Draw perfect pressure-sensitive freehand strokes.

🔗 Demo

Table of Contents

• Installation
• Usage
• Support
• Discussion
• Author

Installation

npm install perfect-freehand

or

yarn add perfect-freehand

Usage

This package's default export is a function 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 as array or an object. In both cases, the value for pressure is optional (it will default to .5).

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.

getStroke(myPoints, {
  size: 8,
  thinning: 0.5,
  smoothing: 0.5,
  streamline: 0.5,
  easing: t => t * t * t,
  simulatePressure: true,
})

Tip: To create a stroke with a steady line, set the thinning option to 0.

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, the function below will turn a stroke into SVG path data for use with either SVG paths or HTML Canvas (using the Path2D constructor).

// Create SVG path data using the points from perfect-freehand.
function getSvgPathFromStroke(points) {
  if (points.length === 0) return ''

  const d = []

  let [p0, p1] = points

  d.push('M', p0[0], p0[1], 'Q')

  for (let i = 1; i < points.length; i++) {
    d.push(p0[0], p0[1], (p0[0] + p1[0]) / 2, (p0[1] + p1[1]) / 2)
    p0 = p1
    p1 = points[i]
  }

  d.push('Z')

  return d.join(' ')
}

To render a stroke as a flat polygon, add the polygon-clipping package and use the following function together with the getSvgPathFromStroke.

import polygonClipping from 'polygon-clipping'

function getFlatSvgPathFromStroke(stroke) {
  const poly = polygonClipping.union([stroke])

  const d = []

  for (let face of poly) {
    for (let points of face) {
      d.push(getSvgPathFromStroke(points))
    }
  }

  return d.join(' ')
}

Tip: For implementations in Typescript, see the example project included in this repository.

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

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

  return (
    <svg
      onPointerDown={handlePointerDown}
      onPointerMove={handlePointerMove}
      style={{ touchAction: 'none' }}
    >
      {currentMark && (
        <path
          d={getSvgPathFromStroke(
            getStroke(currentMark.points, {
              size: 24,
              thinning: 0.75,
              smoothing: 0.5,
              streamline: 0.5,
              simulatePressure: currentMark.type !== 'pen',
            })
          )}
        />
      )}
    </svg>
  )
}

Advanced Usage

StrokeOptions

A TypeScript type for the options object.

import { StrokeOptions } from 'perfect-freehand'

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

const strokePoints = getStrokePoints(rawInputPoints)

Accepts an array of points (formatted either as [x, y, pressure] or { x: number, y: number, pressure: number}) and a streamline value. Returns a set of streamlined points as [x, y, pressure, angle, distance, lengthAtPoint]. 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.

const outlinePoints = getOutlinePoints(strokePoints)

Support

Please open an issue for support.

Discussion

Have an idea or casual question? Visit the discussion page.

Author

• @steveruizok