Spinner.java

package net.squiz.matrix.ui;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import net.squiz.matrix.core.*;
import java.util.*;
import java.awt.image.*;

public class Spinner extends JComponent implements Runnable {

    public static final String SPINNER_ICON = "spinner.png";
    public static final int delay = 40;
    public static final int IMG_OFFSET = 15;

    private Dimension size = new Dimension(IMG_OFFSET, IMG_OFFSET);

    private boolean isStarted = false;
    private int framePtr = 0;
    private volatile Thread animator;
    private Image[] frames;
    private Image stopImage;

    public Spinner() {
        ImageIcon spinner = (ImageIcon) GUIUtilities.getAssetMapIcon(SPINNER_ICON);
        Image spinnerImg = spinner.getImage();

        BufferedImage spinnerSrc = new BufferedImage(
            spinner.getIconWidth(),
            spinner.getIconHeight(),
            BufferedImage.TYPE_INT_ARGB_PRE
        );

        Graphics2D g2d = (Graphics2D) spinnerSrc.createGraphics();
        g2d.drawImage(spinnerImg, 0, 0, null);
        g2d.dispose();

        // the number of frames of animation is one less than the icon width
        // as we need to remove the stop spinner state from the frames
        int numFrames = (spinner.getIconWidth() / IMG_OFFSET) - 1;
        int offset = IMG_OFFSET;
        frames = new Image[numFrames];

        // the stop image is the first image square in the main spinner sequence
        stopImage = spinnerSrc.getSubimage(0, 0, IMG_OFFSET, IMG_OFFSET);

        // all other images are IMG_OFFSET from the stop image
        for (int i = 0; i < numFrames; i++) {
            frames[i] = spinnerSrc.getSubimage(offset, 0, IMG_OFFSET, IMG_OFFSET);
            offset += IMG_OFFSET;
        }
    }

    public void run() {
        Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
        long tm = System.currentTimeMillis();

        while (Thread.currentThread() == animator) {
            Graphics g = getGraphics();
            if (g != null) {
                g.drawImage(frames[framePtr], 0, 0, null);
            }
            if (framePtr == frames.length - 1) {
                framePtr = 0;
            } else {
                framePtr++;
            }

            try {
                tm += delay;
                Thread.sleep(Math.max(0, tm - System.currentTimeMillis()));
            } catch (InterruptedException e) {
                break;
            }
            Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
        }
    }

    public void paint(Graphics g) {
        super.paint(g);
        // if we are not spinning we need to paint the stop spinner state
        // whenever paint gets called
        if (!isStarted) {
            g.drawImage(stopImage, 0, 0, null);
        }
    }

    public Dimension getMaximumSize() {
        return size;
    }

    public Dimension getMinimumSize() {
        return size;
    }

    public Dimension getPreferredSize() {
        return size;
    }

    public void start() {
        if (isStarted)
            return;
        isStarted = true;
        animator = new Thread(this);
        animator.start();
    }

    public void stop() {
        isStarted = false;
        framePtr = 0;
        animator = null;
        Graphics g = getGraphics();
        if (g != null)
            g.drawImage(stopImage, 0, 0, null);
    }

    public boolean isStarted() {
        return isStarted;
    }
}