OpenGL|ES 2.0 glClear command freeze until window state change - qt

Question

My OpenGL|ES 2.0 glClear command freezes until the window state changes (eg. the window gets hidden or shown).
The target platform is ARM7 with a Mali 400 GPU.
All code is mostly copied from the Qt OpenGL ES Cube example.
What am I forgetting?
Leon
Source:
#include "streamplayer.h"
#include <QtOpenGL>
#include <QGLFunctions>
StreamPlayer::StreamPlayer(QWidget *parent) :
QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
{
program = new QGLShaderProgram();
}
StreamPlayer::~StreamPlayer()
{
}
void StreamPlayer::initializeGL()
{
qDebug() << "Initializing GL";
initShaders();
glClearColor(0.5f, 0.5f, 0.7f, 1.0f);
return;
}
void StreamPlayer::paintGL()
{
qDebug() << "Paint GL";
qDebug() << "Clearing buffers";
glClear(GL_COLOR_BUFFER_BIT);
qDebug() << "Never comes here until a window state change";
}
void StreamPlayer::resizeGL(int width, int height)
{
qDebug() << "Resizing GL to " << width << "x" << height;
glViewport(0, 0, width, height);
qDebug() << "Done resizing";
}
void StreamPlayer::initShaders()
{
qDebug() << "Initializing shaders";
setlocale(LC_NUMERIC, "C");
if(!program->addShaderFromSourceFile(QGLShader::Vertex, ":/shaders/vshader.glsl")) {
qDebug() << "Failed to create vertex shader";
}
if(!program->addShaderFromSourceFile(QGLShader::Fragment, ":/shaders/fshader.glsl")) {
qDebug() << "Failed to create fragment shader";
}
if(!program->link()) {
qDebug() << "Failed to link";
}
_gl_vertex = program->attributeLocation("vertex");
_gl_texCoord = program->attributeLocation("texCoord");
_gl_matrix = program->attributeLocation("matrix");
_gl_texture = program->attributeLocation("tex");
if(!program->bind()) {
qDebug() << "Failed to bind";
}
setlocale(LC_ALL, "");
qDebug() << "Shaders ready";
}

Answer 1

Have you kept the timer asking for frame updates ? It is this timer that is asking for openGL redraw by calling updateGL() on the glwidget, that ask for a (delayed) paintGL(). Otherwise paintGL will only be called when Qt estimates necessary (for example window shown).
QTimer *timer = new QTimer(this);
timer->setInterval(10);
QObject::connect(timer, SIGNAL(timeout()), glwidget, SLOT(updateGL()));
//And at the end of MainWindow initialization
timer->start();
See this SO thread for related question.