Create a scrollable canvasTag(s): AWT


JDK1.1 using a ScrollPane
import java.applet.*;
import java.awt.*;

public class apptest extends Applet {
 Canvas c;
 ScrollPane s;

 public void init() {
  setLayout(new BorderLayout());
  s = new ScrollPane();
  s.setSize(100,100);
  add("Center", s);
  c = new myCanvas();
  c.setSize(500,300);
  s.add(c);
  }

 class myCanvas extends Canvas {
  Image    buffImage;
  Graphics offscreen;
  boolean initDone = false;

  myCanvas() { super(); }
    public void paint(Graphics g) {
   if (!initDone)
      initpaint(g);
   else
      g.drawImage(buffImage, 0, 0,  this);
   }

  public void update(Graphics g) {
   g.drawImage(buffImage, 0, 0,  this);
   }

  public void initpaint(Graphics g) {
   try {
    buffImage = this.createImage(500, 500);
    offscreen = buffImage.getGraphics();
    offscreen.setColor(Color.black);
    offscreen.fillRect(0, 0, 500, 500);
    offscreen.setColor(Color.white);
    offscreen.setFont(new Font("Courier", Font.ITALIC, 42));
    offscreen.drawString("Hello World!", 0, 50);
    initDone = true;
    g.drawImage(buffImage,0,0, this);
    }
   catch (Exception e) {
    e.printStackTrace();
    }
   }
  }
}
JDK1.0.2 using a Canvas with Scrollbar
import java.applet.*;
import java.awt.*;

public class apptest extends Applet {
 ScrollCanvas sc;
 public void init() {
  setLayout(new FlowLayout());
  sc = new ScrollCanvas
    (150,150, 300,200, Color.black,
     Color.white);
  add(sc);
  }

 public boolean handleEvent(Event e) {
  if (e.target instanceof Scrollbar) {
    switch (e.id) {
      case Event.SCROLL_ABSOLUTE:
      case Event.SCROLL_PAGE_DOWN:
      case Event.SCROLL_PAGE_UP:
      case Event.SCROLL_LINE_UP:
      case Event.SCROLL_LINE_DOWN:
         sc.redraw();
         return true;
      }
    }
    return super.handleEvent(e);
  }
}

class ScrollCanvas extends Panel {
 int vw,vh;
 int rw,rh;
 Color b,f;
 myCanvas c;
 Scrollbar sv, sh;

 // constructor
 //   visible h w
 //   real    h w
 //   background foreground
 ScrollCanvas
    (int vw1, int vh1,  int rw1, int rh1, Color b1, Color f1) {
  super();
  vw = vw1; vh = vh1;
  rh = rh1; rw = rw1;
  b  = b1;  f  = f1;
  int ScrollIncrement = 10;
  setLayout(new BorderLayout());
  c = new myCanvas(vw, vh, rw, rh, b ,f);
  add("West", c);
  sv = new Scrollbar
    (Scrollbar.VERTICAL,0, ScrollIncrement, 0, rh);
  add("East", sv);
  sh = new Scrollbar
    (Scrollbar.HORIZONTAL, 0, ScrollIncrement, 0, rw);
  add("South", sh);
  }

 public void redraw() {
  int y = sv.getValue();
  int x = sh.getValue();
  c.draw(x,y);
  }

 public Dimension minimumSize() {
  return new Dimension(vw,vh);
  }

 public Dimension preferredSize() {
  return new Dimension(vw,vh);
  }
}

class myCanvas extends Canvas {
 int vw, vh;
 int rw, rh;
 Color b, f;
 int x, y;
 Image buffImage;
 Graphics offscreen;
 boolean initDone;

 myCanvas
    (int vw1, int vh1, int rw1, int rh1, Color b1, Color f1) {
  super();
  vw = vw1; vh = vh1;
  rh = rh1; rw = rw1;
  b  = b1;  f  = f1;
  initDone = false;
  repaint();
  }

 public void paint(Graphics g) {
  if (!initDone)
   initpaint(g);
  else
   g.drawImage(buffImage, x, y,  this);
  }

 public void update(Graphics g) {
  g.drawImage(buffImage, x, y,  this);
  }

 public void initpaint(Graphics g) {
  try {
   buffImage = this.createImage(rw, rh);
   offscreen = buffImage.getGraphics();
   offscreen.setColor(b);
   offscreen.fillRect(0, 0, rw, rh);
   offscreen.setColor(f);
   offscreen.setFont(new Font("Courier", Font.ITALIC, 42));
   offscreen.drawString("Hello World!", 0, 50);
   initDone = true;
   g.drawImage(buffImage,0,0, this);
   }
  catch (Exception e) {
   System.out.println("oups...");
   }
  }

 public void draw (int x1, int y1)  {
  x = -x1;
  y = -y1;
  update(getGraphics());
  }

 public Dimension minimumSize() {
  return new Dimension(vw,vh);
  }

 public Dimension preferredSize() {
  return new Dimension(vw,vh);
  }
}

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