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Re: [csswg-drafts] [css-values-4] Flawed definition of the pixel unit (#5221)

From: fantasai via GitHub <sysbot+gh@w3.org>
Date: Thu, 23 Jul 2020 23:33:49 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-663282588-1595547228-sysbot+gh@w3.org>
> Historically 1 pixel was defined as 1 device pixel. Back then, most screens were 96 DPI, and 1 pixel would be 1/96 in.

This is historically inaccurate. The pixel has always been defined relative to a viewing angle. See the definitions of length units in CSS1 and earlier (pre-2010) versions of CSS2.

> The "recommendation" to define the pixel unit as the closest integer to the reference pixel should be a definition instead.
> Make physical units again physical

We can't do that.

> The physical units could be independent from the pixel unit, no matter what DPI the screen has.

This was CSS's original intention, as you can see from the original texts.

> What does "content relies on [..] 96dpi" mean?  I assume the reason was, that people mixed physical units and the pixel unit in their style sheets, expecting the ratio between physical units and the pixel unit to be fixed by the same ratio as on 96 DPI screens.

Yes, exactly. See the thread at https://lists.w3.org/Archives/Public/www-style/2010Jan/0058.html if you want to read the actual history of this situation. None of us were pleased with the situation, mind you, but we were constrained by reality. The current spec is the compromise we ended up with.

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Received on Thursday, 23 July 2020 23:33:51 UTC

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