perfect-freehand

Perfect Freehand

Perfect freehand is a library for creating freehand paths by @steveruizok.

🔗 Demo

Installation

npm install perfect-freehand

or

yarn add perfect-freehand

Usage

The library exports a default function, getStroke, that:

• accepts an array of points and an (optional) options object
• returns a stroke as an array of points formatted as [x, y]

import getStroke from 'perfect-freehand'

You may format your input points either as an array or an object as shown below. In both cases, the pressure value is optional.

getStroke([
  [0, 0, 0],
  [10, 5, 0.5],
  [20, 8, 0.3],
])

getStroke([
  { x: 0, y: 0, pressure: 0 },
  { x: 10, y: 5, pressure: 0.5 },
  { x: 20, y: 8, pressure: 0.3 },
])

Options

The options object is optional, as are each of its properties.

Property	Type	Default	Description
size	number	8	The base size (diameter) of the stroke.
thinning	number	.5	The effect of pressure on the stroke's size.
smoothing	number	.5	How much to soften the stroke's edges.
streamline	number	.5	How much to streamline the stroke.
simulatePressure	boolean	true	Whether to simulate pressure based on velocity.

getStroke(myPoints, {
  size: 8,
  thinning: 0.5,
  smoothing: 0.5,
  streamline: 0.5,
  simulatePressure: true,
})

Tip: To create a stroke that gets thinner with pressure instead of thicker, use a negative number for the thinning option.

Rendering

While getStroke returns an array of points representing a stroke, it's up to you to decide how you will render the stroke. The library does not export any rendering solutions.

For example, here is a function that takes in a stroke and returns SVG path data. You can use the string returned by this function in two ways. For SVG, you can pass the data into path element's d property. For HTML canvas, you can pass the string into the Path2D constructor and then stroke or fill the path.

// Create SVG path data using the points from perfect-freehand.
function getSvgPathFromStroke(stroke) {
  const d = []

  let [p0, p1] = stroke

  d.push(`M ${p0[0]} ${p0[1]} Q`)

  for (let i = 1; i < stroke.length; i++) {
    const mpx = p0[0] + (p1[0] - p0[0]) / 2
    const mpy = p0[1] + (p1[1] - p0[1]) / 2
    d.push(`${p0[0]},${p0[1]} ${mpx},${mpy}`)
    p0 = p1
    p1 = stroke[i + 1]
  }

  d.push('Z')

  return d.join(' ')
}

Example

import * as React from 'react'
import getStroke from 'perfect-freehand'
import { getSvgPathFromStroke } from './utils'

export default function Example() {
  const [currentMark, setCurrentMark] = React.useState()

  function handlePointerDown(e) {
    setCurrentMark({
      type: e.pointerType,
      points: [[e.pageX, e.pageY, e.pressure]],
    })
  }

  function handlePointerMove(e) {
    if (e.buttons === 1) {
      setCurrentMark({
        ...currentMark,
        points: [...currentMark.points, [e.pageX, e.pageY, e.pressure]],
      })
    }
  }

  const stroke = currentMark
    ? getStroke(currentMark.points, {
        size: 16,
        thinning: 0.75,
        smoothing: 0.5,
        streamline: 0.5,
        simulatePressure: currentMark.type !== 'pen',
      })
    : []

  return (
    <svg
      width={800}
      height={600}
      onPointerDown={handlePointerDown}
      onPointerMove={handlePointerMove}
      style={{ touchAction: 'none' }}
    >
      {currentMark && <path d={getSvgPathFromStroke(stroke)} />}
    </svg>
  )
}

Advanced Usage

Functions

For advanced usage, the library also exports smaller functions that getStroke uses to generate its SVG data. While you can use getStroke's data to render strokes with an HTML canvas (via the Path2D element) or with SVG paths, these new functions will allow you to create paths in other rendering technologies.

getStrokePoints

Accepts an array of points (formatted either as [x, y, pressure] or { x: number, y: number, pressure: number}) and returns a set of streamlined points as [x, y, pressure, angle, distance, length]. The path's total length will be the length of the last point in the array.

getStrokeOutlinePoints

Accepts an array of points (formatted as [x, y, pressure, angle, distance, length], i.e. the output of getStrokePoints) and returns an array of points ([x, y]) defining the outline of a pressure-sensitive stroke.

Rendering a Flattened Stroke

To render a stroke as a flat polygon, add the polygon-clipping package and use (or refer to) the following function.

import getStroke from 'perfect-freehand'
import polygonClipping from 'polygon-clipping'

function getFlatSvgPathFromStroke(stroke) {

  const poly = polygonClipping.union([stroke] as any)

  const d = []

  for (let face of poly) {
    for (let pts of face) {
      let [p0, p1] = pts

      d.push(`M ${p0[0]} ${p0[1]} Q`)

      for (let i = 1; i < pts.length; i++) {
        const mpx = p0[0] + (p1[0] - p0[0]) / 2
        const mpy = p0[1] + (p1[1] - p0[1]) / 2
        d.push(`${p0[0]},${p0[1]} ${mpx},${mpy}`)
        p0 = p1
        p1 = pts[i + 1]
      }

      d.push('Z')
    }
  }

  return d.join(' ')
}