[−][src]Trait ab_glyph::Font

pub trait Font {
    fn units_per_em(&self) -> Option<f32>;
    fn ascent_unscaled(&self) -> f32;
    fn descent_unscaled(&self) -> f32;
    fn line_gap_unscaled(&self) -> f32;
    fn glyph_id(&self, c: char) -> GlyphId;
    fn h_advance_unscaled(&self, id: GlyphId) -> f32;
    fn h_side_bearing_unscaled(&self, id: GlyphId) -> f32;
    fn v_advance_unscaled(&self, id: GlyphId) -> f32;
    fn v_side_bearing_unscaled(&self, id: GlyphId) -> f32;
    fn kern_unscaled(&self, first: GlyphId, second: GlyphId) -> f32;
    fn outline(&self, id: GlyphId) -> Option<Outline>;
    fn glyph_count(&self) -> usize;

    fn height_unscaled(&self) -> f32 { ... }
    fn glyph_bounds(&self, glyph: &Glyph) -> Rect
    where
        Self: Sized,
    { ... }
    fn outline_glyph(&self, glyph: Glyph) -> Option<OutlinedGlyph>
    where
        Self: Sized,
    { ... }
    fn as_scaled<S: Into<PxScale>>(&self, scale: S) -> PxScaleFont<&Self>
    where
        Self: Sized,
    { ... }
    fn into_scaled<S: Into<PxScale>>(self, scale: S) -> PxScaleFont<Self>
    where
        Self: Sized,
    { ... }
}

Functionality required from font data.

See also FontArc, FontRef and FontVec.

Units

Units of unscaled accessors are "font units", which is an arbitrary unit defined by the font. See Font::units_per_em.

Font sizes are typically specified in "points". According to the modern standard, 1pt = 1/72in. The "point size" of a font is the number of points per em.

The DPI (dots-per-inch) of a screen depends on the screen in question; 96 DPI is often considered the "standard". For high-DPI displays the DPI may be specified directly or one may multiply 96 by a scale-factor.

Thus, for example, a 10pt font on a 96 pixels-per-inch display has 10 / 72 * 96 = 13.333... pixels-per-em. If we divide this number by units_per_em we then get a scaling factor: pixels-per-font-unit.

Note however that since PxScale values are relative to the text height, one further step is needed: multiply by Font::height_unscaled.

use ab_glyph::{Font, PxScale};

fn pt_size_to_px_scale<F: Font>(font: &F, pt_size: f32, screen_scale_factor: f32) -> PxScale {
    let px_per_em = pt_size * screen_scale_factor * (96.0 / 72.0);
    let units_per_em = font.units_per_em().unwrap();
    let height = font.height_unscaled();
    PxScale::from(px_per_em * height / units_per_em)
}

Required methods

`fn units_per_em(&self) -> Option<f32>`

Get the size of the font unit

This returns "font units per em", where 1em is a base unit of font scale (typically the width of a capital 'M').

Returns None in case the font unit size exceeds the expected range. See Face::units_per_em.

`fn ascent_unscaled(&self) -> f32`

Unscaled glyph ascent.

Scaling can be done with as_scaled.

`fn descent_unscaled(&self) -> f32`

Unscaled glyph descent.

Scaling can be done with as_scaled.

`fn line_gap_unscaled(&self) -> f32`

Unscaled line gap.

Scaling can be done with as_scaled.

`fn glyph_id(&self, c: char) -> GlyphId`

Lookup a GlyphId matching a given char.

Scaling can be done with as_scaled.

`fn h_advance_unscaled(&self, id: GlyphId) -> f32`

Unscaled horizontal advance for a given glyph id.

Scaling can be done with as_scaled.

`fn h_side_bearing_unscaled(&self, id: GlyphId) -> f32`

Unscaled horizontal side bearing for a given glyph id.

Scaling can be done with as_scaled.

`fn v_advance_unscaled(&self, id: GlyphId) -> f32`

Unscaled vertical advance for a given glyph id.

Scaling can be done with as_scaled.

`fn v_side_bearing_unscaled(&self, id: GlyphId) -> f32`

Unscaled vertical side bearing for a given glyph id.

Scaling can be done with as_scaled.

`fn kern_unscaled(&self, first: GlyphId, second: GlyphId) -> f32`

Returns additional unscaled kerning to apply for a particular pair of glyph ids.

Scaling can be done with as_scaled.

`fn outline(&self, id: GlyphId) -> Option<Outline>`

Compute unscaled glyph outline curves & bounding box.

`fn glyph_count(&self) -> usize`

The number of glyphs present in this font. Glyph identifiers for this font will always be in the range 0..self.glyph_count()

Loading content...

Provided methods

`fn height_unscaled(&self) -> f32`

Unscaled height ascent - descent.

Scaling can be done with as_scaled.

`fn glyph_bounds(&self, glyph: &Glyph) -> Rect where Self: Sized,`

Returns the layout bounds of this glyph. These are different to the outline px_bounds().

Horizontally: Glyph position +/- h_advance/h_side_bearing. Vertically: Glyph position +/- ascent/descent.

`fn outline_glyph(&self, glyph: Glyph) -> Option<OutlinedGlyph> where Self: Sized,`

Compute glyph outline ready for drawing.

`fn as_scaled<S: Into<PxScale>>(&self, scale: S) -> PxScaleFont<&Self> where Self: Sized,`

Construct a PxScaleFontRef by associating with the given pixel scale.

Example

let font = FontRef::try_from_slice(include_bytes!("../../dev/fonts/Exo2-Light.otf"))?;

assert_eq!(font.descent_unscaled(), -201.0);

assert_eq!(font.as_scaled(24.0).descent(), -4.02);
assert_eq!(font.as_scaled(50.0).descent(), -8.375);