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// Copyright 2015 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 "media/capture/content/capture_resolution_chooser.h"
#include <algorithm>
#include <limits>
#include "base/strings/string_util.h"
#include "media/base/video_util.h"
namespace media {
namespace {
// Each snapped frame size is an integer multiple of this many lines apart.
// This is ideal for 16:9 content, but seems to also work well for many
// arbitrary aspect ratios.
const int kSnappedHeightStep = 90;
// The minimum amount of decrease in area between consecutive snapped frame
// sizes. This matters externally, where the end-to-end system is hunting for a
// capture size that works within all resource bottlenecks. If the snapped
// frame sizes are too-close together, the end-to-end system cannot stablize.
// If they are too-far apart, quality is being sacrificed.
const int kMinAreaDecreasePercent = 15;
// Returns |size|, unless it exceeds |max_size| or is under |min_size|. When
// the bounds are exceeded, computes and returns an alternate size of similar
// aspect ratio that is within the bounds.
gfx::Size ComputeBoundedCaptureSize(const gfx::Size& size,
const gfx::Size& min_size,
const gfx::Size& max_size) {
if (size.width() > max_size.width() || size.height() > max_size.height()) {
gfx::Size result = ScaleSizeToFitWithinTarget(size, max_size);
result.SetToMax(min_size);
return result;
} else if (size.width() < min_size.width() ||
size.height() < min_size.height()) {
gfx::Size result = ScaleSizeToEncompassTarget(size, min_size);
result.SetToMin(max_size);
return result;
} else {
return size;
}
}
// Returns true if the area of |a| is less than that of |b|.
bool CompareByArea(const gfx::Size& a, const gfx::Size& b) {
return a.GetArea() < b.GetArea();
}
} // namespace
// static
constexpr gfx::Size CaptureResolutionChooser::kDefaultCaptureSize;
CaptureResolutionChooser::CaptureResolutionChooser()
: min_frame_size_(kDefaultCaptureSize),
max_frame_size_(kDefaultCaptureSize),
apply_aspect_ratio_adjustment_(false),
target_area_(std::numeric_limits<decltype(target_area_)>::max()),
capture_size_(kDefaultCaptureSize),
snapped_sizes_({kDefaultCaptureSize}) {}
CaptureResolutionChooser::~CaptureResolutionChooser() {
}
void CaptureResolutionChooser::SetConstraints(const gfx::Size& min_frame_size,
const gfx::Size& max_frame_size,
bool use_fixed_aspect_ratio) {
DCHECK_LT(0, min_frame_size.width());
DCHECK_LT(0, min_frame_size.height());
DCHECK_LE(min_frame_size.width(), max_frame_size.width());
DCHECK_LE(min_frame_size.height(), max_frame_size.height());
min_frame_size_ = min_frame_size;
max_frame_size_ = max_frame_size;
apply_aspect_ratio_adjustment_ =
(min_frame_size != max_frame_size && use_fixed_aspect_ratio);
UpdateSnappedFrameSizes();
RecomputeCaptureSize();
}
void CaptureResolutionChooser::SetSourceSize(const gfx::Size& source_size) {
source_size_ = source_size;
UpdateSnappedFrameSizes();
RecomputeCaptureSize();
}
void CaptureResolutionChooser::SetTargetFrameArea(int area) {
DCHECK_GE(area, 0);
target_area_ = area;
RecomputeCaptureSize();
}
gfx::Size CaptureResolutionChooser::FindNearestFrameSize(int area) const {
const auto begin = snapped_sizes_.begin();
const auto end = snapped_sizes_.end();
DCHECK(begin != end);
const gfx::Size area_as_size(area, 1); // A facade for CompareByArea().
const auto p = std::lower_bound(begin, end, area_as_size, &CompareByArea);
if (p == end) {
// Boundary case: The target |area| is greater than or equal to the
// largest, so the largest size is closest.
return *(end - 1);
} else if (p == begin) {
// Boundary case: The target |area| is smaller than the smallest, so the
// smallest size is closest.
return *begin;
} else {
// |p| points to the smallest size whose area is greater than or equal to
// the target |area|. The next smaller size could be closer to the target
// |area|, so it must also be considered.
const auto q = p - 1;
return ((p->GetArea() - area) < (area - q->GetArea())) ? *p : *q;
}
}
gfx::Size CaptureResolutionChooser::FindLargerFrameSize(
int area,
int num_steps_up) const {
DCHECK_GT(num_steps_up, 0);
const auto begin = snapped_sizes_.begin();
const auto end = snapped_sizes_.end();
DCHECK(begin != end);
const gfx::Size area_as_size(area, 1); // A facade for CompareByArea().
auto p = std::upper_bound(begin, end, area_as_size, &CompareByArea);
// |p| is already pointing one step up.
const int additional_steps_up = num_steps_up - 1;
if ((end - p) > additional_steps_up)
return *(p + additional_steps_up);
else
return *(end - 1);
}
gfx::Size CaptureResolutionChooser::FindSmallerFrameSize(
int area,
int num_steps_down) const {
DCHECK_GT(num_steps_down, 0);
const auto begin = snapped_sizes_.begin();
const auto end = snapped_sizes_.end();
DCHECK(begin != end);
const gfx::Size area_as_size(area, 1); // A facade for CompareByArea().
const auto p = std::lower_bound(begin, end, area_as_size, &CompareByArea);
if ((p - begin) >= num_steps_down)
return *(p - num_steps_down);
else
return *begin;
}
void CaptureResolutionChooser::RecomputeCaptureSize() {
const gfx::Size old_capture_size = capture_size_;
capture_size_ = FindNearestFrameSize(target_area_);
VLOG_IF(1, capture_size_ != old_capture_size)
<< "Recomputed capture size from " << old_capture_size.ToString()
<< " to " << capture_size_.ToString() << " ("
<< (100.0 * capture_size_.height() / snapped_sizes_.back().height())
<< "% of ideal size)";
}
void CaptureResolutionChooser::UpdateSnappedFrameSizes() {
// Compute the largest snapped frame size, and the one that will determine the
// aspect ratio of all the snapped frame sizes. If the |source_size_| has not
// yet been set, use the |capture_size_| as a substitute.
gfx::Size constrained_size =
source_size_.IsEmpty() ? capture_size_ : source_size_;
constrained_size = ComputeBoundedCaptureSize(
apply_aspect_ratio_adjustment_
? PadToMatchAspectRatio(constrained_size, max_frame_size_)
: constrained_size,
min_frame_size_, max_frame_size_);
// Start with the constrained size as the largest in the set.
snapped_sizes_.clear();
snapped_sizes_.push_back(constrained_size);
// Repeatedly decrease the size in steps, adding each to |snapped_sizes_|.
// However, skip the sizes that do not decrease in area by enough, relative to
// the prior size.
int last_area = constrained_size.GetArea();
for (int height = constrained_size.height() - kSnappedHeightStep;
height >= min_frame_size_.height(); height -= kSnappedHeightStep) {
const int width =
height * constrained_size.width() / constrained_size.height();
if (width < min_frame_size_.width())
break;
const int smaller_area = width * height;
const int percent_decrease = 100 * (last_area - smaller_area) / last_area;
if (percent_decrease >= kMinAreaDecreasePercent) {
snapped_sizes_.push_back(gfx::Size(width, height));
last_area = smaller_area;
}
}
// Reverse ordering, so that sizes are from smallest to largest.
std::reverse(snapped_sizes_.begin(), snapped_sizes_.end());
if (VLOG_IS_ON(1)) {
std::vector<std::string> stringified_sizes;
for (const gfx::Size& size : snapped_sizes_)
stringified_sizes.push_back(size.ToString());
VLOG_STREAM(1) << "Recomputed snapped frame sizes: "
<< base::JoinString(stringified_sizes, " <--> ");
}
}
} // namespace media