Re: Emacs and Gnome Canvas

[Jan Djärv]

Eli Zaretskii skrev 2010-07-15 14.27:
> Inserting one character moves all the attributes after it by one
> character position, doesn't it?

Yes, but that is something the Canvas can do by itself.

> > You wouldn't have to do redisplay all the time just in case
> > something changed (like now)
>
> ?? We don't _do_ redisplay now all the time.  We _enter_ redisplay
> every time Emacs is idle, but if nothing's changed, we exit it almost
> immediately, after testing a bunch of flags.

That is the same thing to me.  With the Canvas design, you would not need to 
check, once it is done Canvas does all repainting as needed.

> > if you propagated the change the whole way when it happened.  This
> > is a big difference on how Emacs works now.
>
> The way it looks, parts of the current redisplay code will have to run
> whenever there's a change, any change, to some buffer or some related
> data structure.  If the parts affected by these changes are not
> displayed, or become not displayed before the GTK+ idle handlers run,
> propagating those changes would be a waste of CPU cycles.

No, they need to be done anyway sometime, it is no waste.  If the text isn't 
displayed, the attributes are nvertheless set up correctly for the time when 
the text is to be displayed later (by scrolling for example).  The Canvas just 
have to scroll things in view and the display is up to date.  If they never 
come into view, then there is a waste of CPU cycles.

Now in Emacs you postpone the update until it is in view.  With the canvas you 
would do the update at once, but you then don't have to bother with it 
anymore, for example if it comes in to view later.  It should be about the 
same CPU-cycles, just distributed differently.

> So you win some and you lose some.  Not sure about the balance.
> Basically, scrolling should be very fast (assuming it is done entirely
> on the Canvas side), but I'm not sure if everything else won't be
> significantly slower.

If done right, I don't think it would be slower.  But someone has to do the 
code before we know.

        Jan D.