Reland "[vr] Tune scroll event stream"

This is a reland of 0e9a15da

In this reland, I've combined the change with https://crrev.com/c/1124405
since the smoothing in the original CL was actually just a scaling.

Original change's description:
> [vr] Tune scroll event stream
>
> This change applies three heuristics to make trackpad scrolling feel
> smoother. We increase the frequency at which we submit scroll events to
> the platform, we also decrease the scroll scale factor (to make the
> scrolls less jumpy), and we do some simple filtering of our scroll
> values.
>
> I pair-programmed much of this change with asimjour@ and he wrote the
> initial code to interpolate events in the android ui gesture target.
>
> Bug: 859075
> Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:linux_vr;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
> Change-Id: I2fe42940214d01d99618ddacd182f202ff271dad
> Reviewed-on: https://chromium-review.googlesource.com/1120425
> Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
> Commit-Queue: Ian Vollick <vollick@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#571535}

Bug: 859075
Change-Id: Ib1a9f801c6930b709624233d8e00aeabc59f576d
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:linux_vr;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/1124908Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: Amirhossein Simjour <asimjour@chromium.org>
Commit-Queue: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572364}

chrome/android/java/src/org/chromium/chrome/browser/vr_shell/AndroidUiGestureTarget.java

@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser.vr_shell;
 
+import android.os.Handler;
 import android.view.InputDevice;
 import android.view.MotionEvent;
 import android.view.View;
@@ -38,6 +39,19 @@ public class AndroidUiGestureTarget {
                 0 /* index */, x, y, 0 /* id */, MotionEvent.TOOL_TYPE_STYLUS);
     }
 
+    @CalledByNative
+    private void setDelayedEvent(int x, int y, int action, long timeInMs, int delayMs) {
+        new Handler().postDelayed(new Runnable() {
+            @Override
+            public void run() {
+                mMotionEventSynthesizer.setPointer(
+                        0 /* index */, x, y, 0 /* id */, MotionEvent.TOOL_TYPE_STYLUS);
+                mMotionEventSynthesizer.inject(action, 1 /* pointerCount */, timeInMs + delayMs,
+                        InputDevice.SOURCE_CLASS_POINTER);
+            }
+        }, delayMs);
+    }
+
     @CalledByNative
     private long getNativeObject() {
         return mNativePointer;

chrome/browser/android/vr/android_ui_gesture_target.cc

@@ -16,6 +16,9 @@ using base::android::JavaParamRef;
 using base::android::JavaRef;
 using content::MotionEventAction;
 
+static constexpr int kFrameDurationMs = 16;
+static constexpr int kScrollEventsPerFrame = 2;
+
 namespace vr {
 
 AndroidUiGestureTarget::AndroidUiGestureTarget(JNIEnv* env,
@@ -77,12 +80,21 @@ void AndroidUiGestureTarget::DispatchWebInputEvent(
       SetPointer(scroll_x_, scroll_y_);
       Inject(content::MOTION_EVENT_ACTION_END, event_time_ms);
       break;
-    case blink::WebGestureEvent::kGestureScrollUpdate:
-      scroll_x_ += (scroll_ratio_ * gesture->data.scroll_update.delta_x);
-      scroll_y_ += (scroll_ratio_ * gesture->data.scroll_update.delta_y);
+    case blink::WebGestureEvent::kGestureScrollUpdate: {
+      float scale = scroll_ratio_ / kScrollEventsPerFrame;
+      scroll_x_ += gesture->data.scroll_update.delta_x * scale;
+      scroll_y_ += gesture->data.scroll_update.delta_y * scale;
+
       SetPointer(scroll_x_, scroll_y_);
       Inject(content::MOTION_EVENT_ACTION_MOVE, event_time_ms);
+
+      scroll_x_ += gesture->data.scroll_update.delta_x * scale;
+      scroll_y_ += gesture->data.scroll_update.delta_y * scale;
+      SetDelayedEvent(scroll_x_, scroll_y_, content::MOTION_EVENT_ACTION_MOVE,
+                      event_time_ms, kFrameDurationMs / kScrollEventsPerFrame);
+
       break;
+    }
     case blink::WebGestureEvent::kGestureTapDown:
       SetPointer(gesture->PositionInWidget().x, gesture->PositionInWidget().y);
       Inject(content::MOTION_EVENT_ACTION_START, event_time_ms);
@@ -146,6 +158,21 @@ void AndroidUiGestureTarget::SetPointer(int x, int y) {
                                          y * scale_factor_);
 }
 
+void AndroidUiGestureTarget::SetDelayedEvent(int x,
+                                             int y,
+                                             MotionEventAction action,
+                                             int64_t time_ms,
+                                             int delay_ms) {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  base::android::ScopedJavaLocalRef<jobject> obj = java_ref_.get(env);
+  if (obj.is_null())
+    return;
+
+  Java_AndroidUiGestureTarget_setDelayedEvent(env, obj, x * scale_factor_,
+                                              y * scale_factor_, action,
+                                              time_ms, delay_ms);
+}
+
 // static
 AndroidUiGestureTarget* AndroidUiGestureTarget::FromJavaObject(
     const JavaRef<jobject>& obj) {

chrome/browser/android/vr/android_ui_gesture_target.h

@@ -34,6 +34,11 @@ class AndroidUiGestureTarget {
  private:
   void Inject(content::MotionEventAction action, int64_t time_ms);
   void SetPointer(int x, int y);
+  void SetDelayedEvent(int x,
+                       int y,
+                       content::MotionEventAction action,
+                       int64_t time_ms,
+                       int delay_ms);
 
   int scroll_x_ = 0;
   int scroll_y_ = 0;

chrome/browser/vr/gesture_detector.cc

@@ -11,7 +11,7 @@ namespace vr {
 
 namespace {
 
-constexpr float kDisplacementScaleFactor = 300.0f;
+constexpr float kDisplacementScaleFactor = 129.0f;
 
 constexpr int kMaxNumOfExtrapolations = 2;