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

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/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
2012-05-21 04:12:37 -07:00
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
package org.mozilla.gecko.ui;
import java.util.Map;
import android.util.Log;
import org.json.JSONArray;
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 {
private static final String LOGTAG = "GeckoAxis";
private static final String PREF_SCROLLING_FRICTION_SLOW = "ui.scrolling.friction_slow";
private static final String PREF_SCROLLING_FRICTION_FAST = "ui.scrolling.friction_fast";
private static final String PREF_SCROLLING_VELOCITY_THRESHOLD = "ui.scrolling.velocity_threshold";
private static final String PREF_SCROLLING_MAX_EVENT_ACCELERATION = "ui.scrolling.max_event_acceleration";
private static final String PREF_SCROLLING_OVERSCROLL_DECEL_RATE = "ui.scrolling.overscroll_decel_rate";
private static final String PREF_SCROLLING_OVERSCROLL_SNAP_LIMIT = "ui.scrolling.overscroll_snap_limit";
private static final String PREF_SCROLLING_MIN_SCROLLABLE_DISTANCE = "ui.scrolling.min_scrollable_distance";
// This fraction of velocity remains after every animation frame when the velocity is low.
private static float FRICTION_SLOW;
// This fraction of velocity remains after every animation frame when the velocity is high.
private static float FRICTION_FAST;
// Below this velocity (in pixels per frame), the friction starts increasing from FRICTION_FAST
// to FRICTION_SLOW.
private static float VELOCITY_THRESHOLD;
// The maximum velocity change factor between events, per ms, in %.
// Direction changes are excluded.
private static float MAX_EVENT_ACCELERATION;
// The rate of deceleration when the surface has overscrolled.
private static float OVERSCROLL_DECEL_RATE;
// The percentage of the surface which can be overscrolled before it must snap back.
private static float SNAP_LIMIT;
// The minimum amount of space that must be present for an axis to be considered scrollable,
// in pixels.
private static float MIN_SCROLLABLE_DISTANCE;
private static float getFloatPref(Map<String, Integer> prefs, String prefName, int defaultValue) {
Integer value = (prefs == null ? null : prefs.get(prefName));
return (float)(value == null || value < 0 ? defaultValue : value) / 1000f;
}
private static int getIntPref(Map<String, Integer> prefs, String prefName, int defaultValue) {
Integer value = (prefs == null ? null : prefs.get(prefName));
return (value == null || value < 0 ? defaultValue : value);
}
static void addPrefNames(JSONArray prefs) {
prefs.put(PREF_SCROLLING_FRICTION_FAST);
prefs.put(PREF_SCROLLING_FRICTION_SLOW);
prefs.put(PREF_SCROLLING_VELOCITY_THRESHOLD);
prefs.put(PREF_SCROLLING_MAX_EVENT_ACCELERATION);
prefs.put(PREF_SCROLLING_OVERSCROLL_DECEL_RATE);
prefs.put(PREF_SCROLLING_OVERSCROLL_SNAP_LIMIT);
prefs.put(PREF_SCROLLING_MIN_SCROLLABLE_DISTANCE);
}
static void setPrefs(Map<String, Integer> prefs) {
FRICTION_SLOW = getFloatPref(prefs, PREF_SCROLLING_FRICTION_SLOW, 850);
FRICTION_FAST = getFloatPref(prefs, PREF_SCROLLING_FRICTION_FAST, 970);
VELOCITY_THRESHOLD = getIntPref(prefs, PREF_SCROLLING_VELOCITY_THRESHOLD, 10);
MAX_EVENT_ACCELERATION = getFloatPref(prefs, PREF_SCROLLING_MAX_EVENT_ACCELERATION, 12);
OVERSCROLL_DECEL_RATE = getFloatPref(prefs, PREF_SCROLLING_OVERSCROLL_DECEL_RATE, 40);
SNAP_LIMIT = getFloatPref(prefs, PREF_SCROLLING_OVERSCROLL_SNAP_LIMIT, 300);
MIN_SCROLLABLE_DISTANCE = getFloatPref(prefs, PREF_SCROLLING_MIN_SCROLLABLE_DISTANCE, 500);
Log.i(LOGTAG, "Prefs: " + FRICTION_SLOW + "," + FRICTION_FAST + "," + VELOCITY_THRESHOLD + ","
+ MAX_EVENT_ACCELERATION + "," + OVERSCROLL_DECEL_RATE + "," + SNAP_LIMIT + "," + MIN_SCROLLABLE_DISTANCE);
}
static {
// set the scrolling parameters to default values on startup
setPrefs(null);
}
// 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. */
private 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 getPageStart();
protected abstract float getPageLength();
Axis(SubdocumentScrollHelper subscroller) {
mSubscroller = subscroller;
}
private float getViewportEnd() {
return getOrigin() + getViewportLength();
}
private float getPageEnd() {
return getPageStart() + getPageLength();
}
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() < getPageStart());
boolean plus = (getViewportEnd() > getPageEnd());
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 getPageStart() - getOrigin();
case PLUS: return getViewportEnd() - getPageEnd();
case BOTH: return (getViewportEnd() - getPageEnd()) + (getPageStart() - 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() {
// If we're scrolling a subdocument, ignore the viewport length restrictions (since those
// apply to the top-level document) and only take into account axis locking.
if (mSubscroller.scrolling()) {
return !mScrollingDisabled;
} else {
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();
Overscroll overscroll = getOverscroll();
boolean decreasingOverscroll = false;
if ((overscroll == Overscroll.MINUS && mVelocity > 0) ||
(overscroll == Overscroll.PLUS && mVelocity < 0))
{
decreasingOverscroll = true;
}
if (mDisableSnap || FloatUtils.fuzzyEquals(excess, 0.0f) || decreasingOverscroll) {
// 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 (overscroll == 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 (!scrollable()) {
return;
}
if (mFlingState == FlingStates.PANNING)
mDisplacement += (mLastTouchPos - mTouchPos) * getEdgeResistance();
else
mDisplacement += mVelocity;
}
float resetDisplacement() {
float d = mDisplacement;
mDisplacement = 0.0f;
return d;
}
}