| /* |
| * Copyright (C) 2019 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.android.server.display.whitebalance; |
| |
| import android.util.Slog; |
| |
| import com.android.internal.annotations.VisibleForTesting; |
| import com.android.server.display.utils.RollingBuffer; |
| |
| import java.io.PrintWriter; |
| import java.util.Arrays; |
| |
| /** |
| * The DisplayWhiteBalanceController uses the AmbientFilter to average ambient changes over time, |
| * filter out the noise, and arrive at an estimate of the actual value. |
| * |
| * When the DisplayWhiteBalanceController detects a change in ambient brightness or color |
| * temperature, it passes it to the AmbientFilter, and when it needs the actual ambient value, it |
| * asks it for an estimate. |
| * |
| * Implementations: |
| * - {@link WeightedMovingAverageAmbientFilter} |
| * A weighted average prioritising recent changes. |
| */ |
| abstract class AmbientFilter { |
| |
| protected static final boolean DEBUG = false; // Enable for verbose logs. |
| |
| protected final String mTag; |
| protected boolean mLoggingEnabled; |
| |
| // How long ambient value changes are kept and taken into consideration. |
| private final int mHorizon; // Milliseconds |
| |
| private final RollingBuffer mBuffer; |
| |
| /** |
| * @param tag |
| * The tag used for dumping and logging. |
| * @param horizon |
| * How long ambient value changes are kept and taken into consideration. |
| * |
| * @throws IllegalArgumentException |
| * - horizon is not positive. |
| */ |
| AmbientFilter(String tag, int horizon) { |
| validateArguments(horizon); |
| mTag = tag; |
| mLoggingEnabled = false; |
| mHorizon = horizon; |
| mBuffer = new RollingBuffer(); |
| } |
| |
| /** |
| * Add an ambient value change. |
| * |
| * @param time |
| * The time. |
| * @param value |
| * The ambient value. |
| * |
| * @return Whether the method succeeded or not. |
| */ |
| public boolean addValue(long time, float value) { |
| if (value < 0.0f) { |
| return false; |
| } |
| truncateOldValues(time); |
| if (mLoggingEnabled) { |
| Slog.d(mTag, "add value: " + value + " @ " + time); |
| } |
| mBuffer.add(time, value); |
| return true; |
| } |
| |
| /** |
| * Get an estimate of the actual ambient color temperature. |
| * |
| * @param time |
| * The time. |
| * |
| * @return An estimate of the actual ambient color temperature. |
| */ |
| public float getEstimate(long time) { |
| truncateOldValues(time); |
| final float value = filter(time, mBuffer); |
| if (mLoggingEnabled) { |
| Slog.d(mTag, "get estimate: " + value + " @ " + time); |
| } |
| return value; |
| } |
| |
| /** |
| * Clears the filter state. |
| */ |
| public void clear() { |
| mBuffer.clear(); |
| } |
| |
| /** |
| * Enable/disable logging. |
| * |
| * @param loggingEnabled |
| * Whether logging is on/off. |
| * |
| * @return Whether the method succeeded or not. |
| */ |
| public boolean setLoggingEnabled(boolean loggingEnabled) { |
| if (mLoggingEnabled == loggingEnabled) { |
| return false; |
| } |
| mLoggingEnabled = loggingEnabled; |
| return true; |
| } |
| |
| /** |
| * Dump the state. |
| * |
| * @param writer |
| * The PrintWriter used to dump the state. |
| */ |
| public void dump(PrintWriter writer) { |
| writer.println(" " + mTag); |
| writer.println(" mLoggingEnabled=" + mLoggingEnabled); |
| writer.println(" mHorizon=" + mHorizon); |
| writer.println(" mBuffer=" + mBuffer); |
| } |
| |
| private void validateArguments(int horizon) { |
| if (horizon <= 0) { |
| throw new IllegalArgumentException("horizon must be positive"); |
| } |
| } |
| |
| private void truncateOldValues(long time) { |
| final long minTime = time - mHorizon; |
| mBuffer.truncate(minTime); |
| } |
| |
| protected abstract float filter(long time, RollingBuffer buffer); |
| |
| /** |
| * A weighted average prioritising recent changes. |
| */ |
| @VisibleForTesting |
| public static class WeightedMovingAverageAmbientFilter extends AmbientFilter { |
| |
| // How long the latest ambient value change is predicted to last. |
| private static final int PREDICTION_TIME = 100; // Milliseconds |
| |
| // Recent changes are prioritised by integrating their duration over y = x + mIntercept |
| // (the higher it is, the less prioritised recent changes are). |
| private final float mIntercept; |
| |
| /** |
| * @param tag |
| * The tag used for dumping and logging. |
| * @param horizon |
| * How long ambient value changes are kept and taken into consideration. |
| * @param intercept |
| * Recent changes are prioritised by integrating their duration over y = x + intercept |
| * (the higher it is, the less prioritised recent changes are). |
| * |
| * @throws IllegalArgumentException |
| * - horizon is not positive. |
| * - intercept is NaN or negative. |
| */ |
| WeightedMovingAverageAmbientFilter(String tag, int horizon, float intercept) { |
| super(tag, horizon); |
| validateArguments(intercept); |
| mIntercept = intercept; |
| } |
| |
| /** |
| * See {@link AmbientFilter#dump base class}. |
| */ |
| @Override |
| public void dump(PrintWriter writer) { |
| super.dump(writer); |
| writer.println(" mIntercept=" + mIntercept); |
| } |
| |
| // Normalise the times to [t1=0, t2, ..., tN, now + PREDICTION_TIME], so the first change |
| // starts at 0 and the last change is predicted to last a bit, and divide them by 1000 as |
| // milliseconds are high enough to overflow. |
| // The weight of the value from t[i] to t[i+1] is the area under (A.K.A. the integral of) |
| // y = x + mIntercept from t[i] to t[i+1]. |
| @Override |
| protected float filter(long time, RollingBuffer buffer) { |
| if (buffer.isEmpty()) { |
| return -1.0f; |
| } |
| float total = 0.0f; |
| float totalWeight = 0.0f; |
| final float[] weights = getWeights(time, buffer); |
| if (DEBUG && mLoggingEnabled) { |
| Slog.v(mTag, "filter: " + buffer + " => " + Arrays.toString(weights)); |
| } |
| for (int i = 0; i < weights.length; i++) { |
| final float value = buffer.getValue(i); |
| final float weight = weights[i]; |
| total += weight * value; |
| totalWeight += weight; |
| } |
| if (totalWeight == 0.0f) { |
| return buffer.getValue(buffer.size() - 1); |
| } |
| return total / totalWeight; |
| } |
| |
| private void validateArguments(float intercept) { |
| if (Float.isNaN(intercept) || intercept < 0.0f) { |
| throw new IllegalArgumentException("intercept must be a non-negative number"); |
| } |
| } |
| |
| private float[] getWeights(long time, RollingBuffer buffer) { |
| float[] weights = new float[buffer.size()]; |
| final long startTime = buffer.getTime(0); |
| float previousTime = 0.0f; |
| for (int i = 1; i < weights.length; i++) { |
| final float currentTime = (buffer.getTime(i) - startTime) / 1000.0f; |
| final float weight = calculateIntegral(previousTime, currentTime); |
| weights[i - 1] = weight; |
| previousTime = currentTime; |
| } |
| final float lastTime = (time + PREDICTION_TIME - startTime) / 1000.0f; |
| final float lastWeight = calculateIntegral(previousTime, lastTime); |
| weights[weights.length - 1] = lastWeight; |
| return weights; |
| } |
| |
| private float calculateIntegral(float from, float to) { |
| return antiderivative(to) - antiderivative(from); |
| } |
| |
| private float antiderivative(float x) { |
| // f(x) = x + c => F(x) = 1/2 * x^2 + c * x |
| return 0.5f * x * x + mIntercept * x; |
| } |
| |
| } |
| |
| } |