The Tor Browser: widget/gonk/libui/VelocityTracker.cpp@fc2d59ddac77 (annotated)

widget/gonk/libui/VelocityTracker.cpp@fc2d59ddac77 (annotated)

widget/gonk/libui/VelocityTracker.cpp

Wed, 31 Dec 2014 07:22:50 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 07:22:50 +0100
branch: TOR_BUG_3246
changeset 4: fc2d59ddac77
permissions: -rw-r--r--

Correct previous dual key logic pending first delivery installment.

 /*
  * Copyright (C) 2012 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.
  */
 #define LOG_TAG "VelocityTracker"
 //#define LOG_NDEBUG 0
 #include "cutils_log.h"
 // Log debug messages about velocity tracking.
 #define DEBUG_VELOCITY 0
 // Log debug messages about the progress of the algorithm itself.
 #define DEBUG_STRATEGY 0
 #include <math.h>
 #include <limits.h>
 #include "VelocityTracker.h"
 #include <utils/BitSet.h>
 #include <utils/String8.h>
 #include <utils/Timers.h>
 #include <cutils/properties.h>
 namespace android {
 // Nanoseconds per milliseconds.
 static const nsecs_t NANOS_PER_MS = 1000000;
 // Threshold for determining that a pointer has stopped moving.
 // Some input devices do not send ACTION_MOVE events in the case where a pointer has
 // stopped.  We need to detect this case so that we can accurately predict the
 // velocity after the pointer starts moving again.
 static const nsecs_t ASSUME_POINTER_STOPPED_TIME = 40 * NANOS_PER_MS;
 static float vectorDot(const float* a, const float* b, uint32_t m) {
     float r = 0;
     while (m--) {
         r += *(a++) * *(b++);
     }
     return r;
 }
 static float vectorNorm(const float* a, uint32_t m) {
     float r = 0;
     while (m--) {
         float t = *(a++);
         r += t * t;
     }
     return sqrtf(r);
 }
 #if DEBUG_STRATEGY || DEBUG_VELOCITY
 static String8 vectorToString(const float* a, uint32_t m) {
     String8 str;
     str.append("[");
     while (m--) {
         str.appendFormat(" %f", *(a++));
         if (m) {
             str.append(",");
         }
     }
     str.append(" ]");
     return str;
 }
 static String8 matrixToString(const float* a, uint32_t m, uint32_t n, bool rowMajor) {
     String8 str;
     str.append("[");
     for (size_t i = 0; i < m; i++) {
         if (i) {
             str.append(",");
         }
         str.append(" [");
         for (size_t j = 0; j < n; j++) {
             if (j) {
                 str.append(",");
             }
             str.appendFormat(" %f", a[rowMajor ? i * n + j : j * m + i]);
         }
         str.append(" ]");
     }
     str.append(" ]");
     return str;
 }
 #endif
 // --- VelocityTracker ---
 // The default velocity tracker strategy.
 // Although other strategies are available for testing and comparison purposes,
 // this is the strategy that applications will actually use.  Be very careful
 // when adjusting the default strategy because it can dramatically affect
 // (often in a bad way) the user experience.
 const char* VelocityTracker::DEFAULT_STRATEGY = "lsq2";
 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);
         }
     }
 }
 VelocityTracker::~VelocityTracker() {
     delete mStrategy;
 }
 bool VelocityTracker::configureStrategy(const char* strategy) {
     mStrategy = createStrategy(strategy);
     return mStrategy != NULL;
 }
 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;
 }
 void VelocityTracker::clear() {
     mCurrentPointerIdBits.clear();
     mActivePointerId = -1;
     mStrategy->clear();
 }
 void VelocityTracker::clearPointers(BitSet32 idBits) {
     BitSet32 remainingIdBits(mCurrentPointerIdBits.value & ~idBits.value);
     mCurrentPointerIdBits = remainingIdBits;
     if (mActivePointerId >= 0 && idBits.hasBit(mActivePointerId)) {
         mActivePointerId = !remainingIdBits.isEmpty() ? remainingIdBits.firstMarkedBit() : -1;
     }
     mStrategy->clearPointers(idBits);
 }
 void VelocityTracker::addMovement(nsecs_t eventTime, BitSet32 idBits, const Position* positions) {
     while (idBits.count() > MAX_POINTERS) {
         idBits.clearLastMarkedBit();
     }
     if ((mCurrentPointerIdBits.value & idBits.value)
             && eventTime >= mLastEventTime + ASSUME_POINTER_STOPPED_TIME) {
 #if DEBUG_VELOCITY
         ALOGD("VelocityTracker: stopped for %0.3f ms, clearing state.",
                 (eventTime - mLastEventTime) * 0.000001f);
 #endif
         // We have not received any movements for too long.  Assume that all pointers
         // have stopped.
         mStrategy->clear();
     }
     mLastEventTime = eventTime;
     mCurrentPointerIdBits = idBits;
     if (mActivePointerId < 0 || !idBits.hasBit(mActivePointerId)) {
         mActivePointerId = idBits.isEmpty() ? -1 : idBits.firstMarkedBit();
     }
     mStrategy->addMovement(eventTime, idBits, positions);
 #if DEBUG_VELOCITY
     ALOGD("VelocityTracker: addMovement eventTime=%lld, idBits=0x%08x, activePointerId=%d",
             eventTime, idBits.value, mActivePointerId);
     for (BitSet32 iterBits(idBits); !iterBits.isEmpty(); ) {
         uint32_t id = iterBits.firstMarkedBit();
         uint32_t index = idBits.getIndexOfBit(id);
         iterBits.clearBit(id);
         Estimator estimator;
         getEstimator(id, &estimator);
         ALOGD("  %d: position (%0.3f, %0.3f), "
                 "estimator (degree=%d, xCoeff=%s, yCoeff=%s, confidence=%f)",
                 id, positions[index].x, positions[index].y,
                 int(estimator.degree),
                 vectorToString(estimator.xCoeff, estimator.degree + 1).string(),
                 vectorToString(estimator.yCoeff, estimator.degree + 1).string(),
                 estimator.confidence);
     }
 #endif
 }
 void VelocityTracker::addMovement(const MotionEvent* event) {
     int32_t actionMasked = event->getActionMasked();
     switch (actionMasked) {
     case AMOTION_EVENT_ACTION_DOWN:
     case AMOTION_EVENT_ACTION_HOVER_ENTER:
         // Clear all pointers on down before adding the new movement.
         clear();
         break;
     case AMOTION_EVENT_ACTION_POINTER_DOWN: {
         // Start a new movement trace for a pointer that just went down.
         // We do this on down instead of on up because the client may want to query the
         // final velocity for a pointer that just went up.
         BitSet32 downIdBits;
         downIdBits.markBit(event->getPointerId(event->getActionIndex()));
         clearPointers(downIdBits);
         break;
     }
     case AMOTION_EVENT_ACTION_MOVE:
     case AMOTION_EVENT_ACTION_HOVER_MOVE:
         break;
     default:
         // Ignore all other actions because they do not convey any new information about
         // pointer movement.  We also want to preserve the last known velocity of the pointers.
         // Note that ACTION_UP and ACTION_POINTER_UP always report the last known position
         // of the pointers that went up.  ACTION_POINTER_UP does include the new position of
         // pointers that remained down but we will also receive an ACTION_MOVE with this
         // information if any of them actually moved.  Since we don't know how many pointers
         // will be going up at once it makes sense to just wait for the following ACTION_MOVE
         // before adding the movement.
         return;
     }
     size_t pointerCount = event->getPointerCount();
     if (pointerCount > MAX_POINTERS) {
         pointerCount = MAX_POINTERS;
     }
     BitSet32 idBits;
     for (size_t i = 0; i < pointerCount; i++) {
         idBits.markBit(event->getPointerId(i));
     }
     uint32_t pointerIndex[MAX_POINTERS];
     for (size_t i = 0; i < pointerCount; i++) {
         pointerIndex[i] = idBits.getIndexOfBit(event->getPointerId(i));
     }
     nsecs_t eventTime;
     Position positions[pointerCount];
     size_t historySize = event->getHistorySize();
     for (size_t h = 0; h < historySize; h++) {
         eventTime = event->getHistoricalEventTime(h);
         for (size_t i = 0; i < pointerCount; i++) {
             uint32_t index = pointerIndex[i];
             positions[index].x = event->getHistoricalX(i, h);
             positions[index].y = event->getHistoricalY(i, h);
         }
         addMovement(eventTime, idBits, positions);
     }
     eventTime = event->getEventTime();
     for (size_t i = 0; i < pointerCount; i++) {
         uint32_t index = pointerIndex[i];
         positions[index].x = event->getX(i);
         positions[index].y = event->getY(i);
     }
     addMovement(eventTime, idBits, positions);
 }
 bool VelocityTracker::getVelocity(uint32_t id, float* outVx, float* outVy) const {
     Estimator estimator;
     if (getEstimator(id, &estimator) && estimator.degree >= 1) {
         *outVx = estimator.xCoeff[1];
         *outVy = estimator.yCoeff[1];
         return true;
     }
     *outVx = 0;
     *outVy = 0;
     return false;
 }
 bool VelocityTracker::getEstimator(uint32_t id, Estimator* outEstimator) const {
     return mStrategy->getEstimator(id, outEstimator);
 }
 // --- LeastSquaresVelocityTrackerStrategy ---
 const nsecs_t LeastSquaresVelocityTrackerStrategy::HORIZON;
 const uint32_t LeastSquaresVelocityTrackerStrategy::HISTORY_SIZE;
 LeastSquaresVelocityTrackerStrategy::LeastSquaresVelocityTrackerStrategy(
         uint32_t degree, Weighting weighting) :
         mDegree(degree), mWeighting(weighting) {
     clear();
 }
 LeastSquaresVelocityTrackerStrategy::~LeastSquaresVelocityTrackerStrategy() {
 }
 void LeastSquaresVelocityTrackerStrategy::clear() {
     mIndex = 0;
     mMovements[0].idBits.clear();
 }
 void LeastSquaresVelocityTrackerStrategy::clearPointers(BitSet32 idBits) {
     BitSet32 remainingIdBits(mMovements[mIndex].idBits.value & ~idBits.value);
     mMovements[mIndex].idBits = remainingIdBits;
 }
 void LeastSquaresVelocityTrackerStrategy::addMovement(nsecs_t eventTime, BitSet32 idBits,
         const VelocityTracker::Position* positions) {
     if (++mIndex == HISTORY_SIZE) {
         mIndex = 0;
     }
     Movement& movement = mMovements[mIndex];
     movement.eventTime = eventTime;
     movement.idBits = idBits;
     uint32_t count = idBits.count();
     for (uint32_t i = 0; i < count; i++) {
         movement.positions[i] = positions[i];
     }
 }
 /**
  * Solves a linear least squares problem to obtain a N degree polynomial that fits
  * the specified input data as nearly as possible.
  *
  * Returns true if a solution is found, false otherwise.
  *
  * The input consists of two vectors of data points X and Y with indices 0..m-1
  * along with a weight vector W of the same size.
  *
  * The output is a vector B with indices 0..n that describes a polynomial
  * that fits the data, such the sum of W[i] * W[i] * abs(Y[i] - (B[0] + B[1] X[i]
  * + B[2] X[i]^2 ... B[n] X[i]^n)) for all i between 0 and m-1 is minimized.
  *
  * Accordingly, the weight vector W should be initialized by the caller with the
  * reciprocal square root of the variance of the error in each input data point.
  * In other words, an ideal choice for W would be W[i] = 1 / var(Y[i]) = 1 / stddev(Y[i]).
  * The weights express the relative importance of each data point.  If the weights are
  * all 1, then the data points are considered to be of equal importance when fitting
  * the polynomial.  It is a good idea to choose weights that diminish the importance
  * of data points that may have higher than usual error margins.
  *
  * Errors among data points are assumed to be independent.  W is represented here
  * as a vector although in the literature it is typically taken to be a diagonal matrix.
  *
  * That is to say, the function that generated the input data can be approximated
  * by y(x) ~= B[0] + B[1] x + B[2] x^2 + ... + B[n] x^n.
  *
  * The coefficient of determination (R^2) is also returned to describe the goodness
  * of fit of the model for the given data.  It is a value between 0 and 1, where 1
  * indicates perfect correspondence.
  *
  * This function first expands the X vector to a m by n matrix A such that
  * A[i][0] = 1, A[i][1] = X[i], A[i][2] = X[i]^2, ..., A[i][n] = X[i]^n, then
  * multiplies it by w[i]./
  *
  * Then it calculates the QR decomposition of A yielding an m by m orthonormal matrix Q
  * and an m by n upper triangular matrix R.  Because R is upper triangular (lower
  * part is all zeroes), we can simplify the decomposition into an m by n matrix
  * Q1 and a n by n matrix R1 such that A = Q1 R1.
  *
  * Finally we solve the system of linear equations given by R1 B = (Qtranspose W Y)
  * to find B.
  *
  * For efficiency, we lay out A and Q column-wise in memory because we frequently
  * operate on the column vectors.  Conversely, we lay out R row-wise.
  *
  * http://en.wikipedia.org/wiki/Numerical_methods_for_linear_least_squares
  * http://en.wikipedia.org/wiki/Gram-Schmidt
  */
 static bool solveLeastSquares(const float* x, const float* y,
         const float* w, uint32_t m, uint32_t n, float* outB, float* outDet) {
 #if DEBUG_STRATEGY
     ALOGD("solveLeastSquares: m=%d, n=%d, x=%s, y=%s, w=%s", int(m), int(n),
             vectorToString(x, m).string(), vectorToString(y, m).string(),
             vectorToString(w, m).string());
 #endif
     // Expand the X vector to a matrix A, pre-multiplied by the weights.
     float a[n][m]; // column-major order
     for (uint32_t h = 0; h < m; h++) {
         a[0][h] = w[h];
         for (uint32_t i = 1; i < n; i++) {
             a[i][h] = a[i - 1][h] * x[h];
         }
     }
 #if DEBUG_STRATEGY
     ALOGD("  - a=%s", matrixToString(&a[0][0], m, n, false /*rowMajor*/).string());
 #endif
     // Apply the Gram-Schmidt process to A to obtain its QR decomposition.
     float q[n][m]; // orthonormal basis, column-major order
     float r[n][n]; // upper triangular matrix, row-major order
     for (uint32_t j = 0; j < n; j++) {
         for (uint32_t h = 0; h < m; h++) {
             q[j][h] = a[j][h];
         }
         for (uint32_t i = 0; i < j; i++) {
             float dot = vectorDot(&q[j][0], &q[i][0], m);
             for (uint32_t h = 0; h < m; h++) {
                 q[j][h] -= dot * q[i][h];
             }
         }
         float norm = vectorNorm(&q[j][0], m);
         if (norm < 0.000001f) {
             // vectors are linearly dependent or zero so no solution
 #if DEBUG_STRATEGY
             ALOGD("  - no solution, norm=%f", norm);
 #endif
             return false;
         }
         float invNorm = 1.0f / norm;
         for (uint32_t h = 0; h < m; h++) {
             q[j][h] *= invNorm;
         }
         for (uint32_t i = 0; i < n; i++) {
             r[j][i] = i < j ? 0 : vectorDot(&q[j][0], &a[i][0], m);
         }
     }
 #if DEBUG_STRATEGY
     ALOGD("  - q=%s", matrixToString(&q[0][0], m, n, false /*rowMajor*/).string());
     ALOGD("  - r=%s", matrixToString(&r[0][0], n, n, true /*rowMajor*/).string());
     // calculate QR, if we factored A correctly then QR should equal A
     float qr[n][m];
     for (uint32_t h = 0; h < m; h++) {
         for (uint32_t i = 0; i < n; i++) {
             qr[i][h] = 0;
             for (uint32_t j = 0; j < n; j++) {
                 qr[i][h] += q[j][h] * r[j][i];
             }
         }
     }
     ALOGD("  - qr=%s", matrixToString(&qr[0][0], m, n, false /*rowMajor*/).string());
 #endif
     // Solve R B = Qt W Y to find B.  This is easy because R is upper triangular.
     // We just work from bottom-right to top-left calculating B's coefficients.
     float wy[m];
     for (uint32_t h = 0; h < m; h++) {
         wy[h] = y[h] * w[h];
     }
     for (uint32_t i = n; i-- != 0; ) {
         outB[i] = vectorDot(&q[i][0], wy, m);
         for (uint32_t j = n - 1; j > i; j--) {
             outB[i] -= r[i][j] * outB[j];
         }
         outB[i] /= r[i][i];
     }
 #if DEBUG_STRATEGY
     ALOGD("  - b=%s", vectorToString(outB, n).string());
 #endif
     // Calculate the coefficient of determination as 1 - (SSerr / SStot) where
     // SSerr is the residual sum of squares (variance of the error),
     // and SStot is the total sum of squares (variance of the data) where each
     // has been weighted.
     float ymean = 0;
     for (uint32_t h = 0; h < m; h++) {
         ymean += y[h];
     }
     ymean /= m;
     float sserr = 0;
     float sstot = 0;
     for (uint32_t h = 0; h < m; h++) {
         float err = y[h] - outB[0];
         float term = 1;
         for (uint32_t i = 1; i < n; i++) {
             term *= x[h];
             err -= term * outB[i];
         }
         sserr += w[h] * w[h] * err * err;
         float var = y[h] - ymean;
         sstot += w[h] * w[h] * var * var;
     }
     *outDet = sstot > 0.000001f ? 1.0f - (sserr / sstot) : 1;
 #if DEBUG_STRATEGY
     ALOGD("  - sserr=%f", sserr);
     ALOGD("  - sstot=%f", sstot);
     ALOGD("  - det=%f", *outDet);
 #endif
     return true;
 }
 bool LeastSquaresVelocityTrackerStrategy::getEstimator(uint32_t id,
         VelocityTracker::Estimator* outEstimator) const {
     outEstimator->clear();
     // Iterate over movement samples in reverse time order and collect samples.
     float x[HISTORY_SIZE];
     float y[HISTORY_SIZE];
     float w[HISTORY_SIZE];
     float time[HISTORY_SIZE];
     uint32_t m = 0;
     uint32_t index = mIndex;
     const Movement& newestMovement = mMovements[mIndex];
     do {
         const Movement& movement = mMovements[index];
         if (!movement.idBits.hasBit(id)) {
             break;
         }
         nsecs_t age = newestMovement.eventTime - movement.eventTime;
         if (age > HORIZON) {
             break;
         }
         const VelocityTracker::Position& position = movement.getPosition(id);
         x[m] = position.x;
         y[m] = position.y;
         w[m] = chooseWeight(index);
         time[m] = -age * 0.000000001f;
         index = (index == 0 ? HISTORY_SIZE : index) - 1;
     } while (++m < HISTORY_SIZE);
     if (m == 0) {
         return false; // no data
     }
     // Calculate a least squares polynomial fit.
     uint32_t degree = mDegree;
     if (degree > m - 1) {
         degree = m - 1;
     }
     if (degree >= 1) {
         float xdet, ydet;
         uint32_t n = degree + 1;
         if (solveLeastSquares(time, x, w, m, n, outEstimator->xCoeff, &xdet)
                 && solveLeastSquares(time, y, w, m, n, outEstimator->yCoeff, &ydet)) {
             outEstimator->time = newestMovement.eventTime;
             outEstimator->degree = degree;
             outEstimator->confidence = xdet * ydet;
 #if DEBUG_STRATEGY
             ALOGD("estimate: degree=%d, xCoeff=%s, yCoeff=%s, confidence=%f",
                     int(outEstimator->degree),
                     vectorToString(outEstimator->xCoeff, n).string(),
                     vectorToString(outEstimator->yCoeff, n).string(),
                     outEstimator->confidence);
 #endif
             return true;
         }
     }
     // No velocity data available for this pointer, but we do have its current position.
     outEstimator->xCoeff[0] = x[0];
     outEstimator->yCoeff[0] = y[0];
     outEstimator->time = newestMovement.eventTime;
     outEstimator->degree = 0;
     outEstimator->confidence = 1;
     return true;
 }
 float LeastSquaresVelocityTrackerStrategy::chooseWeight(uint32_t index) const {
     switch (mWeighting) {
     case WEIGHTING_DELTA: {
         // Weight points based on how much time elapsed between them and the next
         // point so that points that "cover" a shorter time span are weighed less.
         //   delta  0ms: 0.5
         //   delta 10ms: 1.0
         if (index == mIndex) {
             return 1.0f;
         }
         uint32_t nextIndex = (index + 1) % HISTORY_SIZE;
         float deltaMillis = (mMovements[nextIndex].eventTime- mMovements[index].eventTime)
                 * 0.000001f;
         if (deltaMillis < 0) {
             return 0.5f;
         }
         if (deltaMillis < 10) {
             return 0.5f + deltaMillis * 0.05;
         }
         return 1.0f;
     }
     case WEIGHTING_CENTRAL: {
         // Weight points based on their age, weighing very recent and very old points less.
         //   age  0ms: 0.5
         //   age 10ms: 1.0
         //   age 50ms: 1.0
         //   age 60ms: 0.5
         float ageMillis = (mMovements[mIndex].eventTime - mMovements[index].eventTime)
                 * 0.000001f;
         if (ageMillis < 0) {
             return 0.5f;
         }
         if (ageMillis < 10) {
             return 0.5f + ageMillis * 0.05;
         }
         if (ageMillis < 50) {
             return 1.0f;
         }
         if (ageMillis < 60) {
             return 0.5f + (60 - ageMillis) * 0.05;
         }
         return 0.5f;
     }
     case WEIGHTING_RECENT: {
         // Weight points based on their age, weighing older points less.
         //   age   0ms: 1.0
         //   age  50ms: 1.0
         //   age 100ms: 0.5
         float ageMillis = (mMovements[mIndex].eventTime - mMovements[index].eventTime)
                 * 0.000001f;
         if (ageMillis < 50) {
             return 1.0f;
         }
         if (ageMillis < 100) {
             return 0.5f + (100 - ageMillis) * 0.01f;
         }
         return 0.5f;
     }
     case WEIGHTING_NONE:
     default:
         return 1.0f;
     }
 }
 // --- IntegratingVelocityTrackerStrategy ---
 IntegratingVelocityTrackerStrategy::IntegratingVelocityTrackerStrategy(uint32_t degree) :
         mDegree(degree) {
 }
 IntegratingVelocityTrackerStrategy::~IntegratingVelocityTrackerStrategy() {
 }
 void IntegratingVelocityTrackerStrategy::clear() {
     mPointerIdBits.clear();
 }
 void IntegratingVelocityTrackerStrategy::clearPointers(BitSet32 idBits) {
     mPointerIdBits.value &= ~idBits.value;
 }
 void IntegratingVelocityTrackerStrategy::addMovement(nsecs_t eventTime, BitSet32 idBits,
         const VelocityTracker::Position* positions) {
     uint32_t index = 0;
     for (BitSet32 iterIdBits(idBits); !iterIdBits.isEmpty();) {
         uint32_t id = iterIdBits.clearFirstMarkedBit();
         State& state = mPointerState[id];
         const VelocityTracker::Position& position = positions[index++];
         if (mPointerIdBits.hasBit(id)) {
             updateState(state, eventTime, position.x, position.y);
         } else {
             initState(state, eventTime, position.x, position.y);
         }
     }
     mPointerIdBits = idBits;
 }
 bool IntegratingVelocityTrackerStrategy::getEstimator(uint32_t id,
         VelocityTracker::Estimator* outEstimator) const {
     outEstimator->clear();
     if (mPointerIdBits.hasBit(id)) {
         const State& state = mPointerState[id];
         populateEstimator(state, outEstimator);
         return true;
     }
     return false;
 }
 void IntegratingVelocityTrackerStrategy::initState(State& state,
         nsecs_t eventTime, float xpos, float ypos) const {
     state.updateTime = eventTime;
     state.degree = 0;
     state.xpos = xpos;
     state.xvel = 0;
     state.xaccel = 0;
     state.ypos = ypos;
     state.yvel = 0;
     state.yaccel = 0;
 }
 void IntegratingVelocityTrackerStrategy::updateState(State& state,
         nsecs_t eventTime, float xpos, float ypos) const {
     const nsecs_t MIN_TIME_DELTA = 2 * NANOS_PER_MS;
     const float FILTER_TIME_CONSTANT = 0.010f; // 10 milliseconds
     if (eventTime <= state.updateTime + MIN_TIME_DELTA) {
         return;
     }
     float dt = (eventTime - state.updateTime) * 0.000000001f;
     state.updateTime = eventTime;
     float xvel = (xpos - state.xpos) / dt;
     float yvel = (ypos - state.ypos) / dt;
     if (state.degree == 0) {
         state.xvel = xvel;
         state.yvel = yvel;
         state.degree = 1;
     } else {
         float alpha = dt / (FILTER_TIME_CONSTANT + dt);
         if (mDegree == 1) {
             state.xvel += (xvel - state.xvel) * alpha;
             state.yvel += (yvel - state.yvel) * alpha;
         } else {
             float xaccel = (xvel - state.xvel) / dt;
             float yaccel = (yvel - state.yvel) / dt;
             if (state.degree == 1) {
                 state.xaccel = xaccel;
                 state.yaccel = yaccel;
                 state.degree = 2;
             } else {
                 state.xaccel += (xaccel - state.xaccel) * alpha;
                 state.yaccel += (yaccel - state.yaccel) * alpha;
             }
             state.xvel += (state.xaccel * dt) * alpha;
             state.yvel += (state.yaccel * dt) * alpha;
         }
     }
     state.xpos = xpos;
     state.ypos = ypos;
 }
 void IntegratingVelocityTrackerStrategy::populateEstimator(const State& state,
         VelocityTracker::Estimator* outEstimator) const {
     outEstimator->time = state.updateTime;
     outEstimator->confidence = 1.0f;
     outEstimator->degree = state.degree;
     outEstimator->xCoeff[0] = state.xpos;
     outEstimator->xCoeff[1] = state.xvel;
     outEstimator->xCoeff[2] = state.xaccel / 2;
     outEstimator->yCoeff[0] = state.ypos;
     outEstimator->yCoeff[1] = state.yvel;
     outEstimator->yCoeff[2] = state.yaccel / 2;
 }
 // --- LegacyVelocityTrackerStrategy ---
 const nsecs_t LegacyVelocityTrackerStrategy::HORIZON;
 const uint32_t LegacyVelocityTrackerStrategy::HISTORY_SIZE;
 const nsecs_t LegacyVelocityTrackerStrategy::MIN_DURATION;
 LegacyVelocityTrackerStrategy::LegacyVelocityTrackerStrategy() {
     clear();
 }
 LegacyVelocityTrackerStrategy::~LegacyVelocityTrackerStrategy() {
 }
 void LegacyVelocityTrackerStrategy::clear() {
     mIndex = 0;
     mMovements[0].idBits.clear();
 }
 void LegacyVelocityTrackerStrategy::clearPointers(BitSet32 idBits) {
     BitSet32 remainingIdBits(mMovements[mIndex].idBits.value & ~idBits.value);
     mMovements[mIndex].idBits = remainingIdBits;
 }
 void LegacyVelocityTrackerStrategy::addMovement(nsecs_t eventTime, BitSet32 idBits,
         const VelocityTracker::Position* positions) {
     if (++mIndex == HISTORY_SIZE) {
         mIndex = 0;
     }
     Movement& movement = mMovements[mIndex];
     movement.eventTime = eventTime;
     movement.idBits = idBits;
     uint32_t count = idBits.count();
     for (uint32_t i = 0; i < count; i++) {
         movement.positions[i] = positions[i];
     }
 }
 bool LegacyVelocityTrackerStrategy::getEstimator(uint32_t id,
         VelocityTracker::Estimator* outEstimator) const {
     outEstimator->clear();
     const Movement& newestMovement = mMovements[mIndex];
     if (!newestMovement.idBits.hasBit(id)) {
         return false; // no data
     }
     // Find the oldest sample that contains the pointer and that is not older than HORIZON.
     nsecs_t minTime = newestMovement.eventTime - HORIZON;
     uint32_t oldestIndex = mIndex;
     uint32_t numTouches = 1;
     do {
         uint32_t nextOldestIndex = (oldestIndex == 0 ? HISTORY_SIZE : oldestIndex) - 1;
         const Movement& nextOldestMovement = mMovements[nextOldestIndex];
         if (!nextOldestMovement.idBits.hasBit(id)
                 || nextOldestMovement.eventTime < minTime) {
             break;
         }
         oldestIndex = nextOldestIndex;
     } while (++numTouches < HISTORY_SIZE);
     // Calculate an exponentially weighted moving average of the velocity estimate
     // at different points in time measured relative to the oldest sample.
     // This is essentially an IIR filter.  Newer samples are weighted more heavily
     // than older samples.  Samples at equal time points are weighted more or less
     // equally.
     //
     // One tricky problem is that the sample data may be poorly conditioned.
     // Sometimes samples arrive very close together in time which can cause us to
     // overestimate the velocity at that time point.  Most samples might be measured
     // 16ms apart but some consecutive samples could be only 0.5sm apart because
     // the hardware or driver reports them irregularly or in bursts.
     float accumVx = 0;
     float accumVy = 0;
     uint32_t index = oldestIndex;
     uint32_t samplesUsed = 0;
     const Movement& oldestMovement = mMovements[oldestIndex];
     const VelocityTracker::Position& oldestPosition = oldestMovement.getPosition(id);
     nsecs_t lastDuration = 0;
     while (numTouches-- > 1) {
         if (++index == HISTORY_SIZE) {
             index = 0;
         }
         const Movement& movement = mMovements[index];
         nsecs_t duration = movement.eventTime - oldestMovement.eventTime;
         // If the duration between samples is small, we may significantly overestimate
         // the velocity.  Consequently, we impose a minimum duration constraint on the
         // samples that we include in the calculation.
         if (duration >= MIN_DURATION) {
             const VelocityTracker::Position& position = movement.getPosition(id);
             float scale = 1000000000.0f / duration; // one over time delta in seconds
             float vx = (position.x - oldestPosition.x) * scale;
             float vy = (position.y - oldestPosition.y) * scale;
             accumVx = (accumVx * lastDuration + vx * duration) / (duration + lastDuration);
             accumVy = (accumVy * lastDuration + vy * duration) / (duration + lastDuration);
             lastDuration = duration;
             samplesUsed += 1;
         }
     }
     // Report velocity.
     const VelocityTracker::Position& newestPosition = newestMovement.getPosition(id);
     outEstimator->time = newestMovement.eventTime;
     outEstimator->confidence = 1;
     outEstimator->xCoeff[0] = newestPosition.x;
     outEstimator->yCoeff[0] = newestPosition.y;
     if (samplesUsed) {
         outEstimator->xCoeff[1] = accumVx;
         outEstimator->yCoeff[1] = accumVy;
         outEstimator->degree = 1;
     } else {
         outEstimator->degree = 0;
     }
     return true;
 }
 } // namespace android

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widget/gonk/libui/VelocityTracker.cpp@fc2d59ddac77 (annotated)

widget/gonk/libui/VelocityTracker.cpp