Re: There should be an option to set the display size of an image to zero

[Eli Zaretskii <eliz@gnu.org>]

> From: Marc Feeley <feeley@iro.umontreal.ca>
> Date: Tue, 17 Sep 2013 08:50:45 -0400
> Cc: "Stephen J. Turnbull" <stephen@xemacs.org>,
>  emacs-devel@gnu.org
> 
> Let me explain the context so that you better understand my specific needs.  I want to use emacs as a programming tool to display the result of some program analyses of the code currently in the buffer.  Specifically I want to display arrows that indicate how data flows in the program.  For example, what are all the places in the code where the value resulting from a given constructor are referenced, or inversely, what are all the calls to constructors whose resulting value can flow to a particular point in the code.

I vaguely understand, but it is still not clear enough how you would
achieve those goals with "arrows".  Where will the arrows originate,
and where will they point?  Perhaps you could show a screenshot?

> My plan is to display arrows indicating these relationships and to overlay them on top of the program source code.  It would be ideal if it was possible to place an image on top of the text that scrolls with the text.  The arrows would only appear if the cursor (or mouse) is placed on top of a constructor or accessor, so it must be efficient to change the image dynamically.  An SVG image would be ideal because the image can easily be constructed and takes little space.

Did you consider using display margins?  Emacs can show display
strings and images in the display margins, to the left or right of the
text.  These display strings and images are "pinned" to specific
buffer positions, so they scroll with the text.

Since I don't have a clear idea of what you want to accomplish, I
cannot be sure this feature gives you what you need.  If they do, then
making them show when the mouse is at some specific place should not
be too hard, I think.