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 HarfBuzz.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 hb_font_set_ptem(), and the pixel
size using hb_font_set_ppem().
The choice of scale is yours but needs to be consistent between
what you set here, and what you expect out of HarfBuzz.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.
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 HarfBuzz.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
hb_font_set_ptem(), and the pixel size usinghb_font_set_ppem().The choice of scale is yours but needs to be consistent between what you set here, and what you expect out of HarfBuzz.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.