ui/base/win/dpi.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/base/win/dpi.h"

#include <windows.h>
#include "base/command_line.h"
#include "base/win/scoped_hdc.h"
#include "ui/base/layout.h"
#include "base/win/registry.h"
#include "ui/base/ui_base_switches.h"
#include "ui/gfx/display.h"
#include "ui/gfx/point_conversions.h"
#include "ui/gfx/rect_conversions.h"
#include "ui/gfx/size_conversions.h"

namespace {

int kDefaultDPIX = 96;
int kDefaultDPIY = 96;

// Tests to see if the command line flag "--high-dpi-support" is set.
bool IsHighDPIEnabled() {
  // Default is disabled.
  if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kHighDPISupport)) {
    return CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
        switches::kHighDPISupport).compare("1") == 0;
  }
  return false;
}

// Gets the device scale factor. If support is enabled, this will return the
// best available scale based on the screen's pixel density. This can be
// affected (overridden) by --force-device-scale-factor=x
float GetDeviceScaleFactorImpl() {
  if (IsHighDPIEnabled()) {
    float scale = gfx::Display::HasForceDeviceScaleFactor() ?
        gfx::Display::GetForcedDeviceScaleFactor() : ui::GetDPIScale();
    // Quantize to nearest supported scale factor.
    scale = ui::GetScaleFactorScale(ui::GetScaleFactorFromScale(scale));
    return scale;
  }
  return 1.0f;
}

BOOL IsProcessDPIAwareWrapper() {
  typedef BOOL(WINAPI *IsProcessDPIAwarePtr)(VOID);
  IsProcessDPIAwarePtr is_process_dpi_aware_func =
      reinterpret_cast<IsProcessDPIAwarePtr>(
          GetProcAddress(GetModuleHandleA("user32.dll"), "IsProcessDPIAware"));
  if (is_process_dpi_aware_func)
    return is_process_dpi_aware_func();
  return FALSE;
}

}  // namespace

namespace ui {

gfx::Size GetDPI() {
  static int dpi_x = 0;
  static int dpi_y = 0;
  static bool should_initialize = true;

  if (should_initialize) {
    should_initialize = false;
    base::win::ScopedGetDC screen_dc(NULL);
    // This value is safe to cache for the life time of the app since the
    // user must logout to change the DPI setting. This value also applies
    // to all screens.
    dpi_x = GetDeviceCaps(screen_dc, LOGPIXELSX);
    dpi_y = GetDeviceCaps(screen_dc, LOGPIXELSY);
  }
  return gfx::Size(dpi_x, dpi_y);
}

float GetDPIScale() {
  if (IsHighDPIEnabled()) {
    return static_cast<float>(GetDPI().width()) /
        static_cast<float>(kDefaultDPIX);
  }
  return 1.0;
}

bool IsInHighDPIMode() {
  return GetDPIScale() > 1.0;
}

void EnableHighDPISupport() {
  if (IsHighDPIEnabled()) {
    typedef BOOL(WINAPI *SetProcessDPIAwarePtr)(VOID);
    SetProcessDPIAwarePtr set_process_dpi_aware_func =
        reinterpret_cast<SetProcessDPIAwarePtr>(
            GetProcAddress(GetModuleHandleA("user32.dll"),
                           "SetProcessDPIAware"));
    if (set_process_dpi_aware_func)
      set_process_dpi_aware_func();
  }
}

namespace win {

float GetDeviceScaleFactor() {
  static const float device_scale_factor = GetDeviceScaleFactorImpl();
  return device_scale_factor;
}

gfx::Point ScreenToDIPPoint(const gfx::Point& pixel_point) {
  return gfx::ToFlooredPoint(
      gfx::ScalePoint(pixel_point, 1.0f / GetDeviceScaleFactor()));
}

gfx::Point DIPToScreenPoint(const gfx::Point& dip_point) {
  return gfx::ToFlooredPoint(
      gfx::ScalePoint(dip_point, GetDeviceScaleFactor()));
}

gfx::Rect ScreenToDIPRect(const gfx::Rect& pixel_bounds) {
  // TODO(kevers): Switch to non-deprecated method for float to int conversions.
  return gfx::ToFlooredRectDeprecated(
      gfx::ScaleRect(pixel_bounds, 1.0f / GetDeviceScaleFactor()));
}

gfx::Rect DIPToScreenRect(const gfx::Rect& dip_bounds) {
  // TODO(kevers): Switch to non-deprecated method for float to int conversions.
  return gfx::ToFlooredRectDeprecated(
      gfx::ScaleRect(dip_bounds, GetDeviceScaleFactor()));
}

gfx::Size ScreenToDIPSize(const gfx::Size& size_in_pixels) {
  return gfx::ToFlooredSize(
      gfx::ScaleSize(size_in_pixels, 1.0f / GetDeviceScaleFactor()));
}

gfx::Size DIPToScreenSize(const gfx::Size& dip_size) {
  return gfx::ToFlooredSize(gfx::ScaleSize(dip_size, GetDeviceScaleFactor()));
}

int GetSystemMetricsInDIP(int metric) {
  return static_cast<int>(GetSystemMetrics(metric) /
      GetDeviceScaleFactor() + 0.5);
}

double GetUndocumentedDPIScale() {
  // TODO(girard): Remove this code when chrome is DPIAware.
  static double scale = -1.0;
  if (scale == -1.0) {
    scale = 1.0;
    if (!IsProcessDPIAwareWrapper()) {
      base::win::RegKey key(HKEY_CURRENT_USER,
                            L"Control Panel\\Desktop\\WindowMetrics",
                            KEY_QUERY_VALUE);
      if (key.Valid()) {
        DWORD value = 0;
        if (key.ReadValueDW(L"AppliedDPI", &value) == ERROR_SUCCESS) {
          scale = static_cast<double>(value) / kDefaultDPIX;
        }
      }
    }
  }
  return scale;
}

}  // namespace win

}  // namespace ui