Fragment shader with 2d

[krzat]

What should I do to make this simple shader work (everything should be blue I guess)?

class GLWidget : public QGLWidget {
public:
    GLWidget(QWidget *parent = 0): QGLWidget(parent) {}
protected:
    void initializeGL()
    {
        this->setFixedSize(200,200);
        fbo = new QGLFramebufferObject(200, 200);
        QPainter p(fbo);
        p.fillRect(10,10,30,30,Qt::yellow);
 
        QGLShaderProgram shader(this);
        if(shader.addShaderFromSourceCode(QGLShader::Fragment,
         "void main(void) {gl_FragColor = vec4(0, 0, 1, 1.0);}"))
            qDebug("Shader prepared.");
        shader.link();
        shader.bind();
    }
    void paintEvent(QPaintEvent *event)
    {
        QPainter painter(this);
        //painter.fillRect(0,0,200,100, Qt::gray); // line2
        painter.fillRect(60,20,30,30, Qt::gray);
        drawTexture(QPoint(10, 10), fbo->texture());
 
    }
private:
    QGLFramebufferObject *fbo;
};

class GLWidget : public QGLWidget {
public:
    GLWidget(QWidget *parent = 0): QGLWidget(parent) {}
protected:
    void initializeGL()
    {
        this->setFixedSize(200,200);
        fbo = new QGLFramebufferObject(200, 200);
        QPainter p(fbo);
        p.fillRect(10,10,30,30,Qt::yellow);

        QGLShaderProgram shader(this);
        if(shader.addShaderFromSourceCode(QGLShader::Fragment,
         "void main(void) {gl_FragColor = vec4(0, 0, 1, 1.0);}"))
            qDebug("Shader prepared.");
        shader.link();
        shader.bind();
    }
    void paintEvent(QPaintEvent *event)
    {
        QPainter painter(this);
        //painter.fillRect(0,0,200,100, Qt::gray); // line2
        painter.fillRect(60,20,30,30, Qt::gray);
        drawTexture(QPoint(10, 10), fbo->texture());

    }
private:
    QGLFramebufferObject *fbo;
};

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