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.
• Support translucent colors and eraser.
• Support drawing on an image (Thanks to diego-caceres-galvan)
• High performance (See below. Thanks to jeanregisser)
• Can draw multiple canvases in the same screen.
• Can draw multiple multiline text on 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

Methods

Constants

● 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>}
            eraseComponent={<View style={styles.functionButton}><Text style={{color: 'white'}}>Eraser</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

Methods

Constants

Background Image

To use an image as background, localSourceImage(see below) reqires an object, which consists of filename, directory(optional) and mode(optional).
Note: Because native module cannot read the file in JS bundle, file path cannot be relative to JS side. For example, '../assets/image/image.png' will fail to load image.

Typical Usage

• Load image from app native bundle
  
  • Android:
    1. Put your images into android/app/src/main/res/drawable.
    2. Set filename to the name of image files with or without file extension.
    3. Set directory to ''
       
  • iOS:
    1. Open Xcode and add images to project by right clicking Add Files to [YOUR PROJECT NAME].
    2. Set filename to the name of image files with file extension.
    3. Set directory to MAIN_BUNDLE (e.g. RNSketchCanvas.MAIN_BUNDLE or SketchCanvas.MAIN_BUNDLE)
• Load image from camera
  1. Retrive photo complete path (including file extension) after snapping.
  2. Set filename to that path.
  3. Set directory to ''

Content Mode

• AspectFill
  
• AspectFit (default)
  
• ScaleToFill
  

Objects

SavePreference object

{
  folder: 'RNSketchCanvas',
  filename: 'image',
  transparent: true,
  imageType: 'jpg',
  includeImage: true,
  includeText: false,
  cropToImageSize: true
}

Path object

{
  drawer: 'user1',
  size: { // the size of drawer's canvas
    width: 480,
    height: 640
  },
  path: {
    id: 8979841, // path id
    color: '#FF000000', // ARGB or RGB
    width: 5,
    data: [
      "296.11,281.34",  // x,y
      "293.52,284.64",
      "290.75,289.73"
    ]
  }
}

LocalSourceImage object

{
  filename: 'image.png',  // e.g. 'image.png' or '/storage/sdcard0/Pictures/image.png'
  directory: '', // e.g. SketchCanvas.MAIN_BUNDLE or '/storage/sdcard0/Pictures/'
  mode: 'AspectFill'
}

CanvasText object

{
  text: 'TEXT',
  font: '',
  fontSize: 20,
  fontColor: 'red',
  overlay: 'TextOnSketch',
  anchor: { x: 0, y: 1 },
  position: { x: 100, y: 200 },
  coordinate: 'Absolute',
  alignment: 'Center',
  lineHeightMultiple: 1.2
}

Performance

1. For non-transparent path, both Android and iOS performances are good. Because when drawing non-transparent path, only last segment is drawn on canvas, no matter how long the path is, CPU usage is stable at about 20% and 15% in Android and iOS respectively.
2. For transparent path, CPU usage stays at around 25% in Android, however, in iOS, CPU usage grows to 100% :(.
   • Android (https://youtu.be/gXdCEN6Enmk)
         
   • iOS (https://youtu.be/_jO4ky400Eo)
         

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

Troubleshooting

Please refer here.