| 1 | // Copyright (c) 2013 The Chromium Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | package org.chromium.content.browser; |
| 6 | |
| 7 | import android.content.Context; |
| 8 | import android.util.DisplayMetrics; |
| 9 | import android.util.Log; |
| 10 | import android.view.MotionEvent; |
| 11 | |
| 12 | /** |
| 13 | * This objects controls the scroll snapping behavior based on scroll updates. |
| 14 | */ |
| 15 | class SnapScrollController { |
| 16 | private static final String TAG = "SnapScrollController"; |
| 17 | private static final int SNAP_NONE = 0; |
| 18 | private static final int SNAP_HORIZ = 1; |
| 19 | private static final int SNAP_VERT = 2; |
| 20 | private static final int SNAP_BOUND = 16; |
| 21 | |
| 22 | private float mChannelDistance = 16f; |
| 23 | private int mSnapScrollMode = SNAP_NONE; |
| 24 | private int mFirstTouchX = -1; |
| 25 | private int mFirstTouchY = -1; |
| 26 | private float mDistanceX = 0; |
| 27 | private float mDistanceY = 0; |
| 28 | private ZoomManager mZoomManager; |
| 29 | |
| 30 | SnapScrollController(Context context, ZoomManager zoomManager) { |
| 31 | calculateChannelDistance(context); |
| 32 | mZoomManager = zoomManager; |
| 33 | } |
| 34 | |
| 35 | /** |
| 36 | * Updates the snap scroll mode based on the given X and Y distance to be moved on scroll. |
| 37 | * If the scroll update is above a threshold, the snapping behavior is reset. |
| 38 | * @param distanceX X distance for the current scroll update. |
| 39 | * @param distanceY Y distance for the current scroll update. |
| 40 | */ |
| 41 | void updateSnapScrollMode(float distanceX, float distanceY) { |
| 42 | if (mSnapScrollMode == SNAP_HORIZ || mSnapScrollMode == SNAP_VERT) { |
| 43 | mDistanceX += Math.abs(distanceX); |
| 44 | mDistanceY += Math.abs(distanceY); |
| 45 | if (mSnapScrollMode == SNAP_HORIZ) { |
| 46 | if (mDistanceY > mChannelDistance) { |
| 47 | mSnapScrollMode = SNAP_NONE; |
| 48 | } else if (mDistanceX > mChannelDistance) { |
| 49 | mDistanceX = 0; |
| 50 | mDistanceY = 0; |
| 51 | } |
| 52 | } else { |
| 53 | if (mDistanceX > mChannelDistance) { |
| 54 | mSnapScrollMode = SNAP_NONE; |
| 55 | } else if (mDistanceY > mChannelDistance) { |
| 56 | mDistanceX = 0; |
| 57 | mDistanceY = 0; |
| 58 | } |
| 59 | } |
| 60 | } |
| 61 | } |
| 62 | |
| 63 | /** |
| 64 | * Sets the snap scroll mode based on the event type. |
| 65 | * @param event The received MotionEvent. |
| 66 | */ |
| 67 | void setSnapScrollingMode(MotionEvent event) { |
| 68 | switch(event.getAction()) { |
| 69 | case MotionEvent.ACTION_DOWN: |
| 70 | mSnapScrollMode = SNAP_NONE; |
| 71 | mFirstTouchX = (int) event.getX(); |
| 72 | mFirstTouchY = (int) event.getY(); |
| 73 | break; |
| 74 | // Set scrolling mode to SNAP_X if scroll towards x-axis exceeds SNAP_BOUND |
| 75 | // and movement towards y-axis is trivial. |
| 76 | // Set scrolling mode to SNAP_Y if scroll towards y-axis exceeds SNAP_BOUND |
| 77 | // and movement towards x-axis is trivial. |
| 78 | // Scrolling mode will remain in SNAP_NONE for other conditions. |
| 79 | case MotionEvent.ACTION_MOVE: |
| 80 | if (!mZoomManager.isScaleGestureDetectionInProgress() && |
| 81 | mSnapScrollMode == SNAP_NONE) { |
| 82 | int xDiff = (int) Math.abs(event.getX() - mFirstTouchX); |
| 83 | int yDiff = (int) Math.abs(event.getY() - mFirstTouchY); |
| 84 | if (xDiff > SNAP_BOUND && yDiff < SNAP_BOUND) { |
| 85 | mSnapScrollMode = SNAP_HORIZ; |
| 86 | } else if (xDiff < SNAP_BOUND && yDiff > SNAP_BOUND) { |
| 87 | mSnapScrollMode = SNAP_VERT; |
| 88 | } |
| 89 | } |
| 90 | break; |
| 91 | case MotionEvent.ACTION_UP: |
| 92 | case MotionEvent.ACTION_CANCEL: |
| 93 | mFirstTouchX = -1; |
| 94 | mFirstTouchY = -1; |
| 95 | mDistanceX = 0; |
| 96 | mDistanceY = 0; |
| 97 | break; |
| 98 | default: |
| 99 | Log.i(TAG, "setSnapScrollingMode case-default no-op"); |
| 100 | break; |
| 101 | } |
| 102 | } |
| 103 | |
| 104 | private void calculateChannelDistance(Context context) { |
| 105 | // The channel distance is adjusted for density and screen size. |
| 106 | final DisplayMetrics metrics = context.getResources().getDisplayMetrics(); |
| 107 | final double screenSize = Math.hypot((double) metrics.widthPixels / metrics.densityDpi, |
| 108 | (double) metrics.heightPixels / metrics.densityDpi); |
| 109 | if (screenSize < 3.0) { |
| 110 | mChannelDistance = 16f; |
| 111 | } else if (screenSize < 5.0) { |
| 112 | mChannelDistance = 22f; |
| 113 | } else if (screenSize < 7.0) { |
| 114 | mChannelDistance = 28f; |
| 115 | } else { |
| 116 | mChannelDistance = 34f; |
| 117 | } |
| 118 | mChannelDistance = mChannelDistance * metrics.density; |
| 119 | if (mChannelDistance < 16f) mChannelDistance = 16f; |
| 120 | } |
| 121 | |
| 122 | /** |
| 123 | * Resets the snap scroll mode to default. |
| 124 | */ |
| 125 | void resetSnapScrollMode() { |
| 126 | mSnapScrollMode = SNAP_NONE; |
| 127 | } |
| 128 | |
| 129 | /** |
| 130 | * @return Whether current snap scroll mode is vertical. |
| 131 | */ |
| 132 | boolean isSnapVertical() { |
| 133 | return mSnapScrollMode == SNAP_VERT; |
| 134 | } |
| 135 | |
| 136 | /** |
| 137 | * @return Whether current snap scroll mode is horizontal. |
| 138 | */ |
| 139 | boolean isSnapHorizontal() { |
| 140 | return mSnapScrollMode == SNAP_HORIZ; |
| 141 | } |
| 142 | |
| 143 | /** |
| 144 | * @return Whether currently snapping scrolls. |
| 145 | */ |
| 146 | boolean isSnappingScrolls() { |
| 147 | return mSnapScrollMode != SNAP_NONE; |
| 148 | } |
| 149 | } |