/*
* Firetweet - Twitter client for Android
*
* Copyright (C) 2012-2015 Mariotaku Lee <mariotaku.lee@gmail.com>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.getlantern.firetweet.util;
import android.content.Context;
import android.graphics.PointF;
import android.support.v7.widget.RecyclerView;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.DecelerateInterpolator;
/**
* {@link RecyclerView.SmoothScroller} implementation which uses
* {@link android.view.animation.LinearInterpolator} until the target position becames a child of
* the RecyclerView and then uses
* {@link android.view.animation.DecelerateInterpolator} to slowly approach to target position.
*/
abstract public class AccelerateSmoothScroller extends RecyclerView.SmoothScroller {
private static final String TAG = "LinearSmoothScroller";
private static final boolean DEBUG = false;
private static final float MILLISECONDS_PER_INCH = 25f;
private static final int TARGET_SEEK_SCROLL_DISTANCE_PX = 10000;
/**
* Align child view's left or top with parent view's left or top
*
* @see #calculateDtToFit(int, int, int, int, int)
* @see #calculateDxToMakeVisible(android.view.View, int)
* @see #calculateDyToMakeVisible(android.view.View, int)
*/
public static final int SNAP_TO_START = -1;
/**
* Align child view's right or bottom with parent view's right or bottom
*
* @see #calculateDtToFit(int, int, int, int, int)
* @see #calculateDxToMakeVisible(android.view.View, int)
* @see #calculateDyToMakeVisible(android.view.View, int)
*/
public static final int SNAP_TO_END = 1;
/**
* <p>Decides if the child should be snapped from start or end, depending on where it
* currently is in relation to its parent.</p>
* <p>For instance, if the view is virtually on the left of RecyclerView, using
* {@code SNAP_TO_ANY} is the same as using {@code SNAP_TO_START}</p>
*
* @see #calculateDtToFit(int, int, int, int, int)
* @see #calculateDxToMakeVisible(android.view.View, int)
* @see #calculateDyToMakeVisible(android.view.View, int)
*/
public static final int SNAP_TO_ANY = 0;
// Trigger a scroll to a further distance than TARGET_SEEK_SCROLL_DISTANCE_PX so that if target
// view is not laid out until interim target position is reached, we can detect the case before
// scrolling slows down and reschedule another interim target scroll
private static final float TARGET_SEEK_EXTRA_SCROLL_RATIO = 1.2f;
protected final AccelerateInterpolator mLinearInterpolator = new AccelerateInterpolator();
protected final DecelerateInterpolator mDecelerateInterpolator = new DecelerateInterpolator();
protected PointF mTargetVector;
private final float MILLISECONDS_PER_PX;
// Temporary variables to keep track of the interim scroll target. These values do not
// point to a real item position, rather point to an estimated location pixels.
protected int mInterimTargetDx = 0, mInterimTargetDy = 0;
public AccelerateSmoothScroller(Context context, float factor) {
MILLISECONDS_PER_PX = calculateSpeedPerPixel(context.getResources().getDisplayMetrics()) * factor;
}
/**
* {@inheritDoc}
*/
@Override
protected void onStart() {
}
/**
* {@inheritDoc}
*/
@Override
protected void onTargetFound(View targetView, RecyclerView.State state, Action action) {
final int dx = calculateDxToMakeVisible(targetView, getHorizontalSnapPreference());
final int dy = calculateDyToMakeVisible(targetView, getVerticalSnapPreference());
final int distance = (int) Math.sqrt(dx * dx + dy * dy);
final int time = calculateTimeForDeceleration(distance);
if (time > 0) {
action.update(-dx, -dy, time, mDecelerateInterpolator);
}
}
/**
* {@inheritDoc}
*/
@Override
protected void onSeekTargetStep(int dx, int dy, RecyclerView.State state, Action action) {
if (getChildCount() == 0) {
stop();
return;
}
if (DEBUG && mTargetVector != null
&& ((mTargetVector.x * dx < 0 || mTargetVector.y * dy < 0))) {
throw new IllegalStateException("Scroll happened in the opposite direction"
+ " of the target. Some calculations are wrong");
}
mInterimTargetDx = clampApplyScroll(mInterimTargetDx, dx);
mInterimTargetDy = clampApplyScroll(mInterimTargetDy, dy);
if (mInterimTargetDx == 0 && mInterimTargetDy == 0) {
updateActionForInterimTarget(action);
} // everything is valid, keep going
}
/**
* {@inheritDoc}
*/
@Override
protected void onStop() {
mInterimTargetDx = mInterimTargetDy = 0;
mTargetVector = null;
}
/**
* Calculates the scroll speed.
*
* @param displayMetrics DisplayMetrics to be used for real dimension calculations
* @return The time (in ms) it should take for each pixel. For instance, if returned value is
* 2 ms, it means scrolling 1000 pixels with LinearInterpolation should take 2 seconds.
*/
protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
}
/**
* <p>Calculates the time for deceleration so that transition from LinearInterpolator to
* DecelerateInterpolator looks smooth.</p>
*
* @param dx Distance to scroll
* @return Time for DecelerateInterpolator to smoothly traverse the distance when transitioning
* from LinearInterpolation
*/
protected int calculateTimeForDeceleration(int dx) {
// we want to cover same area with the linear interpolator for the first 10% of the
// interpolation. After that, deceleration will take control.
// area under curve (1-(1-x)^2) can be calculated as (1 - x/3) * x * x
// which gives 0.100028 when x = .3356
// this is why we divide linear scrolling time with .3356
return (int) Math.ceil(calculateTimeForScrolling(dx) / .3356);
}
/**
* Calculates the time it should take to scroll the given distance (in pixels)
*
* @param dx Distance in pixels that we want to scroll
* @return Time in milliseconds
* @see #calculateSpeedPerPixel(android.util.DisplayMetrics)
*/
protected int calculateTimeForScrolling(int dx) {
// In a case where dx is very small, rounding may return 0 although dx > 0.
// To avoid that issue, ceil the result so that if dx > 0, we'll always return positive
// time.
return (int) Math.ceil(Math.abs(dx) * MILLISECONDS_PER_PX);
}
/**
* When scrolling towards a child view, this method defines whether we should align the left
* or the right edge of the child with the parent RecyclerView.
*
* @return SNAP_TO_START, SNAP_TO_END or SNAP_TO_ANY; depending on the current target vector
* @see #SNAP_TO_START
* @see #SNAP_TO_END
* @see #SNAP_TO_ANY
*/
protected int getHorizontalSnapPreference() {
return mTargetVector == null || mTargetVector.x == 0 ? SNAP_TO_ANY :
mTargetVector.x > 0 ? SNAP_TO_END : SNAP_TO_START;
}
/**
* When scrolling towards a child view, this method defines whether we should align the top
* or the bottom edge of the child with the parent RecyclerView.
*
* @return SNAP_TO_START, SNAP_TO_END or SNAP_TO_ANY; depending on the current target vector
* @see #SNAP_TO_START
* @see #SNAP_TO_END
* @see #SNAP_TO_ANY
*/
protected int getVerticalSnapPreference() {
return mTargetVector == null || mTargetVector.y == 0 ? SNAP_TO_ANY :
mTargetVector.y > 0 ? SNAP_TO_END : SNAP_TO_START;
}
/**
* When the target scroll position is not a child of the RecyclerView, this method calculates
* a direction vector towards that child and triggers a smooth scroll.
*
* @see #computeScrollVectorForPosition(int)
*/
protected void updateActionForInterimTarget(Action action) {
// find an interim target position
PointF scrollVector = computeScrollVectorForPosition(getTargetPosition());
if (scrollVector == null || (scrollVector.x == 0 && scrollVector.y == 0)) {
Log.e(TAG, "To support smooth scrolling, you should override \n"
+ "LayoutManager#computeScrollVectorForPosition.\n"
+ "Falling back to instant scroll");
final int target = getTargetPosition();
stop();
instantScrollToPosition(target);
return;
}
normalize(scrollVector);
mTargetVector = scrollVector;
mInterimTargetDx = (int) (TARGET_SEEK_SCROLL_DISTANCE_PX * scrollVector.x);
mInterimTargetDy = (int) (TARGET_SEEK_SCROLL_DISTANCE_PX * scrollVector.y);
final int time = calculateTimeForScrolling(TARGET_SEEK_SCROLL_DISTANCE_PX);
// To avoid UI hiccups, trigger a smooth scroll to a distance little further than the
// interim target. Since we track the distance travelled in onSeekTargetStep callback, it
// won't actually scroll more than what we need.
action.update((int) (mInterimTargetDx * TARGET_SEEK_EXTRA_SCROLL_RATIO)
, (int) (mInterimTargetDy * TARGET_SEEK_EXTRA_SCROLL_RATIO)
, (int) (time * TARGET_SEEK_EXTRA_SCROLL_RATIO), mLinearInterpolator);
}
private int clampApplyScroll(int tmpDt, int dt) {
final int before = tmpDt;
tmpDt -= dt;
if (before * tmpDt <= 0) { // changed sign, reached 0 or was 0, reset
return 0;
}
return tmpDt;
}
/**
* Helper method for {@link #calculateDxToMakeVisible(android.view.View, int)} and
* {@link #calculateDyToMakeVisible(android.view.View, int)}
*/
public int calculateDtToFit(int viewStart, int viewEnd, int boxStart, int boxEnd, int
snapPreference) {
switch (snapPreference) {
case SNAP_TO_START:
return boxStart - viewStart;
case SNAP_TO_END:
return boxEnd - viewEnd;
case SNAP_TO_ANY:
final int dtStart = boxStart - viewStart;
if (dtStart > 0) {
return dtStart;
}
final int dtEnd = boxEnd - viewEnd;
if (dtEnd < 0) {
return dtEnd;
}
break;
default:
throw new IllegalArgumentException("snap preference should be one of the"
+ " constants defined in SmoothScroller, starting with SNAP_");
}
return 0;
}
/**
* Calculates the vertical scroll amount necessary to make the given view fully visible
* inside the RecyclerView.
*
* @param view The view which we want to make fully visible
* @param snapPreference The edge which the view should snap to when entering the visible
* area. One of {@link #SNAP_TO_START}, {@link #SNAP_TO_END} or
* {@link #SNAP_TO_END}.
* @return The vertical scroll amount necessary to make the view visible with the given
* snap preference.
*/
public int calculateDyToMakeVisible(View view, int snapPreference) {
final RecyclerView.LayoutManager layoutManager = getLayoutManager();
if (!layoutManager.canScrollVertically()) {
return 0;
}
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)
view.getLayoutParams();
final int top = layoutManager.getDecoratedTop(view) - params.topMargin;
final int bottom = layoutManager.getDecoratedBottom(view) + params.bottomMargin;
final int start = layoutManager.getPaddingTop();
final int end = layoutManager.getHeight() - layoutManager.getPaddingBottom();
return calculateDtToFit(top, bottom, start, end, snapPreference);
}
/**
* Calculates the horizontal scroll amount necessary to make the given view fully visible
* inside the RecyclerView.
*
* @param view The view which we want to make fully visible
* @param snapPreference The edge which the view should snap to when entering the visible
* area. One of {@link #SNAP_TO_START}, {@link #SNAP_TO_END} or
* {@link #SNAP_TO_END}
* @return The vertical scroll amount necessary to make the view visible with the given
* snap preference.
*/
public int calculateDxToMakeVisible(View view, int snapPreference) {
final RecyclerView.LayoutManager layoutManager = getLayoutManager();
if (!layoutManager.canScrollHorizontally()) {
return 0;
}
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)
view.getLayoutParams();
final int left = layoutManager.getDecoratedLeft(view) - params.leftMargin;
final int right = layoutManager.getDecoratedRight(view) + params.rightMargin;
final int start = layoutManager.getPaddingLeft();
final int end = layoutManager.getWidth() - layoutManager.getPaddingRight();
return calculateDtToFit(left, right, start, end, snapPreference);
}
abstract public PointF computeScrollVectorForPosition(int targetPosition);
}