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Jlabels flickering or randomly not showing

I have a problem with a Java 2d game I'm developing.
Some of the game screen elements are drawn in a Jpanel overriding the paint() method and some other elements are Jlabels added to that panel.
The problem is that the elements drawn in the paint() method are always up to date (I recall a Jpanel.repaint() every 30ms from a thread) but the Jlabels often are not shown or are blinking in a random way.
I've searched a lot but couldn't find a way to update all the elements at the same time.
This is the core structure of the code:
Main Class
final class ATC_sim {
// ...
public CustomLabel[] label;
// CustomLabel is just a class in which are organized differents JLabels in
// a certain relative position.
// ...
private ATC_sim(){
initGui();
initGame();
}
private void initGui(){
frame = new JFrame();
pGame = new GamePanel(this);
for(int i=0; i< label.length; i++){
pGame.add(label[i]);
}
frame.add(pGame);
// ...
}
private void initGame(){
loop = new Loop(this, 30);
thread = new Thread(loop);
thread.start();
pGame.repaint();
}
// method recalled every 30ms from thread(loop)
public void updateGame(){
// do the math of the game (in which I also move the position of labels)
// ...
for(int i=0; i< label.length; i++){
label[i].update(); // this method update text in Jlabels and position of label.
}
pGame.repaint();
}
}
GamePanel class
public class GamePanel extends JPanel {
// ...
public GamePanel(ATC_sim a) {
this.atc = a;
// ...
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
// do some drawings according to some variable calculated in updateGame()
}
}

At first, if you want better performance and a lower chance of lagging/stuttering, use paintImmediately() instead of repaint().
It could be, that this solves your problem already.
The second part is: Do you use double buffering? If you use this, this problem will definitely disappear (in my oppinion).

Why is my code in Swing just returning a black screen? [duplicate]

I'm creating a graphical front-end for a JBox2D simulation. The simulation runs incrementally, and in between the updates, the contents of the simulation are supposed to be drawn. Similar to a game except without input.
I only need geometric primitives to draw a JBox2D simulation. This API seemed like the simplest choice, but its design is a bit confusing.
Currently I have one class called Window extending JFrame, that contains as a member another class called Renderer. The Window class only initializes itself and provides an updateDisplay() method (that is called by the main loop), that calls updateDisplay(objects) method on the Renderer. I made these two methods myself and their only purpose is to call repaint() on the Renderer.
Is the JPanel supposed to be used that way? Or am I supposed to use some more sophisticated method for animation (such that involves events and/or time intervals in some back-end thread)?

If you are wanting to schedule the updates at a set interval, javax.swing.Timer provides a Swing-integrated service for it. Timer runs its task on the EDT periodically, without having an explicit loop. (An explicit loop would block the EDT from processing events, which would freeze the UI. I explained this more in-depth here.)
Ultimately doing any kind of painting in Swing you'll still be doing two things:
Overriding paintComponent to do your drawing.
Calling repaint as-needed to request that your drawing be made visible. (Swing normally only repaints when it's needed, for example when some other program's window passes over top of a Swing component.)
If you're doing those two things you're probably doing it right. Swing doesn't really have a high-level API for animation. It's designed primarily with drawing GUI components in mind. It can certainly do some good stuff, but you will have to write a component mostly from scratch, like you're doing.
Painting in AWT and Swing covers some of the 'behind the scenes' stuff if you do not have it bookmarked.
You might look in to JavaFX. I don't know that much about it personally, but it's supposed to be more geared towards animation.
As somewhat of an optimization, one thing that can be done is to paint on a separate image and then paint the image on to the panel in paintComponent. This is especially useful if the painting is long: repaints can be scheduled by the system so this keeps when it happens more under control.
If you aren't drawing to an image, then you'd need to build a model with objects, and paint all of them every time inside paintComponent.
Here's an example of drawing to an image:
import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
/**
* Holding left-click draws, and
* right-clicking cycles the color.
*/
class PaintAnyTime {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new PaintAnyTime();
}
});
}
Color[] colors = {Color.red, Color.blue, Color.black};
int currentColor = 0;
BufferedImage img = new BufferedImage(256, 256, BufferedImage.TYPE_INT_ARGB);
Graphics2D imgG2 = img.createGraphics();
JFrame frame = new JFrame("Paint Any Time");
JPanel panel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
// Creating a copy of the Graphics
// so any reconfiguration we do on
// it doesn't interfere with what
// Swing is doing.
Graphics2D g2 = (Graphics2D) g.create();
// Drawing the image.
int w = img.getWidth();
int h = img.getHeight();
g2.drawImage(img, 0, 0, w, h, null);
// Drawing a swatch.
Color color = colors[currentColor];
g2.setColor(color);
g2.fillRect(0, 0, 16, 16);
g2.setColor(Color.black);
g2.drawRect(-1, -1, 17, 17);
// At the end, we dispose the
// Graphics copy we've created
g2.dispose();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(img.getWidth(), img.getHeight());
}
};
MouseAdapter drawer = new MouseAdapter() {
boolean rButtonDown;
Point prev;
#Override
public void mousePressed(MouseEvent e) {
if (SwingUtilities.isLeftMouseButton(e)) {
prev = e.getPoint();
}
if (SwingUtilities.isRightMouseButton(e) && !rButtonDown) {
// (This just behaves a little better
// than using the mouseClicked event.)
rButtonDown = true;
currentColor = (currentColor + 1) % colors.length;
panel.repaint();
}
}
#Override
public void mouseDragged(MouseEvent e) {
if (prev != null) {
Point next = e.getPoint();
Color color = colors[currentColor];
// We can safely paint to the
// image any time we want to.
imgG2.setColor(color);
imgG2.drawLine(prev.x, prev.y, next.x, next.y);
// We just need to repaint the
// panel to make sure the
// changes are visible
// immediately.
panel.repaint();
prev = next;
}
}
#Override
public void mouseReleased(MouseEvent e) {
if (SwingUtilities.isLeftMouseButton(e)) {
prev = null;
}
if (SwingUtilities.isRightMouseButton(e)) {
rButtonDown = false;
}
}
};
PaintAnyTime() {
// RenderingHints let you specify
// options such as antialiasing.
imgG2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
imgG2.setStroke(new BasicStroke(3));
//
panel.setBackground(Color.white);
panel.addMouseListener(drawer);
panel.addMouseMotionListener(drawer);
Cursor cursor =
Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR);
panel.setCursor(cursor);
frame.setContentPane(panel);
frame.pack();
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
If the routine is long-running and repaints could happen concurrently, double buffering can also be used. Drawing is done to an image which is separate from the one being shown. Then, when the drawing routine is done, the image references are swapped so the update is seamless.
You should typically use double buffering for a game, for example. Double buffering prevents the image from being shown in a partial state. This could happen if, for example, you were using a background thread for the game loop (instead of a Timer) and a repaint happened the game was doing the painting. Without double buffering, this kind of situation would result in flickering or tearing.
Swing components are double buffered by default, so if all of your drawing is happening on the EDT you don't need to write double buffering logic yourself. Swing already does it.
Here is a somewhat more complicated example which shows a long-running task and a buffer swap:
import java.awt.*;
import javax.swing.*;
import java.awt.image.*;
import java.awt.event.*;
import java.util.*;
/**
* Left-click to spawn a new background
* painting task.
*/
class DoubleBuffer {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new DoubleBuffer();
}
});
}
final int width = 640;
final int height = 480;
BufferedImage createCompatibleImage() {
GraphicsConfiguration gc =
GraphicsEnvironment
.getLocalGraphicsEnvironment()
.getDefaultScreenDevice()
.getDefaultConfiguration();
// createCompatibleImage creates an image that is
// optimized for the display device.
// See http://docs.oracle.com/javase/8/docs/api/java/awt/GraphicsConfiguration.html#createCompatibleImage-int-int-int-
return gc.createCompatibleImage(width, height, Transparency.TRANSLUCENT);
}
// The front image is the one which is
// displayed in the panel.
BufferedImage front = createCompatibleImage();
// The back image is the one that gets
// painted to.
BufferedImage back = createCompatibleImage();
boolean isPainting = false;
final JFrame frame = new JFrame("Double Buffer");
final JPanel panel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
// Scaling the image to fit the panel.
Dimension actualSize = getSize();
int w = actualSize.width;
int h = actualSize.height;
g.drawImage(front, 0, 0, w, h, null);
}
};
final MouseAdapter onClick = new MouseAdapter() {
#Override
public void mousePressed(MouseEvent e) {
if (!isPainting) {
isPainting = true;
new PaintTask(e.getPoint()).execute();
}
}
};
DoubleBuffer() {
panel.setPreferredSize(new Dimension(width, height));
panel.setBackground(Color.WHITE);
panel.addMouseListener(onClick);
frame.setContentPane(panel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
void swap() {
BufferedImage temp = front;
front = back;
back = temp;
}
class PaintTask extends SwingWorker<Void, Void> {
final Point pt;
PaintTask(Point pt) {
this.pt = pt;
}
#Override
public Void doInBackground() {
Random rand = new Random();
synchronized(DoubleBuffer.this) {
Graphics2D g2 = back.createGraphics();
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL,
RenderingHints.VALUE_STROKE_PURE);
g2.setBackground(new Color(0, true));
g2.clearRect(0, 0, width, height);
// (This computes pow(2, rand.nextInt(3) + 7).)
int depth = 1 << ( rand.nextInt(3) + 7 );
float hue = rand.nextInt(depth);
int radius = 1;
int c;
// This loop just draws concentric circles,
// starting from the inside and extending
// outwards until it hits the outside of
// the image.
do {
int rgb = Color.HSBtoRGB(hue / depth, 1, 1);
g2.setColor(new Color(rgb));
int x = pt.x - radius;
int y = pt.y - radius;
int d = radius * 2;
g2.drawOval(x, y, d, d);
++radius;
++hue;
c = (int) (radius * Math.cos(Math.PI / 4));
} while (
(0 <= pt.x - c) || (pt.x + c < width)
|| (0 <= pt.y - c) || (pt.y + c < height)
);
g2.dispose();
back.flush();
return (Void) null;
}
}
#Override
public void done() {
// done() is completed on the EDT,
// so for this small program, this
// is the only place where synchronization
// is necessary.
// paintComponent will see the swap
// happen the next time it is called.
synchronized(DoubleBuffer.this) {
swap();
}
isPainting = false;
panel.repaint();
}
}
}
The painting routine is just intended draw garbage which takes a long time:

For a tightly coupled simulation, javax.swing.Timer is a good choice. Let the timer's listener invoke your implementation of paintComponent(), as shown here and in the example cited here.
For a loosely coupled simulation, let the model evolve in the background thread of a SwingWorker, as shown here. Invoke publish() when apropos to you simulation.
The choice is dictated in part by the nature of the simulation and the duty cycle of the model.

Why not just use stuff from the testbed? It already does everything. Just take the JPanel, controller, and debug draw. It uses Java 2D drawing.
See here for the JPanel that does the buffered rendering:
https://github.com/dmurph/jbox2d/blob/master/jbox2d-testbed/src/main/java/org/jbox2d/testbed/framework/j2d/TestPanelJ2D.java
and here for the debug draw:
https://github.com/dmurph/jbox2d/blob/master/jbox2d-testbed/src/main/java/org/jbox2d/testbed/framework/j2d/DebugDrawJ2D.java
See the TestbedMain.java file to see how the normal testbed is launched, and rip out what you don't need :)
Edits:
Disclaimer: I maintain jbox2d
Here is the package for the testbed framework: https://github.com/dmurph/jbox2d/tree/master/jbox2d-testbed/src/main/java/org/jbox2d/testbed/framework
TestbedMain.java is in the j2d folder, here:
https://github.com/dmurph/jbox2d/tree/master/jbox2d-testbed/src/main/java/org/jbox2d/testbed/framework/j2d

Java MouseEvent position is inaccurate

I've got a problem in Java using a "canvas" class I created, which is an extended JPanel, to draw an animated ring chart. This chart is using a MouseListener to fetch click events.
The problem is that the mouse position does not seem to be accurate, meaning it does not seem to be relative to the "canvas" but instead relative to the window (in the left, upper corner I got about 30px for y coord).
This is my code:
I created a class, that extends JPanel and does have a BufferedImage as member.
public class Canvas extends JPanel {
public BufferedImage buf;
private RingChart _parent;
public Canvas(int width, int height, RingChart parent){
buf = new BufferedImage(width, height, 1);
...
In the paint component method I just draw the buffered image, so I am able to paint on the canvas from 'outside' by painting on the buffered image, which is public.
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
g2.drawImage(buf, null, 0, 0);
}
Now there's a class RingChart which contains a "canvas":
public class RingChart extends JFrame{
public Canvas c;
...
And I create a Graphics2D from the bufferedImage in the canvas class. This g2d is used for painting:
public RingChart(){
c = new Canvas(1500,980,this);
add(c);
setSize(1500, 1000);
setTitle("Hans");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
g2d = (Graphics2D)c.buf.createGraphics();
...
What I now was trying to achieve, was a mouse listener that listened to mouse events happening on the canvas. So when the user clicks on the canvas I could retrieve the position he clicked on, upon the canvas, through the event variable.
So I created a mouse listener:
class MouseHandler implements MouseListener {
#Override
public void mouseClicked(MouseEvent e){
RingChart r = ((Canvas)e.getSource()).getParent();
r.mouseClick(e);
}
...
...and added this mouse listener to the canvas of the RingChart class (myChart is an instance of RingChart and c is the canvas it contains):
...
MouseHandler mouse = new MouseHandler();
myChart.c.addMouseListener(mouse);
...
But as I mentioned above, the mouse position, that's returned when the click event is called, does not seem to be accurate. I think the mistake must be somehow in the way I created that mouseListener or maybe assigned it to the wrong element or something like that. But I've tried quite a couple of things and it didn't change. Can maybe someone tell me, what I've done wrong?
UPDATE:
The code of the function "mouseClick" that is a member of RingChart and is called in the mouse listener:
public void mouseClick(MouseEvent evt){
//evt = SwingUtilities.convertMouseEvent(this, evt, c);
if(evt.getButton() == MouseEvent.BUTTON1 && animation == null){
for(Element e : elements){
if(e.getShape() != null && e.getShape().contains(evt.getPoint())){
//do some stuff
}
}
}
}
Again, the hierarchy of my classes:
RingChart --contains a--> Canvas --got a--> MouseListener.
The shapes in this function are shapes that have been painted on the canvas c. Now I want to check, if the user has clicked on one of them. So as I thought, the shapes should be in canvas-coordinates and the event position should be in canvas-coordinates and everything should fit together. But it doesn't.
Now user MadProgrammer told me, to use the ConvertMouseEvent function. But I currently don't see which exact way I should use this sensibly.
UPDATE:
I found a solution: All I had to do is adding the canvas not directly to the JFrame but to the ContentPane of the JFrame instead:
So instead:
public RingChart(){
c = new Canvas(1500,980,this);
add(c);
...
I do:
public RingChart(){
c = new Canvas(1500,980,this);
getContentPane().add(c);
...
Then I give the MouseListener to the ContentPane.
getContentPane().addMouseListener(new MouseHandler());
getContentPane().addMouseMotionListener(new MouseMoveHandler());
I don't know, if this is an elegant solution, but it works.

The mouse event is automatically converted to be relative to the component that it occurred in that is, point 0x0 is always the top left corner of the component.
By using RingChart r = ((Canvas)e.getSource()).getParent(), you've effectively changed the reference, which now means the location is no longer valid.
You need to convert the location so that its coordinates are in the context of the parent component. Take a look at SwingUtilities.convertMouseEvent(Component, MouseEvent, Component)
UPDATE with PICTURES
Lets take this example...
The blue box has a relative position of 50px x 50px to the red box. If you click in the blue box, lets say at 25x25, the mouse coordinates will be relative to the blue box (0x0 will be the top left of the blue box).
If you then pass this event to the red box and try and use the coordinates from it, you will find that the coordinates will now be half way between the top left of the red box and the blue box, because the coordinates are context sensitive.
In order to get it to work, you need to translate the mouse events location from the blue box to the red box, which would make it 75x75
Now, I don't know what you're doing when you pass the mouse event to the RingChart so I'm only guessing that this is the issue you're facing.
UPDATED with Click Code
Okay, lets say, you have a Canvas at 100x100. You click on that Canvas at 50x50. You then pass that value back up the chain.
public void mouseClick(MouseEvent evt){
//evt = SwingUtilities.convertMouseEvent(this, evt, c);
if(evt.getButton() == MouseEvent.BUTTON1 && animation == null){
for(Element e : elements){
// Here, we are asking the shape if it contains the point 50x50...
// Not 150x150 which would be the relative position of the click
// in the context to the RingChart, which is where all your objects
// are laid out.
// So even the original Canvas you clicked on will return
// false because it's position + size (100x100x width x height)
// does not contain the specified point of 50x50...
if(e.getShape() != null && e.getShape().contains(evt.getPoint())){
//do some stuff
}
}
}
}
UPDATED
I think you have your references around the wrong way...
public static MouseEvent convertMouseEvent(Component source,
MouseEvent sourceEvent,
Component destination)
I think it should read something like
evt = SwingUtilities.convertMouseEvent(evt.getComponent(), evt, this);
UPDATE with Code Example
Okay, so, I put this little example together...
public class TestMouseClickPoint extends JFrame {
private ContentPane content;
public TestMouseClickPoint() throws HeadlessException {
setSize(600, 600);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setLayout(new BorderLayout());
content = new ContentPane();
add(content);
}
protected void updateClickPoint(MouseEvent evt) {
content.updateClickPoint(evt);
}
protected class ContentPane extends JPanel {
private Point relativePoint;
private Point absolutePoint;
public ContentPane() {
setPreferredSize(new Dimension(600, 600));
setLayout(null); // For testing purpose only...
MousePane mousePane = new MousePane();
mousePane.setBounds(100, 100, 400, 400);
add(mousePane);
}
protected void updateClickPoint(MouseEvent evt) {
absolutePoint = new Point(evt.getPoint());
evt = SwingUtilities.convertMouseEvent(evt.getComponent(), evt, this);
relativePoint = new Point(evt.getPoint());
System.out.println(absolutePoint);
System.out.println(relativePoint);
repaint();
}
protected void paintCross(Graphics2D g2d, Point p) {
g2d.drawLine(p.x - 5, p.y - 5, p.x + 5, p.y + 5);
g2d.drawLine(p.x - 5, p.y + 5, p.x + 5, p.y - 5);
}
/*
* This is not recommended, but I want to paint ontop of everything...
*/
#Override
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
if (relativePoint != null) {
g2d.setColor(Color.BLACK);
paintCross(g2d, relativePoint);
}
if (absolutePoint != null) {
g2d.setColor(Color.RED);
paintCross(g2d, absolutePoint);
}
}
}
protected class MousePane extends JPanel {
private Point clickPoint;
public MousePane() {
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
clickPoint = e.getPoint();
TestMouseClickPoint.this.updateClickPoint(e);
repaint();
}
});
setBorder(new LineBorder(Color.RED));
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.BLUE);
if (clickPoint != null) {
g2d.drawLine(clickPoint.x, clickPoint.y - 5, clickPoint.x, clickPoint.y + 5);
g2d.drawLine(clickPoint.x - 5, clickPoint.y, clickPoint.x + 5, clickPoint.y);
}
}
}
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException ex) {
} catch (InstantiationException ex) {
} catch (IllegalAccessException ex) {
} catch (UnsupportedLookAndFeelException ex) {
}
new TestMouseClickPoint().setVisible(true);
}
}
Basically, it will paint three points. The point that the mouse was clicked (relative to the source of the event), the unconverted point in the parent container and the converted point with the parent container.
The next thing you need to do is determine the mouse location is actually been converted, failing that. I'd probably need to see a working example of your code to determine what it is you're actually doing.

Java Swing - place image in JLabel to/above second JLabel (map, player indicator)

I have a JFrame window with GridBagLayout(). There is a JLabel with Icon - it's a map. Now I need to show another picture (player position indicator) above map.
Is it possible, how?
Thank you very much!

Subclass JLabel and override the paint method.
public void paintComponent(Graphics g) {
super.paintComponent(g);
// paint player location on map
}
Handle your conversion from in game coordinates to coordinates on the map.

As an alternative to paintComponent(), you might also want to look at OverlayLayout, seen here. For some reason it's not included in the gallery, but it may be of use.

Couldn't resist to take this question as an opportunity to play with new jdk7 api :-)
Override paintComponent definitely is a good solution. Nevertheless, it requires subclassing just to paint something at a given location on top of something else. The ol' way doing so would be a JLayeredPane (which is a pain to handle). The new jdk has a JLayer component which allows to do that (and a lot more) by simple decoration of the component. Here's a snippet which:
has a label with the base image and decorates it with the default JLayer
adds the "player" image to the layer's glassPane
uses Rob's DragLayout (set on the glassPane) to move the player around, bare bones ui with two sliders
Working code (just some outer boiler plate missing, you all have your templates to stick that in :)
// to please Andrew :)
JLabel fooLabel = new JLabel(new ImageIcon(ImageIO.read(
new URL("http://pscode.org/media/stromlo2.jpg"))));
final JLayer<JLabel> layer = new JLayer<JLabel>(fooLabel);
final JLabel player = new JLabel(new CursorIcon(30));
// to please myself (never-ever use a null layout :)
layer.getGlassPane().setLayout(new DragLayout());
layer.getGlassPane().add(player);
layer.getGlassPane().setVisible(true);
final JSlider horizontal = new JSlider(0, fooLabel.getPreferredSize().width, 0);
final JSlider vertical = new JSlider(JSlider.VERTICAL, 0, fooLabel.getPreferredSize().height, 0);
vertical.setInverted(true);
ChangeListener l = new ChangeListener() {
#Override
public void stateChanged(ChangeEvent e) {
player.setLocation(horizontal.getValue(), vertical.getValue());
layer.revalidate();
}
};
horizontal.addChangeListener(l);
vertical.addChangeListener(l);
Quick icon:
public static class CursorIcon implements Icon {
private int size;
public CursorIcon(int size) {
this.size = size;
}
#Override
public void paintIcon(Component c, Graphics g, int x, int y) {
g.setColor(Color.red);
g.drawLine(size/2,y,size/2,size);
g.drawLine(x,size/2,size,size/2);
}
#Override
public int getIconWidth() {
return size;
}
#Override
public int getIconHeight() {
return size;
}
}
For earlier jdk versions, the SwingLabs subproject JXLayer is available

JPanel Repaint Not Clearing

I have a custom, abstract class 'Panel' which extends JPanel. There aren't many differences with the two when painting. I have a Panel and I'm simulating an animation by updating the x value of an image. I have two animations right now, one that properly repaints and another than does not. This is for the one that does not. The one that works will be labelled A, the one that doesn't will be B.
A and B follow the same format. Update some variable on the Panel, calls update (a method in Panel which calls PaintComponent) and then calls repaint. It calls repaint after because this issue was with A before and was solved that way.
A: Updates an image variable.
B: Updates the x variable of an image.
The Problem: The repaint doesn't clear the old image location and so it's a choppy mess across the screen.
What I've tried:
I've seen the super.PaintComponent(g) mentioned a lot, but this
hasn't solved the problem.
I've tried changing the order for when the repaint/update methods are
called.
Repaint does not update the Panel at all. (Probably because the
painting is done in PaintComponent)
Any help would be appreciated.
Code:
Panel:
public Panel (boolean visible){
super();
this.setLayout(new BorderLayout(640, 416));//sets the Layout type of the panel
this.setOpaque(false);//Makes it so that the panel underneath can be seen where images aren't drawn
this.setVisible(visible);
ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
gs = ge.getDefaultScreenDevice();
gc = gs.getDefaultConfiguration();
}
public void paintComponent (Graphics g){
setUp();
drawOff();
setDown(g);
}
private void setUp(){
off_screen = gc.createCompatibleImage(getSize().width, getSize().height, Transparency.TRANSLUCENT);
buffer = off_screen.createGraphics();
}
protected abstract void drawOff();
private void setDown(Graphics g){
g.drawImage(off_screen,0,0,this);
off_screen.flush();
}
public void update(){
paintComponent(this.getGraphics());
}
Animation Methods (mg is the panel in question):
private void battleStart(User user) {
for (int i = 0; i < user.battle.length; i++) {
mg.battleStart(user.battleStart(i));
mg.update();
try {
Thread.sleep(150);
} catch (Exception e) {
}
mg.repaint();
}
}
private void animateStart(User user){
for (int i = 0; i < 10; i++){
mg.x = mg.x + 10;
mg.update();
try {
Thread.sleep(100);
} catch (Exception e) {
}
mg.repaint();
}
}

I think your design is way off and that is why things are not working. I'm not quite sure how your non-abstract JPanels work, but consider making your parent JPanel something more along these lines:
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
public class MyPanel extends JPanel {
private GraphicsEnvironment ge;
private GraphicsDevice gs;
private GraphicsConfiguration gc;
private BufferedImage offScreen;
public MyPanel(boolean visible) {
super();
this.setLayout(new BorderLayout(640, 416)); // strange constants for this layout.
this.setOpaque(false);
this.setVisible(visible);
ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
gs = ge.getDefaultScreenDevice();
gc = gs.getDefaultConfiguration();
addComponentListener(new ComponentAdapter() {
#Override
public void componentResized(ComponentEvent e) {
setUp();
}
});
}
#Override
// don't make this public. Keep it protected like the super's
// just draw in this method. Don't call other methods that create buffers
// or draw to buffers.
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (offScreen != null) {
g.drawImage(offScreen, 0, 0, null);
}
}
private void setUp() {
offScreen = gc.createCompatibleImage(getSize().width, getSize().height,
Transparency.TRANSLUCENT);
}
// draw to the buffer outside of the paintComponent
// and then call repaint() when done
public void upDateOffScreen() {
// ?? offScreen.flush(); // I've never used this before,
// so am not sure if you need this here
Graphics2D osGraphics = offScreen.createGraphics();
// TODO: do drawing with osGraphics object here
osGraphics.dispose();
repaint();
}
}
Also and again,
Do all long processing methods off of the EDT (Event Dispatch Thread).
Never call Thread.sleep(...) on the EDT.
Consider using Swing Timers instead of using Thread.sleep for the animations.
It's OK to call repaint on your JPanel off of the EDT, but for the most part that's about it.
All other Swing methods should be called on the EDT.
Read, re-read, and study the 2D and Swing graphics tutorials.