d3-shape

Visualizations typically consist of discrete graphical marks, such as symbols, arcs, lines and areas. While the rectangles of a bar chart may be easy enough to generate directly using SVG or Canvas, 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 fields of your data to fit the chart:

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:

path.datum(data).attr("d", line);

Or you can use it to render to a Canvas 2D context:

line.context(context)(data);

For more, read Introducing d3-shape.

Installing

If you use npm, npm install d3-shape. You can also download the latest release on GitHub. For vanilla HTML in modern browsers, import d3-shape from jsDelivr:

<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:

<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
• Pies
• Lines
• Areas
• Curves
• Custom Curves
• Links
• Symbols
• Custom Symbol Types
• Stacks

Note: all the methods that accept arrays also accept iterables and convert them to arrays internally.

Arcs

The arc generator produces a circular or annular sector, as in a pie or donut chart. If the absolute difference between the start and end angles (the angular span) is greater than τ, 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 and angular padding. Arcs are always centered at ⟨0,0⟩; use a transform (see: SVG, Canvas) to move the arc to a different position.

See also the pie generator, 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.

# d3.arc() · Source

Constructs a new arc generator with the default settings.

# arc(arguments…) · Source

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:

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:

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, then the arc is rendered to this context as a sequence of path method calls and this function returns void. Otherwise, a path data string is returned.

# arc.centroid(arguments…) · Source

Computes the midpoint [x, y] of the center line of the arc that would be generated 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 + endAngle) / 2 and (innerRadius + outerRadius) / 2. For example:

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.

# arc.innerRadius([radius]) · Source

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:

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. 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.

# arc.outerRadius([radius]) · Source

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:

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. 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.

# arc.cornerRadius([radius]) · Source

If radius is specified, sets the corner radius to the specified function or number and returns this arc generator. If radius is not specified, returns the current corner radius accessor, which defaults to:

function cornerRadius() {
  return 0;
}

If the corner radius is greater than zero, the corners of the arc are rounded using circles of the given radius. For a circular sector, the two outer corners are rounded; for an annular sector, all four corners are rounded. The corner circles are shown in this diagram:

The corner radius may not be larger than (outerRadius - innerRadius) / 2. In addition, for arcs whose angular span is less than π, the corner radius may be reduced as two adjacent rounded corners intersect. This is occurs more often with the inner corners. See the arc corners animation for illustration.

# arc.startAngle([angle]) · Source

If angle is specified, sets the start angle to the specified function or number and returns this arc generator. If angle is not specified, returns the current start angle accessor, which defaults to:

function startAngle(d) {
  return d.startAngle;
}

The angle is specified in radians, with 0 at -y (12 o’clock) and positive angles proceeding clockwise. If |endAngle - startAngle| ≥ τ, a complete circle or annulus is generated rather than a sector.

# arc.endAngle([angle]) · Source

If angle is specified, sets the end angle to the specified function or number and returns this arc generator. If angle is not specified, returns the current end angle accessor, which defaults to:

function endAngle(d) {
  return d.endAngle;
}

The angle is specified in radians, with 0 at -y (12 o’clock) and positive angles proceeding clockwise. If |endAngle - startAngle| ≥ τ, a complete circle or annulus is generated rather than a sector.

# arc.padAngle([angle]) · Source

If angle is specified, sets the pad angle to the specified function or number and returns this arc generator. If angle is not specified, returns the current pad angle accessor, which defaults to:

function padAngle() {
  return d && d.padAngle;
}

The pad angle is converted to a fixed linear distance separating adjacent arcs, defined as padRadius * padAngle. This distance is subtracted equally from the start and end of the arc. If the arc forms a complete circle or annulus, as when |endAngle - startAngle| ≥ τ, the pad angle is ignored.

If the inner radius or angular span is small relative to the pad angle, it may not be possible to maintain parallel edges between adjacent arcs. In this case, the inner edge of the arc may collapse to a point, similar to a circular sector. For this reason, padding is typically only applied to annular sectors (i.e., when innerRadius is positive), as shown in this diagram:

The recommended minimum inner radius when using padding is outerRadius * padAngle / sin(θ), where θ is the angular span of the smallest arc before padding. For example, if the outer radius is 200 pixels and the pad angle is 0.02 radians, a reasonable θ is 0.04 radians, and a reasonable inner radius is 100 pixels. See the arc padding animation for illustration.

Often, the pad angle is not set directly on the arc generator, but is instead computed by the pie generator so as to ensure that the area of padded arcs is proportional to their value; see pie.padAngle. See the pie padding animation for illustration. If you apply a constant pad angle to the arc generator directly, it tends to subtract disproportionately from smaller arcs, introducing distortion.

# arc.padRadius([radius]) · Source

If radius is specified, sets the pad radius to the specified function or number and returns this arc generator. If radius is not specified, returns the current pad radius accessor, which defaults to null, indicating that the pad radius should be automatically computed as sqrt(innerRadius * innerRadius + outerRadius * outerRadius). The pad radius determines the fixed linear distance separating adjacent arcs, defined as padRadius * padAngle.

# arc.context([context]) · Source

If context is specified, sets the context and returns this arc generator. If context is not specified, returns the current context, which defaults to null. If the context is not null, then the generated arc is rendered to this context as a sequence of path method calls. Otherwise, a path data strin