Enable scrolling of UI elements.

chrome/browser/android/vr_shell/vr_shell_gl.cc

Index: chrome/browser/android/vr_shell/vr_shell_gl.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell_gl.cc b/chrome/browser/android/vr_shell/vr_shell_gl.cc
index 0277e5bd2d4c50c63eae9f2f71326bb90b7abaf3..1ebd6b2b0e1eb5f0e9c5a6ca26500cf563a1ce67 100644
--- a/chrome/browser/android/vr_shell/vr_shell_gl.cc
+++ b/chrome/browser/android/vr_shell/vr_shell_gl.cc
@@ -528,8 +528,19 @@ void VrShellGl::UpdateController(const gvr::Vec3f& forward_vector) {
 
       target_point_ = plane_intersection_point;
       target_element_ = plane.get();
-      input_target = (plane->fill == Fill::CONTENT) ? InputTarget::CONTENT
-                                                    : InputTarget::UI;
+      // For now treat UI elements, which do not show web content, as NONE input
+      // targets since they cannot make use of the input anyway.
+      switch (plane->fill) {
+        case Fill::CONTENT:
+          input_target = InputTarget::CONTENT;
+          break;
+        case Fill::SPRITE:
+          input_target = InputTarget::UI;
+          break;
+        default:
+          input_target = InputTarget::NONE;
+          break;
+      }
     }
   }
   SendEventsToTarget(input_target, pixel_x, pixel_y);
@@ -552,22 +563,64 @@ void VrShellGl::SendEventsToTarget(InputTarget input_target,
     gesture_list.push_back(std::move(event));
   }
 
+  // Make sure the user can switch to another input target while scrolling. To
+  // make this switch work we have to send an artificial scroll end event to the
+  // previous target and an artificial scroll begin event to the new target.
+  // Otherwise we will crash.

[cjgrant, 2017/02/13 15:54:51]

No need for the last line here, it's implied.

[tiborg, 2017/02/13 22:15:26]

I reset this due to changes in the scrolling behavior. See asimjour1's comment.

+  if (is_scrolling_ && current_input_target_ != input_target) {
+    if (current_input_target_ != InputTarget::NONE) {
+      // End the scrolling on the previous target.

[mthiesse, 2017/02/13 15:47:08]

Can you merge these two blocks with the "// Hover support" blocks?

[cjgrant, 2017/02/13 15:54:51]

+1. Anything that makes switching input target from one element to another ought
to be centralized.

[tiborg, 2017/02/13 22:15:26]

I reset this due to changes in the scrolling behavior. See asimjour1's comment.

+      std::unique_ptr<WebGestureEvent> scrollEndEvent(
+          new WebGestureEvent(WebInputEvent::GestureScrollEnd,
+                              WebInputEvent::NoModifiers, timestamp));
+      scrollEndEvent->sourceDevice = blink::WebGestureDeviceTouchpad;
+      SendGesture(current_input_target_, std::move(scrollEndEvent));
+    }
+    if (input_target != InputTarget::NONE) {
+      // Start scrolling on the new target.
+      std::unique_ptr<WebGestureEvent> scrollBeginEvent(
+          new WebGestureEvent(WebInputEvent::GestureScrollBegin,
+                              WebInputEvent::NoModifiers, timestamp));
+      scrollBeginEvent->sourceDevice = blink::WebGestureDeviceTouchpad;
+      scrollBeginEvent->x = pixel_x;
+      scrollBeginEvent->y = pixel_y;
+      SendGesture(input_target, std::move(scrollBeginEvent));
+    }
+  }
+
   for (const auto& gesture : gesture_list) {
+    gesture->x = pixel_x;
+    gesture->y = pixel_y;
+    auto movableGesture = base::WrapUnique(new WebGestureEvent(*gesture));
+
     switch (gesture->type()) {
       case WebInputEvent::GestureScrollBegin:
+        is_scrolling_ = true;
+        if (input_target != InputTarget::NONE) {
+          SendGesture(input_target, std::move(movableGesture));
+        }
+        break;
       case WebInputEvent::GestureScrollUpdate:
+        if (input_target != InputTarget::NONE) {
+          SendGesture(input_target, std::move(movableGesture));
+        }
+        break;
       case WebInputEvent::GestureScrollEnd:
+        if (input_target != InputTarget::NONE) {
+          SendGesture(input_target, std::move(movableGesture));
+        }
+        is_scrolling_ = false;
+        break;
       case WebInputEvent::GestureFlingCancel:
       case WebInputEvent::GestureFlingStart:
-        SendGesture(InputTarget::CONTENT,
-                    base::WrapUnique(new WebGestureEvent(*gesture)));
+        if (input_target != InputTarget::NONE) {
+          SendGesture(input_target, std::move(movableGesture));
+        }
         break;
       case WebInputEvent::GestureTapDown:
-        gesture->x = pixel_x;
-        gesture->y = pixel_y;
-        if (input_target != InputTarget::NONE)
-          SendGesture(input_target,
-                      base::WrapUnique(new WebGestureEvent(*gesture)));
+        if (input_target != InputTarget::NONE) {
+          SendGesture(input_target, std::move(movableGesture));
+        }
         break;
       case WebInputEvent::Undefined:
         break;