bug#29279: Sharing the margins

[Dmitry Gutov]

On 11/13/17 9:22 PM, Eli Zaretskii wrote:

> > Still, it seems unnecessary if the somewhat faster C code could
> > implement that for every user.
>
> We could add that later if needed.  It's not rocket science, it's just
> more complexity.

Yup.

> > > posn-at-point goes _once_ from window-start to the specified position,
> > > so on average it traverses half a window, once.  By contrast, we are
> > > now talking about redisplaying the window twice, and one of these 2
> > > times must traverse the entire window.  So we are talking about
> > > threefold slow-down on the average.
> >
> > 3-fold slowdown from 500 FPS seems acceptable to me.
>
> For each redisplay cycle?  On top of disabling most redisplay
> optimizations?  I doubt that.

Hard for me to tell. Like, in the recent discussion of a performance 
problem related to double-buffering, apparently Emacs itself wasn't the 
rendering bottleneck.

You probably know better, though.