Table of Contents

• Features
• Installation
• Usage
  • NativeScript Core / TypeScript
  • Vue (NativeScript-Vue)
• Drawing Modes
• Undo / Redo
• Layer Management
• JSON Serialization
• Path Simplification
• Custom Modes
• Custom Shape Types
• Events
  • Examples:
• Demos and Development
  • Repo Setup
  • Build
  • Demos
• Contributing
  • Update repo
  • Update readme
  • Update doc
  • Publish
  • modifying submodules
• Questions

An interactive drawing canvas plugin for NativeScript, built on top of @nativescript-community/ui-canvas.

Features

• Multiple drawing modes: pen/freehand, rectangle, ellipse, arrow, image placement, select/transform, and move (pan)
• Layer management: access shapes as an ordered list of layers – reorder, remove, duplicate
• Undo / Redo: full history with configurable depth
• Shape selection & transform: resize, rotate and move any shape with on-canvas handles
• Colour & style: stroke colour, fill colour, stroke width and opacity per shape
• JSON serialization: export the entire canvas to a compact JSON string and re-import it later
• Path simplification: automatic Douglas-Peucker + Catmull-Rom smoothing for pen strokes (configurable, extensible)
• Extensible: register custom drawing modes and custom shape types

Installation

Run the following command from the root of your project:

ns plugin add @nativescript-community/ui-drawingcanvas

Usage

NativeScript Core / TypeScript

import { DrawingCanvas } from '@nativescript-community/ui-drawingcanvas';

const dc = new DrawingCanvas();
dc.strokeColor = new Color('red');
dc.strokeWidth = 3;
dc.setMode('pen');          // 'pen' | 'select' | 'move' | 'rectangle' | 'ellipse' | 'arrow' | 'image'

Vue (NativeScript-Vue)

// app.ts / main.ts
import DrawingCanvasPlugin from '@nativescript-community/ui-drawingcanvas/vue';
Vue.use(DrawingCanvasPlugin);

<DrawingCanvas ref="dc" width="100%" height="100%" />

Drawing Modes

| Mode | Description | |------|-------------| | pen | Freehand stroke | | rectangle | Tap-drag to draw a rectangle | | ellipse | Tap-drag to draw an ellipse / circle | | arrow | Tap-drag to draw an arrow | | image | Tap to place an image (set imageSource on the ImageMode first) | | select | Tap to select shapes; drag handles to resize / rotate; drag body to move | | move | Pan gesture (emits pan event with dx/dy) |

Undo / Redo

dc.undo();
dc.redo();
console.log(dc.canUndo, dc.canRedo);

// Configure undo history depth (default: 50)
dc.maxUndoDepth = 30;

Layer Management

const layers = dc.layers;          // DrawableShape[]
dc.moveLayerUp(shape);
dc.moveLayerDown(shape);
dc.duplicateShape(shape);
dc.removeLayer(shape);

JSON Serialization

const json = dc.exportJSON();
// later …
dc.importJSON(json);

Path Simplification

dc.simplificationOptions = {
    enabled: true,
    epsilon: 2,           // Douglas-Peucker tolerance in dp
    smoothing: true,      // apply Catmull-Rom spline
    splineSegments: 8,
    splineAlpha: 0.5      // 0=uniform, 0.5=centripetal (recommended)
};

Custom Modes

import { DrawingMode } from '@nativescript-community/ui-drawingcanvas';

class MyMode extends DrawingMode {
    readonly name = 'mymode';
    onTouchEnd(point) {
        // … create and commit a shape
        this.canvas.commitShape(myShape);
    }
}
dc.registerMode(new MyMode(dc));
dc.setMode('mymode');

Custom Shape Types

import { CustomShape } from '@nativescript-community/ui-drawingcanvas';

// Register a factory so importJSON can recreate the shape
dc.registerShapeFactory('star', () => new StarShape());

Events

| Event | Payload | Description | |-------|---------|-------------| | shapeAdded | { shape } | Fired when a shape is committed | | selectionChange | { shape } | Fired when the selected shape changes in select mode | | modeChange | { mode } | Fired when the active mode changes | | historyChange | { canUndo, canRedo } | Fired after undo / redo stack changes | | pan | { dx, dy } | Fired by move mode on each gesture move |

Examples:

• Basic
  • A basic Drawing example

Demos and Development

Repo Setup

The repo uses submodules. If you did not clone with --recursive then you need to call

git submodule update --init

The package manager used to install and link dependencies must be pnpm or yarn. npm wont work.

To develop and test: if you use yarn then run yarn if you use pnpm then run pnpm i

Interactive Menu:

To start the interactive menu, run npm start (or yarn start or pnpm start). This will list all of the commonly used scripts.

Build

npm run build.all

WARNING: it seems yarn build.all wont always work (not finding binaries in node_modules/.bin) which is why the doc explicitly uses npm run

Demos

npm run demo.[ng|react|svelte|vue].[ios|android]

npm run demo.svelte.ios # Example

Demo setup is a bit special in the sense that if you want to modify/add demos you dont work directly in demo-[ng|react|svelte|vue] Instead you work in demo-snippets/[ng|react|svelte|vue] You can start from the install.ts of each flavor to see how to register new demos

Contributing

Update repo

You can update the repo files quite easily

First update the submodules

npm run update

Then commit the changes Then update common files

npm run sync

Then you can run yarn|pnpm, commit changed files if any

Update readme

npm run readme

Update doc

npm run doc

Publish

The publishing is completely handled by lerna (you can add -- --bump major to force a major release) Simply run

npm run publish

modifying submodules

The repo uses https:// for submodules which means you won't be able to push directly into the submodules. One easy solution is t modify ~/.gitconfig and add

[url "ssh://[email protected]/"]
	pushInsteadOf = https://github.com/

Questions

If you have any questions/issues/comments please feel free to create an issue or start a conversation in the NativeScript Community Discord.