SkAR Java: minor refactoring to TapHelper (now GestureHelper)

Bug: skia:
Change-Id: I1983c6cb1727e86fec91a0c9a5706f26070b1b49
Reviewed-on: https://skia-review.googlesource.com/144021
Reviewed-by: Mike Reed <reed@google.com>

1 files changed, 121 insertions, 0 deletions

diff --git a/platform_tools/android/apps/skar_java/src/main/java/com/google/skar/examples/helloskar/helpers/GestureHelper.java b/platform_tools/android/apps/skar_java/src/main/java/com/google/skar/examples/helloskar/helpers/GestureHelper.java
new file mode 100644
index 0000000000..2cd195fdb1
--- /dev/null
+++ b/platform_tools/android/apps/skar_java/src/main/java/com/google/skar/examples/helloskar/helpers/GestureHelper.java
@@ -0,0 +1,121 @@
+/*
+ * Copyright 2018 Google LLC All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.skar.examples.helloskar.helpers;
+
+import android.content.Context;
+import android.view.GestureDetector;
+import android.view.MotionEvent;
+import android.view.View;
+import android.view.View.OnTouchListener;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.BlockingQueue;
+
+/**
+ * Helper to detect gestures using Android GestureDetector, and pass the taps between UI thread and
+ * render thread.
+ */
+
+public final class GestureHelper implements OnTouchListener {
+    private final GestureDetector gestureDetector;
+    private final BlockingQueue<MotionEvent> queuedSingleTaps = new ArrayBlockingQueue<>(16);
+    private final BlockingQueue<ScrollEvent> queuedFingerHold = new ArrayBlockingQueue<>(16);
+    private boolean isScrolling = false;
+    private boolean previousScroll = true;
+
+    // Struct holding a MotionEvent obtained from onScroll() callbacks, and a boolean evaluating to
+    // true if the MotionEven was the start of the scrolling motion
+    public static class ScrollEvent {
+        public MotionEvent event;
+        public boolean isStartOfScroll;
+
+        public ScrollEvent(MotionEvent e, boolean isStartOfScroll) {
+            this.event = e;
+            this.isStartOfScroll = isStartOfScroll;
+        }
+    }
+
+    /**
+     * Creates the gesture helper.
+     *
+     * @param context the application's context.
+     */
+    public GestureHelper(Context context) {
+        gestureDetector =
+                new GestureDetector(
+                        context,
+                        new GestureDetector.SimpleOnGestureListener() {
+                            @Override
+                            public boolean onSingleTapUp(MotionEvent e) {
+                                // Queue tap if there is space. Tap is lost if queue is full.
+                                queuedSingleTaps.offer(e);
+                                return true;
+                            }
+
+                            @Override
+                            public boolean onScroll (MotionEvent e1, MotionEvent e2,
+                                                     float distanceX, float distanceY) {
+                                // Queue motion events when scrolling
+                                if (e2.getPointerCount() == 1 && e1.getPointerCount() == 1) {
+                                    previousScroll = isScrolling;
+                                    isScrolling = true;
+
+                                    queuedFingerHold.offer(new ScrollEvent(e2,
+                                                                           isStartedScrolling()));
+
+                                    return true;
+                                }
+                                return false;
+                            }
+
+
+                            @Override
+                            public boolean onDown(MotionEvent e) {
+                                return true;
+                            }
+                        });
+    }
+
+    /**
+     * Polls for a tap.
+     *
+     * @return if a tap was queued, a MotionEvent for the tap. Otherwise null if no taps are queued.
+     */
+    public MotionEvent poll() {
+        return queuedSingleTaps.poll();
+    }
+
+    /**
+     * Polls for a scrolling motion.
+     *
+     * @return if a scrolling event was queued, a ScrollEvent for the gesture. Otherwise null
+     */
+    public ScrollEvent holdPoll() { return queuedFingerHold.poll(); }
+
+    @Override
+    public boolean onTouch(View view, MotionEvent motionEvent) {
+        boolean val = gestureDetector.onTouchEvent(motionEvent);
+
+        // If finger is up + is scrolling: don't scroll anymore, and empty touch hold queue
+        if (motionEvent.getAction() == MotionEvent.ACTION_UP && isScrolling) {
+            previousScroll = true;
+            isScrolling = false;
+            queuedFingerHold.clear();
+        }
+        return val;
+    }
+    private boolean isStartedScrolling() { return isScrolling && !previousScroll; }
+}