Allow Chrome's Non-Client Area To Be Scaled on DPI Changes

ui/gfx/win/window_impl.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/gfx/win/window_impl.h"
 
 #include <list>
 
 #include "base/bind.h"
 #include "base/debug/alias.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/synchronization/lock.h"
+#include "base/win/win_util.h"
 #include "base/win/wrapped_window_proc.h"
 #include "ui/gfx/win/hwnd_util.h"
 
 namespace gfx {
 
 static const DWORD kWindowDefaultChildStyle =
     WS_CHILD | WS_VISIBLE | WS_CLIPCHILDREN | WS_CLIPSIBLINGS;
 static const DWORD kWindowDefaultStyle = WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN;
 static const DWORD kWindowDefaultExStyle = 0;
 
@@ skipping 180 matching lines @@
     height = bounds.height();
   }
 
   ATOM atom = GetWindowClassAtom();
   bool destroyed = false;
   destroyed_ = &destroyed;
   HWND hwnd = CreateWindowEx(window_ex_style_,
                              reinterpret_cast<wchar_t*>(atom), NULL,
                              window_style_, x, y, width, height,
                              parent, NULL, NULL, this);
+  if (hwnd && base::win::IsProcessPerMonitorDpiAware()) {
+    static auto enable_child_window_dpi_message_func = []() {
+      // Derived signature; not available in headers.
+      // This call gets Windows to scale the non-client area when WM_DPICHANGED
+      // is fired.

[scottmg, 2016/06/27 19:26:35]

Any semi-documentation you can link here?

[robliao, 2016/06/27 19:58:07]

Unfortunately not that I can find. This is pretty leading edge.

+      using EnableChildWindowDpiMessagePtr = LRESULT (WINAPI*)(HWND, BOOL);
+      HMODULE user32 = GetModuleHandle(L"user32");

[scottmg, 2016/06/27 19:26:35]

Other instances seem to include ".dll".

[robliao, 2016/06/27 19:58:07]

Done.

+      if (user32) {

[scottmg, 2016/06/27 19:26:35]

Don't think you need to check user32 here, just inline into GetProcAddress(); we
just called CreateWindowEx() above.

[robliao, 2016/06/27 19:58:07]

Done. Yup, we seem to do it in other places indeed. Just wanted to guard against
other faliures that GetModuleHandle would encounter, but then we would be in
trouble in other places anyways.

+        return reinterpret_cast<EnableChildWindowDpiMessagePtr>(
+                   GetProcAddress(user32, "EnableChildWindowDpiMessage"));
+      }
+      return reinterpret_cast<EnableChildWindowDpiMessagePtr>(nullptr);
+    }();
+    if (enable_child_window_dpi_message_func)
+      enable_child_window_dpi_message_func(hwnd, TRUE);
+  }
 
   // First nccalcszie (during CreateWindow) for captioned windows is
   // deliberately ignored so force a second one here to get the right
   // non-client set up.
   if (hwnd && (window_style_ & WS_CAPTION)) {
     SetWindowPos(hwnd, NULL, 0, 0, 0, 0,
                  SWP_FRAMECHANGED | SWP_NOMOVE | SWP_NOSIZE |
                  SWP_NOZORDER | SWP_NOACTIVATE | SWP_NOREDRAW);
   }
 
@@ skipping 78 matching lines @@
 }
 
 ATOM WindowImpl::GetWindowClassAtom() {
   HICON icon = GetDefaultWindowIcon();
   HICON small_icon = GetSmallWindowIcon();
   ClassInfo class_info(initial_class_style(), icon, small_icon);
   return ClassRegistrar::GetInstance()->RetrieveClassAtom(class_info);
 }
 
 }  // namespace gfx