1 /* 2 * Copyright (C) 2011 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 17 package com.android.gallery3d.ui; 18 19 20 // This is a customized version of Scroller, with a interface similar to 21 // android.widget.Scroller. It does fling only, not scroll. 22 // 23 // The differences between the this Scroller and the system one are: 24 // 25 // (1) The velocity does not change because of min/max limit. 26 // (2) The duration is different. 27 // (3) The deceleration curve is different. 28 class FlingScroller { 29 private static final String TAG = "FlingController"; 30 31 // The fling duration (in milliseconds) when velocity is 1 pixel/second 32 private static final float FLING_DURATION_PARAM = 50f; 33 private static final int DECELERATED_FACTOR = 4; 34 35 private int mStartX, mStartY; 36 private int mMinX, mMinY, mMaxX, mMaxY; 37 private double mSinAngle; 38 private double mCosAngle; 39 private int mDuration; 40 private int mDistance; 41 private int mFinalX, mFinalY; 42 43 private int mCurrX, mCurrY; 44 private double mCurrV; 45 getFinalX()46 public int getFinalX() { 47 return mFinalX; 48 } 49 getFinalY()50 public int getFinalY() { 51 return mFinalY; 52 } 53 getDuration()54 public int getDuration() { 55 return mDuration; 56 } 57 getCurrX()58 public int getCurrX() { 59 return mCurrX; 60 61 } 62 getCurrY()63 public int getCurrY() { 64 return mCurrY; 65 } 66 getCurrVelocityX()67 public int getCurrVelocityX() { 68 return (int)Math.round(mCurrV * mCosAngle); 69 } 70 getCurrVelocityY()71 public int getCurrVelocityY() { 72 return (int)Math.round(mCurrV * mSinAngle); 73 } 74 fling(int startX, int startY, int velocityX, int velocityY, int minX, int maxX, int minY, int maxY)75 public void fling(int startX, int startY, int velocityX, int velocityY, 76 int minX, int maxX, int minY, int maxY) { 77 mStartX = startX; 78 mStartY = startY; 79 mMinX = minX; 80 mMinY = minY; 81 mMaxX = maxX; 82 mMaxY = maxY; 83 84 double velocity = Math.hypot(velocityX, velocityY); 85 mSinAngle = velocityY / velocity; 86 mCosAngle = velocityX / velocity; 87 // 88 // The position formula: x(t) = s + (e - s) * (1 - (1 - t / T) ^ d) 89 // velocity formula: v(t) = d * (e - s) * (1 - t / T) ^ (d - 1) / T 90 // Thus, 91 // v0 = d * (e - s) / T => (e - s) = v0 * T / d 92 // 93 94 // Ta = T_ref * (Va / V_ref) ^ (1 / (d - 1)); V_ref = 1 pixel/second; 95 mDuration = (int)Math.round(FLING_DURATION_PARAM 96 * Math.pow(Math.abs(velocity), 1.0 / (DECELERATED_FACTOR - 1))); 97 98 // (e - s) = v0 * T / d 99 mDistance = (int)Math.round( 100 velocity * mDuration / DECELERATED_FACTOR / 1000); 101 102 mFinalX = getX(1.0f); 103 mFinalY = getY(1.0f); 104 } 105 computeScrollOffset(float progress)106 public void computeScrollOffset(float progress) { 107 progress = Math.min(progress, 1); 108 float f = 1 - progress; 109 f = 1 - (float) Math.pow(f, DECELERATED_FACTOR); 110 mCurrX = getX(f); 111 mCurrY = getY(f); 112 mCurrV = getV(progress); 113 } 114 getX(float f)115 private int getX(float f) { 116 int r = (int) Math.round(mStartX + f * mDistance * mCosAngle); 117 if (mCosAngle > 0 && mStartX <= mMaxX) { 118 r = Math.min(r, mMaxX); 119 } else if (mCosAngle < 0 && mStartX >= mMinX) { 120 r = Math.max(r, mMinX); 121 } 122 return r; 123 } 124 getY(float f)125 private int getY(float f) { 126 int r = (int) Math.round(mStartY + f * mDistance * mSinAngle); 127 if (mSinAngle > 0 && mStartY <= mMaxY) { 128 r = Math.min(r, mMaxY); 129 } else if (mSinAngle < 0 && mStartY >= mMinY) { 130 r = Math.max(r, mMinY); 131 } 132 return r; 133 } 134 getV(float progress)135 private double getV(float progress) { 136 // velocity formula: v(t) = d * (e - s) * (1 - t / T) ^ (d - 1) / T 137 return DECELERATED_FACTOR * mDistance * 1000 * 138 Math.pow(1 - progress, DECELERATED_FACTOR - 1) / mDuration; 139 } 140 } 141