How to Draw Rectangles Permanently in a JPanel: Using BufferedImages to Avoid Overwriting?

Drawing Rectangles in a Permanent Manner

In your JPanel implementation, rectangles disappear because the paint() method overwrites previous drawings. To prevent this, we modify our approach:

Using a BufferedImage as Painting Surface

Instead of directly drawing on the JPanel, we use a BufferedImage (canvasImage) as our painting surface. This allows us to modify the image permanently without affecting previous drawings.

Customized paint() Method

Here's a modified paint() method that uses canvasImage for drawing:

<code class="java">@Override
public void paint(Graphics g) {
    super.paint(g); // Handle inherited painting tasks

    Graphics2D bg = (Graphics2D) g;
    bg.drawImage(canvasImage, 0, 0, this);
}</code>

Creating the BufferedImage and Setting It Up

Initialize canvasImage in your JPanel constructor like so:

<code class="java">canvasImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);</code>

And set its graphics context for drawing:

<code class="java">Graphics2D cg = canvasImage.createGraphics();
cg.setColor(Color.WHITE);
cg.fillRect(0, 0, width, height);</code>

Drawing Rectangles on the BufferedImage

Now, your DrawRect() method can modify canvasImage directly:

<code class="java">public void DrawRect(int x, int y, int size, Color c) {
    Graphics2D cg = canvasImage.createGraphics();
    cg.setColor(c);
    cg.fillRect(x, y, size, size);
}</code>

Additional Features

This approach provides several benefits:

• Persistent Draw: Rectangles are permanently drawn on the BufferedImage.
• Optimized Drawing: Instead of repainting the entire JPanel, only the modified portions of the image are updated.
• Supports Undo/Redo (Potential): By keeping track of changes to the image, you can implement undo/redo functionality.

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