Re: Rethinking the design of xwidgets

[Akira Kyle]

On Tue, Oct 13, 2020 at 12:45 PM, Eli Zaretskii <eliz@gnu.org> 
wrote:

> > For example is it possible to have a live updating rectangle
> > displayed as one drags the mouse to select a region to inspect?
>
> Can't that be done with a mask on the image?

Perhaps, I have yet to try

> > Is it possible to display a slider which can be dragged by the 
> > mouse
> > to update values on the plot or have a drop down menu to select 
> > a
> > data series?
>
> You'd need to regenerate the plot with the updated values.

What if the computation that generates the plot is expensive? Yes 
one could cache the actual points that the plot draws and update 
based on that, which is what matplotlib already does. I think my 
point is more that a gtk widget already does all of this, so 
rather than reimplementing such functionality between python and 
elisp which will only be useful for one specific python plotting 
library, why not have the ability to display the dynamic widget of 
any given plotting library?

> > It seems it may also be difficult to find a way to have elisp
> > interact with the matplotlib fast enough to not introduce 
> > noticable
> > delay as such actions update the view.
>
> And doing this via a module that is called by a widget won't 
> bump into
> the same problems?  After all, all the interaction with Emacs 
> goes
> through the same mechanism, no matter what the callback does.

I don't think so. In this case the user events don't have to go 
through elisp, they can go directly through the GUI toolkit to 
code behind it. My experience is that elisp is pretty poor at 
handling real time events. Perhaps in part due to its cooperative 
threading model.