計算機プログラミングI

グラフィクス画面を作るクラス

(ファイル名: Drawer2.java)

// 描画用クラス
// Copyright (C) 2000 by Hidehiko Masuhara
// 使い方は Drawer2Sample.java を参照。

// Java のグラフィクスライブラリを使うための宣言
import java.awt.*;
import java.awt.event.*;

public class Drawer2 extends Canvas
  implements Runnable, MouseListener, WindowListener {

    Image offScreenImage;
    static final int topMargin = 0;

    // for flicker-free drawing
    public void update(Graphics g) { paint(g); }
    // merely put the off-screen image on the screen
    public void paint(Graphics g) {
      if (offScreenImage != null)
	g.drawImage(offScreenImage,0,topMargin,this);
    }

    // create a Frame with the specified size,
    // it also sets up the off-screen image, and an updater thread
    // for asynchronous drawing.
    static Graphics createFrame(int width, int height) {
      return new Drawer2(width,height+topMargin).getGraphicsObject();
    }

    // 押されたらプログラムを終了させる
    public void windowClosing(WindowEvent we) {System.exit(0);}
    public void windowActivated(WindowEvent e){}
    public void windowClosed(WindowEvent e){}
    public void windowDeactivated(WindowEvent e){}
    public void windowDeiconified(WindowEvent e){}
    public void windowIconified(WindowEvent e){}
    public void windowOpened(WindowEvent e){}

    // クリックされたらプログラムを終了させる
    public void mouseClicked(MouseEvent me) {System.exit(0);}
    public void mouseEntered(MouseEvent e){}
    public void mouseExited(MouseEvent e){}
    public void mousePressed(MouseEvent e){}
    public void mouseReleased(MouseEvent e) {}
    
    public Drawer2(int width, int height) {
      super();
      Frame f = new Frame("A Graphics Window - Computer Programming I");
      // Closeボタンが押されたときの処理を設定しておく。
      f.addWindowListener(this);
      // 画面をクリックされたときの処理も設定。
      this.addMouseListener(this);

      int margin = 30;
      f.setSize(width,height);	// set the size of the window
      f.add(this);
      f.show();		// put this frame on a screen
      java.awt.Dimension d = this.getSize();
      f.setSize(width-d.width+width, height-d.height+height);
      f.doLayout();

      // create an off-screen image of the window for asynchronous drawing
      this.offScreenImage = this.createImage(width,height); 
    
      Thread updater = new Thread(this);
      updater.setDaemon(true);
      updater.start();
    }

    Graphics getGraphicsObject() {return offScreenImage.getGraphics();}

    // for background repainting
    final static int interval = 100; // msec.
    // a background thread will execute the following method
    public void run() {	       
      try {
	while (true) {
	  if (this.isShowing()) this.repaint();
	  Thread.currentThread().sleep(interval);
	}
      } catch (InterruptedException e) {
	;				// do nothing
      }
    }
}

Hidehiko Masuhara, December 2000