Revert "[vr] Ensure that hit testing uses the same stacking order as rendering"

This reverts commit 053d939f.

Reason for revert: Hit testing artifacts.

Original change's description:
> [vr] Ensure that hit testing uses the same stacking order as rendering
>
> The rendering code was updated to sort elements in tree rather than
> depth order in this cl:
> https://chromium-review.googlesource.com/c/chromium/src/+/727342
>
> The hit testing code, however, was not similarly updated. Consequently,
> there can be discrepancies. This CL updates the hit testing code to
> use nearly the same stacking order as rendering. Note: it is not quite
> perfect because the ui renderer still summons swaths of elements from
> the scene explicitly. Eventually, the ui renderer will simply sort
> and render all elements in the tree and these will be truly identical.
> However, until then, this ensures we do use the same element sorting
> routines.
>
> Bug: None
> Change-Id: I12483713f19b678aa9a69b91e5d910e408b73007
> Reviewed-on: https://chromium-review.googlesource.com/754554
> Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
> Commit-Queue: Ian Vollick <vollick@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#514136}

TBR=vollick@chromium.org,mthiesse@chromium.org,cjgrant@chromium.org

Change-Id: I920d8ffcb2dc7aad53ed021d272302cad060f083
Reviewed-on: https://chromium-review.googlesource.com/763007
Commit-Queue: Ian Vollick <vollick@chromium.org>
Reviewed-by: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515465}

chrome/browser/vr/ui_input_manager.cc

@@ -6,12 +6,10 @@
 
 #include <algorithm>
 
-#include "base/containers/adapters.h"
 #include "base/macros.h"
 #include "chrome/browser/vr/elements/ui_element.h"
 #include "chrome/browser/vr/model/controller_model.h"
 #include "chrome/browser/vr/model/reticle_model.h"
-#include "chrome/browser/vr/ui_renderer.h"
 #include "chrome/browser/vr/ui_scene.h"
 // TODO(tiborg): Remove include once we use a generic type to pass scroll/fling
 // gestures.
@@ -53,6 +51,7 @@ bool IsScrollEvent(const GestureList& list) {
 
 bool GetTargetLocalPoint(const gfx::Vector3dF& eye_to_target,
                          const UiElement& element,
+                         float max_distance_to_plane,
                          gfx::PointF* out_target_local_point,
                          gfx::Point3F* out_target_point,
                          float* out_distance_to_plane) {
@@ -60,7 +59,8 @@ bool GetTargetLocalPoint(const gfx::Vector3dF& eye_to_target,
     return false;
   }
 
-  if (*out_distance_to_plane < 0) {
+  if (*out_distance_to_plane < 0 ||
+      *out_distance_to_plane >= max_distance_to_plane) {
     return false;
   }
 
@@ -74,6 +74,37 @@ bool GetTargetLocalPoint(const gfx::Vector3dF& eye_to_target,
   return true;
 }
 
+void HitTestElements(UiElement* element,
+                     ReticleModel* reticle_model,
+                     gfx::Vector3dF* out_eye_to_target,
+                     float* out_closest_element_distance) {
+  for (auto& child : element->children()) {
+    HitTestElements(child.get(), reticle_model, out_eye_to_target,
+                    out_closest_element_distance);
+  }
+
+  if (!element->IsHitTestable()) {
+    return;
+  }
+
+  gfx::PointF local_point;
+  gfx::Point3F plane_intersection_point;
+  float distance_to_plane;
+  if (!GetTargetLocalPoint(*out_eye_to_target, *element,
+                           *out_closest_element_distance, &local_point,
+                           &plane_intersection_point, &distance_to_plane)) {
+    return;
+  }
+  if (!element->HitTest(local_point)) {
+    return;
+  }
+
+  *out_closest_element_distance = distance_to_plane;
+  reticle_model->target_point = plane_intersection_point;
+  reticle_model->target_element_id = element->id();
+  reticle_model->target_local_point = local_point;
+}
+
 }  // namespace
 
 UiInputManager::UiInputManager(UiScene* scene) : scene_(scene) {}
@@ -99,6 +130,7 @@ void UiInputManager::HandleInput(base::TimeTicks current_time,
       gfx::Point3F plane_intersection_point;
       float distance_to_plane;
       if (!GetTargetLocalPoint(eye_to_target, *target_element,
+                               2 * scene_->background_distance(),
                                &reticle_model->target_local_point,
                                &plane_intersection_point, &distance_to_plane)) {
         reticle_model->target_local_point = kInvalidTargetPoint;
@@ -371,37 +403,13 @@ void UiInputManager::GetVisualTargetElement(
   *out_eye_to_target = reticle_model->target_point - kOrigin;
   out_eye_to_target->GetNormalized(out_eye_to_target);
 
-  std::vector<const UiElement*> elements;
-  for (auto& element : scene_->root_element()) {
-    if (element.IsVisible()) {
-      elements.push_back(&element);
-    }
-  }
-
-  std::vector<const UiElement*> sorted =
-      UiRenderer::GetElementsInDrawOrder(elements);
-
-  for (const auto* element : base::Reversed(sorted)) {
-    if (!element->IsHitTestable()) {
-      continue;
-    }
+  // Determine which UI element (if any) intersects the line between the eyes
+  // and the controller target position.
+  float closest_element_distance =
+      (reticle_model->target_point - kOrigin).Length();
 
-    gfx::PointF local_point;
-    gfx::Point3F plane_intersection_point;
-    float distance_to_plane;
-    if (!GetTargetLocalPoint(*out_eye_to_target, *element, &local_point,
-                             &plane_intersection_point, &distance_to_plane)) {
-      continue;
-    }
-    if (!element->HitTest(local_point)) {
-      continue;
-    }
-
-    reticle_model->target_point = plane_intersection_point;
-    reticle_model->target_element_id = element->id();
-    reticle_model->target_local_point = local_point;
-    break;
-  }
+  HitTestElements(&scene_->root_element(), reticle_model, out_eye_to_target,
+                  &closest_element_distance);
 }
 
 void UiInputManager::UpdateQuiescenceState(

chrome/browser/vr/ui_input_manager_unittest.cc

@@ -265,42 +265,6 @@ TEST_F(UiInputManagerContentTest, NoMouseMovesDuringClick) {
                               &gesture_list);
 }
 
-TEST_F(UiInputManagerContentTest, TreeVsZOrder) {
-  EXPECT_TRUE(AnimateBy(MsToDelta(500)));
-  // It would be nice if the controller weren't platform specific and we could
-  // mock out the underlying sensor data. For now, we will hallucinate
-  // parameters to HandleInput.
-  UiElement* content_quad =
-      scene_->GetUiElementByName(UiElementName::kContentQuad);
-  gfx::Point3F content_quad_center;
-  content_quad->world_space_transform().TransformPoint(&content_quad_center);
-  gfx::Point3F origin;
-
-  ControllerModel controller_model;
-  controller_model.laser_direction = content_quad_center - origin;
-  controller_model.laser_origin = origin;
-  controller_model.touchpad_button_state = UiInputManager::ButtonState::DOWN;
-  ReticleModel reticle_model;
-  GestureList gesture_list;
-  input_manager_->HandleInput(MsToTicks(1), controller_model, &reticle_model,
-                              &gesture_list);
-
-  // We should have hit the content quad if our math was correct.
-  ASSERT_NE(0, reticle_model.target_element_id);
-  EXPECT_EQ(content_quad->id(), reticle_model.target_element_id);
-
-  // We will now move the content quad behind the backplane.
-  content_quad->SetTranslate(0, 0, -2.0 * kTextureOffset);
-  scene_->root_element().UpdateWorldSpaceTransformRecursive();
-  input_manager_->HandleInput(MsToTicks(1), controller_model, &reticle_model,
-                              &gesture_list);
-
-  // We should have hit the content quad even though, geometrically, it stacks
-  // behind the backplane.
-  ASSERT_NE(0, reticle_model.target_element_id);
-  EXPECT_EQ(content_quad->id(), reticle_model.target_element_id);
-}
-
 TEST_F(UiInputManagerContentTest, ExitPromptHitTesting) {
   manager_->SetExitVrPromptEnabled(true, UiUnsupportedMode::kUnhandledPageInfo);
   EXPECT_TRUE(AnimateBy(MsToDelta(500)));