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

From: Nick Sherman via GitHub <sysbot+gh@w3.org>
Date: Tue, 02 Jun 2020 17:29:59 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-637696979-1591118998-sysbot+gh@w3.org>
It’s surprising to me that throughout this whole convoluted discussion, no one has explicitly proposed the idea of linking the `opsz` axis to a unit that is, and always has been, related directly to actual optical size in the most pure sense of **relative/angular measurement** – e.g. arcminutes, degrees, etc.

The CSS “pixel” (a.k.a. the “reference pixel”) was [redefined](https://github.com/w3c/csswg-drafts/issues/614#issuecomment-254571480) by the W3C at some point, via reverse justification, to make it an angular measure, at least in theory (~0.0213 degrees). But in practice, if you do any tests for how that works with different devices when viewed at their typical/intended viewing distances, the unfortunate reality is all over the place. Such an unreliable unit isn’t very helpful for the purposes of fine-tuning optical size designs, not to mention being confusing, thanks to the many conflicting definitions of “1 pixel”.

With that in mind, why not invent a new unit of angular measure that corresponds to the perceived size of a physical typographic point when viewed at a typical viewing distance that designers could understand intuitively. The [`dmm`](https://twitter.com/SizeCalculator/status/866783413205950464) was proposed for VR scenarios (`1dmm` = the perceived size of 1 millimeter when viewed from 1 meter away) … Why not tie `opsz` to a new typographic unit (`dpt`? `oppt`?) that equals, say, 1 physical point when viewed from 16 inches away (i.e. [approximately 3 arcminutes](https://sizecalc.com/#distance=16inches&physical-size=1points&perceived-size-units=arcminutes))? Something like that would correspond very directly to the idea of pure optical sizing as @tiroj mentioned – separate from resolution, inking, output medium, etc.

As an added bonus, this might also provide new opportunities for addressing the relationship between virtual and physical size (which I have [been](https://github.com/w3c/csswg-drafts/issues/614) [writing](https://alistapart.com/column/responsive-typography-is-a-physical-discipline/) and [making](https://sizecalc.com) [tools](https://twitter.com/NickSherman/status/1136590708226179074) about for years).



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Received on Tuesday, 2 June 2020 17:30:02 UTC

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