QOpenGLWidget Stereoscopic Rendering Example

The above image is what will be rendered to the left buffer.

The above image is what will be rendered to the right buffer.

Setting the correct surface flag

To enable stereoscopic rendering you need to set the flag QSurfaceFormat::StereoBuffers globally. Just doing it on the widget is not enough because of how the flag is handled internally. The safest is to do it on QSurfaceFormat::SetDefaultFormat prior to starting the application.

QSurfaceFormat format;
format.setDepthBufferSize(24);
format.setStencilBufferSize(8);

// Enable stereoscopic rendering support
format.setStereo(true);

QSurfaceFormat::setDefaultFormat(format);

Rendering twice

After QSurfaceFormat::StereoBuffers is set, then paintGL() will be called twice, once for each buffer. In paintGL() you can call currentTargetBuffer() to query which TargetBuffer is currently active.

In the following snippet we slightly translate the matrix to not render the vertices on top of each other. This is a simple example just too see that if the necessary support is there, at runtime you should see two objects, one on the left and one on the right.

// Slightly translate the model, so that there's a visible difference in each buffer.
QMatrix4x4 modelview;
if (currentTargetBuffer() == QOpenGLWidget::LeftBuffer)
    modelview.translate(-0.4f, 0.0f, 0.0f);
else if (currentTargetBuffer() == QOpenGLWidget::RightBuffer)
    modelview.translate(0.4f, 0.0f, 0.0f);

Example project @ code.qt.io