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373 lines
15 KiB
Java
373 lines
15 KiB
Java
/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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package org.mozilla.gecko.gfx;
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import org.mozilla.gecko.PrefsHelper;
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import org.mozilla.gecko.util.FloatUtils;
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import org.json.JSONArray;
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import android.util.Log;
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import android.view.View;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* This class represents the physics for one axis of movement (i.e. either
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* horizontal or vertical). It tracks the different properties of movement
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* like displacement, velocity, viewport dimensions, etc. pertaining to
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* a particular axis.
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*/
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abstract class Axis {
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private static final String LOGTAG = "GeckoAxis";
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private static final String PREF_SCROLLING_FRICTION_SLOW = "ui.scrolling.friction_slow";
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private static final String PREF_SCROLLING_FRICTION_FAST = "ui.scrolling.friction_fast";
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private static final String PREF_SCROLLING_MAX_EVENT_ACCELERATION = "ui.scrolling.max_event_acceleration";
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private static final String PREF_SCROLLING_OVERSCROLL_DECEL_RATE = "ui.scrolling.overscroll_decel_rate";
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private static final String PREF_SCROLLING_OVERSCROLL_SNAP_LIMIT = "ui.scrolling.overscroll_snap_limit";
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private static final String PREF_SCROLLING_MIN_SCROLLABLE_DISTANCE = "ui.scrolling.min_scrollable_distance";
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// This fraction of velocity remains after every animation frame when the velocity is low.
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private static float FRICTION_SLOW;
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// This fraction of velocity remains after every animation frame when the velocity is high.
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private static float FRICTION_FAST;
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// Below this velocity (in pixels per frame), the friction starts increasing from FRICTION_FAST
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// to FRICTION_SLOW.
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private static float VELOCITY_THRESHOLD;
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// The maximum velocity change factor between events, per ms, in %.
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// Direction changes are excluded.
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private static float MAX_EVENT_ACCELERATION;
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// The rate of deceleration when the surface has overscrolled.
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private static float OVERSCROLL_DECEL_RATE;
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// The percentage of the surface which can be overscrolled before it must snap back.
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private static float SNAP_LIMIT;
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// The minimum amount of space that must be present for an axis to be considered scrollable,
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// in pixels.
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private static float MIN_SCROLLABLE_DISTANCE;
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private static float getFloatPref(Map<String, Integer> prefs, String prefName, int defaultValue) {
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Integer value = (prefs == null ? null : prefs.get(prefName));
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return (float)(value == null || value < 0 ? defaultValue : value) / 1000f;
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}
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private static int getIntPref(Map<String, Integer> prefs, String prefName, int defaultValue) {
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Integer value = (prefs == null ? null : prefs.get(prefName));
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return (value == null || value < 0 ? defaultValue : value);
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}
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static void initPrefs() {
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JSONArray prefs = new JSONArray();
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prefs.put(PREF_SCROLLING_FRICTION_FAST);
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prefs.put(PREF_SCROLLING_FRICTION_SLOW);
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prefs.put(PREF_SCROLLING_MAX_EVENT_ACCELERATION);
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prefs.put(PREF_SCROLLING_OVERSCROLL_DECEL_RATE);
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prefs.put(PREF_SCROLLING_OVERSCROLL_SNAP_LIMIT);
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prefs.put(PREF_SCROLLING_MIN_SCROLLABLE_DISTANCE);
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PrefsHelper.getPrefs(prefs, new PrefsHelper.PrefHandlerBase() {
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Map<String, Integer> mPrefs = new HashMap<String, Integer>();
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@Override public void prefValue(String name, int value) {
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mPrefs.put(name, value);
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}
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@Override public void finish() {
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setPrefs(mPrefs);
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}
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});
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}
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static final float MS_PER_FRAME = 1000.0f / 60.0f;
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private static final float FRAMERATE_MULTIPLIER = (1000f/60f) / MS_PER_FRAME;
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// The values we use for friction are based on a 16.6ms frame, adjust them to MS_PER_FRAME:
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// FRICTION^1 = FRICTION_ADJUSTED^(16/MS_PER_FRAME)
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// FRICTION_ADJUSTED = e ^ ((ln(FRICTION))/FRAMERATE_MULTIPLIER)
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static float getFrameAdjustedFriction(float baseFriction) {
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return (float)Math.pow(Math.E, (Math.log(baseFriction) / FRAMERATE_MULTIPLIER));
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}
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static void setPrefs(Map<String, Integer> prefs) {
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FRICTION_SLOW = getFrameAdjustedFriction(getFloatPref(prefs, PREF_SCROLLING_FRICTION_SLOW, 850));
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FRICTION_FAST = getFrameAdjustedFriction(getFloatPref(prefs, PREF_SCROLLING_FRICTION_FAST, 970));
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VELOCITY_THRESHOLD = 10 / FRAMERATE_MULTIPLIER;
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MAX_EVENT_ACCELERATION = getFloatPref(prefs, PREF_SCROLLING_MAX_EVENT_ACCELERATION, 12);
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OVERSCROLL_DECEL_RATE = getFrameAdjustedFriction(getFloatPref(prefs, PREF_SCROLLING_OVERSCROLL_DECEL_RATE, 40));
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SNAP_LIMIT = getFloatPref(prefs, PREF_SCROLLING_OVERSCROLL_SNAP_LIMIT, 300);
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MIN_SCROLLABLE_DISTANCE = getFloatPref(prefs, PREF_SCROLLING_MIN_SCROLLABLE_DISTANCE, 500);
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Log.i(LOGTAG, "Prefs: " + FRICTION_SLOW + "," + FRICTION_FAST + "," + VELOCITY_THRESHOLD + ","
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+ MAX_EVENT_ACCELERATION + "," + OVERSCROLL_DECEL_RATE + "," + SNAP_LIMIT + "," + MIN_SCROLLABLE_DISTANCE);
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}
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static {
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// set the scrolling parameters to default values on startup
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setPrefs(null);
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}
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private enum FlingStates {
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STOPPED,
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PANNING,
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FLINGING,
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}
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private enum Overscroll {
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NONE,
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MINUS, // Overscrolled in the negative direction
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PLUS, // Overscrolled in the positive direction
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BOTH, // Overscrolled in both directions (page is zoomed to smaller than screen)
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}
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private final SubdocumentScrollHelper mSubscroller;
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private int mOverscrollMode; /* Default to only overscrolling if we're allowed to scroll in a direction */
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private float mFirstTouchPos; /* Position of the first touch event on the current drag. */
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private float mTouchPos; /* Position of the most recent touch event on the current drag. */
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private float mLastTouchPos; /* Position of the touch event before touchPos. */
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private float mVelocity; /* Velocity in this direction; pixels per animation frame. */
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private boolean mScrollingDisabled; /* Whether movement on this axis is locked. */
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private boolean mDisableSnap; /* Whether overscroll snapping is disabled. */
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private float mDisplacement;
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private FlingStates mFlingState = FlingStates.STOPPED; /* The fling state we're in on this axis. */
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protected abstract float getOrigin();
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protected abstract float getViewportLength();
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protected abstract float getPageStart();
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protected abstract float getPageLength();
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Axis(SubdocumentScrollHelper subscroller) {
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mSubscroller = subscroller;
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mOverscrollMode = View.OVER_SCROLL_IF_CONTENT_SCROLLS;
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}
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public void setOverScrollMode(int overscrollMode) {
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mOverscrollMode = overscrollMode;
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}
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public int getOverScrollMode() {
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return mOverscrollMode;
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}
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private float getViewportEnd() {
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return getOrigin() + getViewportLength();
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}
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private float getPageEnd() {
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return getPageStart() + getPageLength();
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}
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void startTouch(float pos) {
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mVelocity = 0.0f;
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mScrollingDisabled = false;
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mFirstTouchPos = mTouchPos = mLastTouchPos = pos;
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}
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float panDistance(float currentPos) {
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return currentPos - mFirstTouchPos;
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}
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void setScrollingDisabled(boolean disabled) {
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mScrollingDisabled = disabled;
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}
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void saveTouchPos() {
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mLastTouchPos = mTouchPos;
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}
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void updateWithTouchAt(float pos, float timeDelta) {
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float newVelocity = (mTouchPos - pos) / timeDelta * MS_PER_FRAME;
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// If there's a direction change, or current velocity is very low,
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// allow setting of the velocity outright. Otherwise, use the current
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// velocity and a maximum change factor to set the new velocity.
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boolean curVelocityIsLow = Math.abs(mVelocity) < 1.0f / FRAMERATE_MULTIPLIER;
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boolean directionChange = (mVelocity > 0) != (newVelocity > 0);
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if (curVelocityIsLow || (directionChange && !FloatUtils.fuzzyEquals(newVelocity, 0.0f))) {
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mVelocity = newVelocity;
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} else {
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float maxChange = Math.abs(mVelocity * timeDelta * MAX_EVENT_ACCELERATION);
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mVelocity = Math.min(mVelocity + maxChange, Math.max(mVelocity - maxChange, newVelocity));
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}
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mTouchPos = pos;
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}
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boolean overscrolled() {
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return getOverscroll() != Overscroll.NONE;
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}
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private Overscroll getOverscroll() {
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boolean minus = (getOrigin() < getPageStart());
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boolean plus = (getViewportEnd() > getPageEnd());
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if (minus && plus) {
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return Overscroll.BOTH;
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} else if (minus) {
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return Overscroll.MINUS;
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} else if (plus) {
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return Overscroll.PLUS;
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} else {
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return Overscroll.NONE;
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}
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}
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// Returns the amount that the page has been overscrolled. If the page hasn't been
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// overscrolled on this axis, returns 0.
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private float getExcess() {
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switch (getOverscroll()) {
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case MINUS: return getPageStart() - getOrigin();
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case PLUS: return getViewportEnd() - getPageEnd();
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case BOTH: return (getViewportEnd() - getPageEnd()) + (getPageStart() - getOrigin());
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default: return 0.0f;
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}
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}
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/*
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* Returns true if the page is zoomed in to some degree along this axis such that scrolling is
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* possible and this axis has not been scroll locked while panning. Otherwise, returns false.
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*/
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boolean scrollable() {
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// If we're scrolling a subdocument, ignore the viewport length restrictions (since those
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// apply to the top-level document) and only take into account axis locking.
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if (mSubscroller.scrolling()) {
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return !mScrollingDisabled;
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}
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// if we are axis locked, return false
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if (mScrollingDisabled) {
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return false;
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}
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// there is scrollable space, and we're not disabled, or the document fits the viewport
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// but we always allow overscroll anyway
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return getViewportLength() <= getPageLength() - MIN_SCROLLABLE_DISTANCE ||
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getOverScrollMode() == View.OVER_SCROLL_ALWAYS;
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}
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/*
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* Returns the resistance, as a multiplier, that should be taken into account when
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* tracking or pinching.
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*/
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float getEdgeResistance(boolean forPinching) {
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float excess = getExcess();
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if (excess > 0.0f && (getOverscroll() == Overscroll.BOTH || !forPinching)) {
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// excess can be greater than viewport length, but the resistance
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// must never drop below 0.0
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return Math.max(0.0f, SNAP_LIMIT - excess / getViewportLength());
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}
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return 1.0f;
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}
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/* Returns the velocity. If the axis is locked, returns 0. */
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float getRealVelocity() {
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return scrollable() ? mVelocity : 0f;
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}
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void startPan() {
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mFlingState = FlingStates.PANNING;
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}
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void startFling(boolean stopped) {
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mDisableSnap = mSubscroller.scrolling();
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if (stopped) {
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mFlingState = FlingStates.STOPPED;
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} else {
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mFlingState = FlingStates.FLINGING;
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}
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}
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/* Advances a fling animation by one step. */
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boolean advanceFling() {
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if (mFlingState != FlingStates.FLINGING) {
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return false;
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}
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if (mSubscroller.scrolling() && !mSubscroller.lastScrollSucceeded()) {
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// if the subdocument stopped scrolling, it's because it reached the end
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// of the subdocument. we don't do overscroll on subdocuments, so there's
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// no point in continuing this fling.
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return false;
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}
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float excess = getExcess();
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Overscroll overscroll = getOverscroll();
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boolean decreasingOverscroll = false;
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if ((overscroll == Overscroll.MINUS && mVelocity > 0) ||
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(overscroll == Overscroll.PLUS && mVelocity < 0))
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{
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decreasingOverscroll = true;
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}
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if (mDisableSnap || FloatUtils.fuzzyEquals(excess, 0.0f) || decreasingOverscroll) {
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// If we aren't overscrolled, just apply friction.
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if (Math.abs(mVelocity) >= VELOCITY_THRESHOLD) {
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mVelocity *= FRICTION_FAST;
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} else {
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float t = mVelocity / VELOCITY_THRESHOLD;
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mVelocity *= FloatUtils.interpolate(FRICTION_SLOW, FRICTION_FAST, t);
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}
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} else {
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// Otherwise, decrease the velocity linearly.
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float elasticity = 1.0f - excess / (getViewportLength() * SNAP_LIMIT);
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if (overscroll == Overscroll.MINUS) {
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mVelocity = Math.min((mVelocity + OVERSCROLL_DECEL_RATE) * elasticity, 0.0f);
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} else { // must be Overscroll.PLUS
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mVelocity = Math.max((mVelocity - OVERSCROLL_DECEL_RATE) * elasticity, 0.0f);
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}
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}
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return true;
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}
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void stopFling() {
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mVelocity = 0.0f;
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mFlingState = FlingStates.STOPPED;
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}
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// Performs displacement of the viewport position according to the current velocity.
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void displace() {
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// if this isn't scrollable just return
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if (!scrollable())
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return;
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if (mFlingState == FlingStates.PANNING)
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mDisplacement += (mLastTouchPos - mTouchPos) * getEdgeResistance(false);
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else
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mDisplacement += mVelocity * getEdgeResistance(false);
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// if overscroll is disabled and we're trying to overscroll, reset the displacement
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// to remove any excess. Using getExcess alone isn't enough here since it relies on
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// getOverscroll which doesn't take into account any new displacment being applied.
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// If we using a subscroller, we don't want to alter the scrolling being done
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if (getOverScrollMode() == View.OVER_SCROLL_NEVER && !mSubscroller.scrolling()) {
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if (mDisplacement + getOrigin() < getPageStart()) {
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mDisplacement = getPageStart() - getOrigin();
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stopFling();
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} else if (mDisplacement + getViewportEnd() > getPageEnd()) {
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mDisplacement = getPageEnd() - getViewportEnd();
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stopFling();
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}
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}
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}
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float resetDisplacement() {
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float d = mDisplacement;
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mDisplacement = 0.0f;
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return d;
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}
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void setAutoscrollVelocity(float velocity) {
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if (mFlingState != FlingStates.STOPPED) {
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Log.e(LOGTAG, "Setting autoscroll velocity while in a fling is not allowed!");
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return;
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}
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mVelocity = velocity;
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}
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}
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