JPanel paint（）有时不绘制图像

Question

I'm trying to draw a graphical depiction of the moon. For this I am first painting a JPanel black and then painting an Image to depict the moon on it. All fine till here.

Next a second Image (a mask) is painted on top to simulate the Earth's shadow to get the different phases. However, at times the mask is painted but at times it is not painted, leading to a full moon being shown incorrectly. This is happening totally at random! While left clicking , I'm getting this for mask-01.png , mask-06.png , mask-12.png , mask-17.png .

A GIF with the individual frames after each Right click : https://drive.google.com/file/d/0B0lWxG68xR4mTlFYYU81N1kzaVE/view?usp=sharing

What am I doing wrong?

The code:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.AffineTransform;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class App {
    int moonAgeDays = 0;
    float LUNAR_CYCLE_DAYS = 29.5306f;
    JFrame frame;
    MoonImage moonImage;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    App window = new App();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    App() {
        frame = new JFrame("Moon Draw");
        frame.setLocationByPlatform(true);
        frame.setResizable(false);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        moonImage = new MoonImage();
        moonImage.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent mouseEvent) {
                moonAgeDays += mouseEvent.getButton() == MouseEvent.BUTTON1 ? 1 : -1;
                if (moonAgeDays < 0)
                    moonAgeDays = (int) LUNAR_CYCLE_DAYS;
                else if (moonAgeDays > LUNAR_CYCLE_DAYS)
                    moonAgeDays = 0;
                updateMask();
            }
        });
        frame.getContentPane().add(moonImage);

        updateMask();
        frame.pack();
    }

    void updateMask() {
        int phase = (int) Math.toDegrees(Math.acos(-Math.cos(moonAgeDays
                / LUNAR_CYCLE_DAYS * 2 * Math.PI)));
        moonImage.update(phase, moonAgeDays > LUNAR_CYCLE_DAYS / 2 ? 180 : 0);
    }
}

class MoonImage extends JPanel {
    private int phaseAngle = 0;
    private int rotateBy = 0;
    private static final long serialVersionUID = 1L;
    private final int MOON_PADDING = 10;
    private final int MOON_SIZE = 130;
    private final Image IMAGE_MOON = Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/moon.png"));
    private final Image IMAGE_MASK[] = {Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-01.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-02.png"))  ,
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-03.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-04.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-05.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-06.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-07.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-08.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-09.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-10.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-11.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-12.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-13.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-14.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-15.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-16.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-17.png")),
            Toolkit.getDefaultToolkit().createImage(MoonImage.class.getResource("/resources/mask-18.png"))};

    MoonImage() {
        this.setPreferredSize(new Dimension(MOON_SIZE + MOON_PADDING * 2, MOON_SIZE + MOON_PADDING * 2));
    }

    /** Update MoonImage with a Mask and Angle to rotate Mask by*/
    public void update(int phaseAngle, int rotateBy) {
        this.phaseAngle = phaseAngle;
        this.rotateBy = rotateBy;
        repaint();
    }

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

        boolean resultMaskDraw = false;

        Graphics2D graphics2d = (Graphics2D) graphic;
        graphics2d.setColor(Color.BLACK);
        graphics2d.fillRect(0, 0, MOON_SIZE + MOON_PADDING * 2, MOON_SIZE + MOON_PADDING * 2);
        graphics2d.drawImage(IMAGE_MOON, MOON_PADDING, MOON_PADDING, this);
        int phaseBy10 = Math.round(phaseAngle / 10);
        if (phaseBy10 != 0) {
            if (rotateBy != 0) {
                AffineTransform at = new AffineTransform();
                at.translate(MOON_SIZE / 2 + MOON_PADDING, MOON_SIZE / 2 + MOON_PADDING);
                at.rotate(Math.toRadians(rotateBy));
                at.translate(-MOON_SIZE / 2, -MOON_SIZE / 2);
                resultMaskDraw = graphics2d.drawImage(IMAGE_MASK[phaseBy10 - 1], at, this);

            } else
                resultMaskDraw = graphics2d.drawImage(IMAGE_MASK[phaseBy10 - 1], MOON_PADDING, MOON_PADDING, this);
        }
        String maskInfo = phaseBy10 == 0 ? "No mask" : String.format("mask-%02d.png", phaseBy10);
        graphics2d.setColor(phaseBy10 == 0 || resultMaskDraw ? Color.BLUE : Color.RED);
        graphics2d.drawString((phaseBy10 == 0 || resultMaskDraw ? "Drew: " : "Failed: ")
                + maskInfo, 5, MOON_SIZE + MOON_PADDING * 2 - 5);
    }
}

I have tried this in Linux (Kubuntu with OpenJDK) and Windows 7. Same issue in both...

Note :

1. System has decent specs, 8GiB of RAM and a 500GiB SSD with enough free space.
2. What is even more surprising is that there is failure in drawImage() for almost all the images; you'll see the info text painted in red first then in blue!

Answer 1

Figured it!

On line 118 it should be:

resultMaskDraw = graphics2d.drawImage(IMAGE_MASK[phaseBy10 - 1], at, this);

instead of

resultMaskDraw = graphics2d.drawImage(IMAGE_MASK[phaseBy10 - 1], at, null);

But really strange as the draw fails only at some times and not always!