[−]Trait druid::piet::kurbo::Shape

pub trait Shape where
    <Self::BezPathIter as Iterator>::Item == PathEl, {
    type BezPathIter: Iterator;
    fn to_bez_path(&self, tolerance: f64) -> Self::BezPathIter;

    fn area(&self) -> f64;

    fn perimeter(&self, accuracy: f64) -> f64;

    fn winding(&self, pt: Point) -> i32;

    fn bounding_box(&self) -> Rect;

    fn into_bez_path(self, tolerance: f64) -> BezPath { ... }

    fn as_line(&self) -> Option<Line> { ... }

    fn as_rect(&self) -> Option<Rect> { ... }

    fn as_rounded_rect(&self) -> Option<RoundedRect> { ... }

    fn as_circle(&self) -> Option<Circle> { ... }

    fn as_path_slice(&self) -> Option<&[PathEl]> { ... }
}

A generic trait for open and closed shapes.

Associated Types

type BezPathIter: Iterator

The iterator resulting from to_bez_path.

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Required methods

fn to_bez_path(&self, tolerance: f64) -> Self::BezPathIter

Convert to a Bézier path, as an iterator over path elements.

Callers should exhaust the as_ methods first, as those are likely to be more efficient; in the general case, this allocates.

The tolerance parameter controls the accuracy of conversion of geometric primitives to Bézier curves, as curves such as circles cannot be represented exactly but only approximated. For drawing as in UI elements, a value of 0.1 is appropriate, as it is unlikely to be visible to the eye. For scientific applications, a smaller value might be appropriate. Note that in general the number of cubic Bézier segments scales as tolerance ^ (-1/6).

TODO: When GAT's land, the type of this can be changed to contain a &'a self reference, which would let us take iterators from complex shapes without cloning.

fn area(&self) -> f64

Signed area.

This method only produces meaningful results with closed shapes.

The convention for positive area is that y increases when x is positive. Thus, it is clockwise when down is increasing y (the usual convention for graphics), and anticlockwise when up is increasing y (the usual convention for math).

fn perimeter(&self, accuracy: f64) -> f64

Total length of perimeter.

fn winding(&self, pt: Point) -> i32

Winding number of point.

This method only produces meaningful results with closed shapes.

The sign of the winding number is consistent with that of area, meaning it is +1 when the point is inside a positive area shape and -1 when it is inside a negative area shape. Of course, greater magnitude values are also possible when the shape is more complex.

fn bounding_box(&self) -> Rect

The smallest rectangle that encloses the shape.

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Provided methods

fn into_bez_path(self, tolerance: f64) -> BezPath

Convert into a Bézier path.

Currently, this always allocates. It is appropriate when the resulting path is to be retained.

The tolerance parameter is the same as to_bez_path().

fn as_line(&self) -> Option<Line>

If the shape is a line, make it available.

fn as_rect(&self) -> Option<Rect>

If the shape is a rectangle, make it available.

fn as_rounded_rect(&self) -> Option<RoundedRect>

If the shape is a rounded rectangle, make it available.

fn as_circle(&self) -> Option<Circle>

If the shape is a circle, make it available.

fn as_path_slice(&self) -> Option<&[PathEl]>

If the shape is stored as a slice of path elements, make that available.

Note: when GAT's land, a method like to_bez_path would be able to iterate through the slice with no extra allocation, without making any assumption that storage is contiguous.

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Implementations on Foreign Types

impl<'a> Shape for &'a [PathEl]

Implements [Shape] for a slice of [PathEl], provided that the first element of the slice is not a PathEl::ClosePath. If it is, several of these functions will panic.

If the slice starts with LineTo, QuadTo, or CurveTo, it will be treated as a MoveTo.

type BezPathIter = Cloned<Iter<'a, PathEl>>

fn area(&self) -> f64

Signed area.

fn winding(&self, pt: Point) -> i32

Winding number of point.

impl<'a, T> Shape for &'a T where
    T: Shape, 

Blanket implementation so impl Shape will accept owned or reference.

type BezPathIter = <T as Shape>::BezPathIter

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Implementors

impl Shape for Arc

type BezPathIter = Chain<Once<PathEl>, ArcAppendIter>

fn area(&self) -> f64

Note: shape isn't closed so area is not well defined.

fn perimeter(&self, accuracy: f64) -> f64

Note: Finding the perimiter of an ellipse is fairly involved, so for now just approximate by using the bezier curve representation. (See https://en.wikipedia.org/wiki/Ellipse#Circumference)

fn winding(&self, pt: Point) -> i32

Note: shape isn't closed so a point's winding number is not well defined.

impl Shape for BezPath

type BezPathIter = IntoIter<PathEl>

fn area(&self) -> f64

Signed area.

fn winding(&self, pt: Point) -> i32

Winding number of point.

impl Shape for Circle

type BezPathIter = CirclePathIter

impl Shape for CircleSegment

type BezPathIter = Chain<Chain<Chain<Chain<Once<PathEl>, Once<PathEl>>, ArcAppendIter>, Once<PathEl>>, ArcAppendIter>

impl Shape for Ellipse

type BezPathIter = Chain<Once<PathEl>, ArcAppendIter>

impl Shape for Line

type BezPathIter = LinePathIter

fn area(&self) -> f64

Returning zero here is consistent with the contract (area is only meaningful for closed shapes), but an argument can be made that the contract should be tightened to include the Green's theorem contribution.

fn winding(&self, _pt: Point) -> i32

Same consideration as area.

impl Shape for RoundedRect

type BezPathIter = RoundedRectPathIter

impl Shape for Rect

type BezPathIter = RectPathIter

fn winding(&self, pt: Point) -> i32

Note: this function is carefully designed so that if the plane is tiled with rectangles, the winding number will be nonzero for exactly one of them.

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