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

by React Native Example

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

Prop Type Description
style object Styles to be applied on canvas component
strokeColor string Set the color of stroke, which can be #RRGGBB or #RRGGBBAA. If strokeColor is set to #00000000, it will automatically become an eraser.
NOTE: Once an eraser path is sent to Android, Android View will disable hardware acceleration automatically. It might reduce the canvas performance afterward.
strokeWidth number The thickness of stroke
onStrokeStart function An optional function which accpets 2 arguments x and y. Called when user's finger touches the canvas (starts to draw)
onStrokeChanged function An optional function which accpets 2 arguments x and y. 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 2 arguments success and path. If success is true, image is saved successfully and the saved image path might be in second argument. In Android, image path will always be returned. In iOS, image is saved to camera roll or file system, path will be set to null or image location respectively.
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.
localSourceImage object Require an object (see below) which consists of filename, directory(optional) and mode(optional). If set, the image will be loaded and display as a background in canvas. (Thanks to diego-caceres-galvan))(Here for details)
permissionDialogTitle string Android Only: Provide a Dialog Title for the Image Saving PermissionDialog. Defaults to empty string if not set
permissionDialogMessage string Android Only: Provide a Dialog Message for the Image Saving PermissionDialog. Defaults to empty string if not set

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, includeImage, cropToImageSize) Save image to camera roll or filesystem. If localSourceImage is set and a background image is loaded successfully, set includeImage to true to include background image and set cropToImageSize to true to crop output image to background image.
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 or file system. If folder and filename are set, image will save to temporary directory/folder/filename (which is NSTemporaryDirectory())
getPaths() Get the paths that drawn on the canvas
getBase64(imageType, transparent, includeImage, cropToImageSize, 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.

Constants

Constant Description
MAIN_BUNDLE Android: empty string, ''
iOS: equivalent to [[NSBundle mainBundle] bundlePath]
DOCUMENT Android: empty string, ''
iOS: equivalent to NSDocumentDirectory
LIBRARY Android: empty string, ''
iOS: equivalent to NSLibraryDirectory
CACHES Android: empty string, ''
iOS: equivalent to NSCachesDirectory

● 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

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
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
eraseComponent component An optional component for eraser
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

Methods

Method Description
clear() See above
undo() See above
addPath(path) See above
deletePath(id) See above
save()

Constants

Constant Description
MAIN_BUNDLE See above
DOCUMENT See above
LIBRARY See above
CACHES See above

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
}
Property Type Description
folder? string Android: the folder name in Pictures directory
iOS: if filename is not null, image will save to temporary directory with folder and filename, otherwise, it will save to camera roll
filename? string the file name of image
iOS: Set to null to save image to camera roll.
transparent boolean save canvas with transparent background, ignored if imageType is jpg
imageType string image file format
Options: png, jpg
includeImage? boolean Set to true to include the image loaded from LocalSourceImage. (Default is true)
includeImage? boolean Set to true to include the text drawn from Text. (Default is true)
cropToImageSize? boolean Set to true to crop output image to the image loaded from LocalSourceImage. (Default is false)

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'
}
Property Type Description Default
filename string the fold name of the background image file (can be a full path)
directory? string the directory of the background image file (usually used with constants) ''
mode? boolean Specify how the background image resizes itself to fit or fill the canvas.
Options: AspectFill, AspectFit, ScaleToFill		 AspectFit

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
}
Property Type Description Default
text string the text to display (can be multiline by \n)
font? string Android: You can set font to fonts/[filename].ttf to load font in android/app/src/main/assets/fonts/ in your Android project
iOS: Set font that included with iOS
fontSize? number font size 12
fontColor? string text color black
overlay? string Set to TextOnSketch to overlay drawing with text, otherwise the text will be overlaid with drawing.
Options: TextOnSketch, SketchOnText		 SketchOnText
anchor? object Set the origin point of the image. (0, 0) to (1, 1). (0, 0) and (1, 1) indicate the top-left and bottom-right point of the image respectively. { x: 0, y: 0 }
position object Set the position of the image on canvas. If coordinate is Ratio, (0, 0) and (1, 1) indicate the top-left and bottom-right point of the canvas respectively. { x: 0, y: 0 }
coordinate? string Set to Absolute and Ratio to treat position as absolute position (in point) and proportion respectively.
Options: Absolute, Ratio		 Absolute
alignment? string Specify how the text aligns inside container. Only work when text is multiline text. Left
lineHeightMultiple? number Multiply line height by this factor. Only work when text is multiline text. 1.0

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% :(.

GitHub