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/*
* 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 com.android.gallery3d.ui;
import com.android.gallery3d.util.Utils;
public class ScrollerHelper {
private static final long START_ANIMATION = -1;
private static final long NO_ANIMATION = -2;
private static final int ANIM_KIND_FLING = 1;
private static final int ANIM_KIND_SCROLL = 2;
private static final int DECELERATED_FACTOR = 4;
private long mStartTime = NO_ANIMATION;
private int mDuration; // in millisecond
private int mStart;
private int mFinal;
private int mPosition;
private int mMin;
private int mMax;
private int mAnimationKind;
// The fling duration when velocity is 1 pixel / second
private float FLING_DURATION_PARAM = 200f; // 200ms
/**
* Call this when you want to know the new location. The position will be
* updated and can be obtained by getPosition(). Returns true if the
* animation is not yet finished.
*/
public boolean advanceAnimation(long currentTimeMillis) {
if (mStartTime == NO_ANIMATION) return false;
if (mStartTime == START_ANIMATION) mStartTime = currentTimeMillis;
int timePassed = (int)(currentTimeMillis - mStartTime);
if (timePassed < mDuration) {
float progress = (float) timePassed / mDuration;
float f = 1 - progress;
if (mAnimationKind == ANIM_KIND_SCROLL) {
f = 1 - f; // linear
} else if (mAnimationKind == ANIM_KIND_FLING) {
f = 1 - (float) Math.pow(f, DECELERATED_FACTOR);
}
mPosition = Utils.clamp(
Math.round(mStart + (mFinal - mStart) * f), mMin, mMax);
if (mPosition == Utils.clamp(mFinal, mMin, mMax)) {
mStartTime = NO_ANIMATION;
return false;
}
return true;
} else {
mPosition = mFinal;
mStartTime = NO_ANIMATION;
return false;
}
}
public void forceFinished() {
mStartTime = NO_ANIMATION;
mFinal = mPosition;
}
public int getPosition() {
return mPosition;
}
public void setPosition(int position) {
mPosition = position;
}
public void fling(float velocity, int min, int max) {
/*
* The position formula: x(t) = s + (e - s) * (1 - (1 - t / T) ^ d)
* velocity formula: v(t) = d * (e - s) * (1 - t / T) ^ (d - 1) / T
* Thus,
* v0 = (e - s) / T * d => (e - s) = v0 * T / d
*/
mStartTime = START_ANIMATION;
mAnimationKind = ANIM_KIND_FLING;
mStart = mPosition;
mMin = min;
mMax = max;
// Ta = T_ref * (Va / V_ref) ^ (1 / (d - 1)); V_ref = 1 pixel/second;
mDuration = (int) Math.round(FLING_DURATION_PARAM
* Math.pow(Math.abs(velocity), 1.0 / (DECELERATED_FACTOR - 1)));
mFinal = mStart + Math.round(
velocity * mDuration / DECELERATED_FACTOR / 1000);
}
public void startScroll(int distance, int min, int max) {
mPosition = Utils.clamp(mPosition + distance, min, max);
}
}
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