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/*
* Copyright (C) 2008 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.launcher2;
import android.content.Context;
import android.util.AttributeSet;
import android.view.animation.Interpolator;
import android.widget.Scroller;
public abstract class SmoothPagedView extends PagedView {
private static final float SMOOTHING_SPEED = 0.75f;
private static final float SMOOTHING_CONSTANT = (float) (0.016 / Math.log(SMOOTHING_SPEED));
private static final float BASELINE_FLING_VELOCITY = 2500.f;
private static final float FLING_VELOCITY_INFLUENCE = 0.4f;
private WorkspaceOvershootInterpolator mScrollInterpolator;
private static class WorkspaceOvershootInterpolator implements Interpolator {
private static final float DEFAULT_TENSION = 1.3f;
private float mTension;
public WorkspaceOvershootInterpolator() {
mTension = DEFAULT_TENSION;
}
public void setDistance(int distance) {
mTension = distance > 0 ? DEFAULT_TENSION / distance : DEFAULT_TENSION;
}
public void disableSettle() {
mTension = 0.f;
}
public float getInterpolation(float t) {
// _o(t) = t * t * ((tension + 1) * t + tension)
// o(t) = _o(t - 1) + 1
t -= 1.0f;
return t * t * ((mTension + 1) * t + mTension) + 1.0f;
}
}
/**
* Used to inflate the Workspace from XML.
*
* @param context The application's context.
* @param attrs The attributes set containing the Workspace's customization values.
*/
public SmoothPagedView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
/**
* Used to inflate the Workspace from XML.
*
* @param context The application's context.
* @param attrs The attributes set containing the Workspace's customization values.
* @param defStyle Unused.
*/
public SmoothPagedView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mUsePagingTouchSlop = false;
// This means that we'll take care of updating the scroll parameter ourselves (we do it
// in computeScroll)
mDeferScrollUpdate = true;
}
/**
* Initializes various states for this workspace.
*/
@Override
protected void init() {
super.init();
mScrollInterpolator = new WorkspaceOvershootInterpolator();
// overwrite the previous mScroller
mScroller = new Scroller(getContext(), mScrollInterpolator);
}
@Override
protected void snapToDestination() {
snapToPageWithVelocity(mCurrentPage, 0);
}
@Override
protected void snapToPageWithVelocity(int whichPage, int velocity) {
snapToPageWithVelocity(whichPage, 0, true);
}
void snapToPageWithVelocity(int whichPage, int velocity, boolean settle) {
// if (!mScroller.isFinished()) return;
whichPage = Math.max(0, Math.min(whichPage, getChildCount() - 1));
final int screenDelta = Math.max(1, Math.abs(whichPage - mCurrentPage));
final int newX = whichPage * getWidth();
final int delta = newX - mScrollX;
int duration = (screenDelta + 1) * 100;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
if (settle) {
mScrollInterpolator.setDistance(screenDelta);
} else {
mScrollInterpolator.disableSettle();
}
velocity = Math.abs(velocity);
if (velocity > 0) {
duration += (duration / (velocity / BASELINE_FLING_VELOCITY))
* FLING_VELOCITY_INFLUENCE;
} else {
duration += 100;
}
snapToPage(whichPage, delta, duration);
}
@Override
protected void snapToPage(int whichPage) {
snapToPageWithVelocity(whichPage, 0, false);
}
@Override
public void computeScroll() {
boolean scrollComputed = computeScrollHelper();
if (!scrollComputed && mTouchState == TOUCH_STATE_SCROLLING) {
final float now = System.nanoTime() / NANOTIME_DIV;
final float e = (float) Math.exp((now - mSmoothingTime) / SMOOTHING_CONSTANT);
final float dx = mTouchX - mScrollX;
mScrollX += dx * e;
mSmoothingTime = now;
// Keep generating points as long as we're more than 1px away from the target
if (dx > 1.f || dx < -1.f) {
invalidate();
}
}
}
}
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