// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_VIEWS_VIEW_H_
#define UI_VIEWS_VIEW_H_

#include <stddef.h>

#include <algorithm>
#include <map>
#include <memory>
#include <set>
#include <string>
#include <utility>
#include <vector>

#include "base/compiler_specific.h"
#include "base/i18n/rtl.h"
#include "base/logging.h"
#include "base/macros.h"
#include "build/build_config.h"
#include "ui/accessibility/ax_enums.mojom.h"
#include "ui/base/accelerators/accelerator.h"
#include "ui/base/class_property.h"
#include "ui/base/dragdrop/drag_drop_types.h"
#include "ui/base/dragdrop/drop_target_event.h"
#include "ui/base/dragdrop/os_exchange_data.h"
#include "ui/base/ui_base_types.h"
#include "ui/compositor/layer_delegate.h"
#include "ui/compositor/layer_owner.h"
#include "ui/compositor/paint_cache.h"
#include "ui/events/event.h"
#include "ui/events/event_target.h"
#include "ui/gfx/geometry/insets.h"
#include "ui/gfx/geometry/point.h"
#include "ui/gfx/geometry/rect.h"
#include "ui/gfx/geometry/vector2d.h"
#include "ui/gfx/native_widget_types.h"
#include "ui/gfx/path.h"
#include "ui/views/paint_info.h"
#include "ui/views/view_targeter.h"
#include "ui/views/views_export.h"

#if defined(OS_WIN)
#include <wrl/client.h>
#endif

using ui::OSExchangeData;

namespace gfx {
class Canvas;
class Insets;
class Path;
class Transform;
}  // namespace gfx

namespace ui {
struct AXActionData;
struct AXNodeData;
class Compositor;
class InputMethod;
class Layer;
class NativeTheme;
class PaintContext;
class ThemeProvider;
class TransformRecorder;
}  // namespace ui

namespace views {

class Background;
class Border;
class ContextMenuController;
class DragController;
class FocusManager;
class FocusTraversable;
class LayoutManager;
class ViewAccessibility;
class ScrollView;
class ViewObserver;
class Widget;
class WordLookupClient;

namespace internal {
class PreEventDispatchHandler;
class PostEventDispatchHandler;
class RootView;
class ScopedChildrenLock;
}  // namespace internal

/////////////////////////////////////////////////////////////////////////////
//
// View class
//
//   A View is a rectangle within the views View hierarchy. It is the base
//   class for all Views.
//
//   A View is a container of other Views (there is no such thing as a Leaf
//   View - makes code simpler, reduces type conversion headaches, design
//   mistakes etc)
//
//   The View contains basic properties for sizing (bounds), layout (flex,
//   orientation, etc), painting of children and event dispatch.
//
//   The View also uses a simple Box Layout Manager similar to XUL's
//   SprocketLayout system. Alternative Layout Managers implementing the
//   LayoutManager interface can be used to lay out children if required.
//
//   It is up to the subclass to implement Painting and storage of subclass -
//   specific properties and functionality.
//
//   Unless otherwise documented, views is not thread safe and should only be
//   accessed from the main thread.
//
/////////////////////////////////////////////////////////////////////////////
class VIEWS_EXPORT View : public ui::LayerDelegate,
                          public ui::LayerOwner,
                          public ui::AcceleratorTarget,
                          public ui::EventTarget,
                          public ui::EventHandler,
                          public ui::PropertyHandler {
 public:
  using Views = std::vector<View*>;

  enum class FocusBehavior {
    // Use when the View is never focusable. Default.
    NEVER,

    // Use when the View is to be focusable both in regular and accessibility
    // mode.
    ALWAYS,

    // Use when the View is focusable only during accessibility mode.
    ACCESSIBLE_ONLY,
  };

  struct ViewHierarchyChangedDetails {
    ViewHierarchyChangedDetails()
        : is_add(false),
          parent(NULL),
          child(NULL),
          move_view(NULL) {}

    ViewHierarchyChangedDetails(bool is_add,
                                View* parent,
                                View* child,
                                View* move_view)
        : is_add(is_add),
          parent(parent),
          child(child),
          move_view(move_view) {}

    bool is_add;
    // New parent if |is_add| is true, old parent if |is_add| is false.
    View* parent;
    // The view being added or removed.
    View* child;
    // If this is a move (reparent), meaning AddChildViewAt() is invoked with an
    // existing parent, then a notification for the remove is sent first,
    // followed by one for the add.  This case can be distinguished by a
    // non-NULL |move_view|.
    // For the remove part of move, |move_view| is the new parent of the View
    // being removed.
    // For the add part of move, |move_view| is the old parent of the View being
    // added.
    View* move_view;
  };

  // During paint, the origin of each view in physical pixel is calculated by
  //   view_origin_pixel = ROUND(view.origin() * device_scale_factor)
  //
  // Thus in a view hierarchy, the offset between two views, view_i and view_j,
  // is calculated by:
  //   view_offset_ij_pixel = SUM [view_origin_pixel.OffsetFromOrigin()]
  //                        {For all views along the path from view_i to view_j}
  //
  // But the offset between the two layers, the layer in view_i and the layer in
  // view_j, is computed by
  //   view_offset_ij_dip = SUM [view.origin().OffsetFromOrigin()]
  //                        {For all views along the path from view_i to view_j}
  //
  //   layer_offset_ij_pixel = ROUND (view_offset_ij_dip * device_scale_factor)
  //
  // Due to this difference in the logic for computation of offset, the values
  // view_offset_ij_pixel and layer_offset_ij_pixel may not always be equal.
  // They will differ by some subpixel_offset. This leads to bugs like
  // crbug.com/734787.
  // The subpixel offset needs to be applied to the layer to get the correct
  // output during paint.
  //
  // This class manages the computation of subpixel offset internally when
  // working with offsets.
  class LayerOffsetData {
   public:
    LayerOffsetData(float device_scale_factor = 1.f,
                    const gfx::Vector2d& offset = gfx::Vector2d())
        : device_scale_factor_(device_scale_factor) {
      AddOffset(offset);
    }

    const gfx::Vector2d& offset() const { return offset_; }

    const gfx::Vector2dF GetSubpixelOffset() const {
      // |rounded_pixel_offset_| is stored in physical pixel space. Convert it
      // into DIP space before returning.
      gfx::Vector2dF subpixel_offset(rounded_pixel_offset_);
      subpixel_offset.Scale(1.f / device_scale_factor_);
      return subpixel_offset;
    }

    LayerOffsetData& operator+=(const gfx::Vector2d& offset) {
      AddOffset(offset);
      return *this;
    }

    LayerOffsetData operator+(const gfx::Vector2d& offset) const {
      LayerOffsetData offset_data(*this);
      offset_data.AddOffset(offset);
      return offset_data;
    }

   private:
    // Adds the |offset_to_parent| to the total |offset_| and updates the
    // |rounded_pixel_offset_| value.
    void AddOffset(const gfx::Vector2d& offset_to_parent) {
      // Add the DIP |offset_to_parent| amount to the total offset.
      offset_ += offset_to_parent;

      // Convert |offset_to_parent| to physical pixel coordinates.
      gfx::Vector2dF fractional_pixel_offset(
          offset_to_parent.x() * device_scale_factor_,
          offset_to_parent.y() * device_scale_factor_);

      // Since pixels cannot be fractional, we need to round the offset to get
      // the correct physical pixel coordinate.
      gfx::Vector2dF integral_pixel_offset(
          gfx::ToRoundedInt(fractional_pixel_offset.x()),
          gfx::ToRoundedInt(fractional_pixel_offset.y()));

      // |integral_pixel_offset - fractional_pixel_offset| gives the subpixel
      // offset amount for |offset_to_parent|. This is added to
      // |rounded_pixel_offset_| to update the total subpixel offset.
      rounded_pixel_offset_ += integral_pixel_offset - fractional_pixel_offset;
    }

    // Total offset so far. This stores the offset between two nodes in the view
    // hierarchy.
    gfx::Vector2d offset_;

    // This stores the value such that if added to
    // |offset_ * device_scale_factor| will give the correct aligned offset in
    // physical pixels.
    gfx::Vector2dF rounded_pixel_offset_;

    // The device scale factor at which the subpixel offset is being computed.
    float device_scale_factor_;
  };

  // Creation and lifetime -----------------------------------------------------

  View();
  ~View() override;

  // By default a View is owned by its parent unless specified otherwise here.
  void set_owned_by_client() { owned_by_client_ = true; }
  bool owned_by_client() const { return owned_by_client_; }

  // Tree operations -----------------------------------------------------------

  // Get the Widget that hosts this View, if any.
  virtual const Widget* GetWidget() const;
  virtual Widget* GetWidget();

  // Adds |view| as a child of this view, optionally at |index|.
  void AddChildView(View* view);
  void AddChildViewAt(View* view, int index);

  // Moves |view| to the specified |index|. A negative value for |index| moves
  // the view at the end.
  void ReorderChildView(View* view, int index);

  // Removes |view| from this view. The view's parent will change to NULL.
  void RemoveChildView(View* view);

  // Removes all the children from this view. If |delete_children| is true,
  // the views are deleted, unless marked as not parent owned.
  void RemoveAllChildViews(bool delete_children);

  int child_count() const { return static_cast<int>(children_.size()); }
  // See also |GetChildrenInZOrder()| below that returns |children_|
  // in reverse z-order.
  bool has_children() const { return !children_.empty(); }

  // Returns the child view at |index|.
  const View* child_at(int index) const {
    DCHECK_GE(index, 0);
    DCHECK_LT(index, child_count());
    return children_[index];
  }
  View* child_at(int index) {
    return const_cast<View*>(const_cast<const View*>(this)->child_at(index));
  }

  // Returns the parent view.
  const View* parent() const { return parent_; }
  View* parent() { return parent_; }

  // Returns true if |view| is contained within this View's hierarchy, even as
  // an indirect descendant. Will return true if child is also this view.
  bool Contains(const View* view) const;

  // Returns the index of |view|, or -1 if |view| is not a child of this view.
  int GetIndexOf(const View* view) const;

  // Size and disposition ------------------------------------------------------
  // Methods for obtaining and modifying the position and size of the view.
  // Position is in the coordinate system of the view's parent.
  // Position is NOT flipped for RTL. See "RTL positioning" for RTL-sensitive
  // position accessors.
  // Transformations are not applied on the size/position. For example, if
  // bounds is (0, 0, 100, 100) and it is scaled by 0.5 along the X axis, the
  // width will still be 100 (although when painted, it will be 50x100, painted
  // at location (0, 0)).

  void SetBounds(int x, int y, int width, int height);
  void SetBoundsRect(const gfx::Rect& bounds);
  void SetSize(const gfx::Size& size);
  void SetPosition(const gfx::Point& position);
  void SetX(int x);
  void SetY(int y);

  // No transformation is applied on the size or the locations.
  const gfx::Rect& bounds() const { return bounds_; }
  int x() const { return bounds_.x(); }
  int y() const { return bounds_.y(); }
  int width() const { return bounds_.width(); }
  int height() const { return bounds_.height(); }
  const gfx::Point& origin() const { return bounds_.origin(); }
  const gfx::Size& size() const { return bounds_.size(); }

  // Returns the bounds of the content area of the view, i.e. the rectangle
  // enclosed by the view's border.
  gfx::Rect GetContentsBounds() const;

  // Returns the bounds of the view in its own coordinates (i.e. position is
  // 0, 0).
  gfx::Rect GetLocalBounds() const;

  // Returns the insets of the current border. If there is no border an empty
  // insets is returned.
  virtual gfx::Insets GetInsets() const;

  // Returns the visible bounds of the receiver in the receivers coordinate
  // system.
  //
  // When traversing the View hierarchy in order to compute the bounds, the
  // function takes into account the mirroring setting and transformation for
  // each View and therefore it will return the mirrored and transformed version
  // of the visible bounds if need be.
  gfx::Rect GetVisibleBounds() const;

  // Return the bounds of the View in screen coordinate system.
  gfx::Rect GetBoundsInScreen() const;

  // Returns the baseline of this view, or -1 if this view has no baseline. The
  // return value is relative to the preferred height.
  virtual int GetBaseline() const;

  // Get the size the View would like to be, if enough space were available.
  // First checks |preferred_size_|, then CalculatePreferredSize().
  gfx::Size GetPreferredSize() const;

  // Sets the size that this View will request during layout. The actual size
  // may differ. It should rarely be necessary to set this; usually the right
  // approach is controlling the parent's layout via a LayoutManager.
  void SetPreferredSize(const gfx::Size& size);

  // Convenience method that sizes this view to its preferred size.
  void SizeToPreferredSize();

  // Gets the minimum size of the view. View's implementation invokes
  // GetPreferredSize.
  virtual gfx::Size GetMinimumSize() const;

  // Gets the maximum size of the view. Currently only used for sizing shell
  // windows.
  virtual gfx::Size GetMaximumSize() const;

  // Return the preferred height for a specific width. Override if the
  // preferred height depends upon the width (such as a multi-line label). If
  // a LayoutManger has been installed this returns the value of
  // LayoutManager::GetPreferredHeightForWidth(), otherwise this returns
  // GetPreferredSize().height().
  virtual int GetHeightForWidth(int w) const;

  // Sets whether this view is visible. Painting is scheduled as needed. Also,
  // clears focus if the focused view or one of its ancestors is set to be
  // hidden.
  virtual void SetVisible(bool visible);

  // Return whether a view is visible
  bool visible() const { return visible_; }

  // Returns true if this view is drawn on screen.
  virtual bool IsDrawn() const;

  // Set whether this view is enabled. A disabled view does not receive keyboard
  // or mouse inputs. If |enabled| differs from the current value, SchedulePaint
  // is invoked. Also, clears focus if the focused view is disabled.
  void SetEnabled(bool enabled);

  // Returns whether the view is enabled.
  bool enabled() const { return enabled_; }

  // Returns the child views ordered in reverse z-order. That is, views later in
  // the returned vector have a higher z-order (are painted later) than those
  // early in the vector. The returned vector has exactly the same number of
  // Views as |children_|. The default implementation returns |children_|,
  // subclass if the paint order should differ from that of |children_|.
  // This order is taken into account by painting and targeting implementations.
  virtual View::Views GetChildrenInZOrder();

  // Transformations -----------------------------------------------------------

  // Methods for setting transformations for a view (e.g. rotation, scaling).

  gfx::Transform GetTransform() const;

  // Clipping is done relative to the view's local bounds.
  void set_clip_path(const gfx::Path& path) { clip_path_ = path; }

  // Sets the transform to the supplied transform.
  void SetTransform(const gfx::Transform& transform);

  // Sets whether this view paints to a layer. A view paints to a layer if
  // either of the following are true:
  // . the view has a non-identity transform.
  // . SetPaintToLayer(ui::LayerType) has been invoked.
  // View creates the Layer only when it exists in a Widget with a non-NULL
  // Compositor.
  void SetPaintToLayer(ui::LayerType layer_type = ui::LAYER_TEXTURED);

  // Please refer to the comments above the DestroyLayerImpl() function for
  // details.
  void DestroyLayer();

  // Overridden from ui::LayerOwner:
  std::unique_ptr<ui::Layer> RecreateLayer() override;

  // RTL positioning -----------------------------------------------------------

  // Methods for accessing the bounds and position of the view, relative to its
  // parent. The position returned is mirrored if the parent view is using a RTL
  // layout.
  //
  // NOTE: in the vast majority of the cases, the mirroring implementation is
  //       transparent to the View subclasses and therefore you should use the
  //       bounds() accessor instead.
  gfx::Rect GetMirroredBounds() const;
  gfx::Point GetMirroredPosition() const;
  int GetMirroredX() const;

  // Given a rectangle specified in this View's coordinate system, the function
  // computes the 'left' value for the mirrored rectangle within this View. If
  // the View's UI layout is not right-to-left, then bounds.x() is returned.
  //
  // UI mirroring is transparent to most View subclasses and therefore there is
  // no need to call this routine from anywhere within your subclass
  // implementation.
  int GetMirroredXForRect(const gfx::Rect& rect) const;

  // Given a rectangle specified in this View's coordinate system, the function
  // computes the mirrored rectangle.
  gfx::Rect GetMirroredRect(const gfx::Rect& rect) const;

  // Given the X coordinate of a point inside the View, this function returns
  // the mirrored X coordinate of the point if the View's UI layout is
  // right-to-left. If the layout is left-to-right, the same X coordinate is
  // returned.
  //
  // Following are a few examples of the values returned by this function for
  // a View with the bounds {0, 0, 100, 100} and a right-to-left layout:
  //
  // GetMirroredXCoordinateInView(0) -> 100
  // GetMirroredXCoordinateInView(20) -> 80
  // GetMirroredXCoordinateInView(99) -> 1
  int GetMirroredXInView(int x) const;

  // Given a X coordinate and a width inside the View, this function returns
  // the mirrored X coordinate if the View's UI layout is right-to-left. If the
  // layout is left-to-right, the same X coordinate is returned.
  //
  // Following are a few examples of the values returned by this function for
  // a View with the bounds {0, 0, 100, 100} and a right-to-left layout:
  //
  // GetMirroredXCoordinateInView(0, 10) -> 90
  // GetMirroredXCoordinateInView(20, 20) -> 60
  int GetMirroredXWithWidthInView(int x, int w) const;

  // Layout --------------------------------------------------------------------

  // Lay out the child Views (set their bounds based on sizing heuristics
  // specific to the current Layout Manager)
  virtual void Layout();

  // TODO(beng): I think we should remove this.
  // Mark this view and all parents to require a relayout. This ensures the
  // next call to Layout() will propagate to this view, even if the bounds of
  // parent views do not change.
  void InvalidateLayout();

  // Gets/Sets the Layout Manager used by this view to size and place its
  // children.
  //
  // The LayoutManager is owned by the View and is deleted when the view is
  // deleted, or when a new LayoutManager is installed. Call
  // SetLayoutManager(nullptr) to clear it.
  //
  // SetLayoutManager returns a bare pointer version of the input parameter
  // (now owned by the view). If code needs to use the layout manager after
  // being assigned, use this pattern:
  //
  //   views::BoxLayout* box_layout = SetLayoutManager(
  //       std::make_unique<views::BoxLayout>(...));
  //   box_layout->Foo();
  LayoutManager* GetLayoutManager() const;
  template <typename LayoutManager>
  LayoutManager* SetLayoutManager(
      std::unique_ptr<LayoutManager> layout_manager) {
    LayoutManager* lm = layout_manager.get();
    SetLayoutManagerImpl(std::move(layout_manager));
    return lm;
  }
  void SetLayoutManager(std::nullptr_t);

  // Attributes ----------------------------------------------------------------

  // The view class name.
  static const char kViewClassName[];

  // Return the receiving view's class name. A view class is a string which
  // uniquely identifies the view class. It is intended to be used as a way to
  // find out during run time if a view can be safely cast to a specific view
  // subclass. The default implementation returns kViewClassName.
  virtual const char* GetClassName() const;

  // Returns the first ancestor, starting at this, whose class name is |name|.
  // Returns null if no ancestor has the class name |name|.
  const View* GetAncestorWithClassName(const std::string& name) const;
  View* GetAncestorWithClassName(const std::string& name);

  // Recursively descends the view tree starting at this view, and returns
  // the first child that it encounters that has the given ID.
  // Returns NULL if no matching child view is found.
  virtual const View* GetViewByID(int id) const;
  virtual View* GetViewByID(int id);

  // Gets and sets the ID for this view. ID should be unique within the subtree
  // that you intend to search for it. 0 is the default ID for views.
  int id() const { return id_; }
  void set_id(int id) { id_ = id; }

  // A group id is used to tag views which are part of the same logical group.
  // Focus can be moved between views with the same group using the arrow keys.
  // Groups are currently used to implement radio button mutual exclusion.
  // The group id is immutable once it's set.
  void SetGroup(int gid);
  // Returns the group id of the view, or -1 if the id is not set yet.
  int GetGroup() const;

  // If this returns true, the views from the same group can each be focused
  // when moving focus with the Tab/Shift-Tab key.  If this returns false,
  // only the selected view from the group (obtained with
  // GetSelectedViewForGroup()) is focused.
  virtual bool IsGroupFocusTraversable() const;

  // Fills |views| with all the available views which belong to the provided
  // |group|.
  void GetViewsInGroup(int group, Views* views);

  // Returns the View that is currently selected in |group|.
  // The default implementation simply returns the first View found for that
  // group.
  virtual View* GetSelectedViewForGroup(int group);

  // Coordinate conversion -----------------------------------------------------

  // Note that the utility coordinate conversions functions always operate on
  // the mirrored position of the child Views if the parent View uses a
  // right-to-left UI layout.

  // Convert a point from the coordinate system of one View to another.
  //
  // |source| and |target| must be in the same widget, but doesn't need to be in
  // the same view hierarchy.
  // Neither |source| nor |target| can be NULL.
  static void ConvertPointToTarget(const View* source,
                                   const View* target,
                                   gfx::Point* point);

  // Convert |rect| from the coordinate system of |source| to the coordinate
  // system of |target|.
  //
  // |source| and |target| must be in the same widget, but doesn't need to be in
  // the same view hierarchy.
  // Neither |source| nor |target| can be NULL.
  static void ConvertRectToTarget(const View* source,
                                  const View* target,
                                  gfx::RectF* rect);

  // Convert a point from a View's coordinate system to that of its Widget.
  static void ConvertPointToWidget(const View* src, gfx::Point* point);

  // Convert a point from the coordinate system of a View's Widget to that
  // View's coordinate system.
  static void ConvertPointFromWidget(const View* dest, gfx::Point* p);

  // Convert a point from a View's coordinate system to that of the screen.
  static void ConvertPointToScreen(const View* src, gfx::Point* point);

  // Convert a point from the screen coordinate system to that View's coordinate
  // system.
  static void ConvertPointFromScreen(const View* dst, gfx::Point* point);

  // Convert a rect from a View's coordinate system to that of the screen.
  static void ConvertRectToScreen(const View* src, gfx::Rect* rect);

  // Applies transformation on the rectangle, which is in the view's coordinate
  // system, to convert it into the parent's coordinate system.
  gfx::Rect ConvertRectToParent(const gfx::Rect& rect) const;

  // Converts a rectangle from this views coordinate system to its widget
  // coordinate system.
  gfx::Rect ConvertRectToWidget(const gfx::Rect& rect) const;

  // Painting ------------------------------------------------------------------

  // Mark all or part of the View's bounds as dirty (needing repaint).
  // |r| is in the View's coordinates.
  // Rectangle |r| should be in the view's coordinate system. The
  // transformations are applied to it to convert it into the parent coordinate
  // system before propagating SchedulePaint up the view hierarchy.
  // TODO(beng): Make protected.
  void SchedulePaint();
  virtual void SchedulePaintInRect(const gfx::Rect& r);

  // Called by the framework to paint a View. Performs translation and clipping
  // for View coordinates and language direction as required, allows the View
  // to paint itself via the various OnPaint*() event handlers and then paints
  // the hierarchy beneath it.
  void Paint(const PaintInfo& parent_paint_info);

  // The background object may be null.
  void SetBackground(std::unique_ptr<Background> b);
  const Background* background() const { return background_.get(); }
  Background* background() { return background_.get(); }

  // The border object may be null.
  virtual void SetBorder(std::unique_ptr<Border> b);
  const Border* border() const { return border_.get(); }
  Border* border() { return border_.get(); }

  // Get the theme provider from the parent widget.
  const ui::ThemeProvider* GetThemeProvider() const;

  // Returns the NativeTheme to use for this View. This calls through to
  // GetNativeTheme() on the Widget this View is in, or provides a default
  // theme if there's no widget, or returns |native_theme_| if that's
  // set. Warning: the default theme might not be correct; you should probably
  // override OnNativeThemeChanged().
  ui::NativeTheme* GetNativeTheme() {
    return const_cast<ui::NativeTheme*>(
        const_cast<const View*>(this)->GetNativeTheme());
  }
  const ui::NativeTheme* GetNativeTheme() const;

  // Sets the native theme and informs descendants.
  void SetNativeTheme(ui::NativeTheme* theme);

  // RTL painting --------------------------------------------------------------

  // This method determines whether the gfx::Canvas object passed to
  // View::Paint() needs to be transformed such that anything drawn on the
  // canvas object during View::Paint() is flipped horizontally.
  bool flip_canvas_on_paint_for_rtl_ui() const {
    return flip_canvas_on_paint_for_rtl_ui_;
  }

  // Enables or disables flipping of the gfx::Canvas during View::Paint().
  // Note that if canvas flipping is enabled, the canvas will be flipped only
  // if the UI layout is right-to-left; that is, the canvas will be flipped
  // only if base::i18n::IsRTL() returns true.
  //
  // Enabling canvas flipping is useful for leaf views that draw an image that
  // needs to be flipped horizontally when the UI layout is right-to-left
  // (views::Button, for example). This method is helpful for such classes
  // because their drawing logic stays the same and they can become agnostic to
  // the UI directionality.
  virtual void EnableCanvasFlippingForRTLUI(bool enable);

  // Input ---------------------------------------------------------------------
  // The points, rects, mouse locations, and touch locations in the following
  // functions are in the view's coordinates, except for a RootView.

  // A convenience function which calls into GetEventHandlerForRect() with
  // a 1x1 rect centered at |point|. |point| is in the local coordinate
  // space of |this|.
  View* GetEventHandlerForPoint(const gfx::Point& point);

  // Returns the View that should be the target of an event having |rect| as
  // its location, or NULL if no such target exists. |rect| is in the local
  // coordinate space of |this|.
  View* GetEventHandlerForRect(const gfx::Rect& rect);

  // Returns the deepest visible descendant that contains the specified point
  // and supports tooltips. If the view does not contain the point, returns
  // NULL.
  virtual View* GetTooltipHandlerForPoint(const gfx::Point& point);

  // Return the cursor that should be used for this view or the default cursor.
  // The event location is in the receiver's coordinate system. The caller is
  // responsible for managing the lifetime of the returned object, though that
  // lifetime may vary from platform to platform. On Windows and Aura,
  // the cursor is a shared resource.
  virtual gfx::NativeCursor GetCursor(const ui::MouseEvent& event);

  // A convenience function which calls HitTestRect() with a rect of size
  // 1x1 and an origin of |point|. |point| is in the local coordinate space
  // of |this|.
  bool HitTestPoint(const gfx::Point& point) const;

  // Returns true if |rect| intersects this view's bounds. |rect| is in the
  // local coordinate space of |this|.
  bool HitTestRect(const gfx::Rect& rect) const;

  // Returns true if this view or any of its descendants are permitted to
  // be the target of an event.
  virtual bool CanProcessEventsWithinSubtree() const;

  // Sets whether this view or any of its descendants are permitted to be the
  // target of an event.
  void set_can_process_events_within_subtree(bool can_process) {
    can_process_events_within_subtree_ = can_process;
  }

  // Returns true if the mouse cursor is over |view| and mouse events are
  // enabled.
  bool IsMouseHovered() const;

  // This method is invoked when the user clicks on this view.
  // The provided event is in the receiver's coordinate system.
  //
  // Return true if you processed the event and want to receive subsequent
  // MouseDragged and MouseReleased events.  This also stops the event from
  // bubbling.  If you return false, the event will bubble through parent
  // views.
  //
  // If you remove yourself from the tree while processing this, event bubbling
  // stops as if you returned true, but you will not receive future events.
  // The return value is ignored in this case.
  //
  // Default implementation returns true if a ContextMenuController has been
  // set, false otherwise. Override as needed.
  //
  virtual bool OnMousePressed(const ui::MouseEvent& event);

  // This method is invoked when the user clicked on this control.
  // and is still moving the mouse with a button pressed.
  // The provided event is in the receiver's coordinate system.
  //
  // Return true if you processed the event and want to receive
  // subsequent MouseDragged and MouseReleased events.
  //
  // Default implementation returns true if a ContextMenuController has been
  // set, false otherwise. Override as needed.
  //
  virtual bool OnMouseDragged(const ui::MouseEvent& event);

  // This method is invoked when the user releases the mouse
  // button. The event is in the receiver's coordinate system.
  //
  // Default implementation notifies the ContextMenuController is appropriate.
  // Subclasses that wish to honor the ContextMenuController should invoke
  // super.
  virtual void OnMouseReleased(const ui::MouseEvent& event);

  // This method is invoked when the mouse press/drag was canceled by a
  // system/user gesture.
  virtual void OnMouseCaptureLost();

  // This method is invoked when the mouse is above this control
  // The event is in the receiver's coordinate system.
  //
  // Default implementation does nothing. Override as needed.
  virtual void OnMouseMoved(const ui::MouseEvent& event);

  // This method is invoked when the mouse enters this control.
  //
  // Default implementation does nothing. Override as needed.
  virtual void OnMouseEntered(const ui::MouseEvent& event);

  // This method is invoked when the mouse exits this control
  // The provided event location is always (0, 0)
  // Default implementation does nothing. Override as needed.
  virtual void OnMouseExited(const ui::MouseEvent& event);

  // Set the MouseHandler for a drag session.
  //
  // A drag session is a stream of mouse events starting
  // with a MousePressed event, followed by several MouseDragged
  // events and finishing with a MouseReleased event.
  //
  // This method should be only invoked while processing a
  // MouseDragged or MousePressed event.
  //
  // All further mouse dragged and mouse up events will be sent
  // the MouseHandler, even if it is reparented to another window.
  //
  // The MouseHandler is automatically cleared when the control
  // comes back from processing the MouseReleased event.
  //
  // Note: if the mouse handler is no longer connected to a
  // view hierarchy, events won't be sent.
  //
  // TODO(sky): rename this.
  virtual void SetMouseHandler(View* new_mouse_handler);

  // Invoked when a key is pressed or released.
  // Subclasses should return true if the event has been processed and false
  // otherwise. If the event has not been processed, the parent will be given a
  // chance.
  virtual bool OnKeyPressed(const ui::KeyEvent& event);
  virtual bool OnKeyReleased(const ui::KeyEvent& event);

  // Invoked when the user uses the mousewheel. Implementors should return true
  // if the event has been processed and false otherwise. This message is sent
  // if the view is focused. If the event has not been processed, the parent
  // will be given a chance.
  virtual bool OnMouseWheel(const ui::MouseWheelEvent& event);


  // See field for description.
  void set_notify_enter_exit_on_child(bool notify) {
    notify_enter_exit_on_child_ = notify;
  }
  bool notify_enter_exit_on_child() const {
    return notify_enter_exit_on_child_;
  }

  // Convenience method to retrieve the InputMethod associated with the
  // Widget that contains this view.
  ui::InputMethod* GetInputMethod() {
    return const_cast<ui::InputMethod*>(
        const_cast<const View*>(this)->GetInputMethod());
  }
  const ui::InputMethod* GetInputMethod() const;

  // Sets a new ViewTargeter for the view, and returns the previous
  // ViewTargeter.
  std::unique_ptr<ViewTargeter> SetEventTargeter(
      std::unique_ptr<ViewTargeter> targeter);

  // Returns the ViewTargeter installed on |this| if one exists,
  // otherwise returns the ViewTargeter installed on our root view.
  // The return value is guaranteed to be non-null.
  ViewTargeter* GetEffectiveViewTargeter() const;

  ViewTargeter* targeter() const { return targeter_.get(); }

  // Returns the WordLookupClient associated with this view.
  virtual WordLookupClient* GetWordLookupClient();

  // Overridden from ui::EventTarget:
  bool CanAcceptEvent(const ui::Event& event) override;
  ui::EventTarget* GetParentTarget() override;
  std::unique_ptr<ui::EventTargetIterator> GetChildIterator() const override;
  ui::EventTargeter* GetEventTargeter() override;
  void ConvertEventToTarget(ui::EventTarget* target,
                            ui::LocatedEvent* event) override;

  // Overridden from ui::EventHandler:
  void OnKeyEvent(ui::KeyEvent* event) override;
  void OnMouseEvent(ui::MouseEvent* event) override;
  void OnScrollEvent(ui::ScrollEvent* event) override;
  void OnTouchEvent(ui::TouchEvent* event) final;
  void OnGestureEvent(ui::GestureEvent* event) override;

  // Accelerators --------------------------------------------------------------

  // Sets a keyboard accelerator for that view. When the user presses the
  // accelerator key combination, the AcceleratorPressed method is invoked.
  // Note that you can set multiple accelerators for a view by invoking this
  // method several times. Note also that AcceleratorPressed is invoked only
  // when CanHandleAccelerators() is true.
  virtual void AddAccelerator(const ui::Accelerator& accelerator);

  // Removes the specified accelerator for this view.
  virtual void RemoveAccelerator(const ui::Accelerator& accelerator);

  // Removes all the keyboard accelerators for this view.
  virtual void ResetAccelerators();

  // Overridden from AcceleratorTarget:
  bool AcceleratorPressed(const ui::Accelerator& accelerator) override;

  // Returns whether accelerators are enabled for this view. Accelerators are
  // enabled if the containing widget is visible and the view is enabled() and
  // IsDrawn()
  bool CanHandleAccelerators() const override;

  // Focus ---------------------------------------------------------------------

  // Returns whether this view currently has the focus.
  virtual bool HasFocus() const;

  // Returns the view that should be selected next when pressing Tab.
  View* GetNextFocusableView();
  const View* GetNextFocusableView() const;

  // Returns the view that should be selected next when pressing Shift-Tab.
  View* GetPreviousFocusableView();

  // Sets the component that should be selected next when pressing Tab, and
  // makes the current view the precedent view of the specified one.
  // Note that by default views are linked in the order they have been added to
  // their container. Use this method if you want to modify the order.
  // IMPORTANT NOTE: loops in the focus hierarchy are not supported.
  void SetNextFocusableView(View* view);

  // Gets/sets |focus_behavior|. SetFocusBehavior() advances focus if necessary.
  FocusBehavior focus_behavior() const { return focus_behavior_; }
  void SetFocusBehavior(FocusBehavior focus_behavior);

  // Returns true if this view is focusable, |enabled_| and drawn.
  bool IsFocusable() const;

  // Return whether this view is focusable when the user requires full keyboard
  // access, even though it may not be normally focusable.
  bool IsAccessibilityFocusable() const;

  // Convenience method to retrieve the FocusManager associated with the
  // Widget that contains this view.  This can return NULL if this view is not
  // part of a view hierarchy with a Widget.
  virtual FocusManager* GetFocusManager();
  virtual const FocusManager* GetFocusManager() const;

  // Request keyboard focus. The receiving view will become the focused view.
  virtual void RequestFocus();

  // Invoked when a view is about to be requested for focus due to the focus
  // traversal. Reverse is this request was generated going backward
  // (Shift-Tab).
  virtual void AboutToRequestFocusFromTabTraversal(bool reverse) {}

  // Invoked when a key is pressed before the key event is processed (and
  // potentially eaten) by the focus manager for tab traversal, accelerators and
  // other focus related actions.
  // The default implementation returns false, ensuring that tab traversal and
  // accelerators processing is performed.
  // Subclasses should return true if they want to process the key event and not
  // have it processed as an accelerator (if any) or as a tab traversal (if the
  // key event is for the TAB key).  In that case, OnKeyPressed will
  // subsequently be invoked for that event.
  virtual bool SkipDefaultKeyEventProcessing(const ui::KeyEvent& event);

  // Subclasses that contain traversable children that are not directly
  // accessible through the children hierarchy should return the associated
  // FocusTraversable for the focus traversal to work properly.
  virtual FocusTraversable* GetFocusTraversable();

  // Subclasses that can act as a "pane" must implement their own
  // FocusTraversable to keep the focus trapped within the pane.
  // If this method returns an object, any view that's a direct or
  // indirect child of this view will always use this FocusTraversable
  // rather than the one from the widget.
  virtual FocusTraversable* GetPaneFocusTraversable();

  // Tooltips ------------------------------------------------------------------

  // Gets the tooltip for this View. If the View does not have a tooltip,
  // return false. If the View does have a tooltip, copy the tooltip into
  // the supplied string and return true.
  // Any time the tooltip text that a View is displaying changes, it must
  // invoke TooltipTextChanged.
  // |p| provides the coordinates of the mouse (relative to this view).
  virtual bool GetTooltipText(const gfx::Point& p,
                              base::string16* tooltip) const;

  // Returns the location (relative to this View) for the text on the tooltip
  // to display. If false is returned (the default), the tooltip is placed at
  // a default position.
  virtual bool GetTooltipTextOrigin(const gfx::Point& p, gfx::Point* loc) const;

  // Context menus -------------------------------------------------------------

  // Sets the ContextMenuController. Setting this to non-null makes the View
  // process mouse events.
  ContextMenuController* context_menu_controller() {
    return context_menu_controller_;
  }
  void set_context_menu_controller(ContextMenuController* menu_controller) {
    context_menu_controller_ = menu_controller;
  }

  // Provides default implementation for context menu handling. The default
  // implementation calls the ShowContextMenu of the current
  // ContextMenuController (if it is not NULL). Overridden in subclassed views
  // to provide right-click menu display triggered by the keyboard (i.e. for the
  // Chrome toolbar Back and Forward buttons). No source needs to be specified,
  // as it is always equal to the current View.
  virtual void ShowContextMenu(const gfx::Point& p,
                               ui::MenuSourceType source_type);

  // On some platforms, we show context menu on mouse press instead of release.
  // This method returns true for those platforms.
  static bool ShouldShowContextMenuOnMousePress();

  // Returns the location, in screen coordinates, to show the context menu at
  // when the context menu is shown from the keyboard. This implementation
  // returns the middle of the visible region of this view.
  //
  // This method is invoked when the context menu is shown by way of the
  // keyboard.
  virtual gfx::Point GetKeyboardContextMenuLocation();

  // Drag and drop -------------------------------------------------------------

  DragController* drag_controller() { return drag_controller_; }
  void set_drag_controller(DragController* drag_controller) {
    drag_controller_ = drag_controller;
  }

  // During a drag and drop session when the mouse moves the view under the
  // mouse is queried for the drop types it supports by way of the
  // GetDropFormats methods. If the view returns true and the drag site can
  // provide data in one of the formats, the view is asked if the drop data
  // is required before any other drop events are sent. Once the
  // data is available the view is asked if it supports the drop (by way of
  // the CanDrop method). If a view returns true from CanDrop,
  // OnDragEntered is sent to the view when the mouse first enters the view,
  // as the mouse moves around within the view OnDragUpdated is invoked.
  // If the user releases the mouse over the view and OnDragUpdated returns a
  // valid drop, then OnPerformDrop is invoked. If the mouse moves outside the
  // view or over another view that wants the drag, OnDragExited is invoked.
  //
  // Similar to mouse events, the deepest view under the mouse is first checked
  // if it supports the drop (Drop). If the deepest view under
  // the mouse does not support the drop, the ancestors are walked until one
  // is found that supports the drop.

  // Override and return the set of formats that can be dropped on this view.
  // |formats| is a bitmask of the formats defined bye OSExchangeData::Format.
  // The default implementation returns false, which means the view doesn't
  // support dropping.
  virtual bool GetDropFormats(
      int* formats,
      std::set<ui::Clipboard::FormatType>* format_types);

  // Override and return true if the data must be available before any drop
  // methods should be invoked. The default is false.
  virtual bool AreDropTypesRequired();

  // A view that supports drag and drop must override this and return true if
  // data contains a type that may be dropped on this view.
  virtual bool CanDrop(const OSExchangeData& data);

  // OnDragEntered is invoked when the mouse enters this view during a drag and
  // drop session and CanDrop returns true. This is immediately
  // followed by an invocation of OnDragUpdated, and eventually one of
  // OnDragExited or OnPerformDrop.
  virtual void OnDragEntered(const ui::DropTargetEvent& event);

  // Invoked during a drag and drop session while the mouse is over the view.
  // This should return a bitmask of the DragDropTypes::DragOperation supported
  // based on the location of the event. Return 0 to indicate the drop should
  // not be accepted.
  virtual int OnDragUpdated(const ui::DropTargetEvent& event);

  // Invoked during a drag and drop session when the mouse exits the views, or
  // when the drag session was canceled and the mouse was over the view.
  virtual void OnDragExited();

  // Invoked during a drag and drop session when OnDragUpdated returns a valid
  // operation and the user release the mouse.
  virtual int OnPerformDrop(const ui::DropTargetEvent& event);

  // Invoked from DoDrag after the drag completes. This implementation does
  // nothing, and is intended for subclasses to do cleanup.
  virtual void OnDragDone();

  // Returns true if the mouse was dragged enough to start a drag operation.
  // delta_x and y are the distance the mouse was dragged.
  static bool ExceededDragThreshold(const gfx::Vector2d& delta);

  // Accessibility -------------------------------------------------------------

  // Get the object managing the accessibility interface for this View.
  ViewAccessibility& GetViewAccessibility();

  // Modifies |node_data| to reflect the current accessible state of this view.
  virtual void GetAccessibleNodeData(ui::AXNodeData* node_data) {}

  // Handle a request from assistive technology to perform an action on this
  // view. Returns true on success, but note that the success/failure is
  // not propagated to the client that requested the action, since the
  // request is sometimes asynchronous. The right way to send a response is
  // via NotifyAccessibilityEvent(), below.
  virtual bool HandleAccessibleAction(const ui::AXActionData& action_data);

  // Returns an instance of the native accessibility interface for this view.
  virtual gfx::NativeViewAccessible GetNativeViewAccessible();

  // Notifies assistive technology that an accessibility event has
  // occurred on this view, such as when the view is focused or when its
  // value changes. Pass true for |send_native_event| except for rare
  // cases where the view is a native control that's already sending a
  // native accessibility event and the duplicate event would cause
  // problems.
  void NotifyAccessibilityEvent(ax::mojom::Event event_type,
                                bool send_native_event);

  // Views may override this function to know when an accessibility
  // event is fired. This will be called by NotifyAccessibilityEvent.
  virtual void OnAccessibilityEvent(ax::mojom::Event event_type);

  // Scrolling -----------------------------------------------------------------
  // TODO(beng): Figure out if this can live somewhere other than View, i.e.
  //             closer to ScrollView.

  // Scrolls the specified region, in this View's coordinate system, to be
  // visible. View's implementation passes the call onto the parent View (after
  // adjusting the coordinates). It is up to views that only show a portion of
  // the child view, such as Viewport, to override appropriately.
  virtual void ScrollRectToVisible(const gfx::Rect& rect);

  // Scrolls the view's bounds or some subset thereof to be visible. By default
  // this function calls ScrollRectToVisible(GetLocalBounds()).
  virtual void ScrollViewToVisible();

  // The following methods are used by ScrollView to determine the amount
  // to scroll relative to the visible bounds of the view. For example, a
  // return value of 10 indicates the scroll_view should scroll 10 pixels in
  // the appropriate direction.
  //
  // Each method takes the following parameters:
  //
  // is_horizontal: if true, scrolling is along the horizontal axis, otherwise
  //                the vertical axis.
  // is_positive: if true, scrolling is by a positive amount. Along the
  //              vertical axis scrolling by a positive amount equates to
  //              scrolling down.
  //
  // The return value should always be positive and gives the number of pixels
  // to scroll. ScrollView interprets a return value of 0 (or negative)
  // to scroll by a default amount.
  //
  // See VariableRowHeightScrollHelper and FixedRowHeightScrollHelper for
  // implementations of common cases.
  virtual int GetPageScrollIncrement(ScrollView* scroll_view,
                                     bool is_horizontal, bool is_positive);
  virtual int GetLineScrollIncrement(ScrollView* scroll_view,
                                     bool is_horizontal, bool is_positive);

  void AddObserver(ViewObserver* observer);
  void RemoveObserver(ViewObserver* observer);
  bool HasObserver(const ViewObserver* observer) const;

 protected:
  // Used to track a drag. RootView passes this into
  // ProcessMousePressed/Dragged.
  struct DragInfo {
    // Sets possible_drag to false and start_x/y to 0. This is invoked by
    // RootView prior to invoke ProcessMousePressed.
    void Reset();

    // Sets possible_drag to true and start_pt to the specified point.
    // This is invoked by the target view if it detects the press may generate
    // a drag.
    void PossibleDrag(const gfx::Point& p);

    // Whether the press may generate a drag.
    bool possible_drag;

    // Coordinates of the mouse press.
    gfx::Point start_pt;
  };

  // Size and disposition ------------------------------------------------------

  // Calculates the natural size for the View, to be taken into consideration
  // when the parent is performing layout.
  virtual gfx::Size CalculatePreferredSize() const;

  // Override to be notified when the bounds of the view have changed.
  virtual void OnBoundsChanged(const gfx::Rect& previous_bounds);

  // Called when the preferred size of a child view changed.  This gives the
  // parent an opportunity to do a fresh layout if that makes sense.
  virtual void ChildPreferredSizeChanged(View* child) {}

  // Called when the visibility of a child view changed.  This gives the parent
  // an opportunity to do a fresh layout if that makes sense.
  virtual void ChildVisibilityChanged(View* child) {}

  // Invalidates the layout and calls ChildPreferredSizeChanged on the parent
  // if there is one. Be sure to call View::PreferredSizeChanged when
  // overriding such that the layout is properly invalidated.
  virtual void PreferredSizeChanged();

  // Override returning true when the view needs to be notified when its visible
  // bounds relative to the root view may have changed. Only used by
  // NativeViewHost.
  virtual bool GetNeedsNotificationWhenVisibleBoundsChange() const;

  // Notification that this View's visible bounds relative to the root view may
  // have changed. The visible bounds are the region of the View not clipped by
  // its ancestors. This is used for clipping NativeViewHost.
  virtual void OnVisibleBoundsChanged();

  // Override to be notified when the enabled state of this View has
  // changed. The default implementation calls SchedulePaint() on this View.
  virtual void OnEnabledChanged();

  bool needs_layout() const { return needs_layout_; }

  // Tree operations -----------------------------------------------------------

  // This method is invoked when the tree changes.
  //
  // When a view is removed, it is invoked for all children and grand
  // children. For each of these views, a notification is sent to the
  // view and all parents.
  //
  // When a view is added, a notification is sent to the view, all its
  // parents, and all its children (and grand children)
  //
  // Default implementation does nothing. Override to perform operations
  // required when a view is added or removed from a view hierarchy
  //
  // Refer to comments in struct |ViewHierarchyChangedDetails| for |details|.
  //
  // See also AddedToWidget() and RemovedFromWidget() for detecting when the
  // view is added to/removed from a widget.
  virtual void ViewHierarchyChanged(const ViewHierarchyChangedDetails& details);

  // When SetVisible() changes the visibility of a view, this method is
  // invoked for that view as well as all the children recursively.
  virtual void VisibilityChanged(View* starting_from, bool is_visible);

  // This method is invoked when the parent NativeView of the widget that the
  // view is attached to has changed and the view hierarchy has not changed.
  // ViewHierarchyChanged() is called when the parent NativeView of the widget
  // that the view is attached to is changed as a result of changing the view
  // hierarchy. Overriding this method is useful for tracking which
  // FocusManager manages this view.
  virtual void NativeViewHierarchyChanged();

  // This method is invoked for a view when it is attached to a hierarchy with
  // a widget, i.e. GetWidget() starts returning a non-null result.
  // It is also called when the view is moved to a different widget.
  virtual void AddedToWidget();

  // This method is invoked for a view when it is removed from a hierarchy with
  // a widget or moved to a different widget.
  virtual void RemovedFromWidget();

  // Painting ------------------------------------------------------------------

  // Responsible for calling Paint() on child Views. Override to control the
  // order child Views are painted.
  virtual void PaintChildren(const PaintInfo& info);

  // Override to provide rendering in any part of the View's bounds. Typically
  // this is the "contents" of the view. If you override this method you will
  // have to call the subsequent OnPaint*() methods manually.
  virtual void OnPaint(gfx::Canvas* canvas);

  // Override to paint a background before any content is drawn. Typically this
  // is done if you are satisfied with a default OnPaint handler but wish to
  // supply a different background.
  virtual void OnPaintBackground(gfx::Canvas* canvas);

  // Override to paint a border not specified by SetBorder().
  virtual void OnPaintBorder(gfx::Canvas* canvas);

  // Returns the type of scaling to be done for this View. Override this to
  // change the default scaling type from |kScaleToFit|. You would want to
  // override this for a view and return |kScaleToScaleFactor| in cases where
  // scaling should cause no distortion. Such as in the case of an image or
  // an icon.
  virtual PaintInfo::ScaleType GetPaintScaleType() const;

  // Accelerated painting ------------------------------------------------------

  // Returns the offset from this view to the nearest ancestor with a layer. If
  // |layer_parent| is non-NULL it is set to the nearest ancestor with a layer.
  virtual LayerOffsetData CalculateOffsetToAncestorWithLayer(
      ui::Layer** layer_parent);

  // Updates the view's layer's parent. Called when a view is added to a view
  // hierarchy, responsible for parenting the view's layer to the enclosing
  // layer in the hierarchy.
  virtual void UpdateParentLayer();

  // If this view has a layer, the layer is reparented to |parent_layer| and its
  // bounds is set based on |point|. If this view does not have a layer, then
  // recurses through all children. This is used when adding a layer to an
  // existing view to make sure all descendants that have layers are parented to
  // the right layer.
  void MoveLayerToParent(ui::Layer* parent_layer,
                         const LayerOffsetData& offset_data);

  // Called to update the bounds of any child layers within this View's
  // hierarchy when something happens to the hierarchy.
  void UpdateChildLayerBounds(const LayerOffsetData& offset_data);

  // Overridden from ui::LayerDelegate:
  void OnPaintLayer(const ui::PaintContext& context) override;
  void OnDeviceScaleFactorChanged(float old_device_scale_factor,
                                  float new_device_scale_factor) override;

  // Finds the layer that this view paints to (it may belong to an ancestor
  // view), then reorders the immediate children of that layer to match the
  // order of the view tree.
  virtual void ReorderLayers();

  // This reorders the immediate children of |*parent_layer| to match the
  // order of the view tree. Child layers which are owned by a view are
  // reordered so that they are below any child layers not owned by a view.
  // Widget::ReorderNativeViews() should be called to reorder any child layers
  // with an associated view. Widget::ReorderNativeViews() may reorder layers
  // below layers owned by a view.
  virtual void ReorderChildLayers(ui::Layer* parent_layer);

  // Notifies parents about a layer being created or destroyed in a child. An
  // example where a subclass may override this method is when it wants to clip
  // the child by adding its own layer.
  virtual void OnChildLayerChanged(View* child);

  // Input ---------------------------------------------------------------------

  virtual DragInfo* GetDragInfo();

  // Focus ---------------------------------------------------------------------

  // Override to be notified when focus has changed either to or from this View.
  virtual void OnFocus();
  virtual void OnBlur();

  // Handle view focus/blur events for this view.
  void Focus();
  void Blur();

  // System events -------------------------------------------------------------

  // Called when the UI theme (not the NativeTheme) has changed, overriding
  // allows individual Views to do special cleanup and processing (such as
  // dropping resource caches).  To dispatch a theme changed notification, call
  // Widget::ThemeChanged().
  virtual void OnThemeChanged() {}

  // Tooltips ------------------------------------------------------------------

  // Views must invoke this when the tooltip text they are to display changes.
  void TooltipTextChanged();

  // Drag and drop -------------------------------------------------------------

  // These are cover methods that invoke the method of the same name on
  // the DragController. Subclasses may wish to override rather than install
  // a DragController.
  // See DragController for a description of these methods.
  virtual int GetDragOperations(const gfx::Point& press_pt);
  virtual void WriteDragData(const gfx::Point& press_pt, OSExchangeData* data);

  // Returns whether we're in the middle of a drag session that was initiated
  // by us.
  bool InDrag() const;

  // Returns how much the mouse needs to move in one direction to start a
  // drag. These methods cache in a platform-appropriate way. These values are
  // used by the public static method ExceededDragThreshold().
  static int GetHorizontalDragThreshold();
  static int GetVerticalDragThreshold();

  // NativeTheme ---------------------------------------------------------------

  // Invoked when the NativeTheme associated with this View changes, including
  // when one first becomes available (after the view is added to a widget
  // hierarchy).
  virtual void OnNativeThemeChanged(const ui::NativeTheme* theme) {}

  // Debugging -----------------------------------------------------------------

#if !defined(NDEBUG)
  // Returns string containing a graph of the views hierarchy in graphViz DOT
  // language (http://graphviz.org/). Can be called within debugger and save
  // to a file to compile/view.
  // Note: Assumes initial call made with first = true.
  virtual std::string PrintViewGraph(bool first);

  // Some classes may own an object which contains the children to displayed in
  // the views hierarchy. The above function gives the class the flexibility to
  // decide which object should be used to obtain the children, but this
  // function makes the decision explicit.
  std::string DoPrintViewGraph(bool first, View* view_with_children);
#endif

 private:
  friend class internal::PreEventDispatchHandler;
  friend class internal::PostEventDispatchHandler;
  friend class internal::RootView;
  friend class internal::ScopedChildrenLock;
  friend class FocusManager;
  friend class ViewLayerTest;
  friend class ViewLayerPixelCanvasTest;
  friend class Widget;
  FRIEND_TEST_ALL_PREFIXES(ViewTest, PaintWithMovedViewUsesCache);
  FRIEND_TEST_ALL_PREFIXES(ViewTest, PaintWithMovedViewUsesCacheInRTL);
  FRIEND_TEST_ALL_PREFIXES(ViewTest, PaintWithUnknownInvalidation);

  // Painting  -----------------------------------------------------------------

  enum SchedulePaintType {
    // Indicates the size is the same (only the origin changed).
    SCHEDULE_PAINT_SIZE_SAME,

    // Indicates the size changed (and possibly the origin).
    SCHEDULE_PAINT_SIZE_CHANGED
  };

  // Invoked before and after the bounds change to schedule painting the old and
  // new bounds.
  void SchedulePaintBoundsChanged(SchedulePaintType type);

  // Schedules a paint on the parent View if it exists.
  void SchedulePaintOnParent();

  // Returns whether this view is eligible for painting, i.e. is visible and
  // nonempty.  Note that this does not behave like IsDrawn(), since it doesn't
  // check ancestors recursively; rather, it's used to prune subtrees of views
  // during painting.
  bool ShouldPaint() const;

  // Adjusts the transform of |recorder| in advance of painting.
  void SetUpTransformRecorderForPainting(
      const gfx::Vector2d& offset_from_parent,
      ui::TransformRecorder* recorder) const;

  // Recursively calls the painting method |func| on all non-layered children,
  // in Z order.
  void RecursivePaintHelper(void (View::*func)(const PaintInfo&),
                            const PaintInfo& info);

  // Invokes Paint() and, if necessary, PaintDebugRects().  Should be called
  // only on the root of a widget/layer.  PaintDebugRects() is invoked as a
  // separate pass, instead of being rolled into Paint(), so that siblings will
  // not obscure debug rects.
  void PaintFromPaintRoot(const ui::PaintContext& parent_context);

  // Draws a semitransparent rect to indicate the bounds of this view.
  // Recursively does the same for all children.  Invoked only with
  // --draw-view-bounds-rects.
  void PaintDebugRects(const PaintInfo& paint_info);

  // Tree operations -----------------------------------------------------------

  // Removes |view| from the hierarchy tree.  If |update_focus_cycle| is true,
  // the next and previous focusable views of views pointing to this view are
  // updated.  If |update_tool_tip| is true, the tooltip is updated.  If
  // |delete_removed_view| is true, the view is also deleted (if it is parent
  // owned).  If |new_parent| is not NULL, the remove is the result of
  // AddChildView() to a new parent.  For this case, |new_parent| is the View
  // that |view| is going to be added to after the remove completes.
  void DoRemoveChildView(View* view,
                         bool update_focus_cycle,
                         bool update_tool_tip,
                         bool delete_removed_view,
                         View* new_parent);

  // Call ViewHierarchyChanged() for all child views and all parents.
  // |old_parent| is the original parent of the View that was removed.
  // If |new_parent| is not NULL, the View that was removed will be reparented
  // to |new_parent| after the remove operation.
  // If is_removed_from_widget is true, calls RemovedFromWidget for all
  // children.
  void PropagateRemoveNotifications(View* old_parent,
                                    View* new_parent,
                                    bool is_removed_from_widget);

  // Call ViewHierarchyChanged() for all children.
  // If is_added_to_widget is true, calls AddedToWidget for all children.
  void PropagateAddNotifications(const ViewHierarchyChangedDetails& details,
                                 bool is_added_to_widget);

  // Propagates NativeViewHierarchyChanged() notification through all the
  // children.
  void PropagateNativeViewHierarchyChanged();

  // Takes care of registering/unregistering accelerators if
  // |register_accelerators| true and calls ViewHierarchyChanged().
  void ViewHierarchyChangedImpl(bool register_accelerators,
                                const ViewHierarchyChangedDetails& details);

  // Invokes OnNativeThemeChanged() on this and all descendants.
  void PropagateNativeThemeChanged(const ui::NativeTheme* theme);

  // Size and disposition ------------------------------------------------------

  // Call VisibilityChanged() recursively for all children.
  void PropagateVisibilityNotifications(View* from, bool is_visible);

  // Registers/unregisters accelerators as necessary and calls
  // VisibilityChanged().
  void VisibilityChangedImpl(View* starting_from, bool is_visible);

  // Responsible for propagating bounds change notifications to relevant
  // views.
  void BoundsChanged(const gfx::Rect& previous_bounds);

  // Visible bounds notification registration.
  // When a view is added to a hierarchy, it and all its children are asked if
  // they need to be registered for "visible bounds within root" notifications
  // (see comment on OnVisibleBoundsChanged()). If they do, they are registered
  // with every ancestor between them and the root of the hierarchy.
  static void RegisterChildrenForVisibleBoundsNotification(View* view);
  static void UnregisterChildrenForVisibleBoundsNotification(View* view);
  void RegisterForVisibleBoundsNotification();
  void UnregisterForVisibleBoundsNotification();

  // Adds/removes view to the list of descendants that are notified any time
  // this views location and possibly size are changed.
  void AddDescendantToNotify(View* view);
  void RemoveDescendantToNotify(View* view);

  // Non-templatized backend for SetLayoutManager().
  void SetLayoutManagerImpl(std::unique_ptr<LayoutManager> layout);

  // Transformations -----------------------------------------------------------

  // Returns in |transform| the transform to get from coordinates of |ancestor|
  // to this. Returns true if |ancestor| is found. If |ancestor| is not found,
  // or NULL, |transform| is set to convert from root view coordinates to this.
  bool GetTransformRelativeTo(const View* ancestor,
                              gfx::Transform* transform) const;

  // Coordinate conversion -----------------------------------------------------

  // Convert a point in the view's coordinate to an ancestor view's coordinate
  // system using necessary transformations. Returns whether the point was
  // successfully converted to the ancestor's coordinate system.
  bool ConvertPointForAncestor(const View* ancestor, gfx::Point* point) const;

  // Convert a point in the ancestor's coordinate system to the view's
  // coordinate system using necessary transformations. Returns whether the
  // point was successfully converted from the ancestor's coordinate system
  // to the view's coordinate system.
  bool ConvertPointFromAncestor(const View* ancestor, gfx::Point* point) const;

  // Convert a rect in the view's coordinate to an ancestor view's coordinate
  // system using necessary transformations. Returns whether the rect was
  // successfully converted to the ancestor's coordinate system.
  bool ConvertRectForAncestor(const View* ancestor, gfx::RectF* rect) const;

  // Convert a rect in the ancestor's coordinate system to the view's
  // coordinate system using necessary transformations. Returns whether the
  // rect was successfully converted from the ancestor's coordinate system
  // to the view's coordinate system.
  bool ConvertRectFromAncestor(const View* ancestor, gfx::RectF* rect) const;

  // Accelerated painting ------------------------------------------------------

  // Creates the layer and related fields for this view.
  void CreateLayer(ui::LayerType layer_type);

  // Recursively calls UpdateParentLayers() on all descendants, stopping at any
  // Views that have layers. Calls UpdateParentLayer() for any Views that have
  // a layer with no parent. If at least one descendant had an unparented layer
  // true is returned.
  bool UpdateParentLayers();

  // Parents this view's layer to |parent_layer|, and sets its bounds and other
  // properties in accordance to |offset|, the view's offset from the
  // |parent_layer|.
  void ReparentLayer(const gfx::Vector2d& offset, ui::Layer* parent_layer);

  // Called to update the layer visibility. The layer will be visible if the
  // View itself, and all its parent Views are visible. This also updates
  // visibility of the child layers.
  void UpdateLayerVisibility();
  void UpdateChildLayerVisibility(bool visible);

  enum class LayerChangeNotifyBehavior {
    // Notify the parent chain about the layer change.
    NOTIFY,
    // Don't notify the parent chain about the layer change.
    DONT_NOTIFY
  };

  // Destroys the layer associated with this view, and reparents any descendants
  // to the destroyed layer's parent. If the view does not currently have a
  // layer, this has no effect.
  // The |notify_parents| enum controls whether a notification about the layer
  // change is sent to the parents.
  void DestroyLayerImpl(LayerChangeNotifyBehavior notify_parents);

  // Notifies parents about layering changes in the view. This includes layer
  // creation and destruction.
  void NotifyParentsOfLayerChange();


  // Orphans the layers in this subtree that are parented to layers outside of
  // this subtree.
  void OrphanLayers();

  // Adjust the layer's offset so that it snaps to the physical pixel boundary.
  // This has no effect if the view does not have an associated layer.
  void SnapLayerToPixelBoundary(const LayerOffsetData& offset_data);

  // Sets the layer's bounds given in DIP coordinates.
  void SetLayerBounds(const gfx::Size& size_in_dip,
                      const LayerOffsetData& layer_offset_data);

  // Input ---------------------------------------------------------------------

  bool ProcessMousePressed(const ui::MouseEvent& event);
  bool ProcessMouseDragged(const ui::MouseEvent& event);
  void ProcessMouseReleased(const ui::MouseEvent& event);

  // Accelerators --------------------------------------------------------------

  // Registers this view's keyboard accelerators that are not registered to
  // FocusManager yet, if possible.
  void RegisterPendingAccelerators();

  // Unregisters all the keyboard accelerators associated with this view.
  // |leave_data_intact| if true does not remove data from accelerators_ array,
  // so it could be re-registered with other focus manager
  void UnregisterAccelerators(bool leave_data_intact);

  // Focus ---------------------------------------------------------------------

  // Initialize the previous/next focusable views of the specified view relative
  // to the view at the specified index.
  void InitFocusSiblings(View* view, int index);

  // Helper function to advance focus, in case the currently focused view has
  // become unfocusable.
  void AdvanceFocusIfNecessary();

  // System events -------------------------------------------------------------

  // Used to propagate theme changed notifications from the root view to all
  // views in the hierarchy.
  void PropagateThemeChanged();

  // Used to propagate device scale factor changed notifications from the root
  // view to all views in the hierarchy.
  void PropagateDeviceScaleFactorChanged(float old_device_scale_factor,
                                         float new_device_scale_factor);

  // Tooltips ------------------------------------------------------------------

  // Propagates UpdateTooltip() to the TooltipManager for the Widget.
  // This must be invoked any time the View hierarchy changes in such a way
  // the view under the mouse differs. For example, if the bounds of a View is
  // changed, this is invoked. Similarly, as Views are added/removed, this
  // is invoked.
  void UpdateTooltip();

  // Drag and drop -------------------------------------------------------------

  // Starts a drag and drop operation originating from this view. This invokes
  // WriteDragData to write the data and GetDragOperations to determine the
  // supported drag operations. When done, OnDragDone is invoked. |press_pt| is
  // in the view's coordinate system.
  // Returns true if a drag was started.
  bool DoDrag(const ui::LocatedEvent& event,
              const gfx::Point& press_pt,
              ui::DragDropTypes::DragEventSource source);

  //////////////////////////////////////////////////////////////////////////////

  // Creation and lifetime -----------------------------------------------------

  // False if this View is owned by its parent - i.e. it will be deleted by its
  // parent during its parents destruction. False is the default.
  bool owned_by_client_;

  // Attributes ----------------------------------------------------------------

  // The id of this View. Used to find this View.
  int id_;

  // The group of this view. Some view subclasses use this id to find other
  // views of the same group. For example radio button uses this information
  // to find other radio buttons.
  int group_;

  // Tree operations -----------------------------------------------------------

  // This view's parent.
  View* parent_;

  // This view's children.
  Views children_;

#if DCHECK_IS_ON()
  // True while iterating over |children_|. Used to detect and DCHECK when
  // |children_| is mutated during iteration.
  mutable bool iterating_;
#endif

  bool can_process_events_within_subtree_;

  // Size and disposition ------------------------------------------------------

  base::Optional<gfx::Size> preferred_size_;

  // This View's bounds in the parent coordinate system.
  gfx::Rect bounds_;

  // Whether this view is visible.
  bool visible_;

  // Whether this view is enabled.
  bool enabled_;

  // When this flag is on, a View receives a mouse-enter and mouse-leave event
  // even if a descendant View is the event-recipient for the real mouse
  // events. When this flag is turned on, and mouse moves from outside of the
  // view into a child view, both the child view and this view receives
  // mouse-enter event. Similarly, if the mouse moves from inside a child view
  // and out of this view, then both views receive a mouse-leave event.
  // When this flag is turned off, if the mouse moves from inside this view into
  // a child view, then this view receives a mouse-leave event. When this flag
  // is turned on, it does not receive the mouse-leave event in this case.
  // When the mouse moves from inside the child view out of the child view but
  // still into this view, this view receives a mouse-enter event if this flag
  // is turned off, but doesn't if this flag is turned on.
  // This flag is initialized to false.
  bool notify_enter_exit_on_child_;

  // Whether or not RegisterViewForVisibleBoundsNotification on the RootView
  // has been invoked.
  bool registered_for_visible_bounds_notification_;

  // List of descendants wanting notification when their visible bounds change.
  std::unique_ptr<Views> descendants_to_notify_;

  // Transformations -----------------------------------------------------------

  // Painting will be clipped to this path. TODO(estade): this doesn't work for
  // layers.
  gfx::Path clip_path_;

  // Layout --------------------------------------------------------------------

  // Whether the view needs to be laid out.
  bool needs_layout_;

  // The View's LayoutManager defines the sizing heuristics applied to child
  // Views. The default is absolute positioning according to bounds_.
  std::unique_ptr<LayoutManager> layout_manager_;

  // Whether this View's layer should be snapped to the pixel boundary.
  bool snap_layer_to_pixel_boundary_;

  // Painting ------------------------------------------------------------------

  // Background
  std::unique_ptr<Background> background_;

  // Border.
  std::unique_ptr<Border> border_;

  // Cached output of painting to be reused in future frames until invalidated.
  ui::PaintCache paint_cache_;

  // Native theme --------------------------------------------------------------

  // A native theme for this view and its descendants. Typically null, in which
  // case the native theme is drawn from the parent view (eventually the
  // widget).
  ui::NativeTheme* native_theme_ = nullptr;

  // RTL painting --------------------------------------------------------------

  // Indicates whether or not the gfx::Canvas object passed to View::Paint()
  // is going to be flipped horizontally (using the appropriate transform) on
  // right-to-left locales for this View.
  bool flip_canvas_on_paint_for_rtl_ui_;

  // Accelerated painting ------------------------------------------------------

  bool paint_to_layer_;

  // Accelerators --------------------------------------------------------------

  // Focus manager accelerators registered on.
  FocusManager* accelerator_focus_manager_;

  // The list of accelerators. List elements in the range
  // [0, registered_accelerator_count_) are already registered to FocusManager,
  // and the rest are not yet.
  std::unique_ptr<std::vector<ui::Accelerator>> accelerators_;
  size_t registered_accelerator_count_;

  // Focus ---------------------------------------------------------------------

  // Next view to be focused when the Tab key is pressed.
  View* next_focusable_view_;

  // Next view to be focused when the Shift-Tab key combination is pressed.
  View* previous_focusable_view_;

  // The focus behavior of the view in regular and accessibility mode.
  FocusBehavior focus_behavior_;

  // Context menus -------------------------------------------------------------

  // The menu controller.
  ContextMenuController* context_menu_controller_;

  // Drag and drop -------------------------------------------------------------

  DragController* drag_controller_;

  // Input  --------------------------------------------------------------------

  std::unique_ptr<ViewTargeter> targeter_;

  // Accessibility -------------------------------------------------------------

  // Manages the accessibility interface for this View.
  std::unique_ptr<ViewAccessibility> view_accessibility_;

  // Observers -------------------------------------------------------------

  base::ObserverList<ViewObserver> observers_;

  DISALLOW_COPY_AND_ASSIGN(View);
};

}  // namespace views

#endif  // UI_VIEWS_VIEW_H_