MyCanvas.java Source code

Introduction

Here is the source code for MyCanvas.java

Source

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.Arc2D;
import java.awt.image.BufferedImage;

import javax.swing.JComponent;
import javax.swing.JFrame;

class MyCanvas extends JComponent {
    private BufferedImage offImg;

    public void draw(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;

        // Draw the pie chart
        Arc2D.Float arc = new Arc2D.Float(Arc2D.PIE);
        arc.setFrame(140, 200, 67, 46);
        arc.setAngleStart(45);
        arc.setAngleExtent(270);
        g2.setColor(Color.gray);
        g2.draw(arc);
        g2.setColor(Color.red);
        g2.fill(arc);
        g2.setColor(Color.black);
        g2.drawString("Arc2D.PIE", 140, 190);
    }

    public Graphics2D createDemoGraphics2D(Graphics g) {
        Graphics2D g2 = null;

        if (offImg == null || offImg.getWidth() != getSize().width || offImg.getHeight() != getSize().height) {
            offImg = (BufferedImage) createImage(getSize().width, getSize().height);
        }

        if (offImg != null) {
            g2 = offImg.createGraphics();
            g2.setBackground(getBackground());
        }

        // .. set attributes ..
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        // .. clear canvas ..
        g2.clearRect(0, 0, getSize().width, getSize().height);

        return g2;
    }

    public void paint(Graphics g) {
        if (getSize().width <= 0 || getSize().height <= 0)
            return;

        Graphics2D g2 = createDemoGraphics2D(g);
        draw(g2);

        g2.dispose();

        if (offImg != null && isShowing()) {
            g.drawImage(offImg, 0, 0, this);
        }
    }

}

public class OffScreenPaint {
    public static void main(String[] a) {
        JFrame window = new JFrame();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setBounds(30, 30, 300, 300);
        window.getContentPane().add(new MyCanvas());
        window.setVisible(true);
    }
}