How to Smoothly Rotate an Image 90 Degrees in Java Swing Using a Timer?

How to rotate an image gradually in Swing?

This question concerns an issue with rotating an image when a button is clicked in Java Swing. The goal is to have the image rotate smoothly to 90 degrees.

Question Details:

The provided code contains several classes: RotateButtonSSCE, CrossingPanelSSCE, VisualizationPanelSSCE, and a main method in TestGUISSCE. The RotateButtonSSCE class creates a button that triggers rotation, the CrossingPanelSSCE class includes the image that needs to be rotated, and the VisualizationPanelSSCE class provides a surface for drawing the image.

The issue arises when trying to rotate the image gradually. The code attempts to achieve this using a timer that calls a method to rotate the image incrementally, but it doesn't seem to work as intended.

Answer:

In addition to the corrections suggested by @tulskiy, it's important to note that the given code has some structural issues that may contribute to the problem. Here are key observations and recommendations:

• Use top-level or nested classes: An SSCCE (Short, Self Contained, Correct (Compilable), Example) should be easy to understand without requiring the creation of multiple public classes. Consider using top-level (package-private) or nested classes for convenience.
• Construct GUI on the event dispatch thread: Always create your GUI on the event dispatch thread to avoid threading issues.
• Utilize the paintComponent method: In this example, the paintComponent() method in CrossingPanelSSCE is responsible for displaying the image. To rotate the image gradually, you can use the AffineTransform class to alter the graphics context's transform. By applying appropriate rotations and translations, you can achieve a smooth rotation effect.

Revised Code Excerpt:

Here's a revised portion of the CrossingPanelSSCE class that rotates the image using AffineTransform:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;

import javax.swing.*;

public class CrossingPanelSSCE extends JPanel {

    // ... other code

    private BufferedImage image;
    private double rotationAngle = 0;
    private AffineTransform transform = new AffineTransform();

    // ... other methods

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        Graphics2D g2d = (Graphics2D) g;

        // Apply the rotation transform to the graphics context
        g2d.setTransform(transform);

        // Draw the image at its center
        g2d.drawImage(image, -image.getWidth() / 2, -image.getHeight() / 2, null);
    }

    public void rotateImage(double angle) {
        rotationAngle += angle;

        // Update the AffineTransform with the new rotation angle
        transform.rotate(Math.toRadians(angle), image.getWidth() / 2, image.getHeight() / 2);

        // Repaint the panel to display the updated image
        repaint();
    }
}

Usage in RotateButtonSSCE (Button ActionListener):

public void actionPerformed(ActionEvent ev) {
    vis.rotateImage(ROTATE_ANGLE_OFFSET);
}

This code increments the rotation angle by a small value (ROTATE_ANGLE_OFFSET) on each button click and updates the image accordingly. You can adjust the ROTATE_ANGLE_OFFSET to control the speed of the rotation animation.

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