1/*
2 * Copyright (C) 2008 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
17package com.android.launcher2;
18
19import android.content.Context;
20import android.util.AttributeSet;
21import android.view.animation.Interpolator;
22import android.widget.Scroller;
23
24public abstract class SmoothPagedView extends PagedView {
25    private static final float SMOOTHING_SPEED = 0.75f;
26    private static final float SMOOTHING_CONSTANT = (float) (0.016 / Math.log(SMOOTHING_SPEED));
27
28    private float mBaseLineFlingVelocity;
29    private float mFlingVelocityInfluence;
30
31    static final int DEFAULT_MODE = 0;
32    static final int X_LARGE_MODE = 1;
33
34    int mScrollMode;
35
36    private Interpolator mScrollInterpolator;
37
38    public static class OvershootInterpolator implements Interpolator {
39        private static final float DEFAULT_TENSION = 1.3f;
40        private float mTension;
41
42        public OvershootInterpolator() {
43            mTension = DEFAULT_TENSION;
44        }
45
46        public void setDistance(int distance) {
47            mTension = distance > 0 ? DEFAULT_TENSION / distance : DEFAULT_TENSION;
48        }
49
50        public void disableSettle() {
51            mTension = 0.f;
52        }
53
54        public float getInterpolation(float t) {
55            // _o(t) = t * t * ((tension + 1) * t + tension)
56            // o(t) = _o(t - 1) + 1
57            t -= 1.0f;
58            return t * t * ((mTension + 1) * t + mTension) + 1.0f;
59        }
60    }
61
62    /**
63     * Used to inflate the Workspace from XML.
64     *
65     * @param context The application's context.
66     * @param attrs The attributes set containing the Workspace's customization values.
67     */
68    public SmoothPagedView(Context context, AttributeSet attrs) {
69        this(context, attrs, 0);
70    }
71
72    /**
73     * Used to inflate the Workspace from XML.
74     *
75     * @param context The application's context.
76     * @param attrs The attributes set containing the Workspace's customization values.
77     * @param defStyle Unused.
78     */
79    public SmoothPagedView(Context context, AttributeSet attrs, int defStyle) {
80        super(context, attrs, defStyle);
81
82        mUsePagingTouchSlop = false;
83
84        // This means that we'll take care of updating the scroll parameter ourselves (we do it
85        // in computeScroll), we only do this in the OVERSHOOT_MODE, ie. on phones
86        mDeferScrollUpdate = mScrollMode != X_LARGE_MODE;
87    }
88
89    protected int getScrollMode() {
90        return X_LARGE_MODE;
91    }
92
93    /**
94     * Initializes various states for this workspace.
95     */
96    @Override
97    protected void init() {
98        super.init();
99
100        mScrollMode = getScrollMode();
101        if (mScrollMode == DEFAULT_MODE) {
102            mBaseLineFlingVelocity = 2500.0f;
103            mFlingVelocityInfluence = 0.4f;
104            mScrollInterpolator = new OvershootInterpolator();
105            mScroller = new Scroller(getContext(), mScrollInterpolator);
106        }
107    }
108
109    @Override
110    protected void snapToDestination() {
111        if (mScrollMode == X_LARGE_MODE) {
112            super.snapToDestination();
113        } else {
114            snapToPageWithVelocity(getPageNearestToCenterOfScreen(), 0);
115        }
116    }
117
118    @Override
119    protected void snapToPageWithVelocity(int whichPage, int velocity) {
120        if (mScrollMode == X_LARGE_MODE) {
121            super.snapToPageWithVelocity(whichPage, velocity);
122        } else {
123            snapToPageWithVelocity(whichPage, 0, true);
124        }
125    }
126
127    private void snapToPageWithVelocity(int whichPage, int velocity, boolean settle) {
128            // if (!mScroller.isFinished()) return;
129
130        whichPage = Math.max(0, Math.min(whichPage, getChildCount() - 1));
131
132        final int screenDelta = Math.max(1, Math.abs(whichPage - mCurrentPage));
133        final int newX = getChildOffset(whichPage) - getRelativeChildOffset(whichPage);
134        final int delta = newX - mUnboundedScrollX;
135        int duration = (screenDelta + 1) * 100;
136
137        if (!mScroller.isFinished()) {
138            mScroller.abortAnimation();
139        }
140
141        if (settle) {
142            ((OvershootInterpolator) mScrollInterpolator).setDistance(screenDelta);
143        } else {
144            ((OvershootInterpolator) mScrollInterpolator).disableSettle();
145        }
146
147        velocity = Math.abs(velocity);
148        if (velocity > 0) {
149            duration += (duration / (velocity / mBaseLineFlingVelocity)) * mFlingVelocityInfluence;
150        } else {
151            duration += 100;
152        }
153
154        snapToPage(whichPage, delta, duration);
155    }
156
157    @Override
158    protected void snapToPage(int whichPage) {
159       if (mScrollMode == X_LARGE_MODE) {
160           super.snapToPage(whichPage);
161       } else {
162           snapToPageWithVelocity(whichPage, 0, false);
163       }
164    }
165
166    @Override
167    public void computeScroll() {
168        if (mScrollMode == X_LARGE_MODE) {
169            super.computeScroll();
170        } else {
171            boolean scrollComputed = computeScrollHelper();
172
173            if (!scrollComputed && mTouchState == TOUCH_STATE_SCROLLING) {
174                final float now = System.nanoTime() / NANOTIME_DIV;
175                final float e = (float) Math.exp((now - mSmoothingTime) / SMOOTHING_CONSTANT);
176
177                final float dx = mTouchX - mUnboundedScrollX;
178                scrollTo(Math.round(mUnboundedScrollX + dx * e), getScrollY());
179                mSmoothingTime = now;
180
181                // Keep generating points as long as we're more than 1px away from the target
182                if (dx > 1.f || dx < -1.f) {
183                    invalidate();
184                }
185            }
186        }
187    }
188}
189