How to Draw Persistent Rectangles in a JPanel Without Performance Degradation?

Drawing Rectangles that Persist

Problem:

Creating rectangles in a JPanel that remain visible despite repaint calls, without slowing down the system due to excessive redrawing.

Solution:

Utilize a BufferedImage as the painting surface.

Approach:

1. Create a JPanel subclass with a BufferedImage as the canvas for drawing.
2. Implement a paint method that draws rectangles onto the BufferedImage.
3. Invalidate and repaint the JPanel only when necessary, such as when drawing new rectangles.
4. Keep a list of drawn rectangles to avoid repeated drawing.

Example:

<code class="java">// Relevant JPanel subclass
class MyPanel extends JPanel {

    private BufferedImage canvasImage; // Image for drawing rectangles

    // Draw a rectangle
    public void drawRect(int x, int y, int width, int height) {
        Graphics2D g = canvasImage.createGraphics();
        g.setColor(Color.RED);
        g.fillRect(x, y, width, height);
        g.dispose();
        repaint(); // Redraw the panel with updated canvasImage
    }

    // Update view
    @Override
    public void paint(Graphics g) {
        super.paint(g);
        g.drawImage(canvasImage, 0, 0, null); // Draw the canvasImage on the panel
    }
}</code>

Advantages:

• Rectangles remain visible without disappearing in subsequent repaints.
• Drawing and repainting operations are optimized, eliminating performance lags.

The above is the detailed content of How to Draw Persistent Rectangles in a JPanel Without Performance Degradation?. For more information, please follow other related articles on the PHP Chinese website!