Added capability on Windows to get the physical dimensions of your attached monitors. Also added th…

ui/gfx/win/physical_size.cc

+// Copyright 2016 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/physical_size.h"
+
+#include <windows.h>
+#include <setupapi.h>
+#include <iostream>
+
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/scoped_generic.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/win/registry.h"
+
+// This GUID was taken from
+// https://msdn.microsoft.com/en-us/library/windows/hardware/ff545901.aspx
+const GUID GUID_DEVICEINTERFACE_MONITOR = {
+    0xE6F07B5F, 0xEE97, 0x4A90, 0xB0, 0x76, 0x33, 0xF5, 0x7B, 0xF4, 0xEA, 0xA7};
+
+namespace {
+
+struct DeviceInfoListScopedTraits {
+  static HDEVINFO InvalidValue() { return INVALID_HANDLE_VALUE; }
+
+  static void Free(HDEVINFO h) { SetupDiDestroyDeviceInfoList(h); }
+};
+
+bool GetSizeFromRegistry(HDEVINFO device_info_list,
+                         SP_DEVINFO_DATA& device_info,

[scottmg, 2016/01/12 01:03:13]

No non-const references. If it can be a const ref, that's better, or otherwise,
pass it as a pointer if it needs to be mutable.

[Bret, 2016/01/12 22:55:17]

Done.

+                         int* width_mm,
+                         int* height_mm) {
+  base::win::RegKey reg_key(SetupDiOpenDevRegKey(device_info_list, &device_info,
+                                                 DICS_FLAG_GLOBAL, 0, DIREG_DEV,
+                                                 KEY_READ));
+
+  if (!reg_key.Valid())
+    return false;
+
+  BYTE data[128];
+  DWORD data_length = sizeof(data);
+  LONG return_value =
+      reg_key.ReadValue(L"EDID", &data[0], &data_length, nullptr);
+  if (return_value != ERROR_SUCCESS)
+    return false;
+
+  // Byte 54 is the start of the required descriptor block that contains the
+  // required timing information with the highest preference, and 12 bytes
+  // into that block is the size information.
+  // 66: width least significant bits
+  // 67: height least significant bits
+  // 68: 4 bits for each of width and height most significant bits
+  *width_mm = ((data[68] & 0xF0) << 4) + data[66];
+  *height_mm = ((data[68] & 0x0F) << 8) + data[67];
+
+  return true;
+}
+
+bool GetInterfaceDetailAndDeviceInfo(
+    HDEVINFO device_info_list,
+    SP_DEVICE_INTERFACE_DATA& interface_data,

[scottmg, 2016/01/12 01:03:13]

Same.

[Bret, 2016/01/12 22:55:17]

Done.

+    scoped_ptr<SP_DEVICE_INTERFACE_DETAIL_DATA, base::FreeDeleter>*
+        interface_detail,
+    SP_DEVINFO_DATA* device_info) {
+  device_info->cbSize = sizeof(SP_DEVINFO_DATA);
+  DWORD buffer_size;
+  // This call also populates device_info.
+  bool success = SetupDiGetDeviceInterfaceDetail(
+                     device_info_list, &interface_data, nullptr, 0,
+                     &buffer_size, device_info) != 0;
+  if (success || GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
+    // The first call should fail.
+    return false;
+  }
+
+  interface_detail->reset(
+      reinterpret_cast<SP_DEVICE_INTERFACE_DETAIL_DATA*>(malloc(buffer_size)));
+  (*interface_detail)->cbSize = sizeof(SP_DEVICE_INTERFACE_DETAIL_DATA);
+  return SetupDiGetDeviceInterfaceDetail(device_info_list, &interface_data,
+                                         interface_detail->get(), buffer_size,
+                                         nullptr, nullptr) != 0;
+}
+
+}  // namespace
+
+namespace gfx {
+
+void GetPhysicalSizeForDisplays(std::vector<PhysicalDisplaySize>* out) {
+  DCHECK(out);
+
+  // Get a handle to the list of device interfaces that are monitors via Setup.
+  base::ScopedGeneric<HDEVINFO, DeviceInfoListScopedTraits> device_info_list(
+      SetupDiGetClassDevs(&GUID_DEVICEINTERFACE_MONITOR, nullptr, nullptr,
+                          DIGCF_PRESENT | DIGCF_DEVICEINTERFACE));
+
+  if (!device_info_list.is_valid())
+    return;
+
+  // Loop over the device interfaces that are present according to Setup.
+  SP_DEVICE_INTERFACE_DATA interface_data = {0};
+  interface_data.cbSize = sizeof(SP_DEVICE_INTERFACE_DATA);
+  int interface_index = 0;
+  while (SetupDiEnumDeviceInterfaces(device_info_list.get(), nullptr,
+                                     &GUID_DEVICEINTERFACE_MONITOR,
+                                     interface_index++, &interface_data)) {
+    scoped_ptr<SP_DEVICE_INTERFACE_DETAIL_DATA, base::FreeDeleter>
+        interface_detail;
+    SP_DEVINFO_DATA device_info = {0};
+    // This gives us the device path that we need to associate the device
+    // interface from Setup with the display device from EnumDisplayDevices.
+    bool get_info_succeeded =
+        GetInterfaceDetailAndDeviceInfo(device_info_list.get(), interface_data,
+                                        &interface_detail, &device_info);
+    if (!get_info_succeeded)
+      continue;
+
+    // Loop over the display interfaces via EnumDisplayDevices. this will give
+    // us the device name and allow us to loop over its attached monitors.
+    DISPLAY_DEVICE display_device = {0};
+    display_device.cb = sizeof(DISPLAY_DEVICE);
+    int display_index = 0;
+    while (EnumDisplayDevices(nullptr, display_index++, &display_device,
+                              EDD_GET_DEVICE_INTERFACE_NAME)) {
+      // Loop over the monitors attached to the display interface. This gives us
+      // the device ID that associates the monitor with the setup device path
+      // from the earlier step.
+      DISPLAY_DEVICE attached_device = {0};
+      attached_device.cb = sizeof(DISPLAY_DEVICE);
+      int attached_index = 0;
+      while (EnumDisplayDevices(display_device.DeviceName, attached_index++,
+                                &attached_device,
+                                EDD_GET_DEVICE_INTERFACE_NAME)) {
+        wchar_t* attached_device_id = attached_device.DeviceID;
+        wchar_t* setup_device_path = interface_detail->DevicePath;
+        if (wcsicmp(attached_device_id, setup_device_path) == 0) {
+          // We've found the monitor that matches the Setup device.
+          int width_mm;
+          int height_mm;
+          bool found = GetSizeFromRegistry(device_info_list.get(), device_info,
+                                           &width_mm, &height_mm);
+          if (found) {
+            PhysicalDisplaySize size(
+                base::WideToUTF8(display_device.DeviceName), width_mm,
+                height_mm);

[scottmg, 2016/01/12 01:03:13]

nit; I'd probably just put this inline into the push_back as

  out->push_back(PhysicalDisplaySize(...));

rather than making a named temporary.

[Bret, 2016/01/12 22:55:17]

Done.

+            out->push_back(size);
+          }
+          break;

[scottmg, 2016/01/12 01:03:13]

Should this be inside "if (found)"?

[Bret, 2016/01/12 22:55:17]

No, the Device ID should be unique, so if it matches the Setup Device Path
there's no reason to continue looking even if getting the physical size fails.
Ideally we'd continue the outermost loop instead but that'd look even more
confusing.

+        }
+      }
+    }
+  }
+}
+
+}  // namespace gfx