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Commit 0a933141 authored by Michael Wright's avatar Michael Wright Committed by Vineeta Srivastava
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Add new "fast" filter for ambient light. 

The slow filter wasn't converging fast enough when we shortened the
debounce timings but we still want it to ensure there's a long term
change happening, so add a new filter that converges much faster. This
new fast filter is just a weighted sliding window just like the slow
filter, but it has a significantly smaller horizon.

Bug: 64514692
Test: manual
Change-Id: I1e990ac1e6a56268fa42a85399a2d41cc8dd2104
parent 1c414bf3

services/core/java/com/android/server/display/AutomaticBrightnessController.java

+63 −10
Original line number Diff line number Diff line
@@ -59,6 +59,13 @@ class AutomaticBrightnessController { 
    private static final int MSG_UPDATE_AMBIENT_LUX = 1;

    private static final int MSG_BRIGHTNESS_ADJUSTMENT_SAMPLE = 2;



    // Length of the ambient light horizon used to calculate the long term estimate of ambient

    // light.

    private static final int AMBIENT_LIGHT_LONG_HORIZON_MILLIS = 10000;



    // Length of the ambient light horizon used to calculate short-term estimate of ambient light.

    private static final int AMBIENT_LIGHT_SHORT_HORIZON_MILLIS = 2000;



    // Callbacks for requesting updates to the display's power state

    private final Callbacks mCallbacks;
@@ -345,22 +352,51 @@ class AutomaticBrightnessController { 
    }



    private void setAmbientLux(float lux) {

        if (DEBUG) {

            Slog.d(TAG, "setAmbientLux(" + lux + ")");

        }

        mAmbientLux = lux;

        mBrighteningLuxThreshold = mDynamicHysteresis.getBrighteningThreshold(lux);

        mDarkeningLuxThreshold = mDynamicHysteresis.getDarkeningThreshold(lux);

    }



    private float calculateAmbientLux(long now) {

    private float calculateAmbientLux(long now, long horizon) {

        if (DEBUG) {

            Slog.d(TAG, "calculateAmbientLux(" + now + ", " + horizon + ")");

        }

        final int N = mAmbientLightRingBuffer.size();

        if (N == 0) {

            Slog.e(TAG, "calculateAmbientLux: No ambient light readings available");

            return -1;

        }



        // Find the first measurement that is just outside of the horizon.

        int endIndex = 0;

        final long horizonStartTime = now - horizon;

        for (int i = 0; i < N-1; i++) {

            if (mAmbientLightRingBuffer.getTime(i + 1) <= horizonStartTime) {

                endIndex++;

            } else {

                break;

            }

        }

        if (DEBUG) {

            Slog.d(TAG, "calculateAmbientLux: selected endIndex=" + endIndex + ", point=("

                    + mAmbientLightRingBuffer.getTime(endIndex) + ", "

                    + mAmbientLightRingBuffer.getLux(endIndex)

                    + ")");

        }

        float sum = 0;

        float totalWeight = 0;

        long endTime = AMBIENT_LIGHT_PREDICTION_TIME_MILLIS;

        for (int i = N - 1; i >= 0; i--) {

            long startTime = (mAmbientLightRingBuffer.getTime(i) - now);

        for (int i = N - 1; i >= endIndex; i--) {

            long eventTime = mAmbientLightRingBuffer.getTime(i);

            if (i == endIndex && eventTime < horizonStartTime) {

                // If we're at the final value, make sure we only consider the part of the sample

                // within our desired horizon.

                eventTime = horizonStartTime;

            }

            final long startTime = eventTime - now;

            float weight = calculateWeight(startTime, endTime);

            float lux = mAmbientLightRingBuffer.getLux(i);

            if (DEBUG) {
@@ -435,7 +471,7 @@ class AutomaticBrightnessController { 
                        timeWhenSensorWarmedUp);

                return;

            }

            setAmbientLux(calculateAmbientLux(time));

            setAmbientLux(calculateAmbientLux(time, AMBIENT_LIGHT_SHORT_HORIZON_MILLIS));

            mAmbientLuxValid = true;

            if (DEBUG) {

                Slog.d(TAG, "updateAmbientLux: Initializing: "
@@ -447,14 +483,25 @@ class AutomaticBrightnessController { 


        long nextBrightenTransition = nextAmbientLightBrighteningTransition(time);

        long nextDarkenTransition = nextAmbientLightDarkeningTransition(time);

        float ambientLux = calculateAmbientLux(time);



        if (ambientLux >= mBrighteningLuxThreshold && nextBrightenTransition <= time

                || ambientLux <= mDarkeningLuxThreshold && nextDarkenTransition <= time) {

            setAmbientLux(ambientLux);

        // Essentially, we calculate both a slow ambient lux, to ensure there's a true long-term

        // change in lighting conditions, and a fast ambient lux to determine what the new

        // brightness situation is since the slow lux can be quite slow to converge.

        //

        // Note that both values need to be checked for sufficient change before updating the

        // proposed ambient light value since the slow value might be sufficiently far enough away

        // from the fast value to cause a recalculation while its actually just converging on

        // the fast value still.

        float slowAmbientLux = calculateAmbientLux(time, AMBIENT_LIGHT_LONG_HORIZON_MILLIS);

        float fastAmbientLux = calculateAmbientLux(time, AMBIENT_LIGHT_SHORT_HORIZON_MILLIS);



        if (slowAmbientLux >= mBrighteningLuxThreshold &&

                fastAmbientLux >= mBrighteningLuxThreshold && nextBrightenTransition <= time

                || slowAmbientLux <= mDarkeningLuxThreshold

                && fastAmbientLux <= mDarkeningLuxThreshold && nextDarkenTransition <= time) {

            setAmbientLux(fastAmbientLux);

            if (DEBUG) {

                Slog.d(TAG, "updateAmbientLux: "

                        + ((ambientLux > mAmbientLux) ? "Brightened" : "Darkened") + ": "

                        + ((fastAmbientLux > mAmbientLux) ? "Brightened" : "Darkened") + ": "

                        + "mBrighteningLuxThreshold=" + mBrighteningLuxThreshold

                        + ", mAmbientLightRingBuffer=" + mAmbientLightRingBuffer

                        + ", mAmbientLux=" + mAmbientLux);
@@ -616,6 +663,12 @@ class AutomaticBrightnessController { 
        void updateBrightness();

    }



    /**

     * A ring buffer of ambient light measurements sorted by time.

     *

     * Each entry consists of a timestamp and a lux measurement, and the overall buffer is sorted

     * from oldest to newest.

     */

    private static final class AmbientLightRingBuffer {

        // Proportional extra capacity of the buffer beyond the expected number of light samples

        // in the horizon