I'm trying to use the accumulation buffer in QGLWidget class, and wrote the following code:

@
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);

QGLFormat format = QGLFormat::defaultFormat();
format.setAccum(true);
format.setAccumBufferSize(24);
QGLFormat::setDefaultFormat(format);
QGLWidget* testWidget = new QGLWidget(this);
ui->mainLayout->addWidget(testWidget);

assert(testWidget->format().accum());

}
@

The problem is, this code always fails at the assertion test. This means the instantiated QGLWidget does not enable the accumulation buffer feature.

Am I doing something wrong? Any suggestions? Hope someone will help me.

Qt Creator 3.0.1
Qt 5.2.1 (Clang 5.0 (Apple), 64 bit)
MacBook Air (OS X 10.8.5)

Thank you