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Commit 4e325ba2 authored by Marc Capdevielle's avatar Marc Capdevielle Committed by Steve Kondik
Browse files

Use a circular buffer in VelocityTracker 

Optimizes the frequently called addPoint() method while keeping the
same velocity computation.

Thx Cyril Mottier for help and tests.
parent 0a475b12

core/java/android/view/VelocityTracker.java

+33 −55
Original line number Diff line number Diff line
@@ -59,6 +59,8 @@ public final class VelocityTracker implements Poolable<VelocityTracker> { 
    final float mPastY[] = new float[NUM_PAST];

    final long mPastTime[] = new long[NUM_PAST];



    int mLastTouch;



    float mYVelocity;

    float mXVelocity;
@@ -105,7 +107,10 @@ public final class VelocityTracker implements Poolable<VelocityTracker> { 
     * Reset the velocity tracker back to its initial state.

     */

    public void clear() {

        mPastTime[0] = 0;

        final long[] pastTime = mPastTime;

        for (int i = 0; i < NUM_PAST; i++) {

            pastTime[i] = 0;

        }

    }

    

    /**
@@ -128,42 +133,11 @@ public final class VelocityTracker implements Poolable<VelocityTracker> { 
    }



    private void addPoint(float x, float y, long time) {

        int drop = -1;

        int i;

        if (localLOGV) Log.v(TAG, "Adding past y=" + y + " time=" + time);

        final long[] pastTime = mPastTime;

        for (i=0; i<NUM_PAST; i++) {

            if (pastTime[i] == 0) {

                break;

            } else if (pastTime[i] < time-LONGEST_PAST_TIME) {

                if (localLOGV) Log.v(TAG, "Dropping past too old at "

                        + i + " time=" + pastTime[i]);

                drop = i;

            }

        }

        if (localLOGV) Log.v(TAG, "Add index: " + i);

        if (i == NUM_PAST && drop < 0) {

            drop = 0;

        }

        if (drop == i) drop--;

        final float[] pastX = mPastX;

        final float[] pastY = mPastY;

        if (drop >= 0) {

            if (localLOGV) Log.v(TAG, "Dropping up to #" + drop);

            final int start = drop+1;

            final int count = NUM_PAST-drop-1;

            System.arraycopy(pastX, start, pastX, 0, count);

            System.arraycopy(pastY, start, pastY, 0, count);

            System.arraycopy(pastTime, start, pastTime, 0, count);

            i -= (drop+1);

        }

        pastX[i] = x;

        pastY[i] = y;

        pastTime[i] = time;

        i++;

        if (i < NUM_PAST) {

            pastTime[i] = 0;

        }

        final int lastTouch = (mLastTouch + 1) % NUM_PAST;

        mPastX[lastTouch] = x;

        mPastY[lastTouch] = y;

        mPastTime[lastTouch] = time;

        mLastTouch = lastTouch;

    }



    /**
@@ -193,35 +167,39 @@ public final class VelocityTracker implements Poolable<VelocityTracker> { 
        final float[] pastX = mPastX;

        final float[] pastY = mPastY;

        final long[] pastTime = mPastTime;

        final int lastTouch = mLastTouch;

        

        // find oldest acceptable time

        int oldestTouch = lastTouch;

        if (pastTime[lastTouch] > 0) { // cleared ?

            oldestTouch = (lastTouch + 1) % NUM_PAST;

            final float acceptableTime = pastTime[lastTouch] - LONGEST_PAST_TIME;

            while (pastTime[oldestTouch] < acceptableTime) {

                oldestTouch = (oldestTouch + 1) % NUM_PAST;

            }

        }

        

        // Kind-of stupid.

        final float oldestX = pastX[0];

        final float oldestY = pastY[0];

        final long oldestTime = pastTime[0];

        final float oldestX = pastX[oldestTouch];

        final float oldestY = pastY[oldestTouch];

        final long oldestTime = pastTime[oldestTouch];

        float accumX = 0;

        float accumY = 0;

        int N=0;

        while (N < NUM_PAST) {

            if (pastTime[N] == 0) {

                break;

            }

            N++;

        }

        float N = (lastTouch - oldestTouch + NUM_PAST) % NUM_PAST + 1;

        // Skip the last received event, since it is probably pretty noisy.

        if (N > 3) N--;



        for (int i=1; i < N; i++) {

            final int dur = (int)(pastTime[i] - oldestTime);

            final int j = (oldestTouch + i) % NUM_PAST;

            final int dur = (int)(pastTime[j] - oldestTime);

            if (dur == 0) continue;

            float dist = pastX[i] - oldestX;

            float dist = pastX[j] - oldestX;

            float vel = (dist/dur) * units;   // pixels/frame.

            if (accumX == 0) accumX = vel;

            else accumX = (accumX + vel) * .5f;

            accumX = (accumX == 0) ? vel : (accumX + vel) * .5f;

            

            dist = pastY[i] - oldestY;

            dist = pastY[j] - oldestY;

            vel = (dist/dur) * units;   // pixels/frame.

            if (accumY == 0) accumY = vel;

            else accumY = (accumY + vel) * .5f;

            accumY = (accumY == 0) ? vel : (accumY + vel) * .5f;

        }

        mXVelocity = accumX < 0.0f ? Math.max(accumX, -maxVelocity) : Math.min(accumX, maxVelocity);

        mYVelocity = accumY < 0.0f ? Math.max(accumY, -maxVelocity) : Math.min(accumY, maxVelocity);