1 /* 2 * Copyright 2018 Google LLC All Rights Reserved. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.skar.examples.helloskar.helpers; 18 19 import android.content.Context; 20 import android.view.GestureDetector; 21 import android.view.MotionEvent; 22 import android.view.View; 23 import android.view.View.OnTouchListener; 24 import java.util.concurrent.ArrayBlockingQueue; 25 import java.util.concurrent.BlockingQueue; 26 27 /** 28 * Helper to detect gestures using Android GestureDetector, and pass the taps between UI thread and 29 * render thread. 30 */ 31 32 public final class GestureHelper implements OnTouchListener { 33 private final GestureDetector gestureDetector; 34 private final BlockingQueue<MotionEvent> queuedSingleTaps = new ArrayBlockingQueue<>(16); 35 private final BlockingQueue<ScrollEvent> queuedFingerHold = new ArrayBlockingQueue<>(16); 36 private boolean isScrolling = false; 37 private boolean previousScroll = true; 38 39 // Struct holding a MotionEvent obtained from onScroll() callbacks, and a boolean evaluating to 40 // true if the MotionEven was the start of the scrolling motion 41 public static class ScrollEvent { 42 public MotionEvent event; 43 public boolean isStartOfScroll; 44 ScrollEvent(MotionEvent e, boolean isStartOfScroll)45 public ScrollEvent(MotionEvent e, boolean isStartOfScroll) { 46 this.event = e; 47 this.isStartOfScroll = isStartOfScroll; 48 } 49 } 50 51 /** 52 * Creates the gesture helper. 53 * 54 * @param context the application's context. 55 */ GestureHelper(Context context)56 public GestureHelper(Context context) { 57 gestureDetector = 58 new GestureDetector( 59 context, 60 new GestureDetector.SimpleOnGestureListener() { 61 @Override 62 public boolean onSingleTapUp(MotionEvent e) { 63 // Queue tap if there is space. Tap is lost if queue is full. 64 queuedSingleTaps.offer(e); 65 return true; 66 } 67 68 @Override 69 public boolean onScroll (MotionEvent e1, MotionEvent e2, 70 float distanceX, float distanceY) { 71 // Queue motion events when scrolling 72 if (e2.getPointerCount() == 1 && e1.getPointerCount() == 1) { 73 previousScroll = isScrolling; 74 isScrolling = true; 75 76 queuedFingerHold.offer(new ScrollEvent(e2, 77 isStartedScrolling())); 78 79 return true; 80 } 81 return false; 82 } 83 84 85 @Override 86 public boolean onDown(MotionEvent e) { 87 return true; 88 } 89 }); 90 } 91 92 /** 93 * Polls for a tap. 94 * 95 * @return if a tap was queued, a MotionEvent for the tap. Otherwise null if no taps are queued. 96 */ poll()97 public MotionEvent poll() { 98 return queuedSingleTaps.poll(); 99 } 100 101 /** 102 * Polls for a scrolling motion. 103 * 104 * @return if a scrolling event was queued, a ScrollEvent for the gesture. Otherwise null 105 */ holdPoll()106 public ScrollEvent holdPoll() { return queuedFingerHold.poll(); } 107 108 @Override onTouch(View view, MotionEvent motionEvent)109 public boolean onTouch(View view, MotionEvent motionEvent) { 110 boolean val = gestureDetector.onTouchEvent(motionEvent); 111 112 // If finger is up + is scrolling: don't scroll anymore, and empty touch hold queue 113 if (motionEvent.getAction() == MotionEvent.ACTION_UP && isScrolling) { 114 previousScroll = true; 115 isScrolling = false; 116 queuedFingerHold.clear(); 117 } 118 return val; 119 } isStartedScrolling()120 private boolean isStartedScrolling() { return isScrolling && !previousScroll; } 121 } 122