Question

This is my first attempt at using BufferStrategy and I’d really appreciate some hints.

1) Why, in the below code, does getSize() return dimensions of 0 until you have resized the window? How can I detect the size of the window right away?

2) Why when getSize() is returning something is it not the full dimensions of the window? IE why is there a blackless strip to the bottom and right?

3) Is there a way to get rid of the flicker when you resize the window?

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferStrategy;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class BSTest extends JFrame {
    BufferStrategy bs;
    DrawPanel panel = new DrawPanel();

    public BSTest() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800,420);
        setLocationRelativeTo(null);
        setIgnoreRepaint(true);
        setVisible(true);
        createBufferStrategy(2);
        bs = getBufferStrategy();
        panel.setIgnoreRepaint(true);
        add(panel);
        panel.drawStuff();
    }

    public class DrawPanel extends JPanel {
        public void drawStuff() {
            while(true) {
                try {
                    Graphics2D g = (Graphics2D)bs.getDrawGraphics();
                    g.setColor(Color.BLACK);
                    System.out.println("W:"+getSize().width+", H:"+getSize().height);
                    g.fillRect(0,0,getSize().width,getSize().height);
                    bs.show();
                    g.dispose();
                    Thread.sleep(20);
                } catch (Exception e) { System.exit(0); }
            }
        }
     }

    public static void main(String[] args) {
        BSTest bst = new BSTest();
    }
}

Answer 1

1. The size of a JPanel is not valid until validate() has been called, typically as a result invoking pack() on the containing Window.

2. The final size is the result of a combination of factors including the preferred sizes of the enclosed components and the panels UI delegate for a particular Look & Feel.

3. JPanel is double buffered by default; no further effort is required. AnimationTest is an example.