import java.awt.Graphics;

/**
 * <p>Title: UFO_Play</p>
 *
 * <p>Description: 基于applet的攻擊UFO的小游戲，定義UFO模型，繼承于Piece</p>
 *
 * <p>Copyright: Copyright (c) 2007</p>
 *
 * <p>Company: 鹿児島大學</p>
 * @author 柴 智
 * @version 1.0
 */
public class UFO extends Piece {

    //UFO類的構造函數
    public UFO(UFO_Canvas ufo_canvas) {
        //UFO屬性值的初始化
        super(ufo_canvas);
        vx = (Math.random() > 0.5 ? 1 : -1);
        vy = -2;
        w = 20;
        h = 8;
        int aw = ufo_canvas.getWindow_size().width;
        px = opx = (int) (w / 2 + 1 + (aw - w - 2) * Math.random());
        py = opy = ufo_canvas.getWindow_size().height + h / 2 + 1;
        active = true;

        img = ufo_canvas.getUfostrip();
    }

    //UFO對象的移動函數
    public void move() {
        opx = px;
        opy = py;

        px += vx;
        py += vy;

        if (py < -h / 2) {
            active = false;
        }

        if ((px <= w / 2) ||
            (px >= (ufo_canvas.getWindow_size().width - w / 2)) ||
            (Math.random() > 0.96)) {
            vx = -vx;
        }
    }

    int seq = 0;
    int seq2 = 0;
    //UFO對象的繪制函數
    public void draw() {
        //設置對象的繪制區域
        set_draw_rectangles(ufo_canvas.getPaint_area(), ufo_canvas.getNew_area());

        // 清除舊的圖像
        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UFO用的圖片是一個序列圖，要進行剪切再使用
        //根據seq2的值選擇相應的部分
        if ((++seq2 % 4) == 0) {
            seq = ++seq % 4;
        }

        // 繪制新的區域到緩沖中
        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();

        // 使用新的區域
        ufo_canvas.getPaint_area().add(ufo_canvas.getNew_area());

        // 將緩沖繪制到屏幕上
        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();
    }
}