Prepare ScreenWin To Use Per-Monitor DPI

ui/display/win/screen_win.cc

 // 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.
 
 #include "ui/display/win/screen_win.h"
 
 #include <windows.h>
+#include <shellscalingapi.h>
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
+#include "base/win/win_util.h"
 #include "ui/display/display.h"
 #include "ui/display/manager/display_layout.h"
 #include "ui/display/manager/display_layout_builder.h"
 #include "ui/display/win/display_info.h"
 #include "ui/display/win/dpi.h"
 #include "ui/display/win/scaling_util.h"
 #include "ui/display/win/screen_win_display.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/geometry/vector2d.h"
 
 namespace display {
 namespace win {
 namespace {
 
 // TODO(robliao): http://crbug.com/615514 Remove when ScreenWin usage is
 // resolved with Desktop Aura and WindowTreeHost.
 ScreenWin* g_screen_win_instance = nullptr;
 
+float GetMonitorScaleFactor(HMONITOR monitor) {
+  if (base::win::IsProcessPerMonitorDpiAware()) {
+    using GetDpiForMonitorPtr =
+        HRESULT (WINAPI *)(HMONITOR, MONITOR_DPI_TYPE, UINT*, UINT*);

[scottmg, 2016/06/27 17:55:04]

Same here.

nit; This will also requery each time if get_dpi_for_monitor_func is null after
lookup. Consider something like

static auto get_dpi_for_monitor = []() {
  return reinterpret_cast<...>(::GetProcAddress(...));
}();

[robliao, 2016/06/27 18:39:29]

Done.

+    static GetDpiForMonitorPtr get_dpi_for_monitor_func = nullptr;
+    if (!get_dpi_for_monitor_func) {
+      HMODULE shcore_dll = ::LoadLibrary(L"shcore.dll");
+      if (shcore_dll) {
+        get_dpi_for_monitor_func =
+            reinterpret_cast<GetDpiForMonitorPtr>(
+                ::GetProcAddress(shcore_dll, "GetDpiForMonitor"));
+      }
+    }
+
+    UINT dpi_x;
+    UINT dpi_y;
+    if (get_dpi_for_monitor_func &&
+        SUCCEEDED(get_dpi_for_monitor_func(monitor, MDT_EFFECTIVE_DPI,

[scottmg, 2016/06/27 17:55:04]

Maybe DCHECK(monitor)?

[robliao, 2016/06/27 18:39:29]

Done at the top now.

+                                           &dpi_x, &dpi_y))) {
+      DCHECK_EQ(dpi_x, dpi_y);
+      return GetScalingFactorFromDPI(dpi_x);
+    }
+  }
+  return GetDPIScale();
+}
+
 std::vector<DisplayInfo> FindAndRemoveTouchingDisplayInfos(
     const DisplayInfo& ref_display_info,
     std::vector<DisplayInfo>* display_infos) {
   std::vector<DisplayInfo> touching_display_infos;
   display_infos->erase(
       std::remove_if(display_infos->begin(), display_infos->end(),
           [&touching_display_infos, ref_display_info](
               const DisplayInfo& display_info) {
             if (DisplayInfosTouch(ref_display_info, display_info)) {
               touching_display_infos.push_back(display_info);
@@ skipping 94 matching lines @@
   return monitor_info;
 }
 
 BOOL CALLBACK EnumMonitorCallback(HMONITOR monitor,
                                   HDC hdc,
                                   LPRECT rect,
                                   LPARAM data) {
   std::vector<DisplayInfo>* display_infos =
       reinterpret_cast<std::vector<DisplayInfo>*>(data);
   DCHECK(display_infos);
-  // TODO(robliao): When ready, replace the GetDPIScale with GetDpiForMonitor
-  // to get the actual DPI for the HMONITOR.
   display_infos->push_back(DisplayInfo(MonitorInfoFromHMONITOR(monitor),
-                                       GetDPIScale()));
+                                       GetMonitorScaleFactor(monitor)));
   return TRUE;
 }
 
 std::vector<DisplayInfo> GetDisplayInfosFromSystem() {
   std::vector<DisplayInfo> display_infos;
   EnumDisplayMonitors(nullptr, nullptr, EnumMonitorCallback,
                       reinterpret_cast<LPARAM>(&display_infos));
   DCHECK_EQ(static_cast<size_t>(::GetSystemMetrics(SM_CMONITORS)),
             display_infos.size());
   return display_infos;
@@ skipping 336 matching lines @@
 ScreenWinDisplay ScreenWin::GetScreenWinDisplayVia(Getter getter,
                                                    GetterType value) {
   if (!g_screen_win_instance)
     return ScreenWinDisplay();
 
   return (g_screen_win_instance->*getter)(value);
 }
 
 }  // namespace win
 }  // namespace display