Re: how to find out when display property is deleted in C?

[Eli Zaretskii <eliz@gnu.org>]

> From: joakim@verona.se
> Cc: monnier@iro.umontreal.ca, emacs-devel@gnu.org
> cc: emacs-devel@gnu.org
> Date: Tue, 13 May 2008 08:55:48 +0200
> 
> > Forgive me for chiming into a discussion I wasn't following about a
> > subject that I'm mostly ignorant about, but: when the display property
> > goes away, Emacs triggers a redisplay the next moment it doesn't have
> > anything more important to do.  That redisplay should supply you with
> > an event to remove the gtk widgets, no?  Just plug your
> > widget-removing routines into the code that runs during redisplay.
> 
> I tried this and I'm still having difficulties. The redisplay
> code optimizes drawing. It appears these optimizations make it so the
> xwidget glyph draw routine isnt allways called on redisplay.

Search xdisp.c for "optimiz", and you will find quite a few ways of
turning off these optimizations.  For example, you could set the
prevent_redisplay_optimizations_p flag of the buffer, or set the value
of this_line_start_pos variable non-positive.  It could be that this
works, but makes redisplay painfully slow, in which case less naive
coding will be needed to turn off optimizations only sometimes.  But
at least you will know that it works; I was taught to make it right
before I make it fast.