I am trying to use an OpenGL Shader on a QGrapicsView. My graphic card is a NVidia GeForce GT 425M. I made my experiments on a Ubuntu 12.04 with the NVidia driver 295.40.

I Create a QMainWindow containing two QGraphicsView, each graphics view are displaying the same scene. On One of the Graphics View, I setup an OpenGL View port. The OpenGL View Port is a QGLWidget I had overloaded with the loading of the vertex and fragment shader programs.

Look at my QMainWindow constructor :

Qt Code: 
  1. MainWindow::MainWindow(QWidget *parent) :
  2.     QMainWindow(parent),
  3.     ui(new Ui::MainWindow)
  4. {
  5.     ui->setupUi(this);
  6.     m_scene = new QGraphicsScene(this);
  7.     ui->gvShaded->setScene(m_scene);
  8.     ui->gvUnshaded->setScene(m_scene);
  9.     m_glWidget = new QGLScene();
  10.     ui->gvShaded->setViewport(m_glWidget);
  11.     m_glWidget->updateGL();
  12.     if(m_glWidget->context()->isValid())
  13.     {
  14.         qDebug()<<"GL Context is valid";
  15.     }else
  16.     {
  17.         qWarning()<<"GL Context is not valid";
  18.     }
  19.  
  20.     qDebug() << "Opengl Version : " << m_glWidget->context()->format().openGLVersionFlags();
  21.  
  22.     QBrush brush(QLinearGradient(0,0,20,0));
  23.     brush.setColor(Qt::blue);
  24.     QGraphicsRectItem* rect = m_scene->addRect(0,0,20,20,QPen(Qt::black), brush);
  25.  
  26.     ui->gvShaded->ensureVisible(rect);
  27.     ui->gvUnshaded->ensureVisible(rect);
  28. }
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As you can see I instantiate the object QGLScene which is :

Qt Code: 
  1. class QGLScene : public QGLWidget
  2. {
  3. public:
  4.     QGLScene(QWidget* _parent=0);
  5. protected :
  6.     virtual void initializeGL();
  7. };
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My GLWidget Construction is :
Qt Code: 
  1. QGLScene::QGLScene(QWidget *_parent)
  2.     :QGLWidget(QGLFormat(QGL::DepthBuffer), _parent)
  3. {
  4. }
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And definition of initializeGL is :

Qt Code: 
  1. void QGLScene::initializeGL()
  2. {
  3.     qDebug() << __PRETTY_FUNCTION__;
  4.     m_fragmentShader = new QGLShader(QGLShader::Fragment, context(), this);
  5.     m_vertexShader = new QGLShader(QGLShader::Vertex, context(), this);
  6.     m_pgm = new QGLShaderProgram(context(), this);
  7.     if(m_vertexShader->compileSourceFile("./vertexShader.glsl"))
  8.     {
  9.         if(m_fragmentShader->compileSourceFile("./fragmentShader.glsl"))
  10.         {
  11.             m_pgm->addShader(m_fragmentShader);
  12.             m_pgm->addShader(m_vertexShader);
  13.             if(m_pgm->link()==false)
  14.             {
  15.                 qDebug() << "Error When linking: " << m_pgm->log();
  16.             }
  17.             if(m_pgm->bind()==false)
  18.             {
  19.                 qDebug() << "Can't bind.";
  20.             }
  21.             qDebug() << "Shader bien chargé : "<< m_pgm->log();
  22.         }else
  23.         {
  24.             qDebug() << "Problem when loading fragment shader :";
  25.             qDebug() << m_fragmentShader->log();
  26.             qDebug() << QString(m_fragmentShader->sourceCode());
  27.         }
  28.     }else
  29.     {
  30.         qDebug() << "Problem when loading vertex shader :";
  31.         qDebug() << m_vertexShader->log();
  32.         qDebug() << QString(m_vertexShader->sourceCode());
  33.     }
  34. }
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My shaders are very useless shaders : Vertex :

Qt Code: 
  1. #version 150
  2.  
  3. uniform mat4 viewMatrix, projMatrix;
  4.  
  5. in vec4 position;
  6. in vec3 color;
  7.  
  8. out vec3 Color;
  9.  
  10. void main()
  11. {
  12.     Color = color;
  13.     gl_Position = projMatrix * viewMatrix * position ;
  14. }
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Fragment :
Qt Code: 
  1. #version 150
  2.  
  3. in vec3 Color;
  4. out vec4 outputF;
  5.  
  6. void main()
  7. {
  8.     outputF = vec4(1.0, 0, 0, 1.);
  9. }
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So I attempt to have my Shaded Graphics view as a big red square because I think I enforced the pixels to be red (in my fragment shader).

I have no shader compilation error, but my two scene are the same. Of course, the program pass into the initializeGL function (I can read the PRETTY_FUNCTION).

Does some one have an explanation ?