Qt 5:禁用vsync

Question

为了方便第三方渲染系统的集成，我想从vsync格式中禁用QOpenGLContext。

QSurfaceFormat::swapInterval似乎是Qt中唯一相关的参数。

我尝试了几种方法来实现这一点，但是即使我将QSurfaceFormat::swapInterval(0)设置在早期阶段(在QMainWindow构造之前)，QOpenGLContext::create()调用也会恢复它。

// 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
)

有办法强制vsync被禁用吗？

Answer 1

正如peppe在问题的注释中所建议的那样，QOpenGLContext实例创建后的QOpenGLContext格式不幸与内部使用的实际格式不匹配。

这意味着我实现的代码可能正在工作，但是第二个debug语句显示了错误的值。