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//! Backend-neutral path geometry.
use crate::{Point, Rect};
/// One command in a path.
#[derive(Debug, Clone, PartialEq)]
pub enum PathCommand {
MoveTo(Point),
LineTo(Point),
CurveTo { c1: Point, c2: Point, to: Point },
Close,
}
/// The rule used to determine which regions a path fills.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum FillRule {
NonZero,
EvenOdd,
}
/// A backend-neutral path and its fill rule.
#[derive(Debug, Clone, PartialEq)]
pub struct Path {
pub commands: Vec<PathCommand>,
pub fill_rule: FillRule,
}
impl Path {
/// Return conservative bounds containing every endpoint and cubic control.
pub fn bounds(&self) -> Option<Rect> {
let mut points = self.commands.iter().flat_map(|command| match command {
PathCommand::MoveTo(point) | PathCommand::LineTo(point) => [Some(*point), None, None],
PathCommand::CurveTo { c1, c2, to } => [Some(*c1), Some(*c2), Some(*to)],
PathCommand::Close => [None, None, None],
});
let first = points.find_map(|point| point)?;
let (mut min_x, mut min_y, mut max_x, mut max_y) = (first.x, first.y, first.x, first.y);
for point in points.flatten() {
min_x = min_x.min(point.x);
min_y = min_y.min(point.y);
max_x = max_x.max(point.x);
max_y = max_y.max(point.y);
}
Some(Rect {
x: min_x,
y: min_y,
width: max_x - min_x,
height: max_y - min_y,
})
}
/// Construct a closed rectangular path.
pub fn rect(rect: Rect) -> Path {
let right = rect.x + rect.width;
let bottom = rect.y + rect.height;
Path {
commands: vec![
PathCommand::MoveTo(Point {
x: rect.x,
y: rect.y,
}),
PathCommand::LineTo(Point {
x: right,
y: rect.y,
}),
PathCommand::LineTo(Point {
x: right,
y: bottom,
}),
PathCommand::LineTo(Point {
x: rect.x,
y: bottom,
}),
PathCommand::Close,
],
fill_rule: FillRule::NonZero,
}
}
/// Construct a closed rectangle with one circular corner radius.
pub fn round_rect(rect: Rect, radius: f64) -> Path {
let radius = radius
.max(0.0)
.min(rect.width.abs() / 2.0)
.min(rect.height.abs() / 2.0);
if radius == 0.0 {
return Self::rect(rect);
}
const KAPPA: f64 = 0.552_284_749_830_793_6;
let right = rect.x + rect.width;
let bottom = rect.y + rect.height;
let control = radius * KAPPA;
Path {
commands: vec![
PathCommand::MoveTo(Point {
x: rect.x + radius,
y: rect.y,
}),
PathCommand::LineTo(Point {
x: right - radius,
y: rect.y,
}),
PathCommand::CurveTo {
c1: Point {
x: right - radius + control,
y: rect.y,
},
c2: Point {
x: right,
y: rect.y + radius - control,
},
to: Point {
x: right,
y: rect.y + radius,
},
},
PathCommand::LineTo(Point {
x: right,
y: bottom - radius,
}),
PathCommand::CurveTo {
c1: Point {
x: right,
y: bottom - radius + control,
},
c2: Point {
x: right - radius + control,
y: bottom,
},
to: Point {
x: right - radius,
y: bottom,
},
},
PathCommand::LineTo(Point {
x: rect.x + radius,
y: bottom,
}),
PathCommand::CurveTo {
c1: Point {
x: rect.x + radius - control,
y: bottom,
},
c2: Point {
x: rect.x,
y: bottom - radius + control,
},
to: Point {
x: rect.x,
y: bottom - radius,
},
},
PathCommand::LineTo(Point {
x: rect.x,
y: rect.y + radius,
}),
PathCommand::CurveTo {
c1: Point {
x: rect.x,
y: rect.y + radius - control,
},
c2: Point {
x: rect.x + radius - control,
y: rect.y,
},
to: Point {
x: rect.x + radius,
y: rect.y,
},
},
PathCommand::Close,
],
fill_rule: FillRule::NonZero,
}
}
/// Construct a closed four-cubic approximation of an ellipse.
pub fn ellipse(rect: Rect) -> Path {
const KAPPA: f64 = 0.552_284_749_830_793_6;
let cx = rect.x + rect.width / 2.0;
let cy = rect.y + rect.height / 2.0;
let rx = rect.width / 2.0;
let ry = rect.height / 2.0;
let dx = rx * KAPPA;
let dy = ry * KAPPA;
Path {
commands: vec![
PathCommand::MoveTo(Point { x: cx + rx, y: cy }),
PathCommand::CurveTo {
c1: Point {
x: cx + rx,
y: cy + dy,
},
c2: Point {
x: cx + dx,
y: cy + ry,
},
to: Point { x: cx, y: cy + ry },
},
PathCommand::CurveTo {
c1: Point {
x: cx - dx,
y: cy + ry,
},
c2: Point {
x: cx - rx,
y: cy + dy,
},
to: Point { x: cx - rx, y: cy },
},
PathCommand::CurveTo {
c1: Point {
x: cx - rx,
y: cy - dy,
},
c2: Point {
x: cx - dx,
y: cy - ry,
},
to: Point { x: cx, y: cy - ry },
},
PathCommand::CurveTo {
c1: Point {
x: cx + dx,
y: cy - ry,
},
c2: Point {
x: cx + rx,
y: cy - dy,
},
to: Point { x: cx + rx, y: cy },
},
PathCommand::Close,
],
fill_rule: FillRule::NonZero,
}
}
}
#[cfg(test)]
mod tests {
use super::{FillRule, Path, PathCommand};
use crate::{Point, Rect};
#[test]
fn empty_path_has_no_bounds() {
let path = Path {
commands: Vec::new(),
fill_rule: FillRule::NonZero,
};
assert_eq!(path.bounds(), None);
}
#[test]
fn bounds_include_cubic_control_points() {
let path = Path {
commands: vec![
PathCommand::MoveTo(Point { x: 0.0, y: 0.0 }),
PathCommand::CurveTo {
c1: Point { x: -2.0, y: 4.0 },
c2: Point { x: 6.0, y: -3.0 },
to: Point { x: 1.0, y: 2.0 },
},
],
fill_rule: FillRule::NonZero,
};
assert_eq!(
path.bounds(),
Some(Rect {
x: -2.0,
y: -3.0,
width: 8.0,
height: 7.0,
})
);
}
#[test]
fn rect_constructor_emits_a_closed_nonzero_path() {
let path = Path::rect(Rect {
x: 1.0,
y: 2.0,
width: 3.0,
height: 4.0,
});
assert_eq!(path.fill_rule, FillRule::NonZero);
assert!(matches!(path.commands.last(), Some(PathCommand::Close)));
}
#[test]
fn round_rect_clamps_the_radius_to_half_the_shorter_side() {
let rect = Rect {
x: 1.0,
y: 2.0,
width: 10.0,
height: 4.0,
};
assert_eq!(Path::round_rect(rect, 99.0), Path::round_rect(rect, 2.0));
assert_eq!(Path::round_rect(rect, -1.0), Path::rect(rect));
}
#[test]
fn round_rect_with_zero_radius_matches_rect() {
let rect = Rect {
x: 1.0,
y: 2.0,
width: 3.0,
height: 4.0,
};
assert_eq!(Path::round_rect(rect, 0.0), Path::rect(rect));
}
#[test]
fn ellipse_path_bounds_contain_the_ellipse_and_lie_within_its_control_hull() {
let rect = Rect {
x: 10.0,
y: 20.0,
width: 30.0,
height: 40.0,
};
assert_eq!(Path::ellipse(rect).bounds(), Some(rect));
}
#[test]
fn bounds_do_not_depend_on_the_fill_rule() {
let commands = Path::rect(Rect {
x: 1.0,
y: 2.0,
width: 3.0,
height: 4.0,
})
.commands;
let nonzero = Path {
commands: commands.clone(),
fill_rule: FillRule::NonZero,
};
let evenodd = Path {
commands,
fill_rule: FillRule::EvenOdd,
};
assert_eq!(nonzero.bounds(), evenodd.bounds());
}
}