1 files changed, 92 insertions, 0 deletions
diff --git a/core/java/android/view/InputEventAssigner.java b/core/java/android/view/InputEventAssigner.java
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+++ b/core/java/android/view/InputEventAssigner.java
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+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * 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 android.view;
+
+import static android.os.IInputConstants.INVALID_INPUT_EVENT_ID;
+import static android.view.InputDevice.SOURCE_TOUCHSCREEN;
+
+/**
+ * Process input events and assign input event id to a specific frame.
+ *
+ * The assigned input event id is determined by where the current gesture is relative to the vsync.
+ * In the middle of the gesture (we already processed some input events, and already received at
+ * least 1 vsync), the latest InputEvent is assigned to the next frame.
+ * If a gesture just started, then the ACTION_DOWN event will be assigned to the next frame.
+ *
+ * Consider the following sequence:
+ * DOWN -> VSYNC 1 -> MOVE 1 -> MOVE 2 -> VSYNC 2.
+ *
+ * For VSYNC 1, we will assign the "DOWN" input event.
+ * For VSYNC 2, we will assign the "MOVE 2" input event.
+ *
+ * Consider another sequence:
+ * DOWN -> MOVE 1 -> MOVE 2 -> VSYNC 1 -> MOVE 3 -> VSYNC 2.
+ *
+ * For VSYNC 1, we will still assign the "DOWN" input event. That means that "MOVE 1" and "MOVE 2"
+ * events are not attributed to any frame.
+ * For VSYNC 2, the "MOVE 3" input event will be assigned.
+ *
+ * @hide
+ */
+public class InputEventAssigner {
+    private static final String TAG = "InputEventAssigner";
+    private boolean mHasUnprocessedDown = false;
+    private int mEventId = INVALID_INPUT_EVENT_ID;
+
+    /**
+     * Notify InputEventAssigner that the Choreographer callback has been processed. This will reset
+     * the 'down' state to assign the latest input event to the current frame.
+     */
+    public void onChoreographerCallback() {
+        // Mark completion of this frame. Use newest input event from now on.
+        mHasUnprocessedDown = false;
+    }
+
+    /**
+     * Process the provided input event to determine which event id to assign to the current frame.
+     * @param event the input event currently being processed
+     * @return the id of the input event to use for the current frame
+     */
+    public int processEvent(InputEvent event) {
+        if (event instanceof KeyEvent) {
+            // We will not do any special handling for key events
+            return event.getId();
+        }
+
+        if (event instanceof MotionEvent) {
+            MotionEvent motionEvent = (MotionEvent) event;
+            final int action = motionEvent.getActionMasked();
+
+            if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
+                mHasUnprocessedDown = false;
+            }
+            if (motionEvent.isFromSource(SOURCE_TOUCHSCREEN) && action == MotionEvent.ACTION_DOWN) {
+                mHasUnprocessedDown = true;
+                mEventId = event.getId();
+                // This will remain 'true' even if we receive a MOVE event, as long as choreographer
+                // hasn't invoked the 'CALLBACK_INPUT' callback.
+            }
+            // Don't update the event id if we haven't processed DOWN yet.
+            if (!mHasUnprocessedDown) {
+                mEventId = event.getId();
+            }
+            return mEventId;
+        }
+
+        throw new IllegalArgumentException("Received unexpected " + event);
+    }
+}