Thanks, but I'm not sure yet how to connect this to what the display
engine actually does. Are you familiar with what happens in the
display code during a single redisplay cycle? If so, could you
describe that and insert into that description what you say above?
That would go a long way towards making sure we are on the same page,
which I think is a necessary precondition for discussing your
proposal.
I admit I don't know about the internal working of the display engine.
Failing that, I could try asking questions whose answers might help
reconstructing those missing links. For example:
. does this mean you expect the display engine to tell that
display-svg-hook which parts of the display were redrawn?
No, that won't be necessary. After change hooks and other APIs are enough to derive change and context information. In my experience, the characters around the point are usually the most relevant.
. what is the "required information" to be passed to
display-svg-hook, and how will it be generated from the information
that exists in the display engine?
"required information" in my sentence above refers to the parameters of (svg-render) API viz. svg x y width height. display-svg-hook can be a no-arg function.