qffmpegsurfacecapturegrabber.cpp

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// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "qffmpegsurfacecapturegrabber_p.h"
 
#include <qelapsedtimer.h>
#include <qloggingcategory.h>
#include <qthread.h>
#include <qtimer.h>
 
QT_BEGIN_NAMESPACE
 
static Q_LOGGING_CATEGORY(qLcScreenCaptureGrabber, "qt.multimedia.ffmpeg.surfacecapturegrabber");
 
namespace {
 
class GrabbingProfiler
{
public:
    auto measure()
    {
        m_elapsedTimer.start();
        return qScopeGuard([&]() {
            const auto nsecsElapsed = m_elapsedTimer.nsecsElapsed();
            ++m_number;
            m_wholeTime += nsecsElapsed;
 
#ifdef DUMP_SCREEN_CAPTURE_PROFILING
            qDebug() << "screen grabbing time:" << nsecsElapsed << "avg:" << avgTime()
                     << "number:" << m_number;
#endif
        });
    }
 
    qreal avgTime() const
    {
        return m_number ? m_wholeTime / (m_number * 1000000.) : 0.;
    }
 
    qint64 number() const
    {
        return m_number;
    }
 
private:
    QElapsedTimer m_elapsedTimer;
    qint64 m_wholeTime = 0;
    qint64 m_number = 0;
};
 
} // namespace
 
struct QFFmpegSurfaceCaptureGrabber::GrabbingContext
{
    GrabbingProfiler profiler;
    QTimer timer;
    QElapsedTimer elapsedTimer;
    qint64 lastFrameTime = 0;
};
 
class QFFmpegSurfaceCaptureGrabber::GrabbingThread : public QThread
{
public:
    GrabbingThread(QFFmpegSurfaceCaptureGrabber& grabber)
        : m_grabber(grabber)
    {}
 
protected:
    void run() override
    {
        m_grabber.initializeGrabbingContext();
 
        if (!m_grabber.isGrabbingContextInitialized())
            return;
 
        exec();
        m_grabber.finalizeGrabbingContext();
    }
 
private:
    QFFmpegSurfaceCaptureGrabber& m_grabber;
};
 
QFFmpegSurfaceCaptureGrabber::QFFmpegSurfaceCaptureGrabber(ThreadPolicy threadPolicy)
{
    setFrameRate(DefaultScreenCaptureFrameRate);
 
    if (threadPolicy == CreateGrabbingThread)
        m_thread = std::make_unique<GrabbingThread>(*this);
}
 
void QFFmpegSurfaceCaptureGrabber::start()
{
    if (m_thread)
        m_thread->start();
    else if (!isGrabbingContextInitialized())
        initializeGrabbingContext();
}
 
QFFmpegSurfaceCaptureGrabber::~QFFmpegSurfaceCaptureGrabber() = default;
 
void QFFmpegSurfaceCaptureGrabber::setFrameRate(qreal rate)
{
    rate = qBound(MinScreenCaptureFrameRate, rate, MaxScreenCaptureFrameRate);
    if (std::exchange(m_rate, rate) != rate) {
        qCDebug(qLcScreenCaptureGrabber) << "Screen capture rate has been changed:" << m_rate;
 
        updateTimerInterval();
    }
}
 
qreal QFFmpegSurfaceCaptureGrabber::frameRate() const
{
    return m_rate;
}
 
void QFFmpegSurfaceCaptureGrabber::stop()
{
    if (m_thread)
    {
        m_thread->quit();
        m_thread->wait();
    }
    else if (isGrabbingContextInitialized())
    {
        finalizeGrabbingContext();
    }
}
 
void QFFmpegSurfaceCaptureGrabber::updateError(QPlatformSurfaceCapture::Error error,
                                             const QString &description)
{
    const auto prevError = std::exchange(m_prevError, error);
 
    if (error != QPlatformSurfaceCapture::NoError
        || prevError != QPlatformSurfaceCapture::NoError) {
        emit errorUpdated(error, description);
    }
 
    updateTimerInterval();
}
 
void QFFmpegSurfaceCaptureGrabber::updateTimerInterval()
{
    const qreal rate = m_prevError && *m_prevError != QPlatformSurfaceCapture::NoError
            ? MinScreenCaptureFrameRate
            : m_rate;
    const int interval = static_cast<int>(1000 / rate);
    if (m_context && m_context->timer.interval() != interval)
        m_context->timer.setInterval(interval);
}
 
void QFFmpegSurfaceCaptureGrabber::initializeGrabbingContext()
{
    Q_ASSERT(!isGrabbingContextInitialized());
    qCDebug(qLcScreenCaptureGrabber) << "screen capture started";
 
    m_context = std::make_unique<GrabbingContext>();
    m_context->timer.setTimerType(Qt::PreciseTimer);
    updateTimerInterval();
 
    m_context->elapsedTimer.start();
 
    auto doGrab = [this]() {
        auto measure = m_context->profiler.measure();
 
        auto frame = grabFrame();
 
        if (frame.isValid()) {
            frame.setStartTime(m_context->lastFrameTime);
            frame.setEndTime(m_context->elapsedTimer.nsecsElapsed() / 1000);
            m_context->lastFrameTime = frame.endTime();
 
            updateError(QPlatformSurfaceCapture::NoError);
 
            emit frameGrabbed(frame);
        }
    };
 
    doGrab();
 
    m_context->timer.callOnTimeout(&m_context->timer, doGrab);
    m_context->timer.start();
}
 
void QFFmpegSurfaceCaptureGrabber::finalizeGrabbingContext()
{
    Q_ASSERT(isGrabbingContextInitialized());
    qCDebug(qLcScreenCaptureGrabber)
            << "end screen capture thread; avg grabbing time:" << m_context->profiler.avgTime()
            << "ms, grabbings number:" << m_context->profiler.number();
    m_context.reset();
}
 
bool QFFmpegSurfaceCaptureGrabber::isGrabbingContextInitialized() const
{
    return m_context != nullptr;
}
 
QT_END_NAMESPACE
 
#include "moc_qffmpegsurfacecapturegrabber_p.cpp"