere, these already exist.

> See also mid-2002 thread "column->int float diff".
> Gist: rms suggests using (C language) ‘iterator’.

Indeed.  So I think the "float column" approach is not TRT, and we
should instead work in pixels.  That is also how the 'iterator' object
works, so this will naturally plug into the existing infrastructure.
Using a float column solves only half of the problem.  The other half,
how to convert such a column into the actual screen position, is still
there.

The indentation code should use the '(space . (PIXELS))' value of
display property to align text on pixel-granular boundary, instead of
inserting TABs and spaces.  This already works, so does not need any
changes on the C level.

We do need to teach the display engine how to fill and/or justify text
with pixel granularity.  But that's a separate isue.

I asked for someone to show a list of tasks included in this, and no
one did.  I think different people have different ideas about what
needs to be done and how, and also about what's already available.  So
preparing such an agreed-upon list is IMO necessary for any
constructive discussions and advances.