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Merge "Tweak VelocityTracker. Bug: 5265529"

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Jeff Brown 2011-09-09 17:01:25 -07:00 committed by Android (Google) Code Review
commit ec9a0599fa
2 changed files with 35 additions and 63 deletions
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8
include/ui/Input.h
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@ -660,15 +660,19 @@ private:
static const uint32_t HISTORY_SIZE = 10;
// Oldest sample to consider when calculating the velocity.
static const nsecs_t MAX_AGE = 200 * 1000000; // 200 ms
static const nsecs_t MAX_AGE = 100 * 1000000; // 100 ms
// The minimum duration between samples when estimating velocity.
static const nsecs_t MIN_DURATION = 10 * 1000000; // 10 ms
static const nsecs_t MIN_DURATION = 5 * 1000000; // 5 ms
struct Movement {
nsecs_t eventTime;
BitSet32 idBits;
Position positions[MAX_POINTERS];
inline const Position& getPosition(uint32_t id) const {
return positions[idBits.getIndexOfBit(id)];
}
};
uint32_t mIndex;

90
libs/ui/Input.cpp
View File

@ -752,6 +752,7 @@ void VelocityTracker::addMovement(const MotionEvent* event) {
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;
@ -764,12 +765,11 @@ void VelocityTracker::addMovement(const MotionEvent* event) {
clearPointers(downIdBits);
break;
}
case AMOTION_EVENT_ACTION_OUTSIDE:
case AMOTION_EVENT_ACTION_CANCEL:
case AMOTION_EVENT_ACTION_SCROLL:
case AMOTION_EVENT_ACTION_UP:
case AMOTION_EVENT_ACTION_POINTER_UP:
// Ignore these actions because they do not convey any new information about
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
@ -814,68 +814,36 @@ void VelocityTracker::addMovement(const MotionEvent* event) {
bool VelocityTracker::getVelocity(uint32_t id, float* outVx, float* outVy) const {
const Movement& newestMovement = mMovements[mIndex];
if (newestMovement.idBits.hasBit(id)) {
// Find the oldest sample that contains the pointer and that is not older than MAX_AGE.
nsecs_t minTime = newestMovement.eventTime - MAX_AGE;
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.
const Position& newestPosition = newestMovement.getPosition(id);
float accumVx = 0;
float accumVy = 0;
uint32_t index = oldestIndex;
uint32_t samplesUsed = 0;
const Movement& oldestMovement = mMovements[oldestIndex];
const Position& oldestPosition =
oldestMovement.positions[oldestMovement.idBits.getIndexOfBit(id)];
nsecs_t lastDuration = 0;
float duration = 0;
while (numTouches-- > 1) {
if (++index == HISTORY_SIZE) {
index = 0;
}
// Iterate over movement samples in reverse time order and accumulate velocity.
uint32_t index = mIndex;
do {
index = (index == 0 ? HISTORY_SIZE : index) - 1;
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 Position& position = movement.positions[movement.idBits.getIndexOfBit(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;
if (!movement.idBits.hasBit(id)) {
break;
}
}
nsecs_t age = newestMovement.eventTime - movement.eventTime;
if (age > MAX_AGE) {
break;
}
const Position& position = movement.getPosition(id);
accumVx += newestPosition.x - position.x;
accumVy += newestPosition.y - position.y;
duration += age;
} while (index != mIndex);
// Make sure we used at least one sample.
if (samplesUsed != 0) {
*outVx = accumVx;
*outVy = accumVy;
if (duration >= MIN_DURATION) {
float scale = 1000000000.0f / duration; // one over time delta in seconds
*outVx = accumVx * scale;
*outVy = accumVy * scale;
return true;
}
}