Re: Fill column indicator functionality

[Keith David Bershatsky]

I understand that the primary goals are lightweight and speed, and I fully 
appreciate those goals.

I see that the current draft only deals with glyph rows ending _prior_ to the 
fill-column, and then an extra glyph is added subsequent thereto for the 
purposes of creating a visible fill column indicator.

I would suggest devising a mechanism that can intersect characters (at any 
given X coordinate) for glyph rows that extend beyond the fill-column, 
including, variable pitch and mono-spaced fonts.  Attached is a screenshot of 
what this would look like in Emacs.

Admittedly, the code used to create the visible fill column indicator in the 
screenshot (capable of intersecting characters at any given X) is anything but 
lightweight _and_ it is only for GUI versions of Emacs (NS/W32/X11).  It is, 
however, pretty darn quick....

Perhaps there is an overlay that can be used that is capable of intersecting 
characters, or a thin vertical window spanning the window-body-height that is 
one pixel wide; e.g., all three GUI platforms can create a vertical window as 
thin or thick as desired (such as a vertical scroll bar).  There are platform 
options to repaint or suppress repainting when removing windows ....  Emacs 
already has the ability to redraw the glyphs that fall within a given rectangle 
using the w->current_matrix after update_window has already done its thing ....

In case anyone is interested in the code used to generate the screenshot below, 
the latest proof concept patch for feature requests 17684 / 22873 is now at 
version 19.002:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22873#134

17684_22873__19_002.png
Description: application/png