android/source/src/java/org/mozilla/gecko/gfx/SubdocumentScrollHelper.java

   1 /* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
   2  * This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 package org.mozilla.gecko.gfx;
   7
   8 import android.graphics.PointF;
   9 import android.os.Handler;
  10
  11 class SubdocumentScrollHelper {
  12     private static final String LOGTAG = "GeckoSubdocumentScrollHelper";
  13
  14     private final Handler mUiHandler;
  15
  16     /* This is the amount of displacement we have accepted but not yet sent to JS; this is
  17      * only valid when mOverrideScrollPending is true. */
  18     private final PointF mPendingDisplacement;
  19
  20     /* When this is true, we're sending scroll events to JS to scroll the active subdocument. */
  21     private boolean mOverridePanning;
  22
  23     /* When this is true, we have received an ack for the last scroll event we sent to JS, and
  24      * are ready to send the next scroll event. Note we only ever have one scroll event inflight
  25      * at a time. */
  26     private boolean mOverrideScrollAck;
  27
  28     /* When this is true, we have a pending scroll that we need to send to JS; we were unable
  29      * to send it when it was initially requested because mOverrideScrollAck was not true. */
  30     private boolean mOverrideScrollPending;
  31
  32     /* When this is true, the last scroll event we sent actually did some amount of scrolling on
  33      * the subdocument; we use this to decide when we have reached the end of the subdocument. */
  34     private boolean mScrollSucceeded;
  35
  36     SubdocumentScrollHelper() {
  37         // mUiHandler will be bound to the UI thread since that's where this constructor runs
  38         mUiHandler = new Handler();
  39         mPendingDisplacement = new PointF();
  40     }
  41
  42     void destroy() {
  43     }
  44
  45     boolean scrollBy(PointF displacement) {
  46         if (! mOverridePanning) {
  47             return false;
  48         }
  49
  50         if (! mOverrideScrollAck) {
  51             mOverrideScrollPending = true;
  52             mPendingDisplacement.x += displacement.x;
  53             mPendingDisplacement.y += displacement.y;
  54             return true;
  55         }
  56
  57         mOverrideScrollAck = false;
  58         mOverrideScrollPending = false;
  59         // clear the |mPendingDisplacement| after serializing |displacement| to
  60         // JSON because they might be the same object
  61         mPendingDisplacement.x = 0;
  62         mPendingDisplacement.y = 0;
  63
  64         return true;
  65     }
  66
  67     void cancel() {
  68         mOverridePanning = false;
  69     }
  70
  71     boolean scrolling() {
  72         return mOverridePanning;
  73     }
  74
  75     boolean lastScrollSucceeded() {
  76         return mScrollSucceeded;
  77     }
  78 }