Web Front-end
JS Tutorial
How to implement the Command class Command class in Konva.js to support undo and redo functions?
How to implement the Command class Command class in Konva.js to support undo and redo functions?
Apr 04, 2025 pm 04:30 PM
Implementation of undo redo function based on command mode in Konva.js
This article introduces how to use command mode to implement the undo (Ctrl Z) and redo (Ctrl Y) functions in the Konva.js drawing application. We encapsulate graphical operations into command objects and manage these operations using a command stack to achieve fallback and progress in graphical editing.
First, define a basic Command class:
class Command {
constructor() {
this.states = []; // Used to store state snapshots}
execute() {
throw new Error('execute method must be implemented');
}
undo() {
throw new Error('undo method must be implemented');
}
saveState(state) {
this.states.push(state);
}
restoreState() {
return this.states.pop() || null; // Return to the previous state, or null
}
}
Next, create a specific command class, such as the command to draw a rectangle:
class DrawRectangleCommand extends Command {
constructor(stage, layer, rect) {
super();
this.stage = stage;
this.layer = layer;
this.rect = rect;
}
execute() {
this.saveState(this.layer.toJSON()); // Save the current layer state this.layer.add(this.rect);
this.layer.draw();
}
undo() {
this.rect.destroy();
const prevState = this.restoreState();
if (prevState) {
this.layer.destroyChildren(); // Clear the layer this.layer = Konva.Node.create(prevState, this.stage); // Restore the previous state this.stage.add(this.layer);
this.layer.draw();
}
}
}
Then, implement the command manager:
class CommandManager {
constructor() {
this.undoStack = [];
this.redoStack = [];
}
executeCommand(command) {
command.execute();
this.undoStack.push(command);
this.redoStack = []; // After executing the new command, clear the redo stack}
undo() {
if (this.undoStack.length === 0) return;
const command = this.undoStack.pop();
command.undo();
this.redoStack.push(command);
}
redo() {
if (this.redoStack.length === 0) return;
const command = this.redoStack.pop();
command.execute();
this.undoStack.push(command);
}
}
Finally, use in the Konva.js application:
const stage = new Konva.Stage({
container: 'container',
width: window.innerWidth,
height: window.innerHeight
});
const layer = new Konva.Layer();
stage.add(layer);
const commandManager = new CommandManager();
stage.on('click', (e) => {
const rect = new Konva.Rect({
x: e.evt.layerX,
y: e.evt.layerY,
width: 50,
height: 50,
fill: 'red',
draggable: true
});
const command = new DrawRectangleCommand(stage, layer, rect);
commandManager.executeCommand(command);
});
document.addEventListener('keydown', (e) => {
if (e.ctrlKey && e.key === 'z') {
commandManager.undo();
} else if (e.ctrlKey && e.key === 'y') {
commandManager.redo();
}
});
This code implements simple rectangle drawing and undo redoing. You can extend Command class to support other graphical operations such as movement, scaling, rotation, etc. Remember to save the current state in the execute method of each operation and restore the previous state in the undo method. This will ensure that your undo redo feature works correctly.
The above is the detailed content of How to implement the Command class Command class in Konva.js to support undo and redo functions?. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
How to use PHP to build social sharing functions PHP sharing interface integration practice
Jul 25, 2025 pm 08:51 PM
The core method of building social sharing functions in PHP is to dynamically generate sharing links that meet the requirements of each platform. 1. First get the current page or specified URL and article information; 2. Use urlencode to encode the parameters; 3. Splice and generate sharing links according to the protocols of each platform; 4. Display links on the front end for users to click and share; 5. Dynamically generate OG tags on the page to optimize sharing content display; 6. Be sure to escape user input to prevent XSS attacks. This method does not require complex authentication, has low maintenance costs, and is suitable for most content sharing needs.
How to use PHP combined with AI to achieve text error correction PHP syntax detection and optimization
Jul 25, 2025 pm 08:57 PM
To realize text error correction and syntax optimization with AI, you need to follow the following steps: 1. Select a suitable AI model or API, such as Baidu, Tencent API or open source NLP library; 2. Call the API through PHP's curl or Guzzle and process the return results; 3. Display error correction information in the application and allow users to choose whether to adopt it; 4. Use php-l and PHP_CodeSniffer for syntax detection and code optimization; 5. Continuously collect feedback and update the model or rules to improve the effect. When choosing AIAPI, focus on evaluating accuracy, response speed, price and support for PHP. Code optimization should follow PSR specifications, use cache reasonably, avoid circular queries, review code regularly, and use X
PHP calls AI intelligent voice assistant PHP voice interaction system construction
Jul 25, 2025 pm 08:45 PM
User voice input is captured and sent to the PHP backend through the MediaRecorder API of the front-end JavaScript; 2. PHP saves the audio as a temporary file and calls STTAPI (such as Google or Baidu voice recognition) to convert it into text; 3. PHP sends the text to an AI service (such as OpenAIGPT) to obtain intelligent reply; 4. PHP then calls TTSAPI (such as Baidu or Google voice synthesis) to convert the reply to a voice file; 5. PHP streams the voice file back to the front-end to play, completing interaction. The entire process is dominated by PHP to ensure seamless connection between all links.
PHP realizes commodity inventory management and monetization PHP inventory synchronization and alarm mechanism
Jul 25, 2025 pm 08:30 PM
PHP ensures inventory deduction atomicity through database transactions and FORUPDATE row locks to prevent high concurrent overselling; 2. Multi-platform inventory consistency depends on centralized management and event-driven synchronization, combining API/Webhook notifications and message queues to ensure reliable data transmission; 3. The alarm mechanism should set low inventory, zero/negative inventory, unsalable sales, replenishment cycles and abnormal fluctuations strategies in different scenarios, and select DingTalk, SMS or Email Responsible Persons according to the urgency, and the alarm information must be complete and clear to achieve business adaptation and rapid response.
How to use PHP to call AI writing auxiliary tools PHP improves content output efficiency
Jul 25, 2025 pm 08:18 PM
When choosing an AI writing API, you need to examine stability, price, function matching and whether there is a free trial; 2. PHP uses Guzzle to send POST requests and uses json_decode to process the returned JSON data, pay attention to capturing exceptions and error codes; 3. Integrating AI content into the project requires an audit mechanism and supporting personalized customization; 4. Cache, asynchronous queue and current limiting technology can be used to optimize performance to avoid bottlenecks due to high concurrency.
The top 10 most authoritative cryptocurrency market websites in the world (the latest version of 2025)
Jul 29, 2025 pm 12:48 PM
The top ten authoritative cryptocurrency market and data analysis platforms in 2025 are: 1. CoinMarketCap, providing comprehensive market capitalization rankings and basic market data; 2. CoinGecko, providing multi-dimensional project evaluation with independence and trust scores; 3. TradingView, having the most professional K-line charts and technical analysis tools; 4. Binance market, providing the most direct real-time data as the largest exchange; 5. Ouyi market, highlighting key derivative indicators such as position volume and capital rate; 6. Glassnode, focusing on on-chain data such as active addresses and giant whale trends; 7. Messari, providing institutional-level research reports and strict standardized data; 8. CryptoCompa
Twilio call keeping and recovery: Meeting mode with independent call leg processing
Jul 25, 2025 pm 08:42 PM
This article elaborates on two main methods to realize call hold and unhold in Twilio. The preferred option is to leverage Twilio's Conference feature to easily enable call retention and recovery by updating the conference participant resources, and to customize music retention. Another approach is to deal with independent call legs, which requires more complex TwiML logic, passed, and arrived management, but is more cumbersome than meeting mode. The article provides specific code examples and operation steps to help developers efficiently implement Twilio call control.
Get an alternative to a specified column value in an array
Jul 25, 2025 pm 07:39 PM
This article aims to provide an alternative to obtaining the specified column value of an array in PHP, and solve the problem of repeated definition of the array_column() function. For old versions of PHP and new versions of PHP, corresponding solutions are given respectively, and code examples are provided to help developers better process array data.
