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..715f434c0e987243ccaac6c429cc3325bebdc183 100644
--- a/ui/gfx/screen_win.h
+++ b/ui/gfx/screen_win.h
@@ -5,21 +5,108 @@
 #ifndef UI_GFX_SCREEN_WIN_H_
 #define UI_GFX_SCREEN_WIN_H_
 
-#include "base/compiler_specific.h"
-#include "base/gtest_prod_util.h"
+#include <vector>
+
 #include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
 #include "ui/gfx/display_change_notifier.h"
 #include "ui/gfx/gfx_export.h"
 #include "ui/gfx/screen.h"
-#include "ui/gfx/win/singleton_hwnd_observer.h"
+#include "ui/gfx/win/display_manager_observer.h"
 
 namespace gfx {
 
-class GFX_EXPORT ScreenWin : public Screen {
+class Point;
+class Rect;
+class Size;
+
+namespace win {
+
+class DisplayInfo;
+class DisplayManager;
+class ScreenWinDisplay;
+
+}  // namespace win
+
+// 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 gfx::win::DisplayManagerObserver {
  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;
@@ -40,23 +127,22 @@ 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);
-
-  void OnWndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam);
-
-  static std::vector<gfx::Display> GetDisplaysForMonitorInfos(
-      const std::vector<MONITORINFOEX>& monitor_infos);
+  // Overridden from gfx::win::DisplayManagerObserver:
+  void OnDisplaysChanged(
+      const std::vector<gfx::win::ScreenWinDisplay> old_screen_win_displays,
+      const std::vector<gfx::win::ScreenWinDisplay> new_screen_win_displays)
+      override;
 
+ private:
   // Helper implementing the DisplayObserver handling.
   gfx::DisplayChangeNotifier change_notifier_;
 
-  scoped_ptr<SingletonHwndObserver> singleton_hwnd_observer_;
-
-  // Current list of displays.
-  std::vector<gfx::Display> displays_;
+  gfx::win::DisplayManager* display_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenWin);
 };