how to make updateGL() realtime in QT

[wysota]

Then how could I monitor a reliable one?

That's a very good question. Probably using some dedicated instrumentation tool.

Vertices are created at initialization once and then only used. All render functions inside paint do the following:

void PlanPositionIndicator::render(QGLShaderProgram* shaderProgram)
{
//    qDebug() << vertices.size();
 
    shaderProgram->setAttributeArray("vertex", vertices.constData());
    shaderProgram->enableAttributeArray("vertex");
    shaderProgram->setAttributeArray("color", GL_FLOAT,colors,1);
    //    shaderProgram->setAttributeArray("color", GL_FLOAT,colors.data(),1);
    shaderProgram->enableAttributeArray("color");
 
    glEnable    (GL_BLEND);
    glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
    glDrawArrays(GL_TRIANGLES, 0, vertices.size());
}

void PlanPositionIndicator::render(QGLShaderProgram* shaderProgram)
{
//    qDebug() << vertices.size();

    shaderProgram->setAttributeArray("vertex", vertices.constData());
    shaderProgram->enableAttributeArray("vertex");
    shaderProgram->setAttributeArray("color", GL_FLOAT,colors,1);
    //    shaderProgram->setAttributeArray("color", GL_FLOAT,colors.data(),1);
    shaderProgram->enableAttributeArray("color");

    glEnable    (GL_BLEND);
    glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    glDrawArrays(GL_TRIANGLES, 0, vertices.size());
}

To copy to clipboard, switch view to plain text mode 

What is "vertices"? Is it a vertex buffer? Did you tell OpenGL that these values are static?