Variable Fonts

Myles Maxfield, Apple

• contain tables for each glyph
  • sequence of points that define each path
• variable fonts allow parameterization of:
  • control points in glyph contours
  • advances (horizontal space) for each glyph
  • shaping information
  • basically all information specified by table
• parameters held in a vector
  • grouped together into axes
    • e.g. weight, height, etc.
• software sends a value to the font structure that generates a result based on these axes
• SanFransisco only understands weight axis
• Skia has weight, width, etc.
• these axes are animatable
• implemented/used via CSS
• three main components
  • some properties already exists (weight, width, and stretch) which map directly onto axes (weight, width, and slant)
  • remaining axes do not currently have CSS properties, but are used by the browser
  • axes that are unknown to browsers
    • font-variation-settings is a sequence of key-value pairs that define custom axes and their value format
      • due to cascading of CSS, this property must replace the entire list (no append)
• each property can have different syntax/format
• prevents duplication of fonts for different features
• new format will be larger than a single font, but smaller than two forms of the same font (normal and bold > new format > normal)
• support for font files with this format is basically done
• CSS implementation is still being worked out