Qt and OpenGL3.3 Tutorial

SGaist

Hi and welcome to devnet,

You should also check if you really got the format you asked for

milsabor

Hi Sgaist, thank you for your answer.
Unfortunately, I don't understand what you are asking me to check .. which format are you talking about ?
Thanks

SGaist

The QGLFormat created in the main.cpp

milsabor

Ok, so here's what I did, I just added some debug lines to the existing code :
@
#include <QApplication>
#include <QGLFormat>
#include "glwidget.h"

int main( int argc, char* argv[] )
{
QApplication a( argc, argv );

// Specify an OpenGL 3.3 format using the Core profile.
// That is, no old-school fixed pipeline functionality
QGLFormat glFormat;
glFormat.setVersion( 3, 3 );
glFormat.setProfile&#40; QGLFormat::CoreProfile &#41;; // Requires >=Qt-4.8.0
glFormat.setSampleBuffers( true );

qDebug() << "OpenGL context QFlags " << glFormat.openGLVersionFlags();

qDebug() << "OpenGL context " << glFormat;


// Create a GLWidget requesting our format
GLWidget w( glFormat );

qDebug() << "OpenGL context" << w.format();

qDebug() << "Driver Version String:" << glGetString(GL_VERSION);

w.show();

return a.exec&#40;&#41;;

}

@

line 16 returns :
@
OpenGL context QFlags QFlags(0x1|0x2|0x4|0x8|0x10|0x20|0x40|0x1000|0x2000|0x4000|0x8000)
@

So, the flag 0x8000 which stands for opengl 3.3, show that openGL 3.3 is supported.
But line 18 returns :
@
OpenGL context QGLFormat(options QFlags(0x1|0x2|0x4|0x20|0x80|0x200|0x400) , plane 0 , depthBufferSize -1 , accumBufferSize -1 , stencilBufferSize -1 , redBufferSize -1 , greenBufferSize -1 , blueBufferSize -1 , alphaBufferSize -1 , samples -1 , swapInterval -1 , majorVersion 3 , minorVersion 3 , profile 1 )
@
Here, the flag 0x8000 has disappeared. Yet, the openGL major and minor version is still 3.3 ...

And finally, once the QGLWidget has been instanciated, line 24 returns :
@
OpenGL context QGLFormat(options QFlags(0x1|0x2|0x4|0x10|0x20|0x80|0x200|0x400) , plane 0 , depthBufferSize 24 , accumBufferSize 16 , stencilBufferSize 8 , redBufferSize 8 , greenBufferSize 8 , blueBufferSize 8 , alphaBufferSize -1 , samples 4 , swapInterval 0 , majorVersion 3 , minorVersion 3 , profile 1 )
@

I tried on line 26 to display one more information but it returns "0x0", I don't know why.

Could someone help me to identify what's wrong ?

Thanks

tilsitt

Hi,

You should call the show() method before calling glGetString(). Before show(), despite you called the constructor, initializeGL() should'nt have been called and your OpenGL context will not be initialized. I think that is why glGetString() is returning NULL (and it is returning a GLubyte*: you should cast it into a char* to display it with qDebug())..

milsabor

Oh yes thanks !
So, I called glGetString after the call of show() and it returns this :

"3.3.0 NVIDIA 304.88"

So it should be okay, it proves that opengl3.3 is supported right, so why is it not working ?

SGaist

Just to be sure, you are not having any warning shown on the console when running the application ?

milsabor

Nope, no warnings at all ...

SGaist

Just thought about something, did you try to run another OpenGL example/demo from Qt's sources, just to be sure they are doing fine

TheMindWithin

Very same problem here, working on OS X 10.9 with Qt 5.1.1. Has a solution been found so far?