/**
* Compute the current velocity based on the points that have been collected. Only call this when
* you actually want to retrieve velocity information, as it is relatively expensive. You can then
* retrieve the velocity with {@link #getXVelocity()} and {@link #getYVelocity()}.
*
* @param units The units you would like the velocity in. A value of 1 provides pixels per
* millisecond, 1000 provides pixels per second, etc.
* @param maxVelocity The maximum velocity that can be computed by this method. This value must be
* declared in the same unit as the units parameter. This value must be positive.
*/
public void computeCurrentVelocity(int units, float maxVelocity) {
final int lastTouchIndex = mLastTouchIndex;
for (Pointer pointer = mPointerListHead; pointer != null; pointer = pointer.next) {
final long[] pastTime = pointer.pastTime;
// Search backwards in time for oldest acceptable time.
// Stop at the beginning of the trace as indicated by the sentinel time Long.MIN_VALUE.
int oldestTouchIndex = lastTouchIndex;
int numTouches = 1;
final long minTime = pastTime[lastTouchIndex] - MAX_AGE_MILLISECONDS;
while (numTouches < NUM_PAST) {
final int nextOldestTouchIndex = (oldestTouchIndex + NUM_PAST - 1) % NUM_PAST;
final long nextOldestTime = pastTime[nextOldestTouchIndex];
if (nextOldestTime < minTime) { // also handles end of trace sentinel
break;
}
oldestTouchIndex = nextOldestTouchIndex;
numTouches += 1;
}
// If we have a lot of samples, skip the last received sample since it is
// probably pretty noisy compared to the sum of all of the traces already acquired.
if (numTouches > 3) {
numTouches -= 1;
}
// Kind-of stupid.
final float[] pastX = pointer.pastX;
final float[] pastY = pointer.pastY;
final float oldestX = pastX[oldestTouchIndex];
final float oldestY = pastY[oldestTouchIndex];
final long oldestTime = pastTime[oldestTouchIndex];
float accumX = 0;
float accumY = 0;
for (int i = 1; i < numTouches; i++) {
final int touchIndex = (oldestTouchIndex + i) % NUM_PAST;
final int duration = (int) (pastTime[touchIndex] - oldestTime);
if (duration == 0) continue;
float delta = pastX[touchIndex] - oldestX;
float velocity = (delta / duration) * units; // pixels/frame.
accumX = (accumX == 0) ? velocity : (accumX + velocity) * .5f;
delta = pastY[touchIndex] - oldestY;
velocity = (delta / duration) * units; // pixels/frame.
accumY = (accumY == 0) ? velocity : (accumY + velocity) * .5f;
}
if (accumX < -maxVelocity) {
accumX = -maxVelocity;
} else if (accumX > maxVelocity) {
accumX = maxVelocity;
}
if (accumY < -maxVelocity) {
accumY = -maxVelocity;
} else if (accumY > maxVelocity) {
accumY = maxVelocity;
}
pointer.xVelocity = accumX;
pointer.yVelocity = accumY;
if (localLOGV) {
Log.v(
TAG,
"Pointer "
+ pointer.id
+ ": Y velocity="
+ accumX
+ " X velocity="
+ accumY
+ " N="
+ numTouches);
}
}
}
