Android触屏事件处理策略

在frameworks/base/libs/androidfw/VelocityTracker.cpp

VelocityTrackerStrategy* VelocityTracker::createStrategy(const char* strategy) {

    if (!strcmp("lsq1", strategy)) {

        // 1st order least squares.  Quality: POOR.

        // Frequently underfits the touch data especially when the finger accelerates

        // or changes direction.  Often underestimates velocity.  The direction

        // is overly influenced by historical touch points.

        return new LeastSquaresVelocityTrackerStrategy(1);

    }

    if (!strcmp("lsq2", strategy)) {

        // 2nd order least squares.  Quality: VERY GOOD.

        // Pretty much ideal, but can be confused by certain kinds of touch data,

        // particularly if the panel has a tendency to generate delayed,

        // duplicate or jittery touch coordinates when the finger is released.

        return new LeastSquaresVelocityTrackerStrategy(2);

    }

    if (!strcmp("lsq3", strategy)) {

        // 3rd order least squares.  Quality: UNUSABLE.

        // Frequently overfits the touch data yielding wildly divergent estimates

        // of the velocity when the finger is released.

        return new LeastSquaresVelocityTrackerStrategy(3);

    }

    if (!strcmp("wlsq2-delta", strategy)) {

        // 2nd order weighted least squares, delta weighting.  Quality: EXPERIMENTAL

        return new LeastSquaresVelocityTrackerStrategy(2,

                LeastSquaresVelocityTrackerStrategy::WEIGHTING_DELTA);

    }

    if (!strcmp("wlsq2-central", strategy)) {

        // 2nd order weighted least squares, central weighting.  Quality: EXPERIMENTAL

        return new LeastSquaresVelocityTrackerStrategy(2,

                LeastSquaresVelocityTrackerStrategy::WEIGHTING_CENTRAL);

    }

    if (!strcmp("wlsq2-recent", strategy)) {

        // 2nd order weighted least squares, recent weighting.  Quality: EXPERIMENTAL

        return new LeastSquaresVelocityTrackerStrategy(2,

                LeastSquaresVelocityTrackerStrategy::WEIGHTING_RECENT);

    }

    if (!strcmp("int1", strategy)) {

        // 1st order integrating filter.  Quality: GOOD.

        // Not as good as 'lsq2' because it cannot estimate acceleration but it is

        // more tolerant of errors.  Like 'lsq1', this strategy tends to underestimate

        // the velocity of a fling but this strategy tends to respond to changes in

        // direction more quickly and accurately.

        return new IntegratingVelocityTrackerStrategy(1);

    }

    if (!strcmp("int2", strategy)) {

        // 2nd order integrating filter.  Quality: EXPERIMENTAL.

        // For comparison purposes only.  Unlike 'int1' this strategy can compensate

        // for acceleration but it typically overestimates the effect.

        return new IntegratingVelocityTrackerStrategy(2);

    }

    if (!strcmp("legacy", strategy)) {

        // Legacy velocity tracker algorithm.  Quality: POOR.

        // For comparison purposes only.  This algorithm is strongly influenced by

        // old data points, consistently underestimates velocity and takes a very long

        // time to adjust to changes in direction.

        return new LegacyVelocityTrackerStrategy();

    }

    return NULL;

}

默认策略是：

const char* VelocityTracker::DEFAULT_STRATEGY = "lsq2";

可通过

property "debug.velocitytracker.strategy" 修改。如修改为lsq1 。这个需要和kernel中的TP驱动一起调试，

lsq2是最优效果，表示上报的速度是一个抛物线；lsq1上报的速度是一个加速度直线。这个需要和kernel上报一致。才能触动流畅。

 VelocityTracker::VelocityTracker(const char* strategy) :

         mLastEventTime(0), mCurrentPointerIdBits(0), mActivePointerId(-1) {

     char value[PROPERTY_VALUE_MAX];

 

     // Allow the default strategy to be overridden using a system property for debugging.

     if (!strategy) {

         int length = property_get("debug.velocitytracker.strategy", value, NULL);

         if (length > 0) {

             strategy = value;

         } else {

             strategy = DEFAULT_STRATEGY;

         }

     }

 

     // Configure the strategy.

     if (!configureStrategy(strategy)) {

         ALOGD("Unrecognized velocity tracker strategy name '%s'.", strategy);

         if (!configureStrategy(DEFAULT_STRATEGY)) {

             LOG_ALWAYS_FATAL("Could not create the default velocity tracker strategy '%s'!",

                     strategy);

         }

     }

 }