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

From: Laurence Penney via GitHub <sysbot+gh@w3.org>
Date: Mon, 22 Jun 2020 19:09:20 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-647719125-1592852958-sysbot+gh@w3.org>
Does anybody have access to a table of physical measurements of dimensions specified in CSS absolute units, taken from a selection of current devices on default settings and “100% zoom”? For the avoidance of doubt, I mean taking real-world measurements from the screen with a physical ruler. Am I right in thinking no such table is currently published?

**The compilation and publication of such a table – effectively the default scaling factors from real-world pt and mm to CSS pt and mm, that manufacturers embed in their devices – would contribute enormously to this discussion, in particular to help us understand what it is exactly that we want to achieve with `font-optical-sizing: auto`, and whether it is achievable.**

Here is the bare bones of such a table, based on measurements I took from my own devices some time ago. I’d happily transfer this data to Google Sheets and provide write access if there is interest.

| Device | Settings | Browser | CSS 50 mm | Scale | w×h (mm) | w×h (pixels) |
|---|---|---|---|---|---|---|
| MacBook Pro 15" Retina 2012 | Default scale | all* | 43 mm | 0.86 |  331×207.5 | 2880×1800 |
| " | +2 display scale | all* | 61 mm | 1.22 | " | " | 
| " | +1 display scale | all* | 48.5 mm | 0.97 | " | " |
| " | -1 display scale | all* | 37 mm | 0.74 | " | " |
| " | -2 display scale | all* | 32.5 mm | 0.65 | " | " |
| iPhone 5S  | - | Safari | 29 mm | 0.58 | 49.5×88.5 | 640×1136 |
| iPhone 8  | - | Safari | 29 mm | 0.58 | 58.5×104 | 750×1334 |

The key column we should look at is the _Scale_ column. Remember that these scale factors are detemined by device manufacturers and browser makers, who are (I suggest) influenced by at least these three considerations:
1. that users, for convenient website viewing, expect scale factors within a fairly small range from this device format;
2. that CSS measurements maintain a useful relationship with the device’s internal scale factor regarding its text APIs (e.g. 1 CSS px = 1 Cocoa point);
3. to cause the CSS px unit to be align with real pixel boundaries.

To contribute new data, please go to this website and measure the black square with a ruler to the nearest 0.5 mm. It is specified to be 50 mm in CSS units. Make sure your browser is at 100% zoom.

[CodePen: CSS 50 mm](https://codepen.io/lorp/pen/dyGWyPZ)

Caveat: I have not specified browser or platform or browser scale factors for any devices, so would be very pleased to understand this process in more detail including any more considerations and their relative importance. For example, we may also need an “intended viewing distance” column, to separate physical screen size from intended actual device usage.

\* all = Safari, Chrome, Firefox, Edge


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Received on Monday, 22 June 2020 19:09:22 UTC

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