bug#47712: 27.1; Provide `string-display-width` function, which takes properties into account, `substring-width`

[Daniel Mendler]

On 4/12/21 10:53 AM, Lars Ingebrigtsen wrote:
> I can see how that may be useful in some cases (and is very different
> from `window-text-pixel-size'), so I think adding something like that
> would be nice.  But the name is confusing -- it sounds like it's
> computing the displayed width, and it's not -- if there's images or text
> with a different font in there, it's not taken into account?

Yes, a better name could be `string-property-width`? I proposed 
`string-display-width` since it takes the 'display property into 
account, but maybe this gives false associations.

Note that I would like to have an implementation of 
`substring-width`/`string-display-width`/`substring-display-width` which 
does not allocate, since this reduces the GC pressure when formatting 
many items. How do you think about this?

Regarding images, different fonts, maybe a `string-property-pixel-width` 
would be useful too. But for the use cases I have in mind (formatting 
monospaced text) computing columns is sufficient.