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

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Date: Wed, 18 Sep 2013 12:10:44 -0400
> Cc: feeley@IRO.UMontreal.CA, stephen@xemacs.org, emacs-devel@gnu.org
> 
> > One possible idea -- not sure if it fits the purpose -- is to overlay
> > transparent-background images on top of the displayed text, not unlike
> > what we do with mouse pointers.
> 
> That's the idea, I think, yes.
> 
> Combined with posn-point which lets us find the XY coordinates of
> a particular buffer position

It's the other way around: given XY coordinates, it finds buffer
position at those coordinates.  I guess you meant posn-at-point
instead.

> it should be possible to build (in Elisp) the right SVG image and
> tell Emacs to overlay it on top the text.

I believe you; I know nothing about SVG, except that it is a vector
image and is specified in XML.

> Ideally, the primitive could look like a `display' spec which says
> "overlay the image at offset XY relative to the current position".

I guess you mean "relative to specified POSITION", because there's
only one current position, which sounds too restrictive.

> But if it's too difficult to handle it that way, a simpler (from the
> C code PoV) approach might be a window property which says "overlay this
> image over the whole window's text".

I think the difficulty is the same: we need a separate display
operation invoked when the redisplay cycle is completed.  We also need
to figure out what to do when redisplay is preempted before it
completes.  Determining the anchor position, relative to which the
image is displayed, could also need some thought, because that
position might not be visible.