Refactor Windows DPI Point, Rect, and Size for Multiple Monitor DPI Awareness

ui/gfx/screen_win.h

Index: ui/gfx/screen_win.h
diff --git a/ui/gfx/screen_win.h b/ui/gfx/screen_win.h
index b1488ae05bb850b9cfc4cfa762219b56d47ff5d0..fc746909acd5ba8f97c5ad0889903c515920100e 100644
--- a/ui/gfx/screen_win.h
+++ b/ui/gfx/screen_win.h
@@ -16,10 +16,89 @@
 
 namespace gfx {
 
+class Point;
+class Rect;
+class Size;
+
+// Windows historically has had a hard time handling displays of DPIs higher
+// than 96. Handling multiple DPI displays means we have to deal with Windows'
+// monitor physical coordinates and map into Chrome's DIP coordinates.
+//
+// To do this, ScreenWin reasons over monitors as a tree using the primary
+// monitor as the root. Any monitor touching this root is considered a child.
+// Subsequent generations are formed similarly, having preferring parents that
+// are discovered earlier. As a result, if there is a monitor that touches two
+// other monitors, the earliest discovered monitor is the parent.
+//
+// This also presumes that all monitors are connected components. Windows, by UI
+// construction restricts the layout of monitors to connected components.
+//
+// All scaling transformations are performed with respect to this physical-DIP
+// mapping.
+//
+// Note that this does not handle cases where a scaled display may have
+// insufficent room to lay out its children. In these cases, a DIP point could
+// map to multiple screen points due to overlap. The first discovered screen
+// will take precedence.
 class GFX_EXPORT ScreenWin : public Screen {
  public:
   ScreenWin();
-  ~ScreenWin() override;
+  virtual ~ScreenWin() override;
+
+  // Converts a screen pixel point to a DIP point.
+  // The DPI scale is performed relative to the display containing the screen
+  // pixel point maintaining a constant origin on both Screen and DIP (same as
+  // Windows).
+  static Point ScreenToDIPPoint(const Point& pixel_point);
+
+  // Converts a DIP point to a screen pixel point.
+  // The DPI scale is performed relative to the display containing the DIP point
+  // maintaining a constant origin on both Screen and DIP (same as Windows).
+  static Point DIPToScreenPoint(const Point& dip_point);
+
+  // Converts a client pixel point relative to |hwnd| to a DIP point.
+  // The DPI scale is performed relative to |hwnd| using an origin of (0, 0).
+  static Point ClientToDIPPoint(HWND hwnd, const Point& client_point);
+
+  // Converts a client DIP point relative to |hwnd| to a client pixel point.
+  // The DPI scale is performed relative to |hwnd| using an origin of (0, 0).
+  static Point DIPToClientPoint(HWND hwnd, const Point& dip_point);
+
+  // WARNING: there is no right way to scale sizes and rects. The implementation
+  // of these strives to maintain a constant size by scaling the size
+  // independent of the origin. An alternative is to get the enclosing rect,
+  // which is the right way for some situations. Understand which you need
+  // before blindly assuming this is the right way.
+
+  // Converts a screen rect to a DIP rect.
+  // The DPI scale is performed relative to the display nearest to |hwnd|
+  // maintaining a constant origin on both Screen and DIP (same as Windows).
+  // If |hwnd| is null, scaling will be performed to the display nearest to
+  // |pixel_bounds|.
+  static Rect ScreenToDIPRect(HWND hwnd, const Rect& pixel_bounds);
+
+  // Converts a DIP rect to a screen rect.
+  // The DPI scale is performed relative to the display nearest to |hwnd|
+  // maintaining a constant origin on both Screen and DIP (same as Windows).
+  // If |hwnd| is null, scaling will be performed to the display nearest to
+  // |dip_bounds|.
+  static Rect DIPToScreenRect(HWND hwnd, const Rect& dip_bounds);
+
+  // Converts a client rect to a DIP rect.
+  // The DPI scale is performed relative to |hwnd| using an origin of (0, 0).
+  static Rect ClientToDIPRect(HWND hwnd, const Rect& pixel_bounds);
+
+  // Converts a DIP rect to a client rect.
+  // The DPI scale is performed relative to |hwnd| using an origin of (0, 0).
+  static Rect DIPToClientRect(HWND hwnd, const Rect& dip_bounds);
+
+  // Converts a screen size to a DIP size.
+  // The DPI scale is performed relative to the display nearest to |hwnd|.
+  static Size ScreenToDIPSize(HWND hwnd, const Size& size_in_pixels);
+
+  // Converts a DIP size to a screen size.
+  // The DPI scale is performed relative to the display nearest to |hwnd|.
+  static Size DIPToScreenSize(HWND hwnd, const Size& dip_size);
 
   // Returns the HWND associated with the NativeView.
   virtual HWND GetHWNDFromNativeView(NativeView window) const;
@@ -28,7 +107,36 @@ class GFX_EXPORT ScreenWin : public Screen {
   virtual NativeWindow GetNativeWindowFromHWND(HWND hwnd) const;
 
  protected:
-  // Overridden from gfx::Screen:
+  // Holds the parameters used to create a gfx::DisplayWin.
+  class GFX_EXPORT DisplayInfo {
+   public:
+    DisplayInfo(HMONITOR monitor, float device_scale_factor);
+    DisplayInfo(const MONITORINFOEX& monitor_info,
+                gfx::Display::Rotation rotation,
+                float device_scale_factor);
+
+    int64_t id() const { return id_; }
+    gfx::Display::Rotation rotation() const { return rotation_; }
+    const gfx::Rect& screen_rect() const { return screen_rect_; }
+    const gfx::Rect& screen_work_rect() const { return screen_work_rect_; }
+    float device_scale_factor() const { return device_scale_factor_; }
+
+   private:
+    void InitializeFromMonitorInfo(const MONITORINFOEX& monitor_info);
+
+    int64_t id_;
+    gfx::Display::Rotation rotation_;
+    gfx::Rect screen_rect_;
+    gfx::Rect screen_work_rect_;
+    float device_scale_factor_;
+  };
+
+  // For Unit Tests.
+  explicit ScreenWin(const std::vector<DisplayInfo>& display_infos);
+
+  static int64_t HashDeviceName(const wchar_t* device_name);
+
+  // Overridden from gfx::Screen.
   gfx::Point GetCursorScreenPoint() override;
   gfx::NativeWindow GetWindowUnderCursor() override;
   gfx::NativeWindow GetWindowAtScreenPoint(const gfx::Point& point) override;
@@ -40,23 +148,53 @@ class GFX_EXPORT ScreenWin : public Screen {
   gfx::Display GetPrimaryDisplay() const override;
   void AddObserver(DisplayObserver* observer) override;
   void RemoveObserver(DisplayObserver* observer) override;
+  gfx::Rect ScreenToDIPRectInWindow(
+      NativeView view, const gfx::Rect& screen_rect) const override;
+  gfx::Rect DIPToScreenRectInWindow(
+      NativeView view, const gfx::Rect& dip_rect) const override;
 
  private:
-  FRIEND_TEST_ALL_PREFIXES(ScreenWinTest, SingleDisplay1x);
-  FRIEND_TEST_ALL_PREFIXES(ScreenWinTest, SingleDisplay2x);
+  friend class TestScreenWinInitializer;
+
+  // A gfx::Display that knows about its physical bounds.
+  class DisplayWin;
+
+  static DisplayWin GetDisplayNearestHWND(HWND hwnd);
+  static DisplayWin GetDisplayNearestScreenRect(const Rect& screen_rect);
+  static DisplayWin GetDisplayNearestScreenPoint(const Point& screen_point);
+  static DisplayWin GetDisplayNearestDIPRect(const Rect& rect);
+  static DisplayWin GetDisplayNearestDIPPoint(const Point& dip_point);
+  static float GetScaleFactorForHWND(HWND hwnd);
+  static float GetScaleFactorForScreenPoint(const Point& screen_point);
+  static std::vector<DisplayInfo>::const_iterator FindTouchingDisplayInfo(
+      const DisplayWin& display, const std::vector<DisplayInfo>& display_infos);
+  static std::vector<DisplayWin> GetDisplaysFromDisplayInfos(
+      const std::vector<DisplayInfo>& display_infos);
+  static std::vector<DisplayWin> GetDisplayWins();
+  static BOOL CALLBACK EnumMonitorCallback(HMONITOR monitor,
+                                           HDC hdc,
+                                           LPRECT rect,
+                                           LPARAM data);
 
   void OnWndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam);
 
-  static std::vector<gfx::Display> GetDisplaysForMonitorInfos(
-      const std::vector<MONITORINFOEX>& monitor_infos);
+  // For Unit Tests.
+  virtual MONITORINFOEX MonitorInfoFromScreenPoint(
+      const gfx::Point& screen_point) const;
+  virtual MONITORINFOEX MonitorInfoFromScreenRect(const gfx::Rect& screen_rect)
+      const;
+  virtual MONITORINFOEX MonitorInfoFromWindow(HWND hwnd) const;
+  virtual HWND GetRootWindow(HWND hwnd) const;
+
+  DisplayWin GetDisplayWin(const MONITORINFOEX& monitor_info) const;
 
   // Helper implementing the DisplayObserver handling.
   gfx::DisplayChangeNotifier change_notifier_;
 
   scoped_ptr<SingletonHwndObserver> singleton_hwnd_observer_;
 
-  // Current list of displays.
-  std::vector<gfx::Display> displays_;
+  // Current list of DisplayWins.
+  std::vector<DisplayWin> display_wins_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenWin);
 };