ui/display/util/display_util.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "ui/display/util/display_util.h"
   6
   7 #include "base/logging.h"
   8
   9 namespace ui {
  10
  11 namespace {
  12
  13 // A list of bogus sizes in mm that should be ignored.
  14 // See crbug.com/136533. The first element maintains the minimum
  15 // size required to be valid size.
  16 const int kInvalidDisplaySizeList[][2] = {
  17   {40, 30},
  18   {50, 40},
  19   {160, 90},
  20   {160, 100},
  21 };
  22
  23 // The DPI threshold to detect high density screen.
  24 // Higher DPI than this will use device_scale_factor=2.
  25 const unsigned int kHighDensityDPIThresholdSmall = 170;
  26
  27 // The HiDPI threshold for large (usually external) monitors. Lower threshold
  28 // makes sense for large monitors, because such monitors should be located
  29 // farther from the user's face usually. See http://crbug.com/348279
  30 const unsigned int kHighDensityDPIThresholdLarge = 150;
  31
  32 // The width threshold in mm for "large" monitors.
  33 const int kLargeDisplayWidthThresholdMM = 500;
  34
  35 // 1 inch in mm.
  36 const float kInchInMm = 25.4f;
  37
  38 }  // namespace
  39
  40 bool IsDisplaySizeBlackListed(const gfx::Size& physical_size) {
  41   // Ignore if the reported display is smaller than minimum size.
  42   if (physical_size.width() <= kInvalidDisplaySizeList[0][0] ||
  43       physical_size.height() <= kInvalidDisplaySizeList[0][1]) {
  44     VLOG(1) << "Smaller than minimum display size";
  45     return true;
  46   }
  47   for (size_t i = 1; i < arraysize(kInvalidDisplaySizeList); ++i) {
  48     const gfx::Size size(kInvalidDisplaySizeList[i][0],
  49                          kInvalidDisplaySizeList[i][1]);
  50     if (physical_size == size) {
  51       VLOG(1) << "Black listed display size detected:" << size.ToString();
  52       return true;
  53     }
  54   }
  55   return false;
  56 }
  57
  58 float GetScaleFactor(const gfx::Size& physical_size_in_mm,
  59                      const gfx::Size& screen_size_in_pixels) {
  60   if (IsDisplaySizeBlackListed(physical_size_in_mm))
  61     return 1.0f;
  62
  63   const unsigned int dpi = (kInchInMm * screen_size_in_pixels.width() /
  64                             physical_size_in_mm.width());
  65   const unsigned int threshold =
  66       (physical_size_in_mm.width() >= kLargeDisplayWidthThresholdMM) ?
  67       kHighDensityDPIThresholdLarge : kHighDensityDPIThresholdSmall;
  68   return (dpi > threshold) ? 2.0f : 1.0f;
  69 }
  70
  71 }  // namespace ui