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/*
* Copyright (C) 2011 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;
// This is a customized version of Scroller, with a interface similar to
// android.widget.Scroller. It does fling only, not scroll.
//
// The differences between the this Scroller and the system one are:
//
// (1) The velocity does not change because of min/max limit.
// (2) The duration is different.
// (3) The deceleration curve is different.
class FlingScroller {
@SuppressWarnings("unused")
private static final String TAG = "FlingController";
// The fling duration (in milliseconds) when velocity is 1 pixel/second
private static final float FLING_DURATION_PARAM = 50f;
private static final int DECELERATED_FACTOR = 4;
private int mStartX, mStartY;
private int mMinX, mMinY, mMaxX, mMaxY;
private double mSinAngle;
private double mCosAngle;
private int mDuration;
private int mDistance;
private int mFinalX, mFinalY;
private int mCurrX, mCurrY;
private double mCurrV;
public int getFinalX() {
return mFinalX;
}
public int getFinalY() {
return mFinalY;
}
public int getDuration() {
return mDuration;
}
public int getCurrX() {
return mCurrX;
}
public int getCurrY() {
return mCurrY;
}
public int getCurrVelocityX() {
return (int)Math.round(mCurrV * mCosAngle);
}
public int getCurrVelocityY() {
return (int)Math.round(mCurrV * mSinAngle);
}
public void fling(int startX, int startY, int velocityX, int velocityY,
int minX, int maxX, int minY, int maxY) {
mStartX = startX;
mStartY = startY;
mMinX = minX;
mMinY = minY;
mMaxX = maxX;
mMaxY = maxY;
double velocity = Math.hypot(velocityX, velocityY);
mSinAngle = velocityY / velocity;
mCosAngle = velocityX / velocity;
//
// 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 = d * (e - s) / T => (e - s) = v0 * T / d
//
// 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)));
// (e - s) = v0 * T / d
mDistance = (int)Math.round(
velocity * mDuration / DECELERATED_FACTOR / 1000);
mFinalX = getX(1.0f);
mFinalY = getY(1.0f);
}
public void computeScrollOffset(float progress) {
progress = Math.min(progress, 1);
float f = 1 - progress;
f = 1 - (float) Math.pow(f, DECELERATED_FACTOR);
mCurrX = getX(f);
mCurrY = getY(f);
mCurrV = getV(progress);
}
private int getX(float f) {
int r = (int) Math.round(mStartX + f * mDistance * mCosAngle);
if (mCosAngle > 0 && mStartX <= mMaxX) {
r = Math.min(r, mMaxX);
} else if (mCosAngle < 0 && mStartX >= mMinX) {
r = Math.max(r, mMinX);
}
return r;
}
private int getY(float f) {
int r = (int) Math.round(mStartY + f * mDistance * mSinAngle);
if (mSinAngle > 0 && mStartY <= mMaxY) {
r = Math.min(r, mMaxY);
} else if (mSinAngle < 0 && mStartY >= mMinY) {
r = Math.max(r, mMinY);
}
return r;
}
private double getV(float progress) {
// velocity formula: v(t) = d * (e - s) * (1 - t / T) ^ (d - 1) / T
return DECELERATED_FACTOR * mDistance * 1000 *
Math.pow(1 - progress, DECELERATED_FACTOR - 1) / mDuration;
}
}
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