Java tutorial
/* * Copyright (C) 2010 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. */ package android.widget; import android.annotation.UnsupportedAppUsage; import android.content.Context; import android.hardware.SensorManager; import android.util.Log; import android.view.ViewConfiguration; import android.view.animation.AnimationUtils; import android.view.animation.Interpolator; /** * This class encapsulates scrolling with the ability to overshoot the bounds * of a scrolling operation. This class is a drop-in replacement for * {@link android.widget.Scroller} in most cases. */ public class OverScroller { private int mMode; private final SplineOverScroller mScrollerX; @UnsupportedAppUsage private final SplineOverScroller mScrollerY; @UnsupportedAppUsage private Interpolator mInterpolator; private final boolean mFlywheel; private static final int DEFAULT_DURATION = 250; private static final int SCROLL_MODE = 0; private static final int FLING_MODE = 1; /** * Creates an OverScroller with a viscous fluid scroll interpolator and flywheel. * @param context */ public OverScroller(Context context) { this(context, null); } /** * Creates an OverScroller with flywheel enabled. * @param context The context of this application. * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will * be used. */ public OverScroller(Context context, Interpolator interpolator) { this(context, interpolator, true); } /** * Creates an OverScroller. * @param context The context of this application. * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will * be used. * @param flywheel If true, successive fling motions will keep on increasing scroll speed. * @hide */ @UnsupportedAppUsage public OverScroller(Context context, Interpolator interpolator, boolean flywheel) { if (interpolator == null) { mInterpolator = new Scroller.ViscousFluidInterpolator(); } else { mInterpolator = interpolator; } mFlywheel = flywheel; mScrollerX = new SplineOverScroller(context); mScrollerY = new SplineOverScroller(context); } /** * Creates an OverScroller with flywheel enabled. * @param context The context of this application. * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will * be used. * @param bounceCoefficientX A value between 0 and 1 that will determine the proportion of the * velocity which is preserved in the bounce when the horizontal edge is reached. A null value * means no bounce. This behavior is no longer supported and this coefficient has no effect. * @param bounceCoefficientY Same as bounceCoefficientX but for the vertical direction. This * behavior is no longer supported and this coefficient has no effect. * @deprecated Use {@link #OverScroller(Context, Interpolator)} instead. */ @Deprecated public OverScroller(Context context, Interpolator interpolator, float bounceCoefficientX, float bounceCoefficientY) { this(context, interpolator, true); } /** * Creates an OverScroller. * @param context The context of this application. * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will * be used. * @param bounceCoefficientX A value between 0 and 1 that will determine the proportion of the * velocity which is preserved in the bounce when the horizontal edge is reached. A null value * means no bounce. This behavior is no longer supported and this coefficient has no effect. * @param bounceCoefficientY Same as bounceCoefficientX but for the vertical direction. This * behavior is no longer supported and this coefficient has no effect. * @param flywheel If true, successive fling motions will keep on increasing scroll speed. * @deprecated Use {@link #OverScroller(Context, Interpolator)} instead. */ @Deprecated public OverScroller(Context context, Interpolator interpolator, float bounceCoefficientX, float bounceCoefficientY, boolean flywheel) { this(context, interpolator, flywheel); } @UnsupportedAppUsage void setInterpolator(Interpolator interpolator) { if (interpolator == null) { mInterpolator = new Scroller.ViscousFluidInterpolator(); } else { mInterpolator = interpolator; } } /** * The amount of friction applied to flings. The default value * is {@link ViewConfiguration#getScrollFriction}. * * @param friction A scalar dimension-less value representing the coefficient of * friction. */ public final void setFriction(float friction) { mScrollerX.setFriction(friction); mScrollerY.setFriction(friction); } /** * * Returns whether the scroller has finished scrolling. * * @return True if the scroller has finished scrolling, false otherwise. */ public final boolean isFinished() { return mScrollerX.mFinished && mScrollerY.mFinished; } /** * Force the finished field to a particular value. Contrary to * {@link #abortAnimation()}, forcing the animation to finished * does NOT cause the scroller to move to the final x and y * position. * * @param finished The new finished value. */ public final void forceFinished(boolean finished) { mScrollerX.mFinished = mScrollerY.mFinished = finished; } /** * Returns the current X offset in the scroll. * * @return The new X offset as an absolute distance from the origin. */ public final int getCurrX() { return mScrollerX.mCurrentPosition; } /** * Returns the current Y offset in the scroll. * * @return The new Y offset as an absolute distance from the origin. */ public final int getCurrY() { return mScrollerY.mCurrentPosition; } /** * Returns the absolute value of the current velocity. * * @return The original velocity less the deceleration, norm of the X and Y velocity vector. */ public float getCurrVelocity() { return (float) Math.hypot(mScrollerX.mCurrVelocity, mScrollerY.mCurrVelocity); } /** * Returns the start X offset in the scroll. * * @return The start X offset as an absolute distance from the origin. */ public final int getStartX() { return mScrollerX.mStart; } /** * Returns the start Y offset in the scroll. * * @return The start Y offset as an absolute distance from the origin. */ public final int getStartY() { return mScrollerY.mStart; } /** * Returns where the scroll will end. Valid only for "fling" scrolls. * * @return The final X offset as an absolute distance from the origin. */ public final int getFinalX() { return mScrollerX.mFinal; } /** * Returns where the scroll will end. Valid only for "fling" scrolls. * * @return The final Y offset as an absolute distance from the origin. */ public final int getFinalY() { return mScrollerY.mFinal; } /** * Returns how long the scroll event will take, in milliseconds. * * @return The duration of the scroll in milliseconds. * * @hide Pending removal once nothing depends on it * @deprecated OverScrollers don't necessarily have a fixed duration. * This function will lie to the best of its ability. */ @Deprecated public final int getDuration() { return Math.max(mScrollerX.mDuration, mScrollerY.mDuration); } /** * Extend the scroll animation. This allows a running animation to scroll * further and longer, when used with {@link #setFinalX(int)} or {@link #setFinalY(int)}. * * @param extend Additional time to scroll in milliseconds. * @see #setFinalX(int) * @see #setFinalY(int) * * @hide Pending removal once nothing depends on it * @deprecated OverScrollers don't necessarily have a fixed duration. * Instead of setting a new final position and extending * the duration of an existing scroll, use startScroll * to begin a new animation. */ @Deprecated @UnsupportedAppUsage public void extendDuration(int extend) { mScrollerX.extendDuration(extend); mScrollerY.extendDuration(extend); } /** * Sets the final position (X) for this scroller. * * @param newX The new X offset as an absolute distance from the origin. * @see #extendDuration(int) * @see #setFinalY(int) * * @hide Pending removal once nothing depends on it * @deprecated OverScroller's final position may change during an animation. * Instead of setting a new final position and extending * the duration of an existing scroll, use startScroll * to begin a new animation. */ @Deprecated public void setFinalX(int newX) { mScrollerX.setFinalPosition(newX); } /** * Sets the final position (Y) for this scroller. * * @param newY The new Y offset as an absolute distance from the origin. * @see #extendDuration(int) * @see #setFinalX(int) * * @hide Pending removal once nothing depends on it * @deprecated OverScroller's final position may change during an animation. * Instead of setting a new final position and extending * the duration of an existing scroll, use startScroll * to begin a new animation. */ @Deprecated public void setFinalY(int newY) { mScrollerY.setFinalPosition(newY); } /** * Call this when you want to know the new location. If it returns true, the * animation is not yet finished. */ public boolean computeScrollOffset() { if (isFinished()) { return false; } switch (mMode) { case SCROLL_MODE: long time = AnimationUtils.currentAnimationTimeMillis(); // Any scroller can be used for time, since they were started // together in scroll mode. We use X here. final long elapsedTime = time - mScrollerX.mStartTime; final int duration = mScrollerX.mDuration; if (elapsedTime < duration) { final float q = mInterpolator.getInterpolation(elapsedTime / (float) duration); mScrollerX.updateScroll(q); mScrollerY.updateScroll(q); } else { abortAnimation(); } break; case FLING_MODE: if (!mScrollerX.mFinished) { if (!mScrollerX.update()) { if (!mScrollerX.continueWhenFinished()) { mScrollerX.finish(); } } } if (!mScrollerY.mFinished) { if (!mScrollerY.update()) { if (!mScrollerY.continueWhenFinished()) { mScrollerY.finish(); } } } break; } return true; } /** * Start scrolling by providing a starting point and the distance to travel. * The scroll will use the default value of 250 milliseconds for the * duration. * * @param startX Starting horizontal scroll offset in pixels. Positive * numbers will scroll the content to the left. * @param startY Starting vertical scroll offset in pixels. Positive numbers * will scroll the content up. * @param dx Horizontal distance to travel. Positive numbers will scroll the * content to the left. * @param dy Vertical distance to travel. Positive numbers will scroll the * content up. */ public void startScroll(int startX, int startY, int dx, int dy) { startScroll(startX, startY, dx, dy, DEFAULT_DURATION); } /** * Start scrolling by providing a starting point and the distance to travel. * * @param startX Starting horizontal scroll offset in pixels. Positive * numbers will scroll the content to the left. * @param startY Starting vertical scroll offset in pixels. Positive numbers * will scroll the content up. * @param dx Horizontal distance to travel. Positive numbers will scroll the * content to the left. * @param dy Vertical distance to travel. Positive numbers will scroll the * content up. * @param duration Duration of the scroll in milliseconds. */ public void startScroll(int startX, int startY, int dx, int dy, int duration) { mMode = SCROLL_MODE; mScrollerX.startScroll(startX, dx, duration); mScrollerY.startScroll(startY, dy, duration); } /** * Call this when you want to 'spring back' into a valid coordinate range. * * @param startX Starting X coordinate * @param startY Starting Y coordinate * @param minX Minimum valid X value * @param maxX Maximum valid X value * @param minY Minimum valid Y value * @param maxY Minimum valid Y value * @return true if a springback was initiated, false if startX and startY were * already within the valid range. */ public boolean springBack(int startX, int startY, int minX, int maxX, int minY, int maxY) { mMode = FLING_MODE; // Make sure both methods are called. final boolean spingbackX = mScrollerX.springback(startX, minX, maxX); final boolean spingbackY = mScrollerY.springback(startY, minY, maxY); return spingbackX || spingbackY; } public void fling(int startX, int startY, int velocityX, int velocityY, int minX, int maxX, int minY, int maxY) { fling(startX, startY, velocityX, velocityY, minX, maxX, minY, maxY, 0, 0); } /** * Start scrolling based on a fling gesture. The distance traveled will * depend on the initial velocity of the fling. * * @param startX Starting point of the scroll (X) * @param startY Starting point of the scroll (Y) * @param velocityX Initial velocity of the fling (X) measured in pixels per * second. * @param velocityY Initial velocity of the fling (Y) measured in pixels per * second * @param minX Minimum X value. The scroller will not scroll past this point * unless overX > 0. If overfling is allowed, it will use minX as * a springback boundary. * @param maxX Maximum X value. The scroller will not scroll past this point * unless overX > 0. If overfling is allowed, it will use maxX as * a springback boundary. * @param minY Minimum Y value. The scroller will not scroll past this point * unless overY > 0. If overfling is allowed, it will use minY as * a springback boundary. * @param maxY Maximum Y value. The scroller will not scroll past this point * unless overY > 0. If overfling is allowed, it will use maxY as * a springback boundary. * @param overX Overfling range. If > 0, horizontal overfling in either * direction will be possible. * @param overY Overfling range. If > 0, vertical overfling in either * direction will be possible. */ public void fling(int startX, int startY, int velocityX, int velocityY, int minX, int maxX, int minY, int maxY, int overX, int overY) { // Continue a scroll or fling in progress if (mFlywheel && !isFinished()) { float oldVelocityX = mScrollerX.mCurrVelocity; float oldVelocityY = mScrollerY.mCurrVelocity; if (Math.signum(velocityX) == Math.signum(oldVelocityX) && Math.signum(velocityY) == Math.signum(oldVelocityY)) { velocityX += oldVelocityX; velocityY += oldVelocityY; } } mMode = FLING_MODE; mScrollerX.fling(startX, velocityX, minX, maxX, overX); mScrollerY.fling(startY, velocityY, minY, maxY, overY); } /** * Notify the scroller that we've reached a horizontal boundary. * Normally the information to handle this will already be known * when the animation is started, such as in a call to one of the * fling functions. However there are cases where this cannot be known * in advance. This function will transition the current motion and * animate from startX to finalX as appropriate. * * @param startX Starting/current X position * @param finalX Desired final X position * @param overX Magnitude of overscroll allowed. This should be the maximum * desired distance from finalX. Absolute value - must be positive. */ public void notifyHorizontalEdgeReached(int startX, int finalX, int overX) { mScrollerX.notifyEdgeReached(startX, finalX, overX); } /** * Notify the scroller that we've reached a vertical boundary. * Normally the information to handle this will already be known * when the animation is started, such as in a call to one of the * fling functions. However there are cases where this cannot be known * in advance. This function will animate a parabolic motion from * startY to finalY. * * @param startY Starting/current Y position * @param finalY Desired final Y position * @param overY Magnitude of overscroll allowed. This should be the maximum * desired distance from finalY. Absolute value - must be positive. */ public void notifyVerticalEdgeReached(int startY, int finalY, int overY) { mScrollerY.notifyEdgeReached(startY, finalY, overY); } /** * Returns whether the current Scroller is currently returning to a valid position. * Valid bounds were provided by the * {@link #fling(int, int, int, int, int, int, int, int, int, int)} method. * * One should check this value before calling * {@link #startScroll(int, int, int, int)} as the interpolation currently in progress * to restore a valid position will then be stopped. The caller has to take into account * the fact that the started scroll will start from an overscrolled position. * * @return true when the current position is overscrolled and in the process of * interpolating back to a valid value. */ public boolean isOverScrolled() { return ((!mScrollerX.mFinished && mScrollerX.mState != SplineOverScroller.SPLINE) || (!mScrollerY.mFinished && mScrollerY.mState != SplineOverScroller.SPLINE)); } /** * Stops the animation. Contrary to {@link #forceFinished(boolean)}, * aborting the animating causes the scroller to move to the final x and y * positions. * * @see #forceFinished(boolean) */ public void abortAnimation() { mScrollerX.finish(); mScrollerY.finish(); } /** * Returns the time elapsed since the beginning of the scrolling. * * @return The elapsed time in milliseconds. * * @hide */ public int timePassed() { final long time = AnimationUtils.currentAnimationTimeMillis(); final long startTime = Math.min(mScrollerX.mStartTime, mScrollerY.mStartTime); return (int) (time - startTime); } /** * @hide */ @UnsupportedAppUsage public boolean isScrollingInDirection(float xvel, float yvel) { final int dx = mScrollerX.mFinal - mScrollerX.mStart; final int dy = mScrollerY.mFinal - mScrollerY.mStart; return !isFinished() && Math.signum(xvel) == Math.signum(dx) && Math.signum(yvel) == Math.signum(dy); } static class SplineOverScroller { // Initial position private int mStart; // Current position private int mCurrentPosition; // Final position private int mFinal; // Initial velocity private int mVelocity; // Current velocity @UnsupportedAppUsage private float mCurrVelocity; // Constant current deceleration private float mDeceleration; // Animation starting time, in system milliseconds private long mStartTime; // Animation duration, in milliseconds private int mDuration; // Duration to complete spline component of animation private int mSplineDuration; // Distance to travel along spline animation private int mSplineDistance; // Whether the animation is currently in progress private boolean mFinished; // The allowed overshot distance before boundary is reached. private int mOver; // Fling friction private float mFlingFriction = ViewConfiguration.getScrollFriction(); // Current state of the animation. private int mState = SPLINE; // Constant gravity value, used in the deceleration phase. private static final float GRAVITY = 2000.0f; // A context-specific coefficient adjusted to physical values. private float mPhysicalCoeff; private static float DECELERATION_RATE = (float) (Math.log(0.78) / Math.log(0.9)); private static final float INFLEXION = 0.35f; // Tension lines cross at (INFLEXION, 1) private static final float START_TENSION = 0.5f; private static final float END_TENSION = 1.0f; private static final float P1 = START_TENSION * INFLEXION; private static final float P2 = 1.0f - END_TENSION * (1.0f - INFLEXION); private static final int NB_SAMPLES = 100; private static final float[] SPLINE_POSITION = new float[NB_SAMPLES + 1]; private static final float[] SPLINE_TIME = new float[NB_SAMPLES + 1]; private static final int SPLINE = 0; private static final int CUBIC = 1; private static final int BALLISTIC = 2; static { float x_min = 0.0f; float y_min = 0.0f; for (int i = 0; i < NB_SAMPLES; i++) { final float alpha = (float) i / NB_SAMPLES; float x_max = 1.0f; float x, tx, coef; while (true) { x = x_min + (x_max - x_min) / 2.0f; coef = 3.0f * x * (1.0f - x); tx = coef * ((1.0f - x) * P1 + x * P2) + x * x * x; if (Math.abs(tx - alpha) < 1E-5) break; if (tx > alpha) x_max = x; else x_min = x; } SPLINE_POSITION[i] = coef * ((1.0f - x) * START_TENSION + x) + x * x * x; float y_max = 1.0f; float y, dy; while (true) { y = y_min + (y_max - y_min) / 2.0f; coef = 3.0f * y * (1.0f - y); dy = coef * ((1.0f - y) * START_TENSION + y) + y * y * y; if (Math.abs(dy - alpha) < 1E-5) break; if (dy > alpha) y_max = y; else y_min = y; } SPLINE_TIME[i] = coef * ((1.0f - y) * P1 + y * P2) + y * y * y; } SPLINE_POSITION[NB_SAMPLES] = SPLINE_TIME[NB_SAMPLES] = 1.0f; } void setFriction(float friction) { mFlingFriction = friction; } SplineOverScroller(Context context) { mFinished = true; final float ppi = context.getResources().getDisplayMetrics().density * 160.0f; mPhysicalCoeff = SensorManager.GRAVITY_EARTH // g (m/s^2) * 39.37f // inch/meter * ppi * 0.84f; // look and feel tuning } void updateScroll(float q) { mCurrentPosition = mStart + Math.round(q * (mFinal - mStart)); } /* * Get a signed deceleration that will reduce the velocity. */ static private float getDeceleration(int velocity) { return velocity > 0 ? -GRAVITY : GRAVITY; } /* * Modifies mDuration to the duration it takes to get from start to newFinal using the * spline interpolation. The previous duration was needed to get to oldFinal. */ private void adjustDuration(int start, int oldFinal, int newFinal) { final int oldDistance = oldFinal - start; final int newDistance = newFinal - start; final float x = Math.abs((float) newDistance / oldDistance); final int index = (int) (NB_SAMPLES * x); if (index < NB_SAMPLES) { final float x_inf = (float) index / NB_SAMPLES; final float x_sup = (float) (index + 1) / NB_SAMPLES; final float t_inf = SPLINE_TIME[index]; final float t_sup = SPLINE_TIME[index + 1]; final float timeCoef = t_inf + (x - x_inf) / (x_sup - x_inf) * (t_sup - t_inf); mDuration *= timeCoef; } } void startScroll(int start, int distance, int duration) { mFinished = false; mCurrentPosition = mStart = start; mFinal = start + distance; mStartTime = AnimationUtils.currentAnimationTimeMillis(); mDuration = duration; // Unused mDeceleration = 0.0f; mVelocity = 0; } void finish() { mCurrentPosition = mFinal; // Not reset since WebView relies on this value for fast fling. // TODO: restore when WebView uses the fast fling implemented in this class. // mCurrVelocity = 0.0f; mFinished = true; } void setFinalPosition(int position) { mFinal = position; mFinished = false; } void extendDuration(int extend) { final long time = AnimationUtils.currentAnimationTimeMillis(); final int elapsedTime = (int) (time - mStartTime); mDuration = elapsedTime + extend; mFinished = false; } boolean springback(int start, int min, int max) { mFinished = true; mCurrentPosition = mStart = mFinal = start; mVelocity = 0; mStartTime = AnimationUtils.currentAnimationTimeMillis(); mDuration = 0; if (start < min) { startSpringback(start, min, 0); } else if (start > max) { startSpringback(start, max, 0); } return !mFinished; } private void startSpringback(int start, int end, int velocity) { // mStartTime has been set mFinished = false; mState = CUBIC; mCurrentPosition = mStart = start; mFinal = end; final int delta = start - end; mDeceleration = getDeceleration(delta); // TODO take velocity into account mVelocity = -delta; // only sign is used mOver = Math.abs(delta); mDuration = (int) (1000.0 * Math.sqrt(-2.0 * delta / mDeceleration)); } void fling(int start, int velocity, int min, int max, int over) { mOver = over; mFinished = false; mCurrVelocity = mVelocity = velocity; mDuration = mSplineDuration = 0; mStartTime = AnimationUtils.currentAnimationTimeMillis(); mCurrentPosition = mStart = start; if (start > max || start < min) { startAfterEdge(start, min, max, velocity); return; } mState = SPLINE; double totalDistance = 0.0; if (velocity != 0) { mDuration = mSplineDuration = getSplineFlingDuration(velocity); totalDistance = getSplineFlingDistance(velocity); } mSplineDistance = (int) (totalDistance * Math.signum(velocity)); mFinal = start + mSplineDistance; // Clamp to a valid final position if (mFinal < min) { adjustDuration(mStart, mFinal, min); mFinal = min; } if (mFinal > max) { adjustDuration(mStart, mFinal, max); mFinal = max; } } private double getSplineDeceleration(int velocity) { return Math.log(INFLEXION * Math.abs(velocity) / (mFlingFriction * mPhysicalCoeff)); } private double getSplineFlingDistance(int velocity) { final double l = getSplineDeceleration(velocity); final double decelMinusOne = DECELERATION_RATE - 1.0; return mFlingFriction * mPhysicalCoeff * Math.exp(DECELERATION_RATE / decelMinusOne * l); } /* Returns the duration, expressed in milliseconds */ private int getSplineFlingDuration(int velocity) { final double l = getSplineDeceleration(velocity); final double decelMinusOne = DECELERATION_RATE - 1.0; return (int) (1000.0 * Math.exp(l / decelMinusOne)); } private void fitOnBounceCurve(int start, int end, int velocity) { // Simulate a bounce that started from edge final float durationToApex = -velocity / mDeceleration; // The float cast below is necessary to avoid integer overflow. final float velocitySquared = (float) velocity * velocity; final float distanceToApex = velocitySquared / 2.0f / Math.abs(mDeceleration); final float distanceToEdge = Math.abs(end - start); final float totalDuration = (float) Math .sqrt(2.0 * (distanceToApex + distanceToEdge) / Math.abs(mDeceleration)); mStartTime -= (int) (1000.0f * (totalDuration - durationToApex)); mCurrentPosition = mStart = end; mVelocity = (int) (-mDeceleration * totalDuration); } private void startBounceAfterEdge(int start, int end, int velocity) { mDeceleration = getDeceleration(velocity == 0 ? start - end : velocity); fitOnBounceCurve(start, end, velocity); onEdgeReached(); } private void startAfterEdge(int start, int min, int max, int velocity) { if (start > min && start < max) { Log.e("OverScroller", "startAfterEdge called from a valid position"); mFinished = true; return; } final boolean positive = start > max; final int edge = positive ? max : min; final int overDistance = start - edge; boolean keepIncreasing = overDistance * velocity >= 0; if (keepIncreasing) { // Will result in a bounce or a to_boundary depending on velocity. startBounceAfterEdge(start, edge, velocity); } else { final double totalDistance = getSplineFlingDistance(velocity); if (totalDistance > Math.abs(overDistance)) { fling(start, velocity, positive ? min : start, positive ? start : max, mOver); } else { startSpringback(start, edge, velocity); } } } void notifyEdgeReached(int start, int end, int over) { // mState is used to detect successive notifications if (mState == SPLINE) { mOver = over; mStartTime = AnimationUtils.currentAnimationTimeMillis(); // We were in fling/scroll mode before: current velocity is such that distance to // edge is increasing. This ensures that startAfterEdge will not start a new fling. startAfterEdge(start, end, end, (int) mCurrVelocity); } } private void onEdgeReached() { // mStart, mVelocity and mStartTime were adjusted to their values when edge was reached. // The float cast below is necessary to avoid integer overflow. final float velocitySquared = (float) mVelocity * mVelocity; float distance = velocitySquared / (2.0f * Math.abs(mDeceleration)); final float sign = Math.signum(mVelocity); if (distance > mOver) { // Default deceleration is not sufficient to slow us down before boundary mDeceleration = -sign * velocitySquared / (2.0f * mOver); distance = mOver; } mOver = (int) distance; mState = BALLISTIC; mFinal = mStart + (int) (mVelocity > 0 ? distance : -distance); mDuration = -(int) (1000.0f * mVelocity / mDeceleration); } boolean continueWhenFinished() { switch (mState) { case SPLINE: // Duration from start to null velocity if (mDuration < mSplineDuration) { // If the animation was clamped, we reached the edge mCurrentPosition = mStart = mFinal; // TODO Better compute speed when edge was reached mVelocity = (int) mCurrVelocity; mDeceleration = getDeceleration(mVelocity); mStartTime += mDuration; onEdgeReached(); } else { // Normal stop, no need to continue return false; } break; case BALLISTIC: mStartTime += mDuration; startSpringback(mFinal, mStart, 0); break; case CUBIC: return false; } update(); return true; } /* * Update the current position and velocity for current time. Returns * true if update has been done and false if animation duration has been * reached. */ boolean update() { final long time = AnimationUtils.currentAnimationTimeMillis(); final long currentTime = time - mStartTime; if (currentTime == 0) { // Skip work but report that we're still going if we have a nonzero duration. return mDuration > 0; } if (currentTime > mDuration) { return false; } double distance = 0.0; switch (mState) { case SPLINE: { final float t = (float) currentTime / mSplineDuration; final int index = (int) (NB_SAMPLES * t); float distanceCoef = 1.f; float velocityCoef = 0.f; if (index < NB_SAMPLES) { final float t_inf = (float) index / NB_SAMPLES; final float t_sup = (float) (index + 1) / NB_SAMPLES; final float d_inf = SPLINE_POSITION[index]; final float d_sup = SPLINE_POSITION[index + 1]; velocityCoef = (d_sup - d_inf) / (t_sup - t_inf); distanceCoef = d_inf + (t - t_inf) * velocityCoef; } distance = distanceCoef * mSplineDistance; mCurrVelocity = velocityCoef * mSplineDistance / mSplineDuration * 1000.0f; break; } case BALLISTIC: { final float t = currentTime / 1000.0f; mCurrVelocity = mVelocity + mDeceleration * t; distance = mVelocity * t + mDeceleration * t * t / 2.0f; break; } case CUBIC: { final float t = (float) (currentTime) / mDuration; final float t2 = t * t; final float sign = Math.signum(mVelocity); distance = sign * mOver * (3.0f * t2 - 2.0f * t * t2); mCurrVelocity = sign * mOver * 6.0f * (-t + t2); break; } } mCurrentPosition = mStart + (int) Math.round(distance); return true; } } }