Develop Reference

Flickering when drawing onto bufferedImage

I have a 3d-object composed of multiple polygons that I draw using graphics2D. When I rotate it it, it seems as if it has not enough time to draw the entire object at every frame since at some frames, some of the polygons are simply missing(not drawn). I don't understand how that can be since I in paintComponent first draw all the polygons onto the bufferedImage myImg, and then draw the finished image onto the screen. When I remove clearRect, this issue is resolved but then of course it doesn't remove the last frame's drawing before drawing the next.
Note: I'm an amateur but I've tried really hard understanding and so this is my last resort and would be really glad to get some help. The code (with unnecessary code removed is as follows) :
public class Main {
long temp = System.currentTimeMillis() + frameRate;
public static void main(String[] args) {
myGUI = new GUI(width, height);
while(true) {
if (System.currentTimeMillis() >= temp) {
temp += frameRate;
rotateObject();
myGUI.myCanvas.myLabel.repaint();
}
}
}
}
public class GUI extends JFrame {
public Canvas myCanvas;
public GUI(int w, int h) {
this.setSize(w, h);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myCanvas = new Canvas(w, h);
this.getContentPane().add(myCanvas);
this.setVisible(true);
this.pack();
}
}
public class Canvas extends JPanel {
public BufferedImage myImg;
public Graphics2D g2d;
public JLabel myLabel;
public Canvas(int w, int h) {
myImg = new BufferedImage(w, h, BufferedImage.TYPE_4BYTE_ABGR);
myLabel = new JLabel(new ImageIcon(myImg));
this.add(myLabel);
g2d = myImg.createGraphics();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g2d.clearRect(0, 0, myImg.getWidth(), myImg.getHeight());
g2d.setColor(Color.RED));
g2d.fillPolygon(pointsX, pointsY, 3);
g.drawImage(myImg, 0, 0, null);
}
}
This is how my object is flickering

You really need to take the time to read through:
Performing Custom Painting
Painting in AWT and Swing
2D Graphics
Concurrency in Swing
How to Use Swing Timers
These aren't "beginner" topics and a reasonable understanding of Swing in general and the language in particular would be very advantageous.
Don't, ever, use getGraphics on a component. This is simply a bad idea (and I have no idea why this method is public).
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
} catch (IOException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
}
}
});
}
public class TestPane extends JPanel {
private BufferedImage myImg;
private double rotation;
public TestPane() throws IOException {
myImg = ImageIO.read(getClass().getResource("/images/happy.png"));
Timer timer = new Timer(33, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
rotation += Math.toRadians(5);
repaint();
}
});
timer.start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
AffineTransform at = AffineTransform.getTranslateInstance((getWidth() - myImg.getWidth()) / 2, (getHeight() - myImg.getHeight()) / 2);
at.rotate(rotation, myImg.getWidth() / 2, myImg.getHeight() / 2);
g2d.transform(at);
g2d.drawImage(myImg, 0, 0, this);
g2d.dispose();
}
}
}

Drawing a rectangle that moves slowly towards the point of the mouse click rather than jumping to it (JAVA)

I am very new to JAVA and i am just a hobbyist,Just recently I have been following some tutorials on making UI and all thee looking in to learn about this, any code snippets are welcome but also more what is this function / process called so i can look deeper into different parts of swing from the ORACLE DOCS which is really informative, I am still working my way through the components.
I do not have an overall goal at present and am just finding my feet, but i want to try and make a small top-down 2d maze game to learn.
One part got my attention and it was this demo at the bottom of the page
https://docs.oracle.com/javase/tutorial/uiswing/painting/step3.html
Basically this is the code and I am trying to make it so when I click inside the frame the rectangle moves slowly towards the point of the mouse click rather than jumping to it (and later on if possible to click in another location and it would change its course before reaching its destination.
What kind of area do i need to be looking in to learn about this, any code snippets are welcome but also more what is this function / process called so i can look deeper into it.
WORKING DEMO CODE BELOW
package painting;
import javax.swing.SwingUtilities;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.BorderFactory;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseMotionListener;
import java.awt.event.MouseMotionAdapter;
public class SwingPaintDemo3 {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() { I am Trying to make it so when I click inside the
public void run() {
createAndShowGUI();
}
});
}
private static void createAndShowGUI() {
System.out.println("Created GUI on EDT? "+
SwingUtilities.isEventDispatchThread());
JFrame f = new JFrame("Swing Paint Demo");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new MyPanel());
f.pack();
f.setVisible(true);
}
}
class MyPanel extends JPanel {
private int squareX = 50;
private int squareY = 50;
private int squareW = 20;
private int squareH = 20;
public MyPanel() {
setBorder(BorderFactory.createLineBorder(Color.black));
addMouseListener(new MouseAdapter() {
public void mousePressed(MouseEvent e) {
moveSquare(e.getX(),e.getY());
}
});
addMouseMotionListener(new MouseAdapter() {
public void mouseDragged(MouseEvent e) {
moveSquare(e.getX(),e.getY());
}
});
}
private void moveSquare(int x, int y) {
int OFFSET = 1;
if ((squareX!=x) || (squareY!=y)) {
repaint(squareX,squareY,squareW+OFFSET,squareH+OFFSET);
squareX=x;
squareY=y;
repaint(squareX,squareY,squareW+OFFSET,squareH+OFFSET);
}
}
public Dimension getPreferredSize() {
return new Dimension(250,200);
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString("This is my custom Panel!",10,20);
g.setColor(Color.RED);
g.fillRect(squareX,squareY,squareW,squareH);
g.setColor(Color.BLACK);
g.drawRect(squareX,squareY,squareW,squareH);
}
}
Thanks for any advice ;)

Java repaint() not calling paintComponent()

In an attempt to make a very simple bullet-hell game to learn about java, I ran into a roadblock: repaint() wasn't calling paintComponent().
Here is the entire program, which for now simply draws an image I created 50 times per second onto a JPanel, which rests on a JFrame.
/*
* Bullet hell, by Nematodes
*/
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class bulletHell extends JFrame
{
private static final long serialVersionUID = 0L;
JPanel gamePanel = new JPanel();
int gameTimerDelay = 20;
int x, y = 0;
BufferedImage lightOrb;
javax.swing.Timer gameTimer;
public static void main(String[] args)
{
bulletHell createFrame = new bulletHell();
createFrame.frameConstructor();
}
public void frameConstructor()
{
// Construct frame and frame components
setTitle("Bullet hell");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setResizable(false);
getContentPane().setLayout(new GridBagLayout());
setVisible(true);
GridBagConstraints gridConstraints;
gridConstraints = new GridBagConstraints();
gridConstraints.gridx = 0;
gridConstraints.gridy = 0;
gamePanel.setBackground(Color.BLACK);
gamePanel.setPreferredSize(new Dimension(700, 700));
getContentPane().add(gamePanel, gridConstraints);
pack();
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
setBounds((int) (0.5 * (screenSize.width - getWidth())),
(int) (0.5 * (screenSize.height - getHeight())), getWidth(), getHeight());
try
{
lightOrb = ImageIO.read(new File("C:/Users/Owner/Downloads/orb.bmp"));
}
catch(IOException e)
{
System.out.println("An issue occurred while trying to read orb.bmp");
}
// Start timer that draws game objects 50 times per second (50 FPS)
gameTimer = new javax.swing.Timer(gameTimerDelay, gameTimerAction);
gameTimer.setInitialDelay(0);
gameTimer.start();
}
ActionListener gameTimerAction = new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
repaint();
}
};
class GraphicsPanel extends JPanel
{
public GraphicsPanel()
{
}
// Draw all of the components
#Override
public void paintComponent(Graphics g)
{
Graphics2D g2D = (Graphics2D) g;
super.paintComponent(g2D);
g2D.drawImage(lightOrb, x, y, this);
g2D.dispose();
}
}
}
After some debugging with breakpoints and println methods, I can confirm that the correct image is being read, the timer in gameTimerAction is being called 50 times per second, and repaint() is not invoking paintComponent() at all.
I am somewhat new to Java programming, and might just be missing something simple.
Edit: Problem has been solved by changing gamePanel to a GraphicsPanel object. Unfortunately, this also means that my much larger pong project (which this project's flawed drawing logic was essentially copied from) only worked by a miracle, and might be unstable with certain code additions.

I can immediately see several problems:
Most Important: You never instantiate a GraphicsPanel object, nor do you add it to anything. The paintComponent(...) method will never be called on a JPanel that is neither rendered nor created. Why not make your gamePanel variable a GraphicsPanel object and not a JPanel object?
You never change x and y in your Timer, and so without change, no animation will occur.
Also you're calling dispose on a Graphics object given to you by the JVM, something you should never do. This breaks the Swing painting chain making the graphics of your GUI unstable.
So keep at it, you'll get there.
For example:
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;
public class BulletExample extends JPanel {
public static final String IMG_PATH = "http://www.i2clipart.com/cliparts/f/0/5/8/clipart-blue-circle-f058.png";
private static final int PREF_W = 700;
private static final int PREF_H = PREF_W;
private static final int TIMER_DELAY = 20;
private BufferedImage bullet;
private int bulletX;
private int bulletY;
public BulletExample() throws IOException {
URL imgUrl = new URL(IMG_PATH);
bullet = ImageIO.read(imgUrl);
new Timer(TIMER_DELAY, new BulletListener()).start();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (bullet != null) {
g.drawImage(bullet, bulletX, bulletY, this);
}
}
#Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
}
return new Dimension(PREF_W, PREF_H);
}
private class BulletListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
bulletX++;
bulletY++;
repaint();
}
}
private static void createAndShowGui() throws IOException {
// create the drawing JPanel
BulletExample mainPanel = new BulletExample();
JFrame frame = new JFrame("BulletExample");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
// add it to the JFrame
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
try {
createAndShowGui();
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
}

ImageIcon click and drag around the window

I'm trying to make it so I can click and drag an ImageIcon (in this case a card image but I'd like to learn how to do it generally) around the window but I don't really know how. I would like to be able to click and hold the mouse botton, drag the ImageIcon, and have stay where it is whn I release the mouse botton.
This is the code I have so far:
import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
public class MyFirstClass
{
public static void main(String[] args)
{
//load the card image from the gif file.
final ImageIcon cardIcon = new ImageIcon("cardImages/tenClubs.gif");
JLabel lbl = new JLabel(cardIcon);
//create a panel displaying the card image
JPanel panel = new JPanel()
{
//paintComponent is called automatically by the JRE whenever
//the panel needs to be drawn or redrawn
public void paintComponent(Graphics g) {
super.paintComponent(g);
cardIcon.paintIcon(this, g, 20, 20);
}
};
lbl.setTransferHandler(null);
MouseListener listener = new MouseAdapter() {
public void mousePressed(MouseEvent me) {
JComponent comp = (JComponent) me.getSource();
TransferHandler handler = comp.getTransferHandler();
handler.exportAsDrag(comp, me, TransferHandler.COPY);
}
};
lbl.addMouseListener(listener);
//create & make visible a JFrame to contain the panel
JFrame window = new JFrame("Cards");
window.add(panel);
window.setPreferredSize(new Dimension(200,200));
window.pack();
window.setVisible(true);
}
}
Thank you.

The problem is you're mixing paradigms...not to mention you never seem to add lbl to anything, so it could never possible receive events and the fact that the panel is under the control of a layout manager, making moving a component very difficult...
In Swing there are at least three different ways to drag something, which you use comes down to what it is you want to achieve.
You can...
Use MouseListener and MouseMotitionListener to perform the actions manually. This is useful if you want to physical place an object somewhere within the container, like you are trying to do, for example...
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class DragMe {
public static void main(String[] args) {
new DragMe();
}
public DragMe() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private BufferedImage img;
private Point imgPoint = new Point(0, 0);
public TestPane() {
try {
img = ImageIO.read(new File("Computer.png"));
} catch (IOException ex) {
ex.printStackTrace();
}
MouseAdapter ma = new MouseAdapter() {
private Point offset;
#Override
public void mousePressed(MouseEvent e) {
Rectangle bounds = getImageBounds();
Point mp = e.getPoint();
if (bounds.contains(mp)) {
offset = new Point();
offset.x = mp.x - bounds.x;
offset.y = mp.y - bounds.y;
}
}
#Override
public void mouseReleased(MouseEvent e) {
offset = null;
}
#Override
public void mouseDragged(MouseEvent e) {
if (offset != null) {
Point mp = e.getPoint();
imgPoint.x = mp.x - offset.x;
imgPoint.y = mp.y - offset.y;
repaint();
}
}
};
addMouseListener(ma);
addMouseMotionListener(ma);
}
protected Rectangle getImageBounds() {
Rectangle bounds = new Rectangle(0, 0, 0, 0);
if (img != null) {
bounds.setLocation(imgPoint);
bounds.setSize(img.getWidth(), img.getHeight());
}
return bounds;
}
#Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (img != null) {
Graphics2D g2d = (Graphics2D) g.create();
g2d.drawImage(img, imgPoint.x, imgPoint.y, this);
g2d.dispose();
}
}
}
}
You can...
Use the core Drag-n-Drop APIs. This very low level and provides you are wide variety of flexibility. You can drag components, data or sorts of stuff based on your needs...
For example:
java drag and drop
How to drag and drop JPanel with its components
move component after drag and drop
And if you're really adventurous, you can take a look at these...
My Drag Image is Better than Yours
Drop Target Navigation, or You Drag Your Bags, Let the Doorman Get the Door
Smooth JList Drop Target Animation
You can..
Make use of the new transfer API. The intention of this API is to make it easier to transfer data around the application. While, technically, it would be possible to move a component this way, this is not it's intention.
Take a look at...
Drag and Drop and Data Transfer
Introduction to the DnD API
How to drag and drop with Java 2, Part 1
For more details...

Moving images in Java

I want to make an image that I drew in the paint class move left across my JFrame as a timer ticks. But I don't know how to do that. Also, I am trying to get my program to make the image disappear when the image is clicked upon.
movingball class
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import javax.swing.JPanel;
import javax.swing.Timer;
public class movingball extends JPanel{
private int move=50;
private Timer timer = new Timer(move, new TimerListener());
private int radius = 10;
private int x = 300;
private int y = 0;
public movingball() {
timer.start();
}
private class TimerListener implements ActionListener{
public void actionPerformed(ActionEvent e){
x=x-20;
repaint(); }//trying to get the oval to move left 20
}
protected void paintComponent(Graphics2D g){
super.paintComponent(g);
g.fillOval(x, 100 , radius * 2, radius * 2); }
}
movingControl class
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.InputEvent;
import java.awt.event.ItemEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JPanel;
public class movingControl extends JPanel {
private movingball ball= new movingball();
public movingControl(){
JPanel panel = new JPanel();
ball.setBorder(new javax.swing.border.LineBorder(Color.red));
panel.addMouseListener(new movingballListener());
setLayout(new BorderLayout());
add(ball, BorderLayout.CENTER);
add(panel, BorderLayout.SOUTH);
}
}
SnniperGameApp class
I know I spelled sniper wrong
import javax.swing.JApplet;
public class SnniperGameApp extends JApplet {
static final long serialVersionUID = 2777718668465204446L;
//i dont know what this serial thing is. But my program wont start without it
public SnniperGameApp(){
add(new movingControl());
}
}
ClickingEvent class
import java.awt.event.InputEvent;
import java.awt.event.ItemEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
class movingballListener extends MouseAdapter{
public void mouseReleased(MouseEvent e) {
if ((e.getModifiers() & InputEvent.BUTTON1_DOWN_MASK) != 0) {
System.out.println( (e.getPoint()));}}
}

You haven't over-ridden paintComponent() properly.
From the javadoc, the signature of paintComponent() is:
protected void paintComponent(Graphics g)
but you have:
protected void paintComponent(Graphics2D g)
The method signatures must match - you can safely cast the Graphics to a Graphics2D inside the method if needed.
Adding the #Override annotation to a method is a good way to get the compiler to check that you really are over-riding a method, not just writing a method that looks the same!
Here's a working SSCCE (I have inlined some of the constants to save space, don't take that as good practice for real code!):
public class MovingBall extends JPanel
{
private Timer timer = new Timer(50, new TimerListener());
private int x = 300;
public MovingBall()
{
timer.start();
}
private class TimerListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
x -= 20;
repaint();
}
}
#Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
g.fillOval(x, 100, 20, 20);
}
public static void main(String[] args)
{
JFrame frame = new JFrame();
frame.add(new MovingBall());
frame.setSize(500, 500);
frame.setVisible(true);
}
}