Add GetCaptionButtonHeightInDIPs() method

chrome/browser/ui/views/frame/minimize_button_metrics_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 "chrome/browser/ui/views/frame/minimize_button_metrics_win.h"
 
+#include "base/i18n/rtl.h"
 #include "base/logging.h"
-#include "base/i18n/rtl.h"
 #include "base/win/windows_version.h"
 #include "dwmapi.h"
 #include "ui/base/win/shell.h"
+#include "ui/display/display.h"
 #include "ui/display/win/dpi.h"
 #include "ui/display/win/screen_win.h"
 #include "ui/gfx/geometry/point.h"
 
 namespace {
 
 // These constants were determined by manually adding various offsets
 // until the identity switcher was placed at the same location as before.
 // When a new or updated OS version is released, a new constant may need
 // to be added to this list and GetDefaultButtonBoundsOffset() is updated.
@@ skipping 23 matching lines @@
 
 MinimizeButtonMetrics::MinimizeButtonMetrics()
     : hwnd_(nullptr),
       cached_minimize_button_x_delta_(last_cached_minimize_button_x_delta_),
       was_activated_(false) {
 }
 
 MinimizeButtonMetrics::~MinimizeButtonMetrics() {
 }
 
+// static
+int MinimizeButtonMetrics::GetCaptionButtonHeightInDIPs() {
+  // At DPI scaling settings other than 100% the result won't be exactly right.
+  // TODO: return a more accurate approximation [http://crbug.com/716365]
+
+  // SM_CYSIZE returns the caption button height, but to get the full height
+  // from the top of the window we add SM_CYSIZEFRAME.
+  int cysize = GetSystemMetrics(SM_CYSIZE);
+  int cysizeframe = GetSystemMetrics(SM_CYSIZEFRAME);

[Peter Kasting, 2017/05/05 22:41:01]

Nit: Dunno if this would be clearer if these were |caption_height| and
|frame_thickness| or something.  Also these could optionally be declared const.

[emx, 2017/05/09 09:37:58]

Done.

+
+  // The result of GetSystemMetrics depends on the scale factor of the primary
+  // display. Divide the sum by that to convert to DIPs. (Converting SM_CYSIZE
+  // and SM_CYSIZEFRAME to DIPs individually adds a bigger rounding error.)
+  float primary_device_scale_factor =
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor();
+  float height_dips = (cysize + cysizeframe) / primary_device_scale_factor;
+
+  // Testing shows that floor() gives a more accurate approximation than
+  // round() here.
+  return std::floor(height_dips);
+}
+
 void MinimizeButtonMetrics::Init(HWND hwnd) {
   DCHECK(!hwnd_);
   hwnd_ = hwnd;
 }
 
 void MinimizeButtonMetrics::OnHWNDActivated() {
   was_activated_ = true;
   // NOTE: we don't cache here as it seems only after the activate is the value
   // correct.
 }
@@ skipping 51 matching lines @@
   if (!dwm_button_pos) {
     // Fallback to using the message for the titlebar info only if the above
     // code fails. It can fail if DWM is disabled globally or only for the
     // given HWND. The WM_GETTITLEBARINFOEX message can fail if we are not
     // active/visible. By fail we get a location of 0; the return status
     // code is always the same and similarly the state never seems to change
     // (titlebar_info.rgstate).
     TITLEBARINFOEX titlebar_info = {0};
     titlebar_info.cbSize = sizeof(TITLEBARINFOEX);
     SendMessage(hwnd_, WM_GETTITLEBARINFOEX, 0,
-                reinterpret_cast<WPARAM>(&titlebar_info));
+                reinterpret_cast<LPARAM>(&titlebar_info));
 
     // Under DWM WM_GETTITLEBARINFOEX won't return the right thing until after
     // WM_NCACTIVATE (maybe it returns classic values?). In an attempt to
     // return a consistant value we cache the last value across instances and
     // use it until we get the activate.
     if (titlebar_info.rgrect[2].left == titlebar_info.rgrect[2].right ||
         (titlebar_info.rgstate[2] &
          (STATE_SYSTEM_INVISIBLE | STATE_SYSTEM_OFFSCREEN |
           STATE_SYSTEM_UNAVAILABLE)))
       return 0;
@@ skipping 45 matching lines @@
     cached_minimize_button_x_delta_ = minimize_button_offset;
   } else {
     RECT client_rect = {0};
     GetClientRect(hwnd_, &client_rect);
     cached_minimize_button_x_delta_ =
         client_rect.right - minimize_button_offset;
   }
   last_cached_minimize_button_x_delta_ = cached_minimize_button_x_delta_;
   return minimize_button_offset;
 }