package ch09.section05;

import java.util.*;
import javax.microedition.lcdui.*;

//繪制動畫的畫布
public class AnimatedCanvas
    extends Canvas {

  private Display display;
  private Image offscreen;
  private Vector images = new Vector();

  public AnimatedCanvas(Display display) {

    this.display = display;
    if (!isDoubleBuffered()) {

      offscreen = Image.createImage(getWidth(), getHeight());
    }
  }

  //添加一個動畫圖像到列表中
  public void add(AnimatedImage image) {
    images.addElement(image);
  }

  //采用雙緩存技術減少圖像抖動
  protected void paint(Graphics g) {
    Graphics saved = g;
    if (offscreen != null) {
      g = offscreen.getGraphics();
    }
    g.setColor(255, 255, 255);
    g.fillRect(0, 0, getWidth(), getHeight());
    int n = images.size();
    for (int i = 0; i < n; ++i) {
      AnimatedImage img = (AnimatedImage) images.elementAt(i);
      img.draw(g);
    }
    if (g != saved) {
      saved.drawImage(offscreen, 0, 0, Graphics.LEFT | Graphics.TOP);
    }
  }
}