swing
Grafica
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Usando la classe Graphics
Intro
La classe Graphics
ti permette di disegnare su componenti java come un Jpanel
, può essere usato per disegnare stringhe, linee, forme e immagini. Ciò avviene sovrascrivendo il paintComponent(Graphics g)
del JComponent
si sta disegnando utilizzando l'oggetto Graphics
ricevuto come argomento per eseguire il disegno:
Board
classe
import java.awt.*;
import javax.swing.*;
public class Board extends JPanel{
public Board() {
setBackground(Color.WHITE);
}
@override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
// draws a line diagonally across the screen
g.drawLine(0, 0, 400, 400);
// draws a rectangle around "hello there!"
g.drawRect(140, 180, 115, 25);
}
}
classe wrapper DrawingCanvas
import javax.swing.*;
public class DrawingCanvas extends JFrame {
public DrawingCanvas() {
Board board = new Board();
add(board); // adds the Board to our JFrame
pack(); // sets JFrame dimension to contain subcomponents
setResizable(false);
setTitle("Graphics Test");
setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
setLocationRelativeTo(null); // centers window on screen
}
public static void main(String[] args) {
DrawingCanvas canvas = new DrawingCanvas();
canvas.setVisible(true);
}
}
Colori
Per disegnare forme con colori diversi è necessario impostare il colore dell'oggetto Graphics
prima di ogni chiamata di disegno utilizzando setColor
:
g.setColor(Color.BLUE); // draws a blue square
g.fillRect(10, 110, 100, 100);
g.setColor(Color.RED); // draws a red circle
g.fillOval(10, 10, 100, 100);
g.setColor(Color.GREEN); // draws a green triangle
int[] xPoints = {0, 200, 100};
int[] yPoints = {100, 100, 280};
g.fillPolygon(xPoints, yPoints, 3);
Disegno di immagini
Le immagini possono essere disegnate su un JComponent
usando il metodo drawImage
della classe Graphics
:
caricamento di un'immagine
BufferedImage img;
try {
img = ImageIO.read(new File("stackoverflow.jpg"));
} catch (IOException e) {
throw new RuntimeException("Could not load image", e);
}
disegnare l'immagine
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
int x = 0;
int y = 0;
g.drawImage(img, x, y, this);
}
La x
e y
specificano la posizione dei top-sinistra dell'immagine.
Utilizzo del metodo Repaint per creare un'animazione di base
La classe MyFrame estende JFrame e contiene anche il metodo principale
import javax.swing.JFrame;
public class MyFrame extends JFrame{
//main method called on startup
public static void main(String[] args) throws InterruptedException {
//creates a frame window
MyFrame frame = new MyFrame();
//very basic game loop where the graphics are re-rendered
while(true){
frame.getPanel().repaint();
//The program waits a while before rerendering
Thread.sleep(12);
}
}
//the MyPanel is the other class and it extends JPanel
private MyPanel panel;
//constructor that sets some basic staring values
public MyFrame(){
this.setSize(500, 500);
this.setLocationRelativeTo(null);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//creates the MyPanel with paramaters of x=0 and y=0
panel = new MyPanel(0,0);
//adds the panel (which is a JComponent because it extends JPanel)
//into the frame
this.add(panel);
//shows the frame window
this.setVisible(true);
}
//gets the panel
public MyPanel getPanel(){
return panel;
}
}
La classe MyPanel che estende JPanel e ha il metodo paintComponent
import java.awt.Graphics;
import javax.swing.JPanel;
public class MyPanel extends JPanel{
//two int variables to store the x and y coordinate
private int x;
private int y;
//construcor of the MyPanel class
public MyPanel(int x, int y){
this.x = x;
this.y = y;
}
/*the method that deals with the graphics
this method is called when the component is first loaded,
when the component is resized and when the repaint() method is
called for this component
*/
@Override
public void paintComponent(Graphics g){
super.paintComponent(g);
//changes the x and y varible values
x++;
y++;
//draws a rectangle at the x and y values
g.fillRect(x, y, 50, 50);
}
}