> So you use the results of the display engine to display the same stuff
> differently, is that right?
>
> If so, I'm not sure I understand how to do it "properly".  The Emacs
> display engine performs the layout calculations (which determine, for
> example, where each screen line ends and the next one begins, or what
> stuff fits into a window) by examining each character of buffer text
> in turn.  Without this examination, how can we know how to display the
> text as SVG?  And if we use the current code to produce this
> information, then what did we gain?
>
> I'm probably missing something.
>
Do you notice the popup in the top window in the image attached in OP? It
has clean lines over buffer content with mixed (fixed + variable pitch)
fonts. Is it possible to have that in graphical Emacs? Precise positioning
of popups can open up graphical Emacs to immense possibilities like feature
filled tooltips, inline completion popup, multi-column layouts, watermarks
etc.