vsync and QOpenGLContext

[PysCowboy]

I would like to disable vsync from the QOpenGLContext format in order to facilitate the integration of a third party rendering system.

QSurfaceFormat::swapInterval seems to be the only related parameter in Qt.

I tried several ways to implement this on Mac and Windows, but even if I set the QSurfaceFormat::swapInterval(0) at an early stage (before the QMainWindow construction), then the QOpenGLContext::create() call is restoring it.

// at application startup, before creating the Qt windows (or in MyQWindow constructor)
QSurfaceFormat format;
format.setSwapBehavior(QSurfaceFormat::DoubleBuffer);
format.setRedBufferSize(8);
format.setGreenBufferSize(8);
format.setBlueBufferSize(8);
format.setAlphaBufferSize(8);
format.setDepthBufferSize(24);
format.setStencilBufferSize(8);
format.setSwapInterval(0);
QSurfaceFormat::setDefaultFormat(format);

QMainWindow *w = new QMainWindow;
w->show();

.

// at QWindow with QOpenGLContext creation, at the first frame update (or at the constructor)
MyQWindow::initialization() {
    WbOpenGLContext *c = new WbOpenGLContext(this);
    c->setFormat(requestedFormat());
    qDebug() << "requested format:" << c->format();
    c->create();
    qDebug() << "actual format:" << c->format();
}

.

# output
requested format: QSurfaceFormat(
    version 2.0,
    options QFlags(),
    depthBufferSize 24,
    redBufferSize 8,
    greenBufferSize 8,
    blueBufferSize 8,
    alphaBufferSize 8,
    stencilBufferSize 8,
    samples -1,
    swapBehavior 2,
    swapInterval 0,
    profile 0
)
context format: QSurfaceFormat(
    version 3.0,
    options QFlags(0x4),
    depthBufferSize 24,
    redBufferSize 8,
    greenBufferSize 8,
    blueBufferSize 8,
    alphaBufferSize 8,
    stencilBufferSize 8,
    samples 0,
    swapBehavior 2,
    swapInterval 1, # Not what I asked
    profile 0
)

Is there a way to force vsync to be disabled?

[PysCowboy]

I asked the question on stackoverflow too:
http://stackoverflow.com/questions/37319328/qt-5-disable-vsync/37327654?noredirect=1#comment62180852_37327654

It seems that the second debug statement can not work because the WbOpenGLContext::format is not updated in the WbOpenGLContext::create() function.