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Curved Arrows

version license

A set of functions for drawing S-curved arrows between points and shapes.

  • getArrow - For point-to-point arrows (has glitches, not ready yet).
  • getBoxToBoxArrow - For rectangle-to-rectangle arrows.

demo animation

👉 Demo | How it works

You may also want to see steveruizok's perfect-arrows, it's smarter but the start point and the end point are less predictable.

Installation

npm i curved-arrows

or

yarn add curved-arrows

Usage

The functions in this library has similar arguments and return values to steveruizok's perfect-arrows. Notable differences are options and the return values containing two control points, one for start point and one end point, instead of one, to represent an S-curve.

The return values provide only the information needed to draw an arrow. You'll need to draw the arrow yourself using your technology of choice. See below for an example using React and SVG.

getArrow(x0, y0, x1, y1, options)

The getArrow function accepts the position of two points and returns an array containing this information:

  • four points: start, end, and two control points (one for start, one for end)
  • two angles: end and start

You can use this information to draw an S-curve and arrow heads. You can use the options object to tweak the return values.

const arrowHeadSize = 9
const arrow = getArrow(0, 0, 100, 200, {
  padStart: 0,
  padEnd: arrowHeadSize,
})
const [sx, sy, c1x, c1y, c2x, c2y, ex, ey, ae, as] = arrow

Arguments

Argument Type Description
x0 number The x position of the starting point.
y0 number The y position of the starting point.
x1 number The x position of the ending point.
y1 number The y position of the ending point.
options object An (optional) object containing one or more of the options described below.

Options

Option Type Default Description
padStart number 0 How far the arrow's starting point should be from the provided starting point.
padEnd number 0 How far the arrow's ending point should be from the provided ending point.
controlPointStretch number 50 Enforce a minimal distance from the arrow's starting/ending point to the control points making the curve. (demo, more explanation, code)
allowedStartSides RectSide[] ['top', 'right', 'bottom', 'left'] Constrain which sides of the start box allow the arrow to start.
allowedEndSides RectSide[] ['top', 'right', 'bottom', 'left'] Constrain which sides of the end box allow the arrow to end.

Returns

Argument Type Description
sx number The x position of the (padded) starting point.
sy number The y position of the (padded) starting point.
c1x number The x position of the control point of the starting point.
c1y number The y position of the control point of the starting point.
c2x number The x position of the control point of the ending point.
c2y number The y position of the control point of the ending point.
ex number The x position of the (padded) ending point.
ey number The y position of the (padded) ending point.
ae number The angle (in degree) for an ending arrowhead.
as number The angle (in degree) for a starting arrowhead.

getBoxToBoxArrow(x0, y0, w0, h0, x1, y1, w1, h1, options)

The getBoxToBoxArrow function accepts the position and dimensions of two boxes (or rectangles) and returns an array containing this information:

  • four points: start, end, and two control points (one for start, one for end)
  • two angles: end and start

You can use this information to draw an S-curve and arrow heads. You can use the options object to tweak the return values.

Note: The options and values returned by getBoxToBoxArrow are in the same format as the options and values for getArrow.

const arrowHeadSize = 9
const arrow = getArrow(0, 0, 200, 100, 300, 50, 200, 100, {
  padStart: 0,
  padEnd: arrowHeadSize,
})
const [sx, sy, c1x, c1y, c2x, c2y, ex, ey, ae, as] = arrow

Arguments

Argument Type Description
x0 number The x position of the first rectangle.
y0 number The y position of the first rectangle.
w0 number The width of the first rectangle.
h0 number The height of the first rectangle.
x1 number The x position of the second rectangle.
y1 number The y position of the second rectangle.
w1 number The width of the second rectangle.
h1 number The height of the second rectangle.
options object An (optional) object containing one or more of the options described below.

Options

See options in getArrow above. (Both functions use the same options object.)

Returns

See returns in getArrow above. (Both functions return the same set of values.)

Example: A React Arrow Component

import * as React from 'react'
import { getArrow } from 'curved-arrows'

export function Arrow() {
  const p1 = { x: 100, y: 100 }
  const p2 = { x: 300, y: 200 }
  const arrowHeadSize = 9
  const color = 'black'
  const [sx, sy, c1x, c1y, c2x, c2y, ex, ey, ae] = getArrow(p1.x, p1.y, p2.x, p2.y, {
    padEnd: arrowHeadSize,
  })

  return (
    <svg
      width="100%"
      height="100%"
      xmlns="http://www.w3.org/2000/svg">
      <path
        d={`M ${sx} ${sy} C ${c1x} ${c1y}, ${c2x} ${c2y}, ${ex} ${ey}`}
        stroke={color}
        strokeWidth={arrowHeadSize / 2}
        fill="none"
      />
      <polygon
        points={`0,${-arrowHeadSize} ${arrowHeadSize *
          2},0, 0,${arrowHeadSize}`}
        transform={`translate(${ex}, ${ey}) rotate(${ae})`}
        fill={color}
      />
    </svg>
  )
}

Author

@hialexwang