Update font to use v2 of GOV.UK Transport font. #1434

By default v2 font will been used unless the service is running in compatibility mode. Some services still need to use govuk template/elements. In the current state, the user would end up downloading two versions of the font. To avoid this issue we have created another flag to check if the the service is running in compatiblity mode by having any of these flags set: - $govuk-compatibility-govukfrontendtoolkit - $govuk-compatibility-govuktemplate - $govuk-compatibility-govukelements The new flag '$govuk-use-legacy-font' can also be overriden by setting its value to "true" just before importing govuk-frontend.

@Nooshu

Embedded Open Type (.eot) is a proprietary format, which no other browsers use apart from IE8 and older. As v2 font is so similiar to Arial, we have decided to remove EOT format. This means that IE8 and older will not be downloading any custom fonts like v1 and v2 of Transport but will instead use Arial by default. This commit also fixes an existing issue with IE 9-11 using EOT format by default instead of WOFF. This is because the browser would only look for and use the first format it finds that it supports. Thanks goes to Matthew Hobbs (@Nooshu)[https://github.com/Nooshu] for this recommendation. An extract of Matt's recommendation can be found below and at this link: #1356 (comment) I'd recommend removing the EOT versions of the fonts from the `@font-face` declaration. Only IE support this font format (including IE11). All but IE8 also support other font formats that are available. According to the last 30 days GOV.UK analytics, IE8 has had 9,054 "users" out of 50,566,007 (0.018%). EOT files can be compressed with Gzip (or Zopfli for 5% better compression), but even with this compression we are asking old browsers on legacy devices to download a fairly large amount of data (60KB) for unhinted versions of the font ([only Vista and XP require hinted versions](https://docs.google.com/spreadsheets/d/1l2SKP9D3Fm5EVk10j9K1CUSg_jCkW7Pef60TzK0ZKlI/edit#gid=0)). These browsers and devices are the least equipped to manage these assets. Font | Size (bytes) | Saving (bytes) | Saving (%) ------------ | ------------- | ------------- | ------------- Bold EOT uncompressed | 58932 | 0 | 0 Bold EOT gzipped | 30366 | 28566 | 48.4 Bold EOT zopfli | 28115 | 30817 | 52.3 Light EOT uncompressed | 58708 | 0 | 0 Light EOT gzipped | 29885 | 28823 | 49.1 Light EOT zopfli | 27589 | 31119 | 53 **Totals**: Uncompressed download - 118KB, Compressed (gzip) - 60KB, Compressed (Zopfli) - 56KB. I'd say it's a better strategy for this small number of devices is to use the fallback font of Arial, and not have them require to download the additional EOT assets. Since the new font now corrects the glyph placement in the bounding box, the fallback will render correctly without the need for additional adjustments to the vertical placement. If it is we decide to keep the EOT files in the `@font-face` declaration it's worth noting the container order will prevent IE9-11 from receiving the WOFF version of the font. Browsers pick the first font format it supports from the list. It will ignore any declarations after, (even if they are also supported). In the current setup IE9, 10 and 11 will download the EOT format even though they all support WOFF. Since WOFF files are already compressed using Gzip compression, developers don't need to worry about enabling compression on the server. If developers forget to enable Gzip compression on the server for EOT files (since we can't provide compressed versions of the EOT files) these users will be downloading 118KB vs 83KB (WOFF). Due to [all the hacks required](https://www.paulirish.com/2009/bulletproof-font-face-implementation-syntax/) to make fonts work properly in older versions of IE there looks to be no way around this. This seems like another good reason to remove the EOT sources from the declaration. Recommended declaration ```css @font-face { font-family: "nta"; src: govuk-font-url("light-68f0c84f0e-v2.woff2") format("woff2"), govuk-font-url("light-222368e53d-v2.woff") format("woff"); font-weight: normal; font-style: normal; font-display: swap; } @font-face { font-family: "nta"; src: govuk-font-url("bold-9561e2d007-v2.woff2") format("woff2"), govuk-font-url("bold-5d3836b441-v2.woff") format("woff"); font-weight: bold; font-style: normal; font-display: swap; } ```

@Nooshu

Thanks goes to Matthew Hobbs (@Nooshu)[https://github.com/Nooshu] for this recommendation. An extract of Matt's recommendation can be found below and at this link: #1012 Version 1 of the font was missing the details required to enable embedded tabular numbers. Version 2 now allows us to control this tablular number setting using CSS, thus removing the need for two other fonts (tabular-light, tabular-bold). This tabular setting can be enabled using the following example CSS: ``` .tabular { font-feature-settings: "tnum" 1; } @supports(font-variant-numeric: tabular-nums) { .tabular { font-feature-settings: normal; font-variant-numeric: tabular-nums; } }``` The difference this setting makes can be seen in the screenshot below. Older browser will fallback to font-feature-settings, where as newer browser will see the @supports rule and use font-variant-numeric.

Co-authored-by: Oliver Byford <oliver.byford@digital.cabinet-office.gov.uk>

We need to have a better understanding and test what it means for the font-display to use `swap` instead of fallback. A new issue has been created: #1437

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Update font to use v2 of GOV.UK Transport font. #1434

Update font to use v2 of GOV.UK Transport font. #1434

Commits on Jun 7, 2019