Code example for PointF

	// These matrices will be used to move and zoom image 
	Matrix matrix = new Matrix();
	Matrix savedMatrix = new Matrix();
	PointF start = new PointF();
	PointF mid = new PointF();
	DisplayMetrics dm;
	float oldDist = 1f;
	private ImageView imgView;
	private Button zoomIn, zoomOut;
	private ViewSwitcher mViewSwitcher;
	// button zoom 
	private float scaleWidth = 1;
	private float scaleHeight = 1;
	private Bitmap bitmap, zoomedBMP;
	private int zoom_level = 0;
	private static final double ZOOM_IN_SCALE = 1.25;// 放大系数
	private static final double ZOOM_OUT_SCALE = 0.8;// 缩小系数