Different fling (swipe) velocity on different Android devices with same density

Question

I'm writing my own image viewer that enables users to swipe left\right to see the next\previous image. I want to animate the image change according to the fling velocity.

To detect a fling gesture and its velocity, I followed this basic gesture detection and did as the accepted answer suggested:

public class SelectFilterActivity extends Activity implements OnClickListener
{

    private static final int SWIPE_MIN_DISTANCE = 120;
    private static final int SWIPE_MAX_OFF_PATH = 250;
    private static final int SWIPE_THRESHOLD_VELOCITY = 200;
    private GestureDetector gestureDetector;
    View.OnTouchListener gestureListener;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        /* ... */

        // Gesture detection
        gestureDetector = new GestureDetector(this, new MyGestureDetector());
        gestureListener = new View.OnTouchListener() {
            public boolean onTouch(View v, MotionEvent event) {
                return gestureDetector.onTouchEvent(event);
            }
        };

    }

    class MyGestureDetector extends SimpleOnGestureListener {
        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            try {
                if (Math.abs(e1.getY() - e2.getY()) > SWIPE_MAX_OFF_PATH)
                    return false;
                // right to left swipe
                if(e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
                    Toast.makeText(SelectFilterActivity.this, "Left Swipe", Toast.LENGTH_SHORT).show();
                }  else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
                    Toast.makeText(SelectFilterActivity.this, "Right Swipe", Toast.LENGTH_SHORT).show();
                }
            } catch (Exception e) {
                // nothing
            }
            return false;
        }

    }

The problem is that I get different velocity values (velocityX & velocityY) for different Android devices with same density. Basically it means that in one device the swipe feels slow and not-sensitive, and other devices feels too sensitive.

I thought it might have something to do with the "default" maximum velocity on the device, that can be fetched using -

ViewConfiguration.get(mContext).getScaledMaximumFlingVelocity()

The results on different devices with same density aren't the same as expected:

    Samsung S I 480x800 density 1.5 Android 2.1
    getScaledMinimumFlingVelocity(): 75
    getScaledMaximumFlingVelocity(): 3600
    ViewConfiguration.MAXIMUM_FLING_VELOCITY = 4000

    HTC Desire 480x800 density 1.5 Android 2.3.3
    getScaledMinimumFlingVelocity(): 75
    getScaledMaximumFlingVelocity(): 6000
    ViewConfiguration.MAXIMUM_FLING_VELOCITY = 4000

    Samsung S III mini 480x800 density 1.5 Android 4.1
    getScaledMinimumFlingVelocity(): 75
    getScaledMaximumFlingVelocity(): 12000
    ViewConfiguration.MAXIMUM_FLING_VELOCITY = 8000

You can also see that ViewConfiguration has 2 different values for MAXIMUM_FLING_VELOCITY in Android below 4.0 and above.

How come different devices with same density and almost same api level don't have the same max velocity? How can I get the same experience on different devices when a user makes a swipe gesture? Can I use the max velocity data to make a uniform experience across all Android devices?

Answer 1

I had a similar problem. Instead of working directly with the max and min fling velocities from ViewConfiguration, you can normalize the velocity to a value between 0 and 1.

public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
    float maxFlingVelocity    = ViewConfiguration.get(mContext).getScaledMaximumFlingVelocity();
    float velocityPercentX    = velocityX / maxFlingVelocity;          // the percent is a value in the range of (0, 1]
    float normalizedVelocityX = velocityPercentX * PIXELS_PER_SECOND;  // where PIXELS_PER_SECOND is a device-independent measurement

In other words, velocityPercentX gives you the "power" of the fling as a percent, and normalizedVelocityX is the velocity in terms of your application logic (such as an image width in device-independent pixels).