Amin Shaikh | 6b3b4f4 | 2018-02-06 16:35:01 -0500 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2018 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | package com.android.systemui.qs.touch; |
| 17 | |
| 18 | /** |
| 19 | * Utility methods for overscroll damping and related effect. |
| 20 | * |
| 21 | * Copied from packages/apps/Launcher3/src/com/android/launcher3/touch/OverScroll.java |
| 22 | */ |
| 23 | public class OverScroll { |
| 24 | |
| 25 | private static final float OVERSCROLL_DAMP_FACTOR = 0.07f; |
| 26 | |
| 27 | /** |
| 28 | * This curve determines how the effect of scrolling over the limits of the page diminishes |
| 29 | * as the user pulls further and further from the bounds |
| 30 | * |
| 31 | * @param f The percentage of how much the user has overscrolled. |
| 32 | * @return A transformed percentage based on the influence curve. |
| 33 | */ |
| 34 | private static float overScrollInfluenceCurve(float f) { |
| 35 | f -= 1.0f; |
| 36 | return f * f * f + 1.0f; |
| 37 | } |
| 38 | |
| 39 | /** |
| 40 | * @param amount The original amount overscrolled. |
| 41 | * @param max The maximum amount that the View can overscroll. |
| 42 | * @return The dampened overscroll amount. |
| 43 | */ |
| 44 | public static int dampedScroll(float amount, int max) { |
| 45 | if (Float.compare(amount, 0) == 0) return 0; |
| 46 | |
| 47 | float f = amount / max; |
| 48 | f = f / (Math.abs(f)) * (overScrollInfluenceCurve(Math.abs(f))); |
| 49 | |
| 50 | // Clamp this factor, f, to -1 < f < 1 |
| 51 | if (Math.abs(f) >= 1) { |
| 52 | f /= Math.abs(f); |
| 53 | } |
| 54 | |
| 55 | return Math.round(OVERSCROLL_DAMP_FACTOR * f * max); |
| 56 | } |
| 57 | } |