Re: Terminal matrices

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: Emacs Devel <emacs-devel@gnu.org>
> Date: Sun, 19 Jan 2025 09:58:09 +0100
> 
> Good, but to achieve this, combine_updates creates a second pair of
> glyph matrices in addition to the existing frame matrices, which I've
> called terminal matrices. These terminal matrices are created the first
> time combine_updates finds a visible child frame that must be displayed,
> 
> >From then on, terminal matrices are used for the update by setting the
> frame's current and desired matrix to the terminal matrices. After the
> update things are restored to "normal".
> 
> What is displayed on the terminal in found in the terminal current
> matrix, and what should be displayed is in the terminal desired matrix.
> And there's the rub: the construction of the terminal desired matrix
> _requires_ that I copy the frame desired matrix to the terminal desired
> matrix (the part that is enabled_p). That includes a memcpy of the
> glyphs. And in the worst of all cases, say when using my full-screen
> eMacs on MacOS :-), this is in bytes on my arm64
> 
>   (* (frame-width) (frame-height) 56)
>   743008
> 
> It's not that it is always so much, usually it's probably much less, but
> anyway. And it is _unavoidable_ to achieve the independence of the rest
> of redisplay. At least I have no idea how to avoid it. Let me say it
> that way.

How much time does it take to memcpy the above amount of glyphs?

Can we avoid doing that unless there are in fact child frames?

Thanks.