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/*
* Copyright (C) 2017 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.launcher3.touch;
/**
* Utility methods for overscroll damping and related effect.
*/
public class OverScroll {
private static final float OVERSCROLL_DAMP_FACTOR = 0.07f;
/**
* This curve determines how the effect of scrolling over the limits of the page diminishes
* as the user pulls further and further from the bounds
*
* @param f The percentage of how much the user has overscrolled.
* @return A transformed percentage based on the influence curve.
*/
private static float overScrollInfluenceCurve(float f) {
f -= 1.0f;
return f * f * f + 1.0f;
}
/**
* @param amount The original amount overscrolled.
* @param max The maximum amount that the View can overscroll.
* @return The dampened overscroll amount.
*/
public static int dampedScroll(float amount, int max) {
if (Float.compare(amount, 0) == 0) return 0;
float f = amount / max;
f = f / (Math.abs(f)) * (overScrollInfluenceCurve(Math.abs(f)));
// Clamp this factor, f, to -1 < f < 1
if (Math.abs(f) >= 1) {
f /= Math.abs(f);
}
return Math.round(OVERSCROLL_DAMP_FACTOR * f * max);
}
}
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