Hit test on the layer tree rather than the RSLL

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 97e9c1754c9a18eb8f9740101b72ad3849675808..a4d5cab9f94bf866f23e8d35e6fcfa9b107eb0ee 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -4,6 +4,9 @@
 
 #include "cc/trees/layer_tree_impl.h"
 
+#include <limits>
+#include <set>
+
 #include "base/debug/trace_event.h"
 #include "cc/animation/keyframed_animation_curve.h"
 #include "cc/animation/scrollbar_animation_controller.h"
@@ -20,6 +23,7 @@
 #include "cc/resources/ui_resource_request.h"
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/layer_tree_host_impl.h"
+#include "ui/gfx/point_conversions.h"
 #include "ui/gfx/size_conversions.h"
 #include "ui/gfx/vector2d_conversions.h"
 
@@ -1022,4 +1026,262 @@ void LayerTreeImpl::ReleaseResourcesRecursive(LayerImpl* current) {
     ReleaseResourcesRecursive(current->children()[i]);
 }
 
+template <typename LayerType>
+static inline bool LayerClipsSubtree(LayerType* layer) {
+  return layer->masks_to_bounds() || layer->mask_layer();
+}
+
+static bool PointHitsRect(
+    const gfx::PointF& screen_space_point,
+    const gfx::Transform& local_space_to_screen_space_transform,
+    const gfx::RectF& local_space_rect,
+    float* distance_to_camera) {
+  // If the transform is not invertible, then assume that this point doesn't hit
+  // this rect.
+  gfx::Transform inverse_local_space_to_screen_space(
+      gfx::Transform::kSkipInitialization);
+  if (!local_space_to_screen_space_transform.GetInverse(
+          &inverse_local_space_to_screen_space))
+    return false;
+
+  // Transform the hit test point from screen space to the local space of the
+  // given rect.
+  bool clipped = false;
+  gfx::Point3F planar_point = MathUtil::ProjectPoint3D(
+      inverse_local_space_to_screen_space, screen_space_point, &clipped);
+  gfx::PointF hit_test_point_in_local_space =
+      gfx::PointF(planar_point.x(), planar_point.y());
+
+  // If ProjectPoint could not project to a valid value, then we assume that
+  // this point doesn't hit this rect.
+  if (clipped)
+    return false;
+
+  if (!local_space_rect.Contains(hit_test_point_in_local_space))
+    return false;
+
+  if (distance_to_camera) {
+    // To compute the distance to the camera, we have to take the planar point
+    // and pull it back to world space and compute the displacement along the
+    // z-axis.
+    gfx::Point3F planar_point_in_screen_space(planar_point);
+    local_space_to_screen_space_transform.TransformPoint(
+        &planar_point_in_screen_space);
+    *distance_to_camera = planar_point_in_screen_space.z();
+  }
+
+  return true;
+}
+
+static bool PointHitsRegion(const gfx::PointF& screen_space_point,
+                            const gfx::Transform& screen_space_transform,
+                            const Region& layer_space_region,
+                            float layer_content_scale_x,
+                            float layer_content_scale_y) {
+  // If the transform is not invertible, then assume that this point doesn't hit
+  // this region.
+  gfx::Transform inverse_screen_space_transform(
+      gfx::Transform::kSkipInitialization);
+  if (!screen_space_transform.GetInverse(&inverse_screen_space_transform))
+    return false;
+
+  // Transform the hit test point from screen space to the local space of the
+  // given region.
+  bool clipped = false;
+  gfx::PointF hit_test_point_in_content_space = MathUtil::ProjectPoint(
+      inverse_screen_space_transform, screen_space_point, &clipped);
+  gfx::PointF hit_test_point_in_layer_space =
+      gfx::ScalePoint(hit_test_point_in_content_space,
+                      1.f / layer_content_scale_x,
+                      1.f / layer_content_scale_y);
+
+  // If ProjectPoint could not project to a valid value, then we assume that
+  // this point doesn't hit this region.
+  if (clipped)
+    return false;
+
+  return layer_space_region.Contains(
+      gfx::ToRoundedPoint(hit_test_point_in_layer_space));
+}
+
+static bool PointIsClippedBySurfaceOrClipRect(
+    const gfx::PointF& screen_space_point,
+    LayerImpl* layer) {
+  LayerImpl* current_layer = layer;
+
+  // Walk up the layer tree and hit-test any render_surfaces and any layer
+  // clip rects that are active.
+  while (current_layer) {
+    if (current_layer->render_surface() &&
+        !PointHitsRect(
+            screen_space_point,
+            current_layer->render_surface()->screen_space_transform(),
+            current_layer->render_surface()->content_rect(),
+            NULL))
+      return true;
+
+    // Note that drawable content rects are actually in target surface space, so
+    // the transform we have to provide is the target surface's
+    // screen_space_transform.
+    LayerImpl* render_target = current_layer->render_target();
+    if (LayerClipsSubtree(current_layer) &&
+        !PointHitsRect(
+            screen_space_point,
+            render_target->render_surface()->screen_space_transform(),
+            current_layer->drawable_content_rect(),
+            NULL))
+      return true;
+
+    current_layer = current_layer->parent();
+  }
+
+  // If we have finished walking all ancestors without having already exited,
+  // then the point is not clipped by any ancestors.
+  return false;
+}
+
+static bool PointHitsLayer(LayerImpl* layer,
+                           const gfx::PointF& screen_space_point,
+                           float* distance_to_intersection) {
+  gfx::RectF content_rect(layer->content_bounds());
+  if (!PointHitsRect(screen_space_point,
+                     layer->screen_space_transform(),
+                     content_rect,
+                     distance_to_intersection))
+    return false;
+
+  // At this point, we think the point does hit the layer, but we need to walk
+  // up the parents to ensure that the layer was not clipped in such a way
+  // that the hit point actually should not hit the layer.
+  if (PointIsClippedBySurfaceOrClipRect(screen_space_point, layer))
+    return false;
+
+  // Skip the HUD layer.
+  if (layer == layer->layer_tree_impl()->hud_layer())
+    return false;
+
+  return true;
+}
+
+struct FindClosestMatchingLayerDataForRecursion {
+  FindClosestMatchingLayerDataForRecursion()
+      : closest_match(NULL),
+        closest_distance(-std::numeric_limits<float>::infinity()) {}
+  LayerImpl* closest_match;
+  // Note that the positive z-axis points towards the camera, so bigger means
+  // closer in this case, counterintuitively.
+  float closest_distance;
+};
+
+template <typename Functor>
+static void FindClosestMatchingLayer(
+    const gfx::PointF& screen_space_point,
+    LayerImpl* layer,
+    const Functor& func,
+    FindClosestMatchingLayerDataForRecursion* data_for_recursion) {
+  for (int i = layer->children().size() - 1; i >= 0; --i) {
+    FindClosestMatchingLayer(
+        screen_space_point, layer->children()[i], func, data_for_recursion);
+  }
+
+  float distance_to_intersection = 0.f;
+  if (func(layer) &&
+      PointHitsLayer(layer, screen_space_point, &distance_to_intersection) &&
+      ((!data_for_recursion->closest_match ||
+        distance_to_intersection > data_for_recursion->closest_distance))) {
+    data_for_recursion->closest_distance = distance_to_intersection;
+    data_for_recursion->closest_match = layer;
+  }
+}
+
+static bool ScrollsAnyDrawnRenderSurfaceLayerListMember(LayerImpl* layer) {
+  if (!layer->scrollable())
+    return false;
+  if (layer->IsDrawnRenderSurfaceLayerListMember())
+    return true;
+  if (!layer->scroll_children())
+    return false;
+  for (std::set<LayerImpl*>::const_iterator it =
+           layer->scroll_children()->begin();
+       it != layer->scroll_children()->end();
+       ++it) {
+    if ((*it)->IsDrawnRenderSurfaceLayerListMember())
+      return true;
+  }
+  return false;
+}
+
+struct FindScrollingLayerFunctor {
+  bool operator()(LayerImpl* layer) const {
+    return ScrollsAnyDrawnRenderSurfaceLayerListMember(layer);
+  }
+};
+
+LayerImpl* LayerTreeImpl::FindFirstScrollingLayerThatIsHitByPoint(
+    const gfx::PointF& screen_space_point) {
+  FindClosestMatchingLayerDataForRecursion data_for_recursion;
+  FindClosestMatchingLayer(screen_space_point,
+                           root_layer(),
+                           FindScrollingLayerFunctor(),
+                           &data_for_recursion);
+  return data_for_recursion.closest_match;
+}
+
+struct HitTestVisibleScrollableOrTouchableFunctor {
+  bool operator()(LayerImpl* layer) const {
+    return layer->IsDrawnRenderSurfaceLayerListMember() ||
+           ScrollsAnyDrawnRenderSurfaceLayerListMember(layer) ||
+           !layer->touch_event_handler_region().IsEmpty() ||
+           layer->have_wheel_event_handlers();
+  }
+};
+
+LayerImpl* LayerTreeImpl::FindLayerThatIsHitByPoint(
+    const gfx::PointF& screen_space_point) {
+  FindClosestMatchingLayerDataForRecursion data_for_recursion;
+  FindClosestMatchingLayer(screen_space_point,
+                           root_layer(),
+                           HitTestVisibleScrollableOrTouchableFunctor(),
+                           &data_for_recursion);
+  return data_for_recursion.closest_match;
+}
+
+static bool LayerHasTouchEventHandlersAt(const gfx::PointF& screen_space_point,
+                                         LayerImpl* layer_impl) {
+  if (layer_impl->touch_event_handler_region().IsEmpty())
+    return false;
+
+  if (!PointHitsRegion(screen_space_point,
+                       layer_impl->screen_space_transform(),
+                       layer_impl->touch_event_handler_region(),
+                       layer_impl->contents_scale_x(),
+                       layer_impl->contents_scale_y()))
+    return false;
+
+  // At this point, we think the point does hit the touch event handler region
+  // on the layer, but we need to walk up the parents to ensure that the layer
+  // was not clipped in such a way that the hit point actually should not hit
+  // the layer.
+  if (PointIsClippedBySurfaceOrClipRect(screen_space_point, layer_impl))
+    return false;
+
+  return true;
+}
+
+struct FindTouchEventLayerFunctor {
+  bool operator()(LayerImpl* layer) const {
+    return LayerHasTouchEventHandlersAt(screen_space_point, layer);
+  }
+  const gfx::PointF screen_space_point;
+};
+
+LayerImpl* LayerTreeImpl::FindLayerThatIsHitByPointInTouchHandlerRegion(
+    const gfx::PointF& screen_space_point) {
+  FindTouchEventLayerFunctor func = {screen_space_point};
+  FindClosestMatchingLayerDataForRecursion data_for_recursion;
+  FindClosestMatchingLayer(
+      screen_space_point, root_layer(), func, &data_for_recursion);
+  return data_for_recursion.closest_match;
+}
+
 }  // namespace cc