qt5base-lts/tests/manual/qopenglwindow/multiwindow/main.cpp

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#include <QtGui>

const char applicationDescription[] = "\n\
This application opens multiple windows and continuously schedules updates for\n\
them. Each of them is a separate QOpenGLWindow so there will be a separate\n\
context and swapBuffers call for each.\n\
\n\
By default the swap interval is 1 so the effect of multiple blocking swapBuffers\n\
on the main thread can be examined. (the result is likely to be different\n\
between platforms, for example OS X is buffer queuing meaning that it can\n\
block outside swap, resulting in perfect vsync for all three windows, while\n\
other systems that block on swap will kill the frame rate due to blocking the\n\
thread three times)\
";

// For reference, below is a table of some test results.
//
//                                    swap interval 1 for all             swap interval 1 for only one and 0 for others
// --------------------------------------------------------------------------------------------------------------------
// OS X (Intel HD)                    60 FPS for all                      60 FPS for all
// Windows Intel opengl32             20 FPS for all (each swap blocks)   60 FPS for all
// Windows ANGLE D3D9/D3D11           60 FPS for all                      60 FPS for all
// Windows ANGLE D3D11 WARP           20 FPS for all                      60 FPS for all
// Windows Mesa llvmpipe              does not really vsync anyway

class Window : public QOpenGLWindow
{
    Q_OBJECT
public:
    Window(int index) : windowNumber(index + 1), x(0), framesSwapped(0) {

        color = QColor::fromHsl((index * 30) % 360, 255, 127).toRgb();

        resize(200, 200);

        setObjectName(QString("Window %1").arg(windowNumber));

        connect(this, SIGNAL(frameSwapped()), SLOT(frameSwapped()));
    }

    void paintGL() {
        QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();
        f->glClearColor(color.redF(), color.greenF(), color.blueF(), 1);
        f->glClear(GL_COLOR_BUFFER_BIT);

        QPainter painter(this);
        painter.drawLine(x, 0, x, height());
        x = ++x % width();
    }

public slots:
    void frameSwapped() {
        ++framesSwapped;
        update();
    }

protected:
    void mousePressEvent(QMouseEvent *event) {
        qDebug() << this << event;
        color.setHsl((color.hue() + 90) % 360, color.saturation(), color.lightness());
        color = color.toRgb();
    }

private:
    int windowNumber;
    QColor color;
    int x;

    int framesSwapped;
    friend void printFps();
};

static const qreal kFpsInterval = 500;

void printFps()
{
    static QElapsedTimer timer;
    if (!timer.isValid()) {
        timer.start();
        return;
    }

    const qreal frameFactor = (kFpsInterval / timer.elapsed()) * (1000.0 / kFpsInterval);

    QDebug output = qDebug().nospace();

    qreal averageFps = 0;
    const QWindowList windows = QGuiApplication::topLevelWindows();
    for (int i = 0; i < windows.size(); ++i) {
        Window *w = qobject_cast<Window*>(windows.at(i));
        Q_ASSERT(w);

        int fps = qRound(w->framesSwapped * frameFactor);
        output << (i + 1) << "=" << fps << ", ";

        averageFps += fps;
        w->framesSwapped = 0;
    }
    averageFps = qRound(averageFps / windows.size());
    qreal msPerFrame = 1000.0 / averageFps;

    output << "avg=" << averageFps << ", ms=" << msPerFrame;

    timer.restart();
}

int main(int argc, char **argv)
{
    QGuiApplication app(argc, argv);

    QCommandLineParser parser;
    parser.setApplicationDescription(applicationDescription);
    parser.addHelpOption();

    QCommandLineOption noVsyncOption("novsync", "Disable Vsync by setting swap interval to 0. "
        "This should give an unthrottled refresh on all platforms for all windows.");
    parser.addOption(noVsyncOption);

    QCommandLineOption vsyncOneOption("vsyncone", "Enable Vsync only for first window, "
        "by setting swap interval to 1 for the first window and 0 for the others.");
    parser.addOption(vsyncOneOption);

    QCommandLineOption numWindowsOption("numwindows", "Open <N> windows instead of the default 3.", "N", "3");
    parser.addOption(numWindowsOption);

    parser.process(app);

    QSurfaceFormat fmt;
    if (parser.isSet(noVsyncOption)) {
        qDebug("swap interval 0 (no throttling)");
        fmt.setSwapInterval(0);
    } else {
        qDebug("swap interval 1 (sync to vblank)");
    }
    QSurfaceFormat::setDefaultFormat(fmt);

    QRect availableGeometry = app.primaryScreen()->availableGeometry();

    int numberOfWindows = qMax(parser.value(numWindowsOption).toInt(), 1);
    QList<QWindow *> windows;
    for (int i = 0; i < numberOfWindows; ++i) {
        Window *w = new Window(i);
        windows << w;

        if (i == 0 && parser.isSet(vsyncOneOption)) {
            qDebug("swap interval 1 for first window only");
            QSurfaceFormat vsyncedSurfaceFormat = fmt;
            vsyncedSurfaceFormat.setSwapInterval(1);
            w->setFormat(vsyncedSurfaceFormat);
            fmt.setSwapInterval(0);
            QSurfaceFormat::setDefaultFormat(fmt);
        }

        static int windowWidth = w->width() + 20;
        static int windowHeight = w->height() + 20;

        static int windowsPerRow = availableGeometry.width() / windowWidth;

        int col = i;
        int row = col / windowsPerRow;
        col -= row * windowsPerRow;

        QPoint position = availableGeometry.topLeft();
        position += QPoint(col * windowWidth, row * windowHeight);
        w->setFramePosition(position);
        w->showNormal();
    }

    QTimer fpsTimer;
    fpsTimer.setInterval(kFpsInterval);
    fpsTimer.setTimerType(Qt::PreciseTimer);
    QObject::connect(&fpsTimer, &QTimer::timeout, &printFps);
    fpsTimer.start();

    int r = app.exec();
    qDeleteAll(windows);
    return r;
}

#include "main.moc"