Android碰撞检测——矩形检查

　　碰撞检测常用的分三类：圆形检测、矩形检测、像素检测。像素检测是最为精确的一种，但是它对性能消耗也是最大的一种，因为一般游戏中很少用到。

　　矩形检查

　　思路：可以检查两个矩形的相对位置，如果RectA在RectB的上下左右，且两个矩形没有挨着，则可以判定他们没有碰撞，反之就发生碰撞了。

    /**
     * 
     * @param x1 矩形1的X坐标
     * @param y1 矩形1的Y坐标
     * @param w1 矩形1的宽
     * @param h1 矩形1的高
     * @param x2 矩形2的X坐标
     * @param y2  矩形2的Y坐标
     * @param w2 矩形2的宽
     * @param h2 矩形的高
     * @return
     */
    public boolean CheckRectCollsion(int x1, int y1, int w1, int h1, int x2, int y2, int w2, int h2) {
        if (x1 >= x2 && x1 >= x2 + w2) {
            return false;
        } else if (x1 <= x2 && x1 + w1 <= x2) {
            return false;
        } else if (y1 >= y2 && y1 >= y2 + h2) {
            return false;
        } else if (y1 <= y2 && y1 + h1 <= y2) {
            return false;
        }
        return true;
    }

      实现一个完整的例子

public class MySurfaceView extends SurfaceView implements Callback,Runnable {
    private SurfaceHolder surfaceHolder;
    private Paint paint;
    private Thread thread;
    private boolean flag;
    int sleeptime=100;
    //定义两个矩形的宽高坐标
    private int x1 = 10, y1 = 110, w1 = 40, h1 = 40;
    private int x2 = 100, y2 = 110, w2 = 40, h2 = 40;
    //便于观察是否发生了碰撞设置一个标识位
    private boolean isCollsion;
    public MySurfaceView(Context context) {
        super(context);
        surfaceHolder = this.getHolder();
        surfaceHolder.addCallback(this);
        paint = new Paint();
        paint.setColor(Color.WHITE);
        paint.setAntiAlias(true);
        setFocusable(true); //设置焦点
    }

    @Override
    public void run() {
        Canvas canvas=null;
        while (flag) {
            try {
                canvas=surfaceHolder.lockCanvas();
                synchronized (canvas) {
                    myDraw(canvas);
                }
            } catch (Exception e) {
                Log.e("collsion", e.getMessage());
            }finally{
                if(canvas!=null){
                    surfaceHolder.unlockCanvasAndPost(canvas);
                }
            }
            try {
                Thread.sleep(sleeptime);
            } catch (Exception e) {
                Log.e("collsion", e.getMessage());
            }
        }
    }
    
    /**
     * 触屏事件监听
     */
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //让矩形1随着触屏位置移动
        x1 = (int) event.getX() - w1 / 2;
        y1 = (int) event.getY() - h1 / 2;
        if (CheckRectCollsion(x1, y1, w1, h1, x2, y2, w2, h2)) {
            isCollsion = true;
        } else {
            isCollsion = false;
        }
        return true;
    }
    
    public void myDraw(Canvas canvas) {
            canvas.drawColor(Color.BLACK);
            if (isCollsion) {
                paint.setColor(Color.RED);
                paint.setTextSize(20);
                canvas.drawText("碰撞了！", 0, 30, paint);
            } else {
                paint.setColor(Color.WHITE);
            }
            //绘制两个矩形
            canvas.drawRect(x1, y1, x1 + w1, y1 + h1, paint);
            canvas.drawRect(x2, y2, x2 + w2, y2 + h2, paint);
        }
    
    @Override
    public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void surfaceCreated(SurfaceHolder arg0) {
        flag = true;
        //实例线程
        thread = new Thread(this);
        if(!thread.isAlive()){
        //启动线程
        thread.start();
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder arg0) {
        // TODO Auto-generated method stub
        
    }
    /**
     * 
     * @param x1 矩形1的X坐标
     * @param y1 矩形1的Y坐标
     * @param w1 矩形1的宽
     * @param h1 矩形1的高
     * @param x2 矩形2的X坐标
     * @param y2  矩形2的Y坐标
     * @param w2 矩形2的宽
     * @param h2 矩形的高
     * @return
     */
    public boolean CheckRectCollsion(int x1, int y1, int w1, int h1, int x2, int y2, int w2, int h2) {
        if (x1 >= x2 && x1 >= x2 + w2) {
            return false;
        } else if (x1 <= x2 && x1 + w1 <= x2) {
            return false;
        } else if (y1 >= y2 && y1 >= y2 + h2) {
            return false;
        } else if (y1 <= y2 && y1 + h1 <= y2) {
            return false;
        }
        return true;
    }