我以 SensorManager 的加速器为例，其中画布（球）根据设备加速器的旋转来更新其位置。这是图像：
如图所示，有一个球和一条线。球的位置经常更新，而线的位置是静态的。
我想让球在触线时反弹回来。我从 3 天开始就尝试过，但不明白我该怎么做。
这是我的代码：
public class ballsensor extends Activity implements SensorEventListener {
// sensor-related
private SensorManager mSensorManager;
private Sensor mAccelerometer;
// animated view
private ShapeView mShapeView;
// screen size
private int mWidthScreen;
private int mHeightScreen;
// motion parameters
private final float FACTOR_FRICTION = 0.5f; // imaginary friction on the
// screen
private final float GRAVITY = 9.8f; // acceleration of gravity
private float mAx; // acceleration along x axis
private float mAy; // acceleration along y axis
private final float mDeltaT = 0.5f; // imaginary time interval between each
// acceleration updates
// timer
private Timer mTimer;
private Handler mHandler;
private boolean isTimerStarted = false;
private long mStart;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// set the screen always portait
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
// initializing sensors
mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
mAccelerometer = mSensorManager
.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
// obtain screen width and height
Display display = ((WindowManager) this
.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
mWidthScreen = display.getWidth();
mHeightScreen = display.getHeight() - 35;
// initializing the view that renders the ball
mShapeView = new ShapeView(this);
mShapeView.setOvalCenter((int) (mWidthScreen * 0.6),
(int) (mHeightScreen * 0.6));
setContentView(mShapeView);
}
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
@Override
public void onSensorChanged(SensorEvent event) {
// obtain the three accelerations from sensors
mAx = event.values[0];
mAy = event.values[1];
float mAz = event.values[2];
// taking into account the frictions
mAx = Math.signum(mAx) * Math.abs(mAx)
* (1 - FACTOR_FRICTION * Math.abs(mAz) / GRAVITY);
mAy = Math.signum(mAy) * Math.abs(mAy)
* (1 - FACTOR_FRICTION * Math.abs(mAz) / GRAVITY);
}
@Override
protected void onResume() {
super.onResume();
// start sensor sensing
mSensorManager.registerListener(this, mAccelerometer,
SensorManager.SENSOR_DELAY_NORMAL);
}
@Override
protected void onPause() {
super.onPause();
// stop senser sensing
mSensorManager.unregisterListener(this);
}
// the view that renders the ball
private class ShapeView extends SurfaceView implements
SurfaceHolder.Callback {
private final int RADIUS = 30;
private final float FACTOR_BOUNCEBACK = 0.50f;
private int mXCenter;
private int mYCenter;
private RectF mRectF;
private final Paint mPaint;
private ShapeThread mThread;
private float mVx;
private float mVy;
public ShapeView(Context context) {
super(context);
getHolder().addCallback(this);
mThread = new ShapeThread(getHolder(), this);
setFocusable(true);
mPaint = new Paint();
mPaint.setColor(0xFFFFFFFF);
mPaint.setAlpha(192);
mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
mPaint.setAntiAlias(true);
mRectF = new RectF();
}
// set the position of the ball
public boolean setOvalCenter(int x, int y) {
mXCenter = x;
mYCenter = y;
return true;
}
// calculate and update the ball's position
public boolean updateOvalCenter() {
mVx -= mAx * mDeltaT;
mVy += mAy * mDeltaT;
System.out.println("mVx is ::" + mVx);
System.out.println("mVy is ::" + mVy);
mXCenter += (int) (mDeltaT * (mVx + 0.6 * mAx * mDeltaT));
mYCenter += (int) (mDeltaT * (mVy + 0.6 * mAy * mDeltaT));
if (mXCenter < RADIUS) {
mXCenter = RADIUS;
mVx = -mVx * FACTOR_BOUNCEBACK;
}
if (mYCenter < RADIUS) {
mYCenter = RADIUS;
mVy = -mVy * FACTOR_BOUNCEBACK;
}
if (mXCenter > mWidthScreen - RADIUS) {
mXCenter = mWidthScreen - RADIUS;
mVx = -mVx * FACTOR_BOUNCEBACK;
}
if (mYCenter > mHeightScreen - 2 * RADIUS) {
mYCenter = mHeightScreen - 2 * RADIUS;
mVy = -mVy * FACTOR_BOUNCEBACK;
}
return true;
}
// update the canvas.
@Override
protected void onDraw(Canvas canvas) {
if (mRectF != null) {
mRectF.set(mXCenter - RADIUS, mYCenter - RADIUS, mXCenter
+ RADIUS, mYCenter + RADIUS);
canvas.drawColor(0XFF000000);
// canvas.drawOval(mRectF, mPaint);
Bitmap kangoo = BitmapFactory.decodeResource(getResources(),
R.drawable.stripe1);
Bitmap ball = BitmapFactory.decodeResource(getResources(),
R.drawable.blackwhiteball);
canvas.drawBitmap(ball, mXCenter - RADIUS, mYCenter - RADIUS,
mPaint);
canvas.drawBitmap(kangoo, 130, 10, null);
}
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
mThread.setRunning(true);
mThread.start();
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
boolean retry = true;
mThread.setRunning(false);
while (retry) {
try {
mThread.join();
retry = false;
} catch (InterruptedException e) {
}
}
}
}
class ShapeThread extends Thread {
private SurfaceHolder mSurfaceHolder;
private ShapeView mShapeView;
private boolean mRun = false;
public ShapeThread(SurfaceHolder surfaceHolder, ShapeView shapeView) {
mSurfaceHolder = surfaceHolder;
mShapeView = shapeView;
}
public void setRunning(boolean run) {
mRun = run;
}
public SurfaceHolder getSurfaceHolder() {
return mSurfaceHolder;
}
@Override
public void run() {
Canvas c;
while (mRun) {
mShapeView.updateOvalCenter();
c = null;
try {
c = mSurfaceHolder.lockCanvas(null);
synchronized (mSurfaceHolder) {
mShapeView.onDraw(c);
}
} finally {
if (c != null) {
mSurfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
}
}