Re: How to obtain x/y/hpos/vpos at eol -- excluding overlay 'after-string.

[Keith David Bershatsky <esq@lawlist.com>]

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I forgot to cc the mailing list -- so here is a carbon copy.

Keith

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From: Keith David Bershatsky <esq@lawlist.com>
To: Eli Zaretskii <eliz@gnu.org>
Subject: Re: How to obtain x/y/hpos/vpos at eol -- excluding overlay 'after-string.
Date: Mon, 04 Apr 2016 14:06:08 -0700
Message-ID: <m2oa9paxtr.wl%esq@lawlist.com>

Thank you, Eli, for taking a look at this particular thread.

There are a couple of applications where this would be useful.

The first application is a common function available interactively called `posn-at-point` which cannot return the desired `x` and `hpos` when an 'after-string is present at point.  For example, line-move-visual in simple.el has never worked correctly when I have overlay 'after-string at the end of the line.  So, I have been using a workaround with `vertical-motion` to calculate the desired `temporary-goal-column`.  Here is the link to a thread on emacs.stackexchange.com from about a year ago relating to this issue:

http://emacs.stackexchange.com/questions/7957/calculating-cursor-position-excluding-the-overlay-after-string

The second application is related to feature request 22873 (multiple fake cursors) and a dormant (yet related) feature request 17684 (drawing a vertical line the length of the window).  I have not been able to accurately predict programmatically where the fake cursors are located subsequent to the screen scrolling when overlay 'after-string are present.  [I spent a day writing up a function to calculate the differential of `y` and `vpos` based on previous and current window-start/end, only to discover that the Little Rascals (fake cursors) were still somewhere else when scrolling.]  The function `erase_phys_cursor` redraws the character (where the cursor was) based upon (in part) the values of x/y/hpos/vpos.  Until I can figure out how to accurately predict where those Little Rascals (fake
  cursors) have gone to when scrolling occurs, the easiest thing to do is erase/redraw everything along the `x` axis.  `erase_phys_cursor` should not be used, however, when there is no TEXT along the `x` axis - because that yields strange looking glyphs along the right side of the screen.  Before calling `erase_phys_cursor` (or my custom function `mc_erase`), I want to check to see where the end of the visual line is -- i.e., x/y/hpos/vpos at the end of each visual line -- and only erase/redraw characters when the `x` axis is less than the end of the visual line

Keith

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At Mon, 04 Apr 2016 23:30:04 +0300,
Eli Zaretskii wrote:
> 
> * * *
> 
> Please tell what problem you are trying to solve, and why.  Obtaining
> coordinates is a means, but I don't yet see the end, so please help us
> understand that.