1 files changed, 45 insertions, 4 deletions

diff --git a/core/java/android/inputmethodservice/InputMethodService.java b/core/java/android/inputmethodservice/InputMethodService.java
index 656aea18fe50..b46bb3257c86 100644
--- a/core/java/android/inputmethodservice/InputMethodService.java
+++ b/core/java/android/inputmethodservice/InputMethodService.java
@@ -143,6 +143,7 @@ import com.android.internal.inputmethod.ImeTracing;
 import com.android.internal.inputmethod.InputMethodNavButtonFlags;
 import com.android.internal.inputmethod.InputMethodPrivilegedOperations;
 import com.android.internal.inputmethod.InputMethodPrivilegedOperationsRegistry;
+import com.android.internal.util.RingBuffer;
 import com.android.internal.view.IInlineSuggestionsRequestCallback;
 import com.android.internal.view.IInputContext;
 import com.android.internal.view.InlineSuggestionsRequestInfo;
@@ -334,6 +335,17 @@ public class InputMethodService extends AbstractInputMethodService {
             "persist.sys.ime.can_render_gestural_nav_buttons";
 
     /**
+     * Number of {@link MotionEvent} to buffer if IME is not ready with Ink view.
+     * This number may be configured eventually based on device's touch sampling frequency.
+     */
+    private static final int MAX_EVENTS_BUFFER = 500;
+
+    /**
+     * A circular buffer of size MAX_EVENTS_BUFFER in case IME is taking too long to add ink view.
+     **/
+    private RingBuffer<MotionEvent> mPendingEvents;
+
+    /**
      * Returns whether {@link InputMethodService} is responsible for rendering the back button and
      * the IME switcher button or not when the gestural navigation is enabled.
      *
@@ -954,7 +966,8 @@ public class InputMethodService extends AbstractInputMethodService {
             mInkWindow.show();
 
             // deliver previous @param stylusEvents
-            stylusEvents.forEach(mInkWindow.getDecorView()::dispatchTouchEvent);
+            stylusEvents.forEach(InputMethodService.this::onStylusHandwritingMotionEvent);
+
             // create receiver for channel
             mHandwritingEventReceiver = new SimpleBatchedInputEventReceiver(
                     channel,
@@ -963,11 +976,11 @@ public class InputMethodService extends AbstractInputMethodService {
                         if (!(event instanceof MotionEvent)) {
                             return false;
                         }
-                        return mInkWindow.getDecorView().dispatchTouchEvent((MotionEvent) event);
+                        onStylusHandwritingMotionEvent((MotionEvent) event);
+                        return true;
                     });
         }
 
-
         /**
          * {@inheritDoc}
          * @hide
@@ -2357,7 +2370,8 @@ public class InputMethodService extends AbstractInputMethodService {
      *
      * If the IME supports handwriting for the current input, it should return {@code true},
      * ensure its inking views are attached to the {@link #getStylusHandwritingWindow()}, and handle
-     * stylus input received on the ink window via {@link #getCurrentInputConnection()}.
+     * stylus input received from {@link #onStylusHandwritingMotionEvent(MotionEvent)} on the
+     * {@link #getStylusHandwritingWindow()} via {@link #getCurrentInputConnection()}.
      * @return {@code true} if IME can honor the request, {@code false} if IME cannot at this time.
      */
     public boolean onStartStylusHandwriting() {
@@ -2366,6 +2380,33 @@ public class InputMethodService extends AbstractInputMethodService {
     }
 
     /**
+     * Called after {@link #onStartStylusHandwriting()} returns {@code true} for every Stylus
+     * {@link MotionEvent}.
+     * By default, this method forwards all {@link MotionEvent}s to the
+     * {@link #getStylusHandwritingWindow()} once its visible, however IME can override it to
+     * receive them sooner.
+     * @param motionEvent {@link MotionEvent} from stylus.
+     */
+    public void onStylusHandwritingMotionEvent(@NonNull MotionEvent motionEvent) {
+        if (mInkWindow.isInkViewVisible()) {
+            mInkWindow.getDecorView().dispatchTouchEvent(motionEvent);
+        } else {
+            if (mPendingEvents == null) {
+                mPendingEvents = new RingBuffer(MotionEvent.class, MAX_EVENTS_BUFFER);
+            }
+            mPendingEvents.append(motionEvent);
+            mInkWindow.setInkViewVisibilityListener(() -> {
+                if (mPendingEvents != null && !mPendingEvents.isEmpty()) {
+                    for (MotionEvent event : mPendingEvents.toArray()) {
+                        mInkWindow.getDecorView().dispatchTouchEvent(event);
+                    }
+                    mPendingEvents.clear();
+                }
+            });
+        }
+    }
+
+    /**
      * Called when the current stylus handwriting session was finished (either by the system or
      * via {@link #finishStylusHandwriting()}.
      *