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44 lines
2.9 KiB
Markdown
44 lines
2.9 KiB
Markdown
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# GF Axis Registry
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This package contains a collection of metadata source files that collectively form the Google Fonts Axis Registry.
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The live Axis Registry is at [fonts.google.com/variablefonts](https://fonts.google.com/variablefonts), and axis definitions are only final when they appear on that page.
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When the registry is updated here, a line like `axisregistry/axis_name.textproto` should be added to the `to_sandbox.txt` file.
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## Axis Metadata Fields
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* `tag`
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* Tag for the axis used to specify an axis in `font-variation-settings` and CSS API requests.
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* `display_name`
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* Readable name for the axis, generally the expanded form of `tag`.
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* `min_value`
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* Lower bound of the axis. Inclusive.
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* `max_value`
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* Upper bound of the axis. Inclusive.
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* `default_value`
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* Default position of the aixs.
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* `precision`
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* Describes the specificity at which an axis position can be specified.
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For example, `0` means values must be specified as whole numbers while `-1` means values can be as precise as one decimal place.
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* `fallback` (repeated)
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* Instance positions along the axis, such as wght 100,200,300,400,500,600,700,800,900.
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* A cross-product of fallback positions along all supported axes is created to support legacy browsers that lack variable font support.
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For axes with CSS3 properties (such as [font-weight](https://drafts.csswg.org/css-fonts-3/#font-weight-prop)), the positions accessible
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to CSS3 should be specified. For axes lacking CSS3 properties a legacy browser is limited to a single position and that position must
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be at a fallback.
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* `fallback_only`
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* Describes whether to only use fallback values when presenting to users.
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* `description`
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* A description of the axis.
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## Why does Google Fonts have its own Axis Registry?
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We support a superset of the [OpenType axis registry](https://docs.microsoft.com/en-us/typography/opentype/spec/dvaraxisreg) axis set, and use additional metadata for each axis.
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Axes present in a font file but not in this registry will not function via our API.
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No variable font is expected to support all of the axes here.
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Any font foundry or distributor library that offers variable fonts has a implicit, latent, de-facto axis registry, which can be extracted by scanning the library for axes' tags, labels, and min/def/max values.
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While in 2016 Microsoft originally offered to include more axes in the OpenType 1.8 specification ([github.com/microsoft/OpenTypeDesignVariationAxisTags](https://github.com/microsoft/OpenTypeDesignVariationAxisTags)), as of August 2020, this effort has stalled.
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We hope more foundries and distributors will publish documents like this that make their axes explicit, to encourage of adoption of variable fonts throughout the industry, and provide source material for a future update to the OpenType specification's axis registry.
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