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# d3-shape Visualizations typically consist of discrete graphical marks, such as [symbols](#symbols), [arcs](#arcs), [lines](#lines) and [areas](#areas). While the rectangles of a bar chart may be easy enough to generate directly using [SVG](http://www.w3.org/TR/SVG/paths.html#PathData) or [Canvas](http://www.w3.org/TR/2dcontext/#canvaspathmethods), other shapes are complex, such as rounded annular sectors and centripetal Catmull–Rom splines. This module provides a variety of shape generators for your convenience. As with other aspects of D3, these shapes are driven by data: each shape generator exposes accessors that control how the input data are mapped to a visual representation. For example, you might define a line generator for a time series by [scaling](https://github.com/d3/d3-scale) fields of your data to fit the chart: ```js const line = d3.line() .x(d => x(d.date)) .y(d => y(d.value)); ``` This line generator can then be used to compute the `d` attribute of an SVG path element: ```js path.datum(data).attr("d", line); ``` Or you can use it to render to a Canvas 2D context: ```js line.context(context)(data); ``` For more, read [Introducing d3-shape](https://medium.com/@mbostock/introducing-d3-shape-73f8367e6d12). ## Installing If you use npm, `npm install d3-shape`. You can also download the [latest release on GitHub](https://github.com/d3/d3-shape/releases/latest). For vanilla HTML in modern browsers, import d3-shape from jsDelivr: ```html <script type="module"> import {line} from "https://cdn.jsdelivr.net/npm/d3-shape@3/+esm"; const l = line(); </script> ``` For legacy environments, you can load d3-shape’s UMD bundle; a `d3` global is exported: ```html <script src="https://cdn.jsdelivr.net/npm/d3-path@3"></script> <script src="https://cdn.jsdelivr.net/npm/d3-shape@3"></script> <script> const l = d3.line(); </script> ``` ## API Reference * [Arcs](#arcs) * [Pies](#pies) * [Lines](#lines) * [Areas](#areas) * [Curves](#curves) * [Custom Curves](#custom-curves) * [Links](#links) * [Symbols](#symbols) * [Custom Symbol Types](#custom-symbol-types) * [Stacks](#stacks) Note: all the methods that accept arrays also accept iterables and convert them to arrays internally. ### Arcs [<img alt="Pie Chart" src="./img/pie.png" width="295" height="295">](https://observablehq.com/@d3/pie-chart)[<img alt="Donut Chart" src="./img/donut.png" width="295" height="295">](https://observablehq.com/@d3/donut-chart) The arc generator produces a [circular](https://en.wikipedia.org/wiki/Circular_sector) or [annular](https://en.wikipedia.org/wiki/Annulus_\(mathematics\)) sector, as in a pie or donut chart. If the absolute difference between the [start](#arc_startAngle) and [end](#arc_endAngle) angles (the *angular span*) is greater than [τ](https://en.wikipedia.org/wiki/Turn_\(geometry\)#Tau_proposal), the arc generator will produce a complete circle or annulus. If it is less than τ, the arc’s angular length will be equal to the absolute difference between the two angles (going clockwise if the signed difference is positive and anticlockwise if it is negative). If the absolute difference is less than τ, the arc may have [rounded corners](#arc_cornerRadius) and [angular padding](#arc_padAngle). Arcs are always centered at ⟨0,0⟩; use a transform (see: [SVG](http://www.w3.org/TR/SVG/coords.html#TransformAttribute), [Canvas](http://www.w3.org/TR/2dcontext/#transformations)) to move the arc to a different position. See also the [pie generator](#pies), which computes the necessary angles to represent an array of data as a pie or donut chart; these angles can then be passed to an arc generator. <a name="arc" href="#arc">#</a> d3.<b>arc</b>() · [Source](https://github.com/d3/d3-shape/blob/main/src/arc.js) Constructs a new arc generator with the default settings. <a name="_arc" href="#_arc">#</a> <i>arc</i>(<i>arguments…</i>) · [Source](https://github.com/d3/d3-shape/blob/main/src/arc.js) Generates an arc for the given *arguments*. The *arguments* are arbitrary; they are simply propagated to the arc generator’s accessor functions along with the `this` object. For example, with the default settings, an object with radii and angles is expected: ```js const arc = d3.arc(); arc({ innerRadius: 0, outerRadius: 100, startAngle: 0, endAngle: Math.PI / 2 }); // "M0,-100A100,100,0,0,1,100,0L0,0Z" ``` If the radii and angles are instead defined as constants, you can generate an arc without any arguments: ```js const arc = d3.arc() .innerRadius(0) .outerRadius(100) .startAngle(0) .endAngle(Math.PI / 2); arc(); // "M0,-100A100,100,0,0,1,100,0L0,0Z" ``` If the arc generator has a [context](#arc_context), then the arc is rendered to this context as a sequence of [path method](http://www.w3.org/TR/2dcontext/#canvaspathmethods) calls and this function returns void. Otherwise, a [path data](http://www.w3.org/TR/SVG/paths.html#PathData) string is returned. <a name="arc_centroid" href="#arc_centroid">#</a> <i>arc</i>.<b>centroid</b>(<i>arguments…</i>) · [Source](https://github.com/d3/d3-shape/blob/main/src/arc.js) Computes the midpoint [*x*, *y*] of the center line of the arc that would be [generated](#_arc) by the given *arguments*. The *arguments* are arbitrary; they are simply propagated to the arc generator’s accessor functions along with the `this` object. To be consistent with the generated arc, the accessors must be deterministic, *i.e.*, return the same value given the same arguments. The midpoint is defined as ([startAngle](#arc_startAngle) + [endAngle](#arc_endAngle)) / 2 and ([innerRadius](#arc_innerRadius) + [outerRadius](#arc_outerRadius)) / 2. For example: [<img alt="Circular Sector Centroids" src="./img/centroid-circular-sector.png" width="250" height="250">](https://observablehq.com/@d3/pie-settings)[<img alt="Annular Sector Centroids" src="./img/centroid-annular-sector.png" width="250" height="250">](https://observablehq.com/@d3/pie-settings) Note that this is **not the geometric center** of the arc, which may be outside the arc; this method is merely a convenience for positioning labels. <a name="arc_innerRadius" href="#arc_innerRadius">#</a> <i>arc</i>.<b>innerRadius</b>([<i>radius</i>]) · [Source](https://github.com/d3/d3-shape/blob/main/src/arc.js) If *radius* is specified, sets the inner radius to the specified function or number and returns this arc generator. If *radius* is not specified, returns the current inner radius accessor, which defaults to: ```js function innerRadius(d) { return d.innerRadius; } ``` Specifying the inner radius as a function is useful for constructing a stacked polar bar chart, often in conjunction with a [sqrt scale](https://github.com/d3/d3-scale#sqrt). More commonly, a constant inner radius is used for a donut or pie chart. If the outer radius is smaller than the inner radius, the inner and outer radii are swapped. A negative value is treated as zero. <a name="arc_outerRadius" href="#arc_outerRadius">#</a> <i>arc</i>.<b>outerRadius</b>([<i>radius</i>]) · [Source](https://github.com/d3/d3-shape/blob/main/src/arc.js) If *radius* is specified, sets the outer radius to the specified function or number and returns this arc generator. If *radius* is not specified, returns the current outer radius accessor, which defaults to: ```js function outerRadius(d) { return d.outerRadius; } ``` Specifying the outer radius as a function is useful for constructing a coxcomb or polar bar chart, often in conjunction with a [sqrt scale](https://github.com/d3/d3-scale#sqrt). More commonly, a constant outer radius is used for a pie or donut chart. If the outer radius is smaller than the inner radius, the inner and outer radii are swapped. A negative value is treated as zero. <a name="arc_cornerRadius" href="#arc_cornerRadius">#</a> <i>arc</i>.<b>cornerRadius</b>([<i>radius</i>]) · [Source](https://github.com/d3/d3-shape/blob/main/src/arc.js) If *radius* is speci