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

[Stefan Monnier <monnier@iro.umontreal.ca>]

>>> How do I find out when a display property is deleted in C?
>> You don't/can't.
> Hmm.

>>> In the xwidget patch I need to delete the corresponding xwdiget when
>>> the display property is deleted.
>> What happens if the display property is later re-added?
>> If that situations is not problematic, then you can keep your xwidgets
>> in a cache which you can flush every once in a while.

> But I need to remove the gtk widget from display the precise moment the
> display property goes away, or there will be very awkward display bugs.

how do you deal with the case where the widget is scrolled out of view?

> I could maybe have a new phase at the end of emacs redisplay, where all
> xwidgets which haven't been drawn in this redisplay will be deleted.

Or marked as "out of view".  Yes, that sounds sensible.

>> Also what happens if the same display property gets added at two places
>> (either in the same buffer or in different buffers)?

> They cant be the same, because I require a unique id for every xwidget
> in the display property:

> (put-text-property (point) (+ 1 (point)) 'display '(xwidget :xwidget-id 3 :type 3 :title "3" :width 400 :height 200))

> adding the same id twice is an error, as currently designed.

Is this error properly caught and signalled to the user?


        Stefan