Variable fonts

A variable font is one file for a whole family: its axes, such as the weight or the width, vary its outlines, its metrics and the positions of its layout tables continuously.

Get an instance

FontFace.Axes describes the axes, and WithCoordinates gives the face of an instance from the value of each axis:

static FontFace WithWeight(FontFace face, int weight)
{
    // One value per axis, in the order of the axes, as 16.16 fixed-point numbers
    var coordinates = new int[face.Axes.Length];
    for (var i = 0; i < face.Axes.Length; i++)
    {
        coordinates[i] = face.Axes[i].Tag == ShapingFeature.ToTag("wght") ? weight << 16 : face.Axes[i].Default;
    }

    // The face of the instance shares the data of the font
    return face.WithCoordinates(coordinates);
}

With the variable Noto Sans, the letter o is 605 units wide in the default instance (weight 400) and 637 units wide at weight 900.

• The values are 16.16 fixed-point numbers in the units of the axis: shift a weight of 700 by 16 bits (700 << 16).
• WithCoordinates takes one value per axis, in the order of Axes; an axis without a value stays at its default, and a value out of range is brought to the nearest end.
• The face of an instance shares the bytes of the font and is cheap to create. It is a FontFace like any other: decode its outlines, read its metrics and shape text with it. Instance gives its coordinates; it is null for the default instance.
• A font that does not vary has no axis.

Axes and named instances

NamedInstances lists the instances the font names, such as "Light" or "Bold Condensed": Coordinates are the values to pass to WithCoordinates, and NameId their name.

To choose instances by their axis tags without handling coordinates, use the variable fonts of Meziantou.Framework.Imaging (Font.WithVariations).