I am trying to call the paint() method from another class, but it just doesn't work.
Here is the code:
Main.java:
public class Main extends JFrame {
private static final long serialVersionUID = 1L;
private int WIDTH = 600;
private int HEIGHT = 400;
private String NAME = "Dark Ages";
private String VERSION = "0.0.1 Pre-Alpha";
static boolean running = false;
private Image dbImage;
private Graphics dbg;
public Main() {
//Initialize window
JFrame frame = new JFrame();
frame.setTitle(NAME + " - " + VERSION);
frame.setSize(WIDTH, HEIGHT);
frame.setVisible(true);
frame.setResizable(false);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
//Running
running = true;
}
public void paint(Graphics g) {
dbImage = createImage(getWidth(), getHeight());
dbg = dbImage.getGraphics();
paintComponent(dbg);
g.drawImage(dbImage, 0, 0, this);
}
public void paintComponent(Graphics g) {
// Draw Images
repaint();
}
public static void main(String args[]) {
new Main();
Player player = new Player();
}
}
Player.java:
public class Player {
public void paint(Graphics g) {
g.drawRect(100, 100, 100, 100);
}
}
How do I call the paint() method from another class in java?
In brief, you don't. And in fact, you shouldn't call it directly from the same class either. Instead you should change the state of the class (change its fields), and then call repaint() on it, which will suggest to the JVM that the component should be painted.
Other issues and suggestions:
An obvious issue I see immediately in your code is that your class has a Graphics field, something that is dangerous to do. I suggest that you get rid of that field so that you're not tempted to use it.
Do not draw directly within a JFrame, JDialog or other top-level window. These windows have too many roles to play behind the scenes that you don't really want to mess with how they render themselves or their children (unless you really know what you're doing and have definite need).
Better to draw in the paintComponent(...) method override of a JPanel or other JComponents.
In your paintComponent(...) override, don't forget to call the super's method: super.paintComponent(g);. This will allow Swing to do housekeeping drawing, such as erasing old out of date or deleted images, before you do your drawing.
Run, don't walk to your nearest Swing painting tutorial.
Your current Player class extends no Swing component and is added to no top level window, so its code will do nothing useful. Again, read the tutorials.
Never call repaint() from within paint(...) or paintComponent(...).
Please post modified code if possible.: please don't ask us to create code for you as that's your job. Please understand that the more code you create, the better a coder you'll be, and because of this, most of us don't feel that we should cheat you out of the opportunity to create your own code.
Useful Java Tutorials:
The Really Big Index: The main tutorial where you should start.
Using Swing Components: How to create Swing GUI's
Lesson: Performing Custom Painting: Introductory tutorial to Swing graphics
Painting in AWT and Swing: Advanced tutorial on Swing graphics
Related
This is my first java project and I am trying to draw a simple rectangle on my JPanel inside my JFrame. Been trying to solve this issue with the help of the same topics on stackoverflow but still no success.
The exception I get when I run the program is java.lang.NullPointerException. From my understanding I can not draw on the JPanel itself? which is created in mainWindow.
Main:
public class Main {
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
GameBoard game = new GameBoard();
mainWindow view = new mainWindow(game);
mainModel model = new mainModel();
mainController cont = new mainController(model, view, game);
cont.controllerInit();
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
}
View:
public class mainWindow{
public JFrame frame;
public JPanel panel;
GameBoard game = new GameBoard();
frame = new JFrame();
frame.getContentPane().setBackground(SystemColor.control);
frame.setBounds(100, 100, 728, 435);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(game);
frame.getContentPane().setLayout(null);
panel = new JPanel();
FlowLayout flowLayout = (FlowLayout) panel.getLayout();
panel.setBounds(166, 44, 550, 349);
frame.getContentPane().add(panel);
frame.setVisible(true);
}
Game:
public class GameBoard extends JPanel{
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
g.setColor(Color.BLUE);
g.drawRect(200, 200, 200, 200);
}
}
Never, ever call paintComponent directly, no external source has any reason to do so. Also, what do you thing would happen if you passed it null?
You should start by having a look at Performing Custom Painting and Painting in AWT and Swing to get a better understand of how paint in Swing works.
The Swing API basically uses a delegate model, where the system delegates responsibility of the paint of each component to the component. This is achieved by the system calling the components paint method, which in-turn calls (among a few others) paintComponent.
Swing also uses a passive rendering approaching, meaning that painting occurs at the discretion of the paint system. You component is notified of the need when its paint method is called. This may occur at any time.
In order for a component to be painted, it must first be added to container which is realised on the screen (has a native peer), in most cases, this means that the component hierarchy needs to resolve to some kind of window based class, like JFrame.
So, the answer to your question is:
Read the above documentation (and get a better understanding of how the API works)
Add your GameBoard to a container which can be resolved to a window based class
Never call paint or paintComponent directly
Reflection....
private mainWindow view;
private mainModel model;
public GameBoard(mainModel m, mainWindow v)
{
view = v;
model = m;
}
To me, this makes no sense. There is no reasonable reason why GameBoard needs a reference to mainWindow. GameBoard is, in of itself, a "view". If anything, the only thing you "should" be passing to GameBoard (assuming you're trying to use a MVC) is a controller
I am fairly new to java programming and I am trying to make a simple game however, I need to render my image I have made here is the code I put in eclipse:
public class MainMenu extends JFrame{
public static void main(String[] args){
new MainMenu();
}
public MainMenu(){
this.setSize(300, 450);
this.setLocationRelativeTo(null);
this.setResizable(true);
Toolkit tk = Toolkit.getDefaultToolkit();
Dimension dim = tk.getScreenSize();
int xPos = (dim.width / 2) - (this.getWidth() / 2);
int yPos = (dim.height / 2) - (this.getHeight() / 2);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setLocation(xPos, yPos);
this.setTitle("Frame For Flamedash Testing");
this.setVisible(true);
}
public void paint(Graphics g){
Image img1 = Toolkit.getDefaultToolkit().getImage("mainmenuscreen.png");
g.drawImage(img1, 20, 20, null);
} // public void paint(Graphics g)
public void putit() {
boolean MainMenu = true;
while (MainMenu == true){
repaint();
}
}
}
When I put that it is all fine and it does not give me any errors what so ever then I run it and it shows the frame but shows no picture than I full screen it because I set re-sizable true and it shows the default color in one spot with the size I set the frame too and another one identical but on the corner and black everywhere else. Any help to rendering this .png image will help, thank you in advance.
Don't override paint() in a JFrame.
The easiest way to display an image is to use a JLabel with an Icon.
Read the section from the Swing tutorial on How to Use Icons for more information and examples. The tutorial will show you how to better structure your code.
The tutorial also has a section on Custom Painting, if you really want to paint the image yourself. Custom painting is done by overriding the paintComponent() of a JPanel and then you add the panel to the frame.
First of all, in your paint method you should always call super.paint, else you break the paint chaining.
As for your issue,
You can call the repaint to force the painting. Keep a variable to hold the instance in your main and call repaint :
public MainMenu() {
...
repaint();
}
Note that loading an image from the paint method is a really bad idea as it will be loaded each time the frame is painted.
You've got several problems in that code including:
Drawing directly within the JFrame, something that can have unpleasant side effects
Trying to read in an image from within a painting method.
Your actual problem is often due to specifying the wrong path to the image, and to solve this you need to identify the actual user's directory that Java is looking at as the base of the path. This can be found by calling
System.out.println(System.getProperty("user.dir"));
JPanel Initiation
p = new JPanel() {
private static final long serialVersionUID = 1L;
public void paintComponent(Graphics g) {
if(errors == 1)
g.drawOval(215, 50, 75, 75);
else if(errors == 2)
g.drawOval(200,200,200,200);
}
};
Method that calls repaint
static void drawHead() {
System.out.println("Head");
errors = 1;
p.removeAll();
p.revalidate();
p.repaint();
}
Before repaint my frame looks like this, http://i.imgur.com/XQlQeul.png
And afterwards it looks like this, http://i.imgur.com/RnVuUzt.png
I'm thinking there is an error in my drawHead() method but I cannot seem to resolve the issue. Does anyone know what is going on? My desired outcome would be the first image, but with a head drawn in.
You've broken the paint chain by failing to call super.paintComponent first before you performed any custom painting
Graphics is shared resource, every component painted in a during a paint cycle will share the same Graphics context, this means that whatever was previously painted to the Graphics context will remain unless you clear it.
One of the jobs of paintComponent is to prepare the Graphics context for painting by filling it with the background color of the component
I'm attempting to code a simple animation or physics example in a Java Swing application. I have the actual windows application open and working, but I can't figure out how to actually draw my shapes, and how I'd format the code for calculations between frames, that sort of stuff.
I've read some stuff about over riding a paint method, but I don't know what that means, and I don't believe I'm using it in the code I'm using right now. This is my code:
public class Physics extends JFrame{
public Physics() {
initUI();
}
private void initUI() {
JPanel panel = new JPanel();
getContentPane().add(panel);
panel.setLayout(null);
final JLabel label = new JLabel("Hi, press the button to do something");
label.setBounds(20, 0, 2000, 60);
final JButton submitButton = new JButton("Start");
submitButton.setBounds(20, 150, 80, 20);
submitButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
//Put button code here later
}
});
panel.add(label);
panel.add(submitButton);
setTitle("Program");
setSize(300, 250);
setLocationRelativeTo(null);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
Physics ex = new Physics();
ex.setVisible(true);
}
});
}
}
So I have some blank space above my button where I'd like to draw maybe a square or circle moving across the screen to start off with, once I get that down I can start getting into the more advanced stuff. Any hints on how to do that would be appriciated :D
Thanks!
"I've read some stuff about over riding a paint method, but I don't know what that means"
So you've overridden actionPerformed, so you know what an #Override is. As you'll notice from the ActionListener, you never actually explicitly call actionPerformed, but whatever you put in the there, still get's used. That's because the ActionListener implicitly call it for you.
The same is true with painting. In the Swing painting process, there is a paint chain that Swing uses to paint components. Along the way paint is called somewhere. So just like actionPerformed, you can override paint and it will get implicitly called for you.
#Override
public void paint(Graphics g) {
super.paint(g);
}
The Graphics object passed to the method is the graphics context that Swing will use for the painting. You can look at the Graphics API to see the methods you can use. You can use drawOval to draw a circle
#Override
public void paint(Graphics g) {
super.paint(g);
g.drawOval(x, y, width, height);
}
Now here's the thing. You don't actually want to override paint. In the tutorials linked above, some of the examples will use applets and override paint, but you shouldn'y paint on top level containers like JFrame or JApplet. Instead paint on a JPanel or JComponent and just add it the JFrame. When you do paint on JPanel or JComponent, you'll instead override paintComponent (which also gets called along the paint chain), instead of paint
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawOval(x, y, width, height);
}
You see how I used variables for the drawOval method. The x is the x location from the top-let of the screen, and y and the y point. width and height are width and height of the circle. The great thing about using variables is that their values can be changed at runtime.
That's where the animation comes to play. As pointed out, you an use a javax.swing.Timer
The basic construct is
public Timer(int delay, ActionListener listener) {
}
The delay is the milliseconds to delay each call to the listener. The listener will have your actionPerformed call back that will do what's inside, every delay milliseconds. So what you can do, is just change the x from the drawOval and repaint(), and it will animate. Something like
Timer timer = new Timer(40, new ActionListener(){
#Override
public void actionPerformed(ActionEvent e) {
x += 5;
repaint();
}
});
timer.start();
The timer code you can just put in the constructor. That's probably simplest explanation I can give. Hope it helps.
Don't forget the to see Custom Painting and Grapics2D for more advance topics on graphics. Also see some example of timers and animation here and here and here and here and here
Also avoid using null layouts. See Laying out Components Within a Container to learn how to use layout managers, as should be done with Swing apps.
Take a look at the Swing tutorial on Custom Painting.
The example shows you how to do painting. If you want animation, then you would use a Swing Timer to schedule the animation. The tutorial also has a section on How to use a Swing Timer.
Put the two tutorial together and you have a solution.
There are any number of ways to achieve this.
Start by taking a look at:
Performing Custom Painting
2D Graphics
For details about how painting in Swing is done.
Animation is not as simple as just pausing a small period of time and then repainting, theres acceleration and deceleration and other concepts that need to be considered.
While you could write your own, that's not a small task, a better solution might be to use a pre-existing engine, for example...
Then take a look at:
Timing Framework
Trident
java-universal-tween-engine
Which are all examples of animation engines in Swing. While I prefer the Timing Framework as it provides me with a lower level API, this is a personal opinion. Both Trident and the JUWE seem to be geared more towards component/property based animation (which the Timing Framework can do if you want to build some of the feature sets up)
I created a simple animation with two rockets blasting off. The full eclipse project is here: https://github.com/CoachEd/JavaExamples/tree/master/RaceToSpace. Here's a screenshot:
I'm working on a project and I've read up as much as I can on double buffering in java. What I want to do is add a component or panel or something to my JFrame that contains the double buffered surface to draw to. I want to use hardware acceleration if possible, otherwise use regular software renderer. My code looks like this so far:
public class JFrameGame extends Game {
protected final JFrame frame;
protected final GamePanel panel;
protected Graphics2D g2;
public class GamePanel extends JPanel {
public GamePanel() {
super(true);
}
#Override
public void paintComponent(Graphics g) {
g2 = (Graphics2D)g;
g2.clearRect(0, 0, getWidth(), getHeight());
}
}
public JFrameGame() {
super();
gameLoop = new FixedGameLoop();
frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel = new GamePanel();
panel.setIgnoreRepaint(true);
frame.add(panel);
panel.setVisible(true);
frame.setVisible(true);
}
#Override
protected void Draw() {
panel.repaint(); // aquire the graphics - can I acquire the graphics another way?
super.Draw(); // draw components
// draw stuff here
// is the buffer automatically swapped?
}
#Override
public void run() {
super.run();
}
}
I created an abstract game class and a game loop that calls Update and Draw. Now, if you see my comments, that's my main area of concern. Is there a way to get the graphics once instead of going through repaint and paintComponent and then assigning a variable every redraw? Also, is this hardware accelerated by default? If not what should I do to make it hardware accelerated?
If you want more control over when the window is updated and to take advantage of hardware page flipping (if available), you can use the BufferStrategy class.
Your Draw method would then look something like this:
#Override
protected void Draw() {
BufferStrategy bs = getBufferStrategy();
Graphics g = bs.getDrawGraphics(); // acquire the graphics
// draw stuff here
bs.show(); // swap buffers
}
The downside is that this approach does not mix well with event-driven rendering. You generally have to choose one or the other. Also getBufferStrategy is implemented only in Canvas and Window making it incompatible with Swing components.
Tutorials can be found here, here and here.
Don't extend JPanel. Extend JComponent. It's virtually the same and has less interfering code. Also, you'd do the drawing code in paintComponent only. If you need to manually refresh the component, you'd use component.redraw().