fontSetScale

Sets the horizontal and vertical scale of a font.

The font scale is a number related to, but not the same as, font size. Typically the client establishes a scale factor to be used between the two. For example, 64, or 256, which would be the fractional-precision part of the font scale. This is necessary because #hb_position_t values are integer types and you need to leave room for fractional values in there.

For example, to set the font size to 20, with 64 levels of fractional precision you would call hb_font_set_scale(font, 20 * 64, 20 * 64).

In the example above, even what font size 20 means is up to you. It might be 20 pixels, or 20 points, or 20 millimeters. HarfBuzz does not care about that. You can set the point size of the font using [harfbuzz.global.fontSetPtem], and the pixel size using [harfbuzz.global.fontSetPpem].

The choice of scale is yours but needs to be consistent between what you set here, and what you expect out of #hb_position_t as well has draw / paint API output values.

Fonts default to a scale equal to the UPEM value of their face. A font with this setting is sometimes called an "unscaled" font.