Trait ab_glyph::Font

source · [−]
pub trait Font {

Show 19 methods    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 codepoint_ids(&self) -> CodepointIdIter<'_>ⓘNotable traits for CodepointIdIter<'a>impl<'a> Iterator for CodepointIdIter<'a>    type Item = (GlyphId, char);;

    fn glyph_raster_image(
        &self, 
        id: GlyphId, 
        pixel_size: u16
    ) -> Option<GlyphImage<'_>>;

    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,
    { ... }

}
Expand description

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

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.

Unscaled glyph ascent.

Scaling can be done with as_scaled.

Unscaled glyph descent.

Scaling can be done with as_scaled.

Unscaled line gap.

Scaling can be done with as_scaled.

Lookup a GlyphId matching a given char.

Scaling can be done with as_scaled.

Unscaled horizontal advance for a given glyph id.

Scaling can be done with as_scaled.

Unscaled horizontal side bearing for a given glyph id.

Scaling can be done with as_scaled.

Unscaled vertical advance for a given glyph id.

Scaling can be done with as_scaled.

Unscaled vertical side bearing for a given glyph id.

Scaling can be done with as_scaled.

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

Scaling can be done with as_scaled.

Compute unscaled glyph outline curves & bounding box.

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

Returns an iterator of all distinct (GlyphId, char) pairs. Not ordered.

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

// Iterate over pairs, each id will appear at most once.
let mut codepoint_ids = font.codepoint_ids();
assert_eq!(codepoint_ids.next(), Some((GlyphId(408), '\r')));
assert_eq!(codepoint_ids.next(), Some((GlyphId(1), ' ')));
assert_eq!(codepoint_ids.next(), Some((GlyphId(75), '!')));

// Build a lookup map for all ids
let map: HashMap<_, _> = font.codepoint_ids().collect();
assert_eq!(map.get(&GlyphId(75)), Some(&'!'));

Returns a pre-rendered image of the glyph.

This is normally only present when an outline is not sufficient to describe the glyph, such as emojis (particularly color ones). The pixel_size parameter is in pixels per em, and will be used to select between multiple possible images (if present); the returned image will likely not match this value, requiring you to scale it to match the target resolution. To get the largest image use u16::MAX.

Provided methods

Unscaled height ascent - descent.

Scaling can be done with as_scaled.

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.

Compute glyph outline ready for drawing.

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);

Move into a PxScaleFont associated with the given pixel scale.

Implementations on Foreign Types

Implementors