react-native-sketch-canvas

A React Native component for drawing by touching on both iOS and Android.

Features

• Support iOS and Android
• Stroke thickness and color are changable while drawing.
• Can undo strokes one by one.
• Can serialize path data to JSON. So it can sync other devices or someone else and continue to edit.
• Save drawing to a non-transparent image (png or jpg) or a transparent image (png only)
• Use vector concept. So sketches won't be cropped in different sizes of canvas.

Installation

---

Install from npm (only support RN >= 0.40)

npm install @terrylinla/react-native-sketch-canvas --save

Link native code

react-native link @terrylinla/react-native-sketch-canvas

Usage

---

● Using without UI component (for customizing UI)

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  View,
} from 'react-native';

import { SketchCanvas } from '@terrylinla/react-native-sketch-canvas';

export default class example extends Component {
  render() {
    return (
      <View style={styles.container}>
        <View style={{ flex: 1, flexDirection: 'row' }}>
          <SketchCanvas
            style={{ flex: 1 }}
            strokeColor={'red'}
            strokeWidth={7}
          />
        </View>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1, justifyContent: 'center', alignItems: 'center', backgroundColor: '#F5FCFF',
  },
});

AppRegistry.registerComponent('example', () => example);

Properties

---

Prop	Type	Description
style	object	Styles to be applied on canvas component
strokeColor	string	The color of stroke
strokeWidth	number	The thickness of stroke
onStrokeStart	function	An optional function called when user's finger touches the canvas (starts to draw)
onStrokeChanged	function	An optional function called when user's finger moves
onStrokeEnd	function	An optional function called when user's finger leaves the canvas (end drawing)
onSketchSaved	function	An optional function which accpets 1 argument success, true if image is saved successfully
onPathsChange	function	An optional function which accpets 1 argument pathsCount, which indicates the number of paths. Useful for UI controls. (Thanks to toblerpwn)
user	string	An identifier to identify who draws the path. Useful when undo between two users
touchEnabled	bool	If false, disable touching. Default is true.

Methods

---

Method	Description
clear()	Clear all the paths
undo()	Delete the latest path. Can undo multiple times.
addPath(path)	Add a path (see below) to canvas.
deletePath(id)	Delete a path with its id
save(imageType, transparent, folder, filename)	Android: Save image in imageType format with transparent background (if transparent sets to True) to /sdcard/Pictures/folder/filename (which is Environment.DIRECTORY_PICTURES). iOS: Save image in imageType format with transparent background (if transparent sets to True) to camera roll. (folder and filename are ignored automatically)
getPaths()	Get the paths that drawn on the canvas
getBase64(imageType, transparent, callback)	Get the base64 of image and receive data in callback function, which called with 2 arguments. First one is error (null if no error) and second one is base64 result.

● Using with build-in UI components

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  Text,
  View,
  Alert,
} from 'react-native';

import RNSketchCanvas from '@terrylinla/react-native-sketch-canvas';

export default class example extends Component {
  render() {
    return (
      <View style={styles.container}>
        <View style={{ flex: 1, flexDirection: 'row' }}>
          <RNSketchCanvas
            containerStyle={{ backgroundColor: 'transparent', flex: 1 }}
            canvasStyle={{ backgroundColor: 'transparent', flex: 1 }}
            defaultStrokeIndex={0}
            defaultStrokeWidth={5}
            closeComponent={<View style={styles.functionButton}><Text style={{color: 'white'}}>Close</Text></View>}
            undoComponent={<View style={styles.functionButton}><Text style={{color: 'white'}}>Undo</Text></View>}
            clearComponent={<View style={styles.functionButton}><Text style={{color: 'white'}}>Clear</Text></View>}
            infoComponent={<View style={styles.functionButton}><Text style={{color: 'white'}}>Info</Text></View>}
            strokeComponent={color => (
              <View style={[{ backgroundColor: color }, styles.strokeColorButton]} />
            )}
            strokeSelectedComponent={(color, index, changed) => {
              return (
                <View style={[{ backgroundColor: color, borderWidth: 2 }, styles.strokeColorButton]} />
              )
            }}
            strokeWidthComponent={(w) => {
              return (<View style={styles.strokeWidthButton}>
                <View  style={{
                  backgroundColor: 'white', marginHorizontal: 2.5,
                  width: Math.sqrt(w / 3) * 10, height: Math.sqrt(w / 3) * 10, borderRadius: Math.sqrt(w / 3) * 10 / 2
                }} />
              </View>
            )}}
            saveComponent={<View style={styles.functionButton}><Text style={{color: 'white'}}>Save</Text></View>}
            savePreference={() => {
              return {
                folder: 'RNSketchCanvas',
                filename: String(Math.ceil(Math.random() * 100000000)),
                transparent: false,
                imageType: 'png'
              }
            }}
          />
        </View>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1, justifyContent: 'center', alignItems: 'center', backgroundColor: '#F5FCFF',
  },
  strokeColorButton: {
    marginHorizontal: 2.5, marginVertical: 8, width: 30, height: 30, borderRadius: 15,
  },
  strokeWidthButton: {
    marginHorizontal: 2.5, marginVertical: 8, width: 30, height: 30, borderRadius: 15,
    justifyContent: 'center', alignItems: 'center', backgroundColor: '#39579A'
  },
  functionButton: {
    marginHorizontal: 2.5, marginVertical: 8, height: 30, width: 60,
    backgroundColor: '#39579A', justifyContent: 'center', alignItems: 'center', borderRadius: 5,
  }
});

AppRegistry.registerComponent('example', () => example);

Properties

---

Prop	Type	Description
containerStyle	object	Styles to be applied on container
canvasStyle	object	Styles to be applied on canvas component
onStrokeStart	function	See above
onStrokeChanged	function	See above
onStrokeEnd	function	See above
onPathsChange	function	See above
onClosePressed	function	An optional function called when user taps closeComponent
onInfoPressed	function	An optional function called when user taps infoComponent
onUndoPressed	function	An optional function that accepts a argument id (the deleted id of path) and is called when user taps "undo"
onClearPressed	function	An optional function called when user taps clearComponent
user	string	See above
closeComponent	component	An optional component for closing
infoComponent	component	An optional component for showing info
undoComponent	component	An optional component for undoing
clearComponent	component	An optional component for clearing
saveComponent	component	An optional component for saving
strokeComponent	function	An optional function which accpets 1 argument color and should return a component.
strokeSelectedComponent	function	An optional function which accpets 3 arguments color, selectedIndex, isColorChanged and should return a component. isColorChanged is useful for animating when changing color. Because rerendering also calls this function, we need isColorChanged to determine whether the component is rerendering or the selected color is changed.
strokeWidthComponent	function	An optional function which accpets 1 argument width and should return a component.
strokeColors	array	An array of colors. Example: [{ color: '#000000' }, {color: '#FF0000'}]
defaultStrokeIndex	numbber	The default index of selected stroke color
defaultStrokeWidth	number	The default thickness of stroke
minStrokeWidth	number	The minimum value of thickness
maxStrokeWidth	number	The maximum value of thickness
strokeWidthStep	number	The step value of thickness when tapping strokeWidthComponent.
savePreference	function	A function which is called when saving image and should return an object (see below).
onSketchSaved	function	See above

Objects

Use for saving image

{
  folder: 'RNSketchCanvas', // use in Android, the folder name in Pictures
  filename: 'image',  // use in Android, the file name of image
  transparent: true,  // true for transparent background, ignored when imageType sets to 'jpg'
  imageType: 'jpg'  // one of 'jpg' or 'png'
}

Path format

{
  drawer: 'user1',
  size: { // the size of drawer's canvas
    width: 480,
    height: 640
  },
  path: {
    id: 8979841, // path id
    color: '#000000', 
    width: 5,
    data: [
      "296.11,281.34",  // x,y
      "293.52,284.64",
      "290.75,289.73"
    ]
  }
}

Example

---

The source code includes 3 examples, using build-in UI components, using with only canvas, and sync between two canvases.

Check full example app in the example folder

Note: The example which showing synchronization between two canvases only works on Android device. For iOS, only one canvas can be shown at the same time. So if the path data can be transmitted to another device via internet, it still works.