Add glyf bbox fallback

[alexheretic]

Using airstrip.ttf https://dl.dafont.com/dl/?f=airstrip_four character v returns a zero bounding box result from outline_glyph which seems wrong.

Reproduce

const AIRSTRIP: &[u8] = include_bytes!("../airstrip.ttf");

fn main() {
    let airstrip = ttf_parser::Face::from_slice(AIRSTRIP, 0).unwrap();

    let v = airstrip.glyph_index('v').unwrap();
    let bounds = airstrip.outline_glyph(v, &mut OutlinePrinter);

    dbg!(bounds);
}

struct OutlinePrinter;

impl ttf_parser::OutlineBuilder for OutlinePrinter {
    fn move_to(&mut self, x: f32, y: f32) {
        eprintln!("outline-move_to({}, {})", x, y);
    }
    fn line_to(&mut self, x: f32, y: f32) {
        eprintln!("outline-line_to({}, {})", x, y);
    }
    fn quad_to(&mut self, x1: f32, y1: f32, x: f32, y: f32) {
        eprintln!("outline-quad_to({}, {}, {}, {})", x1, y1, x, y);
    }
    fn curve_to(&mut self, x1: f32, y1: f32, x2: f32, y2: f32, x: f32, y: f32) {
        eprintln!("outline-curve_to({}, {}, {}, {}, {}, {})", x1, y1, x2, y2, x, y);
    }
    fn close(&mut self) {
        eprintln!("outline-close");
    }
}

outline-move_to(955, 1301)
outline-quad_to(864, 1298, 833, 1247)
outline-quad_to(802, 1196, 552, 447)
outline-quad_to(300, 1196, 272.5, 1248.5)
outline-quad_to(245, 1301, 150, 1301)
outline-quad_to(0, 1301, 0, 1151)
outline-line_to(401, 99)
outline-quad_to(443, 14, 493.5, 5.5)
outline-quad_to(544, -3, 602.5, 2.5)
outline-quad_to(661, 8, 697, 99)
outline-line_to(1102, 1149)
outline-quad_to(1102, 1301, 955, 1301)
outline-close
[src/main.rs:11] bounds = Some(
    Rect {
        x_min: 0,
        y_min: 0,
        x_max: 0,
        y_max: 0,
    },
)

[RazrFalcon]

Glyph 89 indeed has a zero bbox. So this a malformed font.
Surprisingly, FreeType actually recovers/calculates the bbox somehow, but harfbuzz is not.

I guess you should calculate the bbox manually and/or use glyph_hor_advance and glyph_hor_side_bearing.
Not sure if ttf-parser should do it automatically.

[alexheretic]

Thanks for the info. I'll put a workaround fix in downstream for the time being.