Android 物理游戏之重力系统开发示例代码

package com.himi;  
import java.util.Random;  
import android.graphics.Canvas;  
import android.graphics.Color;  
import android.graphics.Paint;  
import android.graphics.RectF;  
/** 
 * @author Himi 
 * @自定义圆形类 
 */ 
public class MyArc {  
  private int arc_x, arc_y, arc_r;//圆形的X,Y坐标和半径  
  private float speed_x = 1.2f, speed_y = 1.2f;//小球的x、y的速度  
  private float vertical_speed;//加速度  
  private float horizontal_speed;//水平加速度,大家自己试着添加吧  
  private final float ACC = 0.135f;//为了模拟加速度的偏移值  
  private final float RECESSION = 0.2f;//每次弹起的衰退系数  
  private boolean isDown = true;//是否处于下落 状态  
  private Random ran;//随即数库  
  /** 
   * @定义圆形的构造函数 
   * @param x 圆形X坐标 
   * @param y 圆形Y坐标 
   * @param r 圆形半径 
   */ 
  public MyArc(int x, int y, int r) {  
    ran = new Random();  
    this.arc_x = x;  
    this.arc_y = y;  
    this.arc_r = r;  
  }  
  public void drawMyArc(Canvas canvas, Paint paint) {//每个圆形都应该拥有一套绘画方法  
    paint.setColor(getRandomColor());//不断的获取随即颜色，对圆形进行填充(实现圆形闪烁效果)  
    canvas.drawArc(new RectF(arc_x + speed_x, arc_y + speed_y, arc_x + 2 *  
        arc_r + speed_x, arc_y + 2 * arc_r + speed_y), 0, 360, true, paint);  
  }  
  /** 
   * @return 
   * @返回一个随即颜色 
   */ 
  public int getRandomColor() {  
    int ran_color = ran.nextInt(8);  
    int temp_color = 0;  
    switch (ran_color) {  
    case 0:  
      temp_color = Color.WHITE;  
      break;  
    case 1:  
      temp_color = Color.BLUE;  
      break;  
    case 2:  
      temp_color = Color.CYAN;  
      break;  
    case 3:  
      temp_color = Color.DKGRAY;  
      break;  
    case 4:  
      temp_color = Color.RED;  
      break;  
    case 6:  
      temp_color = Color.GREEN;  
    case 7:  
      temp_color = Color.GRAY;  
    case 8:  
      temp_color = Color.YELLOW;  
      break;  
    }  
    return temp_color;  
  }  
  /** 
   * 圆形的逻辑 
   */ 
  public void logic() {//每个圆形都应该拥有一套逻辑  
    if (isDown) {//圆形下落逻辑  
/*--备注1-*/speed_y += vertical_speed;//圆形的Y轴速度加上加速度  
      int count = (int) vertical_speed++;  
      //这里拿另外一个变量记下当前速度偏移量  
      //如果下面的for (int i = 0; i < vertical_speed++; i++) {}这样就就死循环了 - -  
      for (int i = 0; i < count; i++) {//备注1  
/*--备注2-*/ vertical_speed += ACC;  
      }  
    } else {//圆形反弹逻辑  
      speed_y -= vertical_speed;  
      int count = (int) vertical_speed--;  
      for (int i = 0; i < count; i++) {  
        vertical_speed -= ACC;  
      }  
    }  
    if (isCollision()) {  
      isDown = !isDown;//当发生碰撞说明圆形的方向要改变一下了！  
      vertical_speed -= vertical_speed * RECESSION;//每次碰撞都会衰减反弹的加速度  
    }  
  }  
  /** 
   * 圆形与屏幕底部的碰撞 
   * @return 
   * @返回true 发生碰撞 
   */ 
  public boolean isCollision() {  
    return arc_y + 2 * arc_r + speed_y >= MySurfaceViee.screenH;  
  }  
} 

 for (int i = 0; i < count; i++) {

        vertical_speed += ACC;

    }

package com.himi;  
import java.util.Random;  
import java.util.Vector;  
import android.content.Context;  
import android.graphics.Canvas;  
import android.graphics.Color;  
import android.graphics.Paint;  
import android.util.Log;  
import android.view.KeyEvent;  
import android.view.SurfaceHolder;  
import android.view.SurfaceView;  
import android.view.SurfaceHolder.Callback;  
public class MySurfaceViee extends SurfaceView implements Callback, Runnable {  
  private Thread th;  
  private SurfaceHolder sfh;  
  private Canvas canvas;  
  private Paint paint;  
  private boolean flag;  
  public static int screenW, screenH;  
  private Vector<MyArc> vc;//这里定义装我们自定义圆形的容器  
  private Random ran;//随即库  
  public MySurfaceViee(Context context) {  
    super(context);  
    this.setKeepScreenOn(true);  
    vc = new Vector<MyArc>();  
    ran = new Random();//备注1  
    sfh = this.getHolder();  
    sfh.addCallback(this);  
    paint = new Paint();  
    paint.setAntiAlias(true);  
    setFocusable(true);  
  }  
  public void surfaceCreated(SurfaceHolder holder) {  
    flag = true;//这里都是上一篇刚讲过的。。。  
    th = new Thread(this);  
    screenW = this.getWidth();  
    screenH = this.getHeight();  
    th.start();  
  }  
  public void draw() {  
    try {  
      canvas = sfh.lockCanvas();  
      canvas.drawColor(Color.BLACK);  
      if (vc != null) {//当容器不为空，遍历容器中所有圆形画方法  
        for (int i = 0; i < vc.size(); i++) {  
          vc.elementAt(i).drawMyArc(canvas, paint);  
        }  
      }  
    } catch (Exception e) {  
      // TODO: handle exception  
    } finally {  
      try {  
        if (canvas != null)  
          sfh.unlockCanvasAndPost(canvas);  
      } catch (Exception e2) {  
      }  
    }  
  }  
  private void logic() {//主逻辑  
    if (vc != null) {//当容器不为空，遍历容器中所有圆形逻辑  
      for (int i = 0; i < vc.size(); i++) {  
        vc.elementAt(i).logic();  
      }  
    }  
  }  
  @Override 
  public boolean onKeyDown(int keyCode, KeyEvent event) {  
    //当按键事件响应，我们往容器中仍个我们的圆形实例  
    vc.addElement(new MyArc(ran.nextInt(this.getWidth()), ran.nextInt(100), ran.nextInt(50)));  
    return true;  
  }  
  public void run() {  
    // TODO Auto-generated method stub  
    while (flag) {  
      logic();  
      draw();  
      try {  
        Thread.sleep(100);  
      } catch (Exception ex) {  
      }  
    }  
  }  
  public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {  
    Log.v("Himi", "surfaceChanged");  
  }  
  public void surfaceDestroyed(SurfaceHolder holder) {  
    flag = false;  
  }