ui/display/manager/display_util.cc

// Copyright 2014 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/display/manager/display_util.h"

#include <stddef.h>
#include <algorithm>
#include <cmath>

#include "base/logging.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/stringprintf.h"
#include "ui/display/manager/managed_display_info.h"
#include "ui/display/types/display_snapshot.h"

namespace display {
namespace {

// The total number of display zoom factors to enumerate.
constexpr int kNumOfZoomFactors = 9;

// A pair representing the list of zoom values for a given minimum display
// resolution width.
using ZoomListBucket = std::pair<int, std::array<float, kNumOfZoomFactors>>;

// For displays with a device scale factor of unity, we use a static list of
// initialized zoom values. For a given resolution width of a display, we can
// find its associated list of zoom values by simply finding the last bucket
// with a width less than the given resolution width.
// Ex. A resolution width of 1024, we will use the bucket with the width of 960.
constexpr std::array<ZoomListBucket, 8> kZoomListBuckets{{
    {0, {0.60f, 0.65f, 0.70f, 0.75f, 0.80f, 0.85f, 0.90f, 0.95f, 1.f}},
    {720, {0.70f, 0.75f, 0.80f, 0.85f, 0.90f, 0.95f, 1.f, 1.05f, 1.10f}},
    {800, {0.75f, 0.80f, 0.85f, 0.90f, 0.95f, 1.f, 1.05f, 1.10f, 1.15f}},
    {960, {0.90f, 0.95f, 1.f, 1.05f, 1.10f, 1.15f, 1.20f, 1.25f, 1.30f}},
    {1280, {1.f, 1.10f, 1.15f, 1.20f, 1.25f, 1.30f, 1.50f, 1.70f, 1.80f}},
    {1920, {1.f, 1.10f, 1.15f, 1.20f, 1.30f, 1.40f, 1.50f, 1.75f, 2.00f}},
    {3840, {1.f, 1.10f, 1.20f, 1.40f, 1.60f, 1.80f, 2.00f, 2.20f, 2.40f}},
    {5120, {1.f, 1.25f, 1.50f, 1.75f, 2.00f, 2.25f, 2.50f, 2.75f, 3.00f}},
}};

bool WithinEpsilon(float a, float b) {
  return std::abs(a - b) < std::numeric_limits<float>::epsilon();
}

// Returns the user friendly delta to be used for the given |dsf|.
float FindDeltaForDsf(float dsf) {
  DCHECK_GT(dsf, 1.f);
  const float raw_delta = (1.f - 1.f / dsf) / (kNumOfZoomFactors - 1.f);
  return raw_delta > 0.05f ? 0.1f : 0.05f;
}

}  // namespace

std::string DisplayPowerStateToString(chromeos::DisplayPowerState state) {
  switch (state) {
    case chromeos::DISPLAY_POWER_ALL_ON:
      return "ALL_ON";
    case chromeos::DISPLAY_POWER_ALL_OFF:
      return "ALL_OFF";
    case chromeos::DISPLAY_POWER_INTERNAL_OFF_EXTERNAL_ON:
      return "INTERNAL_OFF_EXTERNAL_ON";
    case chromeos::DISPLAY_POWER_INTERNAL_ON_EXTERNAL_OFF:
      return "INTERNAL_ON_EXTERNAL_OFF";
    default:
      return "unknown (" + base::IntToString(state) + ")";
  }
}

std::string MultipleDisplayStateToString(MultipleDisplayState state) {
  switch (state) {
    case MULTIPLE_DISPLAY_STATE_INVALID:
      return "INVALID";
    case MULTIPLE_DISPLAY_STATE_HEADLESS:
      return "HEADLESS";
    case MULTIPLE_DISPLAY_STATE_SINGLE:
      return "SINGLE";
    case MULTIPLE_DISPLAY_STATE_DUAL_MIRROR:
      return "DUAL_MIRROR";
    case MULTIPLE_DISPLAY_STATE_MULTI_EXTENDED:
      return "MULTI_EXTENDED";
  }
  NOTREACHED() << "Unknown state " << state;
  return "INVALID";
}

int GetDisplayPower(const std::vector<DisplaySnapshot*>& displays,
                    chromeos::DisplayPowerState state,
                    std::vector<bool>* display_power) {
  int num_on_displays = 0;
  if (display_power)
    display_power->resize(displays.size());

  for (size_t i = 0; i < displays.size(); ++i) {
    bool internal = displays[i]->type() == DISPLAY_CONNECTION_TYPE_INTERNAL;
    bool on =
        state == chromeos::DISPLAY_POWER_ALL_ON ||
        (state == chromeos::DISPLAY_POWER_INTERNAL_OFF_EXTERNAL_ON &&
         !internal) ||
        (state == chromeos::DISPLAY_POWER_INTERNAL_ON_EXTERNAL_OFF && internal);
    if (display_power)
      (*display_power)[i] = on;
    if (on)
      num_on_displays++;
  }
  return num_on_displays;
}

bool IsPhysicalDisplayType(DisplayConnectionType type) {
  return !(type & DISPLAY_CONNECTION_TYPE_NETWORK);
}

std::vector<float> GetDisplayZoomFactors(const ManagedDisplayMode& mode) {
  // Internal displays have an internal device scale factor greater than 1
  // associated with them. This means that if we use the usual logic, we would
  // end up with a list of zoom levels that the user may not find very useful.
  // Take for example the pixelbook with device scale factor of 2. Based on the
  // usual approach, we would get a zoom range of 100% to 180% with a step of
  // 10% between each consecutive levels. This means:
  //   1. Users will not be able to go to the native resolution which is
  //      achieved at 50% zoom level.
  //   2. Due to the device scale factor, the display already has a low DPI and
  //      users dont want to zoom in, they mostly want to zoom out and add more
  //      pixels to the screen. But we only provide a zoom list of 90% to 130%.
  // This clearly shows we need a different logic to handle internal displays
  // which have lower DPI due to the device scale factor associated with them.
  //
  // OTOH if we look at an external display with a device scale factor of 1 but
  // the same resolution as the pixel book, the DPI would usually be very high
  // and users mostly want to zoom in to reduce the number of pixels on the
  // screen. So having a range of 90% to 130% makes sense.
  // TODO(malaykeshav): Investigate if we can use DPI instead of resolution or
  // device scale factor to decide the list of zoom levels.
  if (mode.device_scale_factor() > 1.f)
    return GetDisplayZoomFactorForDsf(mode.device_scale_factor());

  // There may be cases where the device scale factor is less than 1. This can
  // happen during testing or local linux builds.
  const int effective_width = std::round(
      static_cast<float>(mode.size().width()) / mode.device_scale_factor());

  std::size_t index = kZoomListBuckets.size() - 1;
  while (index > 0 && effective_width < kZoomListBuckets[index].first)
    index--;
  DCHECK_GE(effective_width, kZoomListBuckets[index].first);

  const auto& zoom_array = kZoomListBuckets[index].second;
  return std::vector<float>(zoom_array.begin(), zoom_array.end());
}

std::vector<float> GetDisplayZoomFactorForDsf(float dsf) {
  DCHECK(!WithinEpsilon(dsf, 1.f));
  DCHECK_GT(dsf, 1.f);

  const float delta = FindDeltaForDsf(dsf);
  const float inverse_dsf = 1.f / dsf;
  int zoom_out_count = std::ceil((1.f - inverse_dsf) / delta);
  zoom_out_count = std::min(zoom_out_count, kNumOfZoomFactors - 1);

  const float min_zoom = 1.f - delta * zoom_out_count;

  std::vector<float> zoom_values;
  for (int i = 0; i < kNumOfZoomFactors; i++)
    zoom_values.push_back(min_zoom + i * delta);

  // Ensure the inverse dsf is in the list.
  zoom_values[0] = inverse_dsf;
  return zoom_values;
}

void InsertDsfIntoList(std::vector<float>* zoom_values, float dsf) {
  // 1.0 is already in the list of |zoom_values|. We do not need to add it.
  if (WithinEpsilon(dsf, 1.f))
    return;

  if (dsf > 1.f && WithinEpsilon(*(zoom_values->rbegin()), 1.f)) {
    // If the last element of the vector is 1 then |dsf|, which is greater than
    // 1, will simply be inserted after that.
    zoom_values->push_back(dsf);
    zoom_values->erase(zoom_values->begin());
    return;
  } else if (dsf < 1.f && WithinEpsilon(*(zoom_values->begin()), 1.f)) {
    // If the first element in the list is 1 then |dsf|, which is less than 1,
    // will simply be inseted before that.
    zoom_values->insert(zoom_values->begin(), dsf);
    zoom_values->pop_back();
    return;
  }

  // We dont need to add |dsf| to the list if it is already in the list.
  auto it = std::lower_bound(zoom_values->begin(), zoom_values->end(), dsf);
  if (it != zoom_values->end() && WithinEpsilon(*it, dsf))
    return;

  if (it == zoom_values->begin()) {
    DCHECK_LT(dsf, 1.f);
    *(zoom_values->begin()) = dsf;
  } else if (it == zoom_values->end()) {
    DCHECK_GT(dsf, 1.f);
    *(zoom_values->rbegin()) = dsf;
  } else {
    // There can only be 1 entry for 1.f value.
    DCHECK(!(WithinEpsilon(*(it - 1), 1.f) && WithinEpsilon(*it, 1.f)));

    // True if |dsf| is closer to |it| than it is to |it-1|.
    const bool dsf_closer_to_it =
        std::abs(*it - dsf) < std::abs(*(it - 1) - dsf);
    if (WithinEpsilon(*(it - 1), 1.f) ||
        (dsf_closer_to_it && !WithinEpsilon(*it, 1.f))) {
      *it = dsf;
    } else {
      *(it - 1) = dsf;
    }
  }
}

}  // namespace display