Android如何判断当前点击位置是否在圆的内部

public class MainActivity extends Activity {

 int lastX;
 int lastY;
 boolean isView = false;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);

 final CircleImageView civ = (CircleImageView) findViewById(R.id.civ_levitate);

 civ.setOnTouchListener(new View.OnTouchListener() {
  @Override
  public boolean onTouch(View v, MotionEvent event) {

  switch (event.getAction()){
   case MotionEvent.ACTION_DOWN:

   lastX = (int) event.getRawX();
   lastY = (int) event.getRawY();

   //获取控件在屏幕的位置
   int[] location = new int[2];
   civ.getLocationOnScreen(location);

   //控件相对于屏幕的x与y坐标
   int x = location[0];
   int y = location[1];


   //圆半径 通过左右坐标计算获得getLeft
   int r = (civ.getRight()-civ.getLeft())/2;

   //圆心坐标
   int vCenterX = x+r;
   int vCenterY = y+r;

   //点击位置x坐标与圆心的x坐标的距离
   int distanceX = Math.abs(vCenterX-lastX);
   //点击位置y坐标与圆心的y坐标的距离
   int distanceY = Math.abs(vCenterY-lastY);
   //点击位置与圆心的直线距离
   int distanceZ = (int) Math.sqrt(Math.pow(distanceX,2)+Math.pow(distanceY,2));

   //如果点击位置与圆心的距离大于圆的半径，证明点击位置没有在圆内
   if(distanceZ > r){
    return false;
   }

   isView = true;

   break;

   case MotionEvent.ACTION_MOVE:

   if(isView){

    int moveX = (int) event.getRawX();
    int moveY = (int) event.getRawY();

    int disX = moveX - lastX;
    int disY = moveY - lastY;

    int left = civ.getLeft()+disX;
    int right = civ.getRight()+disX;
    int top = civ.getTop()+disY;
    int bottom = 
    civ.getBottom()+disY;

    civ.layout(left,top,right,bottom);

    lastX = moveX;
    lastY = moveY;
   }


   break;

   case MotionEvent.ACTION_UP:


   isView = false;


   break;
  }

  return true;
  }
 });

 }
}