diff options
Diffstat (limited to 'widget/gonk/libui/VelocityTracker.cpp')
| -rw-r--r-- | widget/gonk/libui/VelocityTracker.cpp | 929 |
1 files changed, 929 insertions, 0 deletions
diff --git a/widget/gonk/libui/VelocityTracker.cpp b/widget/gonk/libui/VelocityTracker.cpp new file mode 100644 index 000000000..11a8bf7fc --- /dev/null +++ b/widget/gonk/libui/VelocityTracker.cpp @@ -0,0 +1,929 @@ +/* + * 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 |