- From: Myles C. Maxfield via GitHub <sysbot+gh@w3.org>
- Date: Wed, 08 Mar 2017 00:18:51 +0000
- To: public-css-archive@w3.org
Because `font-optical-size` doesn't actually let web authors set the optical size value directly, I'd imagine this description is most valuable to implementors to figure out what to do when `font-optical-size` is `auto`. I think the best way forward is to summarize this advice and put it into a non-normative section in the fonts spec. @robmck-ms: Is it okay if I put the following text into the spec? (Also please feel free to revise / comment on it) > This section is non-normative. > > Selecting a value to supply for the 'opsz' variation axis when the 'font-optical-size' property computes to 'auto' is explicitly not defined here. However, there are some best practices found experimentally for selecting this value. > > In an ideal world, the optical size value would select the optical style of a font based strictly on the visual angle that the text subtends as light enters your eye. Unfortunately, visual angle as an input variable to optical style selection breaks down when we try to apply it in the real, digital world. > > People have a wide range of visual acuity, even corrected, thus the visual angle you might want to use to transition to a caption style for one person may be very different for another. One could also look at using physical, rendered size on screen, but that too has many problems. In accessibility scenarios, you end up with a floor function in the design of the font, with all text displaying at the optically smallest style, eliminating information about hierarchy and semantic relationship. In projection scenarios, you'd have the reverse - everything displayed in the optically largest style, which not only loses hierarchy, but is inappropriate. > > In the end, one approach that could work well would be that optical style is a function of the text size within the document. For example, if the content specifies 10pt type, then that is used to select the optical size, regardless of how big the letters end up in the real world. -- GitHub Notification of comment by litherum Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/807#issuecomment-284904568 using your GitHub account
Received on Wednesday, 8 March 2017 00:18:57 UTC