The Tor Browser: comparison widget/gonk/libui/VelocityTracker.cpp

--1:000000000000
+:64a09faf1606
+/*
+* 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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comparison: widget/gonk/libui/VelocityTracker.cpp

widget/gonk/libui/VelocityTracker.cpp