gecko/mobile/android/base/ui/Axis.java

272 lines
10 KiB
Java

/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (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.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla Android code.
*
* The Initial Developer of the Original Code is Mozilla Foundation.
* Portions created by the Initial Developer are Copyright (C) 2012
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Patrick Walton <pcwalton@mozilla.com>
* Kartikaya Gupta <kgupta@mozilla.com>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
package org.mozilla.gecko.ui;
import org.mozilla.gecko.FloatUtils;
/**
* This class represents the physics for one axis of movement (i.e. either
* horizontal or vertical). It tracks the different properties of movement
* like displacement, velocity, viewport dimensions, etc. pertaining to
* a particular axis.
*/
abstract class Axis {
// This fraction of velocity remains after every animation frame when the velocity is low.
private static final float FRICTION_SLOW = 0.85f;
// This fraction of velocity remains after every animation frame when the velocity is high.
private static final float FRICTION_FAST = 0.97f;
// Below this velocity (in pixels per frame), the friction starts increasing from FRICTION_FAST
// to FRICTION_SLOW.
private static final float VELOCITY_THRESHOLD = 10.0f;
// The maximum velocity change factor between events, per ms, in %.
// Direction changes are excluded.
private static final float MAX_EVENT_ACCELERATION = 0.012f;
// The rate of deceleration when the surface has overscrolled.
private static final float OVERSCROLL_DECEL_RATE = 0.04f;
// The percentage of the surface which can be overscrolled before it must snap back.
private static final float SNAP_LIMIT = 0.3f;
// The minimum amount of space that must be present for an axis to be considered scrollable,
// in pixels.
private static final float MIN_SCROLLABLE_DISTANCE = 0.5f;
// The number of milliseconds per frame assuming 60 fps
private static final float MS_PER_FRAME = 1000.0f / 60.0f;
private enum FlingStates {
STOPPED,
PANNING,
FLINGING,
}
private enum Overscroll {
NONE,
MINUS, // Overscrolled in the negative direction
PLUS, // Overscrolled in the positive direction
BOTH, // Overscrolled in both directions (page is zoomed to smaller than screen)
}
private final SubdocumentScrollHelper mSubscroller;
private float mFirstTouchPos; /* Position of the first touch event on the current drag. */
private float mTouchPos; /* Position of the most recent touch event on the current drag. */
private float mLastTouchPos; /* Position of the touch event before touchPos. */
private float mVelocity; /* Velocity in this direction; pixels per animation frame. */
public boolean mScrollingDisabled; /* Whether movement on this axis is locked. */
private boolean mDisableSnap; /* Whether overscroll snapping is disabled. */
private float mDisplacement;
private FlingStates mFlingState; /* The fling state we're in on this axis. */
protected abstract float getOrigin();
protected abstract float getViewportLength();
protected abstract float getPageLength();
Axis(SubdocumentScrollHelper subscroller) {
mSubscroller = subscroller;
}
private float getViewportEnd() {
return getOrigin() + getViewportLength();
}
void startTouch(float pos) {
mVelocity = 0.0f;
mScrollingDisabled = false;
mFirstTouchPos = mTouchPos = mLastTouchPos = pos;
}
float panDistance(float currentPos) {
return currentPos - mFirstTouchPos;
}
void setScrollingDisabled(boolean disabled) {
mScrollingDisabled = disabled;
}
void saveTouchPos() {
mLastTouchPos = mTouchPos;
}
void updateWithTouchAt(float pos, float timeDelta) {
float newVelocity = (mTouchPos - pos) / timeDelta * MS_PER_FRAME;
// If there's a direction change, or current velocity is very low,
// allow setting of the velocity outright. Otherwise, use the current
// velocity and a maximum change factor to set the new velocity.
boolean curVelocityIsLow = Math.abs(mVelocity) < 1.0f;
boolean directionChange = (mVelocity > 0) != (newVelocity > 0);
if (curVelocityIsLow || (directionChange && !FloatUtils.fuzzyEquals(newVelocity, 0.0f))) {
mVelocity = newVelocity;
} else {
float maxChange = Math.abs(mVelocity * timeDelta * MAX_EVENT_ACCELERATION);
mVelocity = Math.min(mVelocity + maxChange, Math.max(mVelocity - maxChange, newVelocity));
}
mTouchPos = pos;
}
boolean overscrolled() {
return getOverscroll() != Overscroll.NONE;
}
private Overscroll getOverscroll() {
boolean minus = (getOrigin() < 0.0f);
boolean plus = (getViewportEnd() > getPageLength());
if (minus && plus) {
return Overscroll.BOTH;
} else if (minus) {
return Overscroll.MINUS;
} else if (plus) {
return Overscroll.PLUS;
} else {
return Overscroll.NONE;
}
}
// Returns the amount that the page has been overscrolled. If the page hasn't been
// overscrolled on this axis, returns 0.
private float getExcess() {
switch (getOverscroll()) {
case MINUS: return -getOrigin();
case PLUS: return getViewportEnd() - getPageLength();
case BOTH: return getViewportEnd() - getPageLength() - getOrigin();
default: return 0.0f;
}
}
/*
* Returns true if the page is zoomed in to some degree along this axis such that scrolling is
* possible and this axis has not been scroll locked while panning. Otherwise, returns false.
*/
private boolean scrollable() {
return getViewportLength() <= getPageLength() - MIN_SCROLLABLE_DISTANCE &&
!mScrollingDisabled;
}
/*
* Returns the resistance, as a multiplier, that should be taken into account when
* tracking or pinching.
*/
float getEdgeResistance() {
float excess = getExcess();
if (excess > 0.0f) {
// excess can be greater than viewport length, but the resistance
// must never drop below 0.0
return Math.max(0.0f, SNAP_LIMIT - excess / getViewportLength());
}
return 1.0f;
}
/* Returns the velocity. If the axis is locked, returns 0. */
float getRealVelocity() {
return scrollable() ? mVelocity : 0f;
}
void startPan() {
mFlingState = FlingStates.PANNING;
}
void startFling(boolean stopped) {
mDisableSnap = mSubscroller.scrolling();
if (stopped) {
mFlingState = FlingStates.STOPPED;
} else {
mFlingState = FlingStates.FLINGING;
}
}
/* Advances a fling animation by one step. */
boolean advanceFling() {
if (mFlingState != FlingStates.FLINGING) {
return false;
}
if (mSubscroller.scrolling() && !mSubscroller.lastScrollSucceeded()) {
// if the subdocument stopped scrolling, it's because it reached the end
// of the subdocument. we don't do overscroll on subdocuments, so there's
// no point in continuing this fling.
return false;
}
float excess = getExcess();
if (mDisableSnap || FloatUtils.fuzzyEquals(excess, 0.0f)) {
// If we aren't overscrolled, just apply friction.
if (Math.abs(mVelocity) >= VELOCITY_THRESHOLD) {
mVelocity *= FRICTION_FAST;
} else {
float t = mVelocity / VELOCITY_THRESHOLD;
mVelocity *= FloatUtils.interpolate(FRICTION_SLOW, FRICTION_FAST, t);
}
} else {
// Otherwise, decrease the velocity linearly.
float elasticity = 1.0f - excess / (getViewportLength() * SNAP_LIMIT);
if (getOverscroll() == Overscroll.MINUS) {
mVelocity = Math.min((mVelocity + OVERSCROLL_DECEL_RATE) * elasticity, 0.0f);
} else { // must be Overscroll.PLUS
mVelocity = Math.max((mVelocity - OVERSCROLL_DECEL_RATE) * elasticity, 0.0f);
}
}
return true;
}
void stopFling() {
mVelocity = 0.0f;
mFlingState = FlingStates.STOPPED;
}
// Performs displacement of the viewport position according to the current velocity.
void displace() {
if (!mSubscroller.scrolling() && !scrollable())
return;
if (mFlingState == FlingStates.PANNING)
mDisplacement += (mLastTouchPos - mTouchPos) * getEdgeResistance();
else
mDisplacement += mVelocity;
}
float resetDisplacement() {
float d = mDisplacement;
mDisplacement = 0.0f;
return d;
}
}