@terrylinla/react-native-sketch-canvas

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% :(.

• 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.