missile.java

一个完美的applet游戏

import java.awt.Graphics;


/**
 * <p>Title: UFO_Play</p>
 *
 * <p>Description: 基于applet的攻击UFO的小游戏中的导弹类</p>
 *
 * <p>Copyright: Copyright (c) 2007</p>
 *
 * <p>Company: 鹿児島大学</p>
 * @author 柴 智
 * @version 1.0
 */
public class Missile extends Piece {
    //导弹类的构造函数
    public Missile(UFO_Canvas ufo_canvas) {
        //导弹属性值的初始化
        super(ufo_canvas);
        px = opx = 0;
        py = opy = 0;
        vx = 0;
        vy = 7;
        w = 12;
        h = 22;
        active = false;
        img = ufo_canvas.getMissile();
    }

    //对象的移动函数
    public void move() {
        opx = px;
        opy = py;

        px = ufo_canvas.getL().px;

        // 使移动的速度更加实际化
        int dx = px - opx;
        int nvy = vy * vy - dx * dx;
        if (nvy > 0) {
            nvy = (int) Math.sqrt(nvy); // Should exceptions
        }
        if (nvy < 1) {
            nvy = 1;
        }

        py += nvy;

        if (py > ufo_canvas.getWindow_size().height + 2 * h) {
            active = false;
        }
    }

    int seq = 0;
    //导弹对象的绘制
    public void draw() {
        //设置绘制区域
        set_draw_rectangles(ufo_canvas.getPaint_area(), ufo_canvas.getNew_area());

        //先将变化绘制到缓冲中
        Graphics bg = ufo_canvas.getBuffer().getGraphics();
        bg.clipRect(ufo_canvas.getPaint_area().x, ufo_canvas.getPaint_area().y,
                    w, h);
        bg.drawImage(ufo_canvas.getBackdrop(), 0, 0, ufo_canvas.getBaseApplet());
        bg.dispose();

        //由于导弹所用的图片是一个序列图，所以要从中剪切，然后再使用
        //根据seq的值来显示此序列图的一部分
        seq = ++seq % 1;
        int dx = px - opx;
        seq = 0;
        if (dx > 0) {
            seq = 1;
        } else if (dx < 0) {
            seq = 2;
        }
        //将变化绘制到缓冲上
        bg = ufo_canvas.getBuffer().getGraphics();
        bg.clipRect(ufo_canvas.getNew_area().x, ufo_canvas.getNew_area().y, w,
                    h);
        bg.drawImage(img, ufo_canvas.getNew_area().x - w * seq,
                     ufo_canvas.getNew_area().y, ufo_canvas.getBaseApplet());

        bg.dispose();
        //使用新的区域
        ufo_canvas.getPaint_area().add(ufo_canvas.getNew_area());
        //将缓冲绘制到屏幕上
        Graphics g = ufo_canvas.getBaseApplet().getGraphics();
        g.clipRect(ufo_canvas.getPaint_area().x, ufo_canvas.getPaint_area().y,
                   ufo_canvas.getPaint_area().width,
                   ufo_canvas.getPaint_area().height);
        g.drawImage(ufo_canvas.getBuffer(), 0, 0, ufo_canvas.getBaseApplet());
        g.dispose();
    }
}