services/surfaceflinger/RegionSamplingThread.cpp - third_party/android/platform/frameworks/native - Git at Google

 /*
  * Copyright 2019 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 // TODO(b/129481165): remove the #pragma below and fix conversion issues
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wconversion"
 #pragma clang diagnostic ignored "-Wextra"

 //#define LOG_NDEBUG 0
 #define ATRACE_TAG ATRACE_TAG_GRAPHICS
 #undef LOG_TAG
 #define LOG_TAG "RegionSamplingThread"

 #include "RegionSamplingThread.h"

 #include <compositionengine/Display.h>
 #include <compositionengine/impl/OutputCompositionState.h>
 #include <cutils/properties.h>
 #include <ftl/future.h>
 #include <gui/IRegionSamplingListener.h>
 #include <gui/SyncScreenCaptureListener.h>
 #include <ui/DisplayStatInfo.h>
 #include <utils/Trace.h>

 #include <string>

 #include "DisplayDevice.h"
 #include "DisplayRenderArea.h"
 #include "Layer.h"
 #include "Scheduler/VsyncController.h"
 #include "SurfaceFlinger.h"

 namespace android {
 using namespace std::chrono_literals;

 template <typename T>
 struct SpHash {
     size_t operator()(const sp<T>& p) const { return std::hash<T*>()(p.get()); }
 };

 constexpr auto lumaSamplingStepTag = "LumaSamplingStep";
 enum class samplingStep {
     noWorkNeeded,
     idleTimerWaiting,
     waitForQuietFrame,
     waitForSamplePhase,
     sample
 };

 constexpr auto defaultRegionSamplingWorkDuration = 3ms;
 constexpr auto defaultRegionSamplingPeriod = 100ms;
 constexpr auto defaultRegionSamplingTimerTimeout = 100ms;
 constexpr auto maxRegionSamplingDelay = 100ms;
 // TODO: (b/127403193) duration to string conversion could probably be constexpr
 template <typename Rep, typename Per>
 inline std::string toNsString(std::chrono::duration<Rep, Per> t) {
     return std::to_string(std::chrono::duration_cast<std::chrono::nanoseconds>(t).count());
 }

 RegionSamplingThread::EnvironmentTimingTunables::EnvironmentTimingTunables() {
     char value[PROPERTY_VALUE_MAX] = {};

     property_get("debug.sf.region_sampling_duration_ns", value,
                  toNsString(defaultRegionSamplingWorkDuration).c_str());
     int const samplingDurationNsRaw = atoi(value);

     property_get("debug.sf.region_sampling_period_ns", value,
                  toNsString(defaultRegionSamplingPeriod).c_str());
     int const samplingPeriodNsRaw = atoi(value);

     property_get("debug.sf.region_sampling_timer_timeout_ns", value,
                  toNsString(defaultRegionSamplingTimerTimeout).c_str());
     int const samplingTimerTimeoutNsRaw = atoi(value);

     if ((samplingPeriodNsRaw < 0) || (samplingTimerTimeoutNsRaw < 0)) {
         ALOGW("User-specified sampling tuning options nonsensical. Using defaults");
         mSamplingDuration = defaultRegionSamplingWorkDuration;
         mSamplingPeriod = defaultRegionSamplingPeriod;
         mSamplingTimerTimeout = defaultRegionSamplingTimerTimeout;
     } else {
         mSamplingDuration = std::chrono::nanoseconds(samplingDurationNsRaw);
         mSamplingPeriod = std::chrono::nanoseconds(samplingPeriodNsRaw);
         mSamplingTimerTimeout = std::chrono::nanoseconds(samplingTimerTimeoutNsRaw);
     }
 }

 RegionSamplingThread::RegionSamplingThread(SurfaceFlinger& flinger, const TimingTunables& tunables)
       : mFlinger(flinger),
         mTunables(tunables),
         mIdleTimer(
                 "RegSampIdle",
                 std::chrono::duration_cast<std::chrono::milliseconds>(
                         mTunables.mSamplingTimerTimeout),
                 [] {}, [this] { checkForStaleLuma(); }),
         mLastSampleTime(0ns) {
     mThread = std::thread([this]() { threadMain(); });
     pthread_setname_np(mThread.native_handle(), "RegionSampling");
     mIdleTimer.start();
 }

 RegionSamplingThread::RegionSamplingThread(SurfaceFlinger& flinger)
       : RegionSamplingThread(flinger,
                              TimingTunables{defaultRegionSamplingWorkDuration,
                                             defaultRegionSamplingPeriod,
                                             defaultRegionSamplingTimerTimeout}) {}

 RegionSamplingThread::~RegionSamplingThread() {
     mIdleTimer.stop();

     {
         std::lock_guard lock(mThreadControlMutex);
         mRunning = false;
         mCondition.notify_one();
     }

     if (mThread.joinable()) {
         mThread.join();
     }
 }

 void RegionSamplingThread::addListener(const Rect& samplingArea, const wp<Layer>& stopLayer,
                                        const sp<IRegionSamplingListener>& listener) {
     sp<IBinder> asBinder = IInterface::asBinder(listener);
     asBinder->linkToDeath(this);
     std::lock_guard lock(mSamplingMutex);
     mDescriptors.emplace(wp<IBinder>(asBinder), Descriptor{samplingArea, stopLayer, listener});
 }

 void RegionSamplingThread::removeListener(const sp<IRegionSamplingListener>& listener) {
     std::lock_guard lock(mSamplingMutex);
     mDescriptors.erase(wp<IBinder>(IInterface::asBinder(listener)));
 }

 void RegionSamplingThread::checkForStaleLuma() {
     std::lock_guard lock(mThreadControlMutex);

     if (mSampleRequestTime.has_value()) {
         ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::waitForSamplePhase));
         mSampleRequestTime.reset();
         mFlinger.scheduleRegionSamplingThread();
     }
 }

 void RegionSamplingThread::onCompositionComplete(
         std::optional<std::chrono::steady_clock::time_point> samplingDeadline) {
     doSample(samplingDeadline);
 }

 void RegionSamplingThread::doSample(
         std::optional<std::chrono::steady_clock::time_point> samplingDeadline) {
     std::lock_guard lock(mThreadControlMutex);
     const auto now = std::chrono::steady_clock::now();
     if (mLastSampleTime + mTunables.mSamplingPeriod > now) {
         // content changed, but we sampled not too long ago, so we need to sample some time in the
         // future.
         ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::idleTimerWaiting));
         mSampleRequestTime = now;
         return;
     }
     if (!mSampleRequestTime.has_value() || now - *mSampleRequestTime < maxRegionSamplingDelay) {
         // If there is relatively little time left for surfaceflinger
         // until the next vsync deadline, defer this sampling work
         // to a later frame, when hopefully there will be more time.
         if (samplingDeadline.has_value() && now + mTunables.mSamplingDuration > *samplingDeadline) {
             ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::waitForQuietFrame));
             mSampleRequestTime = mSampleRequestTime.value_or(now);
             return;
         }
     }

     ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::sample));

     mSampleRequestTime.reset();
     mLastSampleTime = now;

     mIdleTimer.reset();

     mSampleRequested = true;
     mCondition.notify_one();
 }

 void RegionSamplingThread::binderDied(const wp<IBinder>& who) {
     std::lock_guard lock(mSamplingMutex);
     mDescriptors.erase(who);
 }

 float sampleArea(const uint32_t* data, int32_t width, int32_t height, int32_t stride,
                  uint32_t orientation, const Rect& sample_area) {
     if (!sample_area.isValid() || (sample_area.getWidth() > width) ||
         (sample_area.getHeight() > height)) {
         ALOGE("invalid sampling region requested");
         return 0.0f;
     }

     // (b/133849373) ROT_90 screencap images produced upside down
     auto area = sample_area;
     if (orientation & ui::Transform::ROT_90) {
         area.top = height - area.top;
         area.bottom = height - area.bottom;
         std::swap(area.top, area.bottom);

         area.left = width - area.left;
         area.right = width - area.right;
         std::swap(area.left, area.right);
     }

     const uint32_t pixelCount = (area.bottom - area.top) * (area.right - area.left);
     uint32_t accumulatedLuma = 0;

     // Calculates luma with approximation of Rec. 709 primaries
     for (int32_t row = area.top; row < area.bottom; ++row) {
         const uint32_t* rowBase = data + row * stride;
         for (int32_t column = area.left; column < area.right; ++column) {
             uint32_t pixel = rowBase[column];
             const uint32_t r = pixel & 0xFF;
             const uint32_t g = (pixel >> 8) & 0xFF;
             const uint32_t b = (pixel >> 16) & 0xFF;
             const uint32_t luma = (r * 7 + b * 2 + g * 23) >> 5;
             accumulatedLuma += luma;
         }
     }

     return accumulatedLuma / (255.0f * pixelCount);
 }

 std::vector<float> RegionSamplingThread::sampleBuffer(
         const sp<GraphicBuffer>& buffer, const Point& leftTop,
         const std::vector<RegionSamplingThread::Descriptor>& descriptors, uint32_t orientation) {
     void* data_raw = nullptr;
     buffer->lock(GRALLOC_USAGE_SW_READ_OFTEN, &data_raw);
     std::shared_ptr<uint32_t> data(reinterpret_cast<uint32_t*>(data_raw),
                                    [&buffer](auto) { buffer->unlock(); });
     if (!data) return {};

     const int32_t width = buffer->getWidth();
     const int32_t height = buffer->getHeight();
     const int32_t stride = buffer->getStride();
     std::vector<float> lumas(descriptors.size());
     std::transform(descriptors.begin(), descriptors.end(), lumas.begin(),
                    [&](auto const& descriptor) {
                        return sampleArea(data.get(), width, height, stride, orientation,
                                          descriptor.area - leftTop);
                    });
     return lumas;
 }

 void RegionSamplingThread::captureSample() {
     ATRACE_CALL();
     std::lock_guard lock(mSamplingMutex);

     if (mDescriptors.empty()) {
         return;
     }

     wp<const DisplayDevice> displayWeak;

     ui::LayerStack layerStack;
     ui::Transform::RotationFlags orientation;
     ui::Size displaySize;

     {
         // TODO(b/159112860): Don't keep sp<DisplayDevice> outside of SF main thread
         const sp<const DisplayDevice> display = mFlinger.getDefaultDisplayDevice();
         displayWeak = display;
         layerStack = display->getLayerStack();
         orientation = ui::Transform::toRotationFlags(display->getOrientation());
         displaySize = display->getSize();
     }

     std::vector<RegionSamplingThread::Descriptor> descriptors;
     Region sampleRegion;
     for (const auto& [listener, descriptor] : mDescriptors) {
         sampleRegion.orSelf(descriptor.area);
         descriptors.emplace_back(descriptor);
     }

     const Rect sampledBounds = sampleRegion.bounds();
     constexpr bool kUseIdentityTransform = false;

     SurfaceFlinger::RenderAreaFuture renderAreaFuture = ftl::defer([=] {
         return DisplayRenderArea::create(displayWeak, sampledBounds, sampledBounds.getSize(),
                                          ui::Dataspace::V0_SRGB, kUseIdentityTransform);
     });

     std::unordered_set<sp<IRegionSamplingListener>, SpHash<IRegionSamplingListener>> listeners;

     auto traverseLayers = [&](const LayerVector::Visitor& visitor) {
         bool stopLayerFound = false;
         auto filterVisitor = [&](Layer* layer) {
             // We don't want to capture any layers beyond the stop layer
             if (stopLayerFound) return;

             // Likewise if we just found a stop layer, set the flag and abort
             for (const auto& [area, stopLayer, listener] : descriptors) {
                 if (layer == stopLayer.promote().get()) {
                     stopLayerFound = true;
                     return;
                 }
             }

             // Compute the layer's position on the screen
             const Rect bounds = Rect(layer->getBounds());
             const ui::Transform transform = layer->getTransform();
             constexpr bool roundOutwards = true;
             Rect transformed = transform.transform(bounds, roundOutwards);

             // If this layer doesn't intersect with the larger sampledBounds, skip capturing it
             Rect ignore;
             if (!transformed.intersect(sampledBounds, &ignore)) return;

             // If the layer doesn't intersect a sampling area, skip capturing it
             bool intersectsAnyArea = false;
             for (const auto& [area, stopLayer, listener] : descriptors) {
                 if (transformed.intersect(area, &ignore)) {
                     intersectsAnyArea = true;
                     listeners.insert(listener);
                 }
             }
             if (!intersectsAnyArea) return;

             ALOGV("Traversing [%s] [%d, %d, %d, %d]", layer->getDebugName(), bounds.left,
                   bounds.top, bounds.right, bounds.bottom);
             visitor(layer);
         };
         mFlinger.traverseLayersInLayerStack(layerStack, CaptureArgs::UNSET_UID, filterVisitor);
     };

     std::shared_ptr<renderengine::ExternalTexture> buffer = nullptr;
     if (mCachedBuffer && mCachedBuffer->getBuffer()->getWidth() == sampledBounds.getWidth() &&
         mCachedBuffer->getBuffer()->getHeight() == sampledBounds.getHeight()) {
         buffer = mCachedBuffer;
     } else {
         const uint32_t usage =
                 GRALLOC_USAGE_SW_READ_OFTEN | GRALLOC_USAGE_HW_RENDER | GRALLOC_USAGE_HW_TEXTURE;
         sp<GraphicBuffer> graphicBuffer =
                 new GraphicBuffer(sampledBounds.getWidth(), sampledBounds.getHeight(),
                                   PIXEL_FORMAT_RGBA_8888, 1, usage, "RegionSamplingThread");
         const status_t bufferStatus = graphicBuffer->initCheck();
         LOG_ALWAYS_FATAL_IF(bufferStatus != OK, "captureSample: Buffer failed to allocate: %d",
                             bufferStatus);
         buffer = std::make_shared<
                 renderengine::ExternalTexture>(graphicBuffer, mFlinger.getRenderEngine(),
                                                renderengine::ExternalTexture::Usage::WRITEABLE);
     }

     const sp<SyncScreenCaptureListener> captureListener = new SyncScreenCaptureListener();
     mFlinger.captureScreenCommon(std::move(renderAreaFuture), traverseLayers, buffer,
                                  true /* regionSampling */, false /* grayscale */, captureListener);
     ScreenCaptureResults captureResults = captureListener->waitForResults();

     std::vector<Descriptor> activeDescriptors;
     for (const auto& descriptor : descriptors) {
         if (listeners.count(descriptor.listener) != 0) {
             activeDescriptors.emplace_back(descriptor);
         }
     }

     ALOGV("Sampling %zu descriptors", activeDescriptors.size());
     std::vector<float> lumas = sampleBuffer(buffer->getBuffer(), sampledBounds.leftTop(),
                                             activeDescriptors, orientation);
     if (lumas.size() != activeDescriptors.size()) {
         ALOGW("collected %zu median luma values for %zu descriptors", lumas.size(),
               activeDescriptors.size());
         return;
     }

     for (size_t d = 0; d < activeDescriptors.size(); ++d) {
         activeDescriptors[d].listener->onSampleCollected(lumas[d]);
     }

     mCachedBuffer = buffer;
     ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::noWorkNeeded));
 }

 // NO_THREAD_SAFETY_ANALYSIS is because std::unique_lock presently lacks thread safety annotations.
 void RegionSamplingThread::threadMain() NO_THREAD_SAFETY_ANALYSIS {
     std::unique_lock<std::mutex> lock(mThreadControlMutex);
     while (mRunning) {
         if (mSampleRequested) {
             mSampleRequested = false;
             lock.unlock();
             captureSample();
             lock.lock();
         }
         mCondition.wait(lock, [this]() REQUIRES(mThreadControlMutex) {
             return mSampleRequested || !mRunning;
         });
     }
 }

 } // namespace android

 // TODO(b/129481165): remove the #pragma below and fix conversion issues
 #pragma clang diagnostic pop // ignored "-Wconversion -Wextra"
	/*
	* Copyright 2019 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	// TODO(b/129481165): remove the #pragma below and fix conversion issues
	#pragma clang diagnostic push
	#pragma clang diagnostic ignored "-Wconversion"
	#pragma clang diagnostic ignored "-Wextra"

	//#define LOG_NDEBUG 0
	#define ATRACE_TAG ATRACE_TAG_GRAPHICS
	#undef LOG_TAG
	#define LOG_TAG "RegionSamplingThread"

	#include "RegionSamplingThread.h"

	#include <compositionengine/Display.h>
	#include <compositionengine/impl/OutputCompositionState.h>
	#include <cutils/properties.h>
	#include <ftl/future.h>
	#include <gui/IRegionSamplingListener.h>
	#include <gui/SyncScreenCaptureListener.h>
	#include <ui/DisplayStatInfo.h>
	#include <utils/Trace.h>

	#include <string>

	#include "DisplayDevice.h"
	#include "DisplayRenderArea.h"
	#include "Layer.h"
	#include "Scheduler/VsyncController.h"
	#include "SurfaceFlinger.h"

	namespace android {
	using namespace std::chrono_literals;

	template <typename T>
	struct SpHash {
	size_t operator()(const sp<T>& p) const { return std::hash<T*>()(p.get()); }
	};

	constexpr auto lumaSamplingStepTag = "LumaSamplingStep";
	enum class samplingStep {
	noWorkNeeded,
	idleTimerWaiting,
	waitForQuietFrame,
	waitForSamplePhase,
	sample
	};

	constexpr auto defaultRegionSamplingWorkDuration = 3ms;
	constexpr auto defaultRegionSamplingPeriod = 100ms;
	constexpr auto defaultRegionSamplingTimerTimeout = 100ms;
	constexpr auto maxRegionSamplingDelay = 100ms;
	// TODO: (b/127403193) duration to string conversion could probably be constexpr
	template <typename Rep, typename Per>
	inline std::string toNsString(std::chrono::duration<Rep, Per> t) {
	return std::to_string(std::chrono::duration_cast<std::chrono::nanoseconds>(t).count());
	}

	RegionSamplingThread::EnvironmentTimingTunables::EnvironmentTimingTunables() {
	char value[PROPERTY_VALUE_MAX] = {};

	property_get("debug.sf.region_sampling_duration_ns", value,
	toNsString(defaultRegionSamplingWorkDuration).c_str());
	int const samplingDurationNsRaw = atoi(value);

	property_get("debug.sf.region_sampling_period_ns", value,
	toNsString(defaultRegionSamplingPeriod).c_str());
	int const samplingPeriodNsRaw = atoi(value);

	property_get("debug.sf.region_sampling_timer_timeout_ns", value,
	toNsString(defaultRegionSamplingTimerTimeout).c_str());
	int const samplingTimerTimeoutNsRaw = atoi(value);

	if ((samplingPeriodNsRaw < 0) \|\| (samplingTimerTimeoutNsRaw < 0)) {
	ALOGW("User-specified sampling tuning options nonsensical. Using defaults");
	mSamplingDuration = defaultRegionSamplingWorkDuration;
	mSamplingPeriod = defaultRegionSamplingPeriod;
	mSamplingTimerTimeout = defaultRegionSamplingTimerTimeout;
	} else {
	mSamplingDuration = std::chrono::nanoseconds(samplingDurationNsRaw);
	mSamplingPeriod = std::chrono::nanoseconds(samplingPeriodNsRaw);
	mSamplingTimerTimeout = std::chrono::nanoseconds(samplingTimerTimeoutNsRaw);
	}
	}

	RegionSamplingThread::RegionSamplingThread(SurfaceFlinger& flinger, const TimingTunables& tunables)
	: mFlinger(flinger),
	mTunables(tunables),
	mIdleTimer(
	"RegSampIdle",
	std::chrono::duration_cast<std::chrono::milliseconds>(
	mTunables.mSamplingTimerTimeout),
	[] {}, [this] { checkForStaleLuma(); }),
	mLastSampleTime(0ns) {
	mThread = std::thread([this]() { threadMain(); });
	pthread_setname_np(mThread.native_handle(), "RegionSampling");
	mIdleTimer.start();
	}

	RegionSamplingThread::RegionSamplingThread(SurfaceFlinger& flinger)
	: RegionSamplingThread(flinger,
	TimingTunables{defaultRegionSamplingWorkDuration,
	defaultRegionSamplingPeriod,
	defaultRegionSamplingTimerTimeout}) {}

	RegionSamplingThread::~RegionSamplingThread() {
	mIdleTimer.stop();

	{
	std::lock_guard lock(mThreadControlMutex);
	mRunning = false;
	mCondition.notify_one();
	}

	if (mThread.joinable()) {
	mThread.join();
	}
	}

	void RegionSamplingThread::addListener(const Rect& samplingArea, const wp<Layer>& stopLayer,
	const sp<IRegionSamplingListener>& listener) {
	sp<IBinder> asBinder = IInterface::asBinder(listener);
	asBinder->linkToDeath(this);
	std::lock_guard lock(mSamplingMutex);
	mDescriptors.emplace(wp<IBinder>(asBinder), Descriptor{samplingArea, stopLayer, listener});
	}

	void RegionSamplingThread::removeListener(const sp<IRegionSamplingListener>& listener) {
	std::lock_guard lock(mSamplingMutex);
	mDescriptors.erase(wp<IBinder>(IInterface::asBinder(listener)));
	}

	void RegionSamplingThread::checkForStaleLuma() {
	std::lock_guard lock(mThreadControlMutex);

	if (mSampleRequestTime.has_value()) {
	ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::waitForSamplePhase));
	mSampleRequestTime.reset();
	mFlinger.scheduleRegionSamplingThread();
	}
	}

	void RegionSamplingThread::onCompositionComplete(
	std::optional<std::chrono::steady_clock::time_point> samplingDeadline) {
	doSample(samplingDeadline);
	}

	void RegionSamplingThread::doSample(
	std::optional<std::chrono::steady_clock::time_point> samplingDeadline) {
	std::lock_guard lock(mThreadControlMutex);
	const auto now = std::chrono::steady_clock::now();
	if (mLastSampleTime + mTunables.mSamplingPeriod > now) {
	// content changed, but we sampled not too long ago, so we need to sample some time in the
	// future.
	ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::idleTimerWaiting));
	mSampleRequestTime = now;
	return;
	}
	if (!mSampleRequestTime.has_value() \|\| now - *mSampleRequestTime < maxRegionSamplingDelay) {
	// If there is relatively little time left for surfaceflinger
	// until the next vsync deadline, defer this sampling work
	// to a later frame, when hopefully there will be more time.
	if (samplingDeadline.has_value() && now + mTunables.mSamplingDuration > *samplingDeadline) {
	ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::waitForQuietFrame));
	mSampleRequestTime = mSampleRequestTime.value_or(now);
	return;
	}
	}

	ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::sample));

	mSampleRequestTime.reset();
	mLastSampleTime = now;

	mIdleTimer.reset();

	mSampleRequested = true;
	mCondition.notify_one();
	}

	void RegionSamplingThread::binderDied(const wp<IBinder>& who) {
	std::lock_guard lock(mSamplingMutex);
	mDescriptors.erase(who);
	}

	float sampleArea(const uint32_t* data, int32_t width, int32_t height, int32_t stride,
	uint32_t orientation, const Rect& sample_area) {
	if (!sample_area.isValid() \|\| (sample_area.getWidth() > width) \|\|
	(sample_area.getHeight() > height)) {
	ALOGE("invalid sampling region requested");
	return 0.0f;
	}

	// (b/133849373) ROT_90 screencap images produced upside down
	auto area = sample_area;
	if (orientation & ui::Transform::ROT_90) {
	area.top = height - area.top;
	area.bottom = height - area.bottom;
	std::swap(area.top, area.bottom);

	area.left = width - area.left;
	area.right = width - area.right;
	std::swap(area.left, area.right);
	}

	const uint32_t pixelCount = (area.bottom - area.top) * (area.right - area.left);
	uint32_t accumulatedLuma = 0;

	// Calculates luma with approximation of Rec. 709 primaries
	for (int32_t row = area.top; row < area.bottom; ++row) {
	const uint32_t* rowBase = data + row * stride;
	for (int32_t column = area.left; column < area.right; ++column) {
	uint32_t pixel = rowBase[column];
	const uint32_t r = pixel & 0xFF;
	const uint32_t g = (pixel >> 8) & 0xFF;
	const uint32_t b = (pixel >> 16) & 0xFF;
	const uint32_t luma = (r * 7 + b * 2 + g * 23) >> 5;
	accumulatedLuma += luma;
	}
	}

	return accumulatedLuma / (255.0f * pixelCount);
	}

	std::vector<float> RegionSamplingThread::sampleBuffer(
	const sp<GraphicBuffer>& buffer, const Point& leftTop,
	const std::vector<RegionSamplingThread::Descriptor>& descriptors, uint32_t orientation) {
	void* data_raw = nullptr;
	buffer->lock(GRALLOC_USAGE_SW_READ_OFTEN, &data_raw);
	std::shared_ptr<uint32_t> data(reinterpret_cast<uint32_t*>(data_raw),
	[&buffer](auto) { buffer->unlock(); });
	if (!data) return {};

	const int32_t width = buffer->getWidth();
	const int32_t height = buffer->getHeight();
	const int32_t stride = buffer->getStride();
	std::vector<float> lumas(descriptors.size());
	std::transform(descriptors.begin(), descriptors.end(), lumas.begin(),
	[&](auto const& descriptor) {
	return sampleArea(data.get(), width, height, stride, orientation,
	descriptor.area - leftTop);
	});
	return lumas;
	}

	void RegionSamplingThread::captureSample() {
	ATRACE_CALL();
	std::lock_guard lock(mSamplingMutex);

	if (mDescriptors.empty()) {
	return;
	}

	wp<const DisplayDevice> displayWeak;

	ui::LayerStack layerStack;
	ui::Transform::RotationFlags orientation;
	ui::Size displaySize;

	{
	// TODO(b/159112860): Don't keep sp<DisplayDevice> outside of SF main thread
	const sp<const DisplayDevice> display = mFlinger.getDefaultDisplayDevice();
	displayWeak = display;
	layerStack = display->getLayerStack();
	orientation = ui::Transform::toRotationFlags(display->getOrientation());
	displaySize = display->getSize();
	}

	std::vector<RegionSamplingThread::Descriptor> descriptors;
	Region sampleRegion;
	for (const auto& [listener, descriptor] : mDescriptors) {
	sampleRegion.orSelf(descriptor.area);
	descriptors.emplace_back(descriptor);
	}

	const Rect sampledBounds = sampleRegion.bounds();
	constexpr bool kUseIdentityTransform = false;

	SurfaceFlinger::RenderAreaFuture renderAreaFuture = ftl::defer([=] {
	return DisplayRenderArea::create(displayWeak, sampledBounds, sampledBounds.getSize(),
	ui::Dataspace::V0_SRGB, kUseIdentityTransform);
	});

	std::unordered_set<sp<IRegionSamplingListener>, SpHash<IRegionSamplingListener>> listeners;

	auto traverseLayers = [&](const LayerVector::Visitor& visitor) {
	bool stopLayerFound = false;
	auto filterVisitor = [&](Layer* layer) {
	// We don't want to capture any layers beyond the stop layer
	if (stopLayerFound) return;

	// Likewise if we just found a stop layer, set the flag and abort
	for (const auto& [area, stopLayer, listener] : descriptors) {
	if (layer == stopLayer.promote().get()) {
	stopLayerFound = true;
	return;
	}
	}

	// Compute the layer's position on the screen
	const Rect bounds = Rect(layer->getBounds());
	const ui::Transform transform = layer->getTransform();
	constexpr bool roundOutwards = true;
	Rect transformed = transform.transform(bounds, roundOutwards);

	// If this layer doesn't intersect with the larger sampledBounds, skip capturing it
	Rect ignore;
	if (!transformed.intersect(sampledBounds, &ignore)) return;

	// If the layer doesn't intersect a sampling area, skip capturing it
	bool intersectsAnyArea = false;
	for (const auto& [area, stopLayer, listener] : descriptors) {
	if (transformed.intersect(area, &ignore)) {
	intersectsAnyArea = true;
	listeners.insert(listener);
	}
	}
	if (!intersectsAnyArea) return;

	ALOGV("Traversing [%s] [%d, %d, %d, %d]", layer->getDebugName(), bounds.left,
	bounds.top, bounds.right, bounds.bottom);
	visitor(layer);
	};
	mFlinger.traverseLayersInLayerStack(layerStack, CaptureArgs::UNSET_UID, filterVisitor);
	};

	std::shared_ptr<renderengine::ExternalTexture> buffer = nullptr;
	if (mCachedBuffer && mCachedBuffer->getBuffer()->getWidth() == sampledBounds.getWidth() &&
	mCachedBuffer->getBuffer()->getHeight() == sampledBounds.getHeight()) {
	buffer = mCachedBuffer;
	} else {
	const uint32_t usage =
	GRALLOC_USAGE_SW_READ_OFTEN \| GRALLOC_USAGE_HW_RENDER \| GRALLOC_USAGE_HW_TEXTURE;
	sp<GraphicBuffer> graphicBuffer =
	new GraphicBuffer(sampledBounds.getWidth(), sampledBounds.getHeight(),
	PIXEL_FORMAT_RGBA_8888, 1, usage, "RegionSamplingThread");
	const status_t bufferStatus = graphicBuffer->initCheck();
	LOG_ALWAYS_FATAL_IF(bufferStatus != OK, "captureSample: Buffer failed to allocate: %d",
	bufferStatus);
	buffer = std::make_shared<
	renderengine::ExternalTexture>(graphicBuffer, mFlinger.getRenderEngine(),
	renderengine::ExternalTexture::Usage::WRITEABLE);
	}

	const sp<SyncScreenCaptureListener> captureListener = new SyncScreenCaptureListener();
	mFlinger.captureScreenCommon(std::move(renderAreaFuture), traverseLayers, buffer,
	true /* regionSampling /, false / grayscale */, captureListener);
	ScreenCaptureResults captureResults = captureListener->waitForResults();

	std::vector<Descriptor> activeDescriptors;
	for (const auto& descriptor : descriptors) {
	if (listeners.count(descriptor.listener) != 0) {
	activeDescriptors.emplace_back(descriptor);
	}
	}

	ALOGV("Sampling %zu descriptors", activeDescriptors.size());
	std::vector<float> lumas = sampleBuffer(buffer->getBuffer(), sampledBounds.leftTop(),
	activeDescriptors, orientation);
	if (lumas.size() != activeDescriptors.size()) {
	ALOGW("collected %zu median luma values for %zu descriptors", lumas.size(),
	activeDescriptors.size());
	return;
	}

	for (size_t d = 0; d < activeDescriptors.size(); ++d) {
	activeDescriptors[d].listener->onSampleCollected(lumas[d]);
	}

	mCachedBuffer = buffer;
	ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::noWorkNeeded));
	}

	// NO_THREAD_SAFETY_ANALYSIS is because std::unique_lock presently lacks thread safety annotations.
	void RegionSamplingThread::threadMain() NO_THREAD_SAFETY_ANALYSIS {
	std::unique_lock<std::mutex> lock(mThreadControlMutex);
	while (mRunning) {
	if (mSampleRequested) {
	mSampleRequested = false;
	lock.unlock();
	captureSample();
	lock.lock();
	}
	mCondition.wait(lock, [this]() REQUIRES(mThreadControlMutex) {
	return mSampleRequested \|\| !mRunning;
	});
	}
	}

	} // namespace android

	// TODO(b/129481165): remove the #pragma below and fix conversion issues
	#pragma clang diagnostic pop // ignored "-Wconversion -Wextra"