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Re: [csswg-drafts] [css-fonts] Proposal to extend CSS font-optical-sizing (#4430)

From: jfkthame via GitHub <sysbot+gh@w3.org>
Date: Mon, 22 Jun 2020 18:06:03 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-647687965-1592849162-sysbot+gh@w3.org>
> > If I hit Cmd-+ to zoom a webpage that uses optically-sized fonts, should the browser use a new opsz value to account for the new physical size?
> 
> > What about if I pinch-zoom the display on a mobile device?
> 
> The types of zoom that _do not trigger re-layout_, should not change `opsz` variant either.

That seems reasonable at first glance, but I'm not sure whether it's really the right answer. In a typical desktop browser, full-page zoom *does* trigger re-layout, but I'm unconvinced that it is appropriate for it to change `opsz` variants.

Imagine I'm viewing a page where the author has given the body text `font-size: 12pt`, captions have `font-size: 9pt', and the title has `font-size: 18pt`. The font being used has an optical size axis that ranges from 9 to 18, so I see clear differences between these sizes: the captions are wider, with less contrast and more letter-spacing, while the title is significantly tighter and has more contrast in its strokes.

Now I press `Cmd-+` a couple of times to zoom the page for more comfortable reading, as I'm lounging back in my chair. This causes re-layout, because while the font sizes in CSS pixels are unchanged, the viewport width has effectively been reduced. But I would find it surprising (and unwelcome) for this to affect the choice of font faces (or used values of `opsz`), and perhaps erase the intended design difference between the elements.

Another surprising result would be that line breaks within a fixed-width block on the page (e.g. a sidebar that has an absolute `width` set in CSS pixels (or em units, or whatever) will change when the page is zoomed, if this results in an `opsz` change. I believe that is unexpected and unwanted.


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Received on Monday, 22 June 2020 18:06:09 UTC

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