glreadpixels with FBO attachment

Question

Ok, so I have this FBO with a depth buffer and 4 color attachments. I want to read the dept buffer at the place where I hold the cursor and a value from the fourth color attachment. I don't seem to manage any of the two. I've wrote this class :

class Picker3D{
    public:
bool useAtachment;
GLenum  atachment;
float PickerLastSignature;
point3f PickerLastPos;

Picker3D( bool useAtachment = true , GLenum atachment = GL_COLOR_ATTACHMENT3 ) : useAtachment(useAtachment) , atachment(atachment) {

}

void SetObjectSignature( float signature , GLSL_Prog prog ){
    glUniform1f( glGetUniformLocation( prog.PR , "Signature" ) , signature );
}

float getSignature( float x , float y , float height ){
    glGetError();
    if( useAtachment )
        glReadBuffer( atachment );

    cout << " Error message1 : " << glGetError() << endl ;

    float *pixels = new float[4];
    glReadPixels( x , height - y , 1 , 1 , GL_RGB , GL_FLOAT , pixels );
    PickerLastSignature = pixels[1];

    cout << " Error message2 : " << glGetError() << endl ;

    return PickerLastSignature;
}

point3f get3DPosition( float x , float y , float height ){
    //glReadBuffer( GL_DEPTH_ATTACHMENT );

    double depth;
    glReadPixels( x , y , 1 , 1 , GL_DEPTH_COMPONENT , GL_FLOAT , &depth );

    cout << depth << endl;

    int viewport[4];
    float *modelview;
    double projection[16];
    double ModelView[16];

    modelview = mat4f::GetTopMatrix().returnTransposedMatrix().returnFloatArray();
    for( int i = 0 ; i < 16 ; i++ ){
        ModelView[i] = modelview[i];
    }

    glGetDoublev(GL_PROJECTION_MATRIX, projection);
    glGetIntegerv(GL_VIEWPORT, viewport);

    double x1 , y1 , z1;

    gluUnProject( x , height - y , depth , ModelView  , projection , viewport , &x1 , &y1 , &z1 );

    PickerLastPos = point3f( x1 , y1 , z1 );
    return PickerLastPos;
}

};

and I use it like so

// in main loop

BindFrameBuffer(); 
drawStuff(); 
Picker.get3DPosition( x , y , height );
Picker.getSignature( x , y , height );
UnbindBuffer();
drawSecondPass(); 
endDrawSecondPass();
// check Values of PickerLastPos and PickerLastSignature 
SwapBuffers();  

the depth is not changing altrough it is working on the screen and the getSignature gives error 1282( invalid operation, I think ) at the line with glReadBuffer.

the main loop is :

               glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT );

            /// deferred pass

            DefFBO->drawFBO();
            GeometryShader.UseNow();

            glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT );

            // load the view matrix and set the camera
            cam.camera_set();
            cam.camera_get( GeometryShader );

            // load identity for model matrix
            mat4f::LoadIdentity();

            /// Geometry Drawing

            mat4f::PushMatrix();

                mat4f::Translate( 0 , 0 , -10 );
                Picker.SetObjectSignature( 1.0f , GeometryShader );
                T90.obj_rend( GeometryShader );
                Picker.SetObjectSignature( 2.0f , GeometryShader );
                Town.obj_rend( GeometryShader );

            mat4f::PopMatrix();

            Picker.get3DPosition( Window.Mouse->mouse_x , Window.Mouse->mouse_y , Window.Height );

            /// setting the deferred read from buffer part

            // last read from  framebuffer
            Picker.getSignature( Window.Mouse->mouse_x , Window.Mouse->mouse_y , Window.Height );

            // unbind FBO
            DefFBO->readFBO();

            // use fragment shader, for lights and for post processing
            FragmentShader.UseNow();

            // send windows width and height and bind multiple textures
            DefFBO->send_to_GLSL( FragmentShader.PR );

            // send view matrix to the shader
            cam.camera_get( FragmentShader );

            glDepthMask(GL_FALSE);
            glEnable(GL_DEPTH_TEST);

            glUniform3f( glGetUniformLocation( FragmentShader.PR , "CameraPosition" ) , cam.x , cam.y , cam.z );

            /// final draw
            DefFBO->sendGlobalLight( FragmentShader , point3f( 0 , 1 , 0 ) , point3f( 0.3 , 0.3 , 0.3 ) , point3f( 0.9 , 0.9 , 0.9 ) );

            cout << Picker.PickerLastPos << endl;

            DefFBO->end_read();

            glEnable(GL_DEPTH_TEST);
            glDepthMask(GL_TRUE);

Answer 1

It seems that I had to bind the fbo for reading for geting data out of it, as @Andon pointed out. I was binding with GL_DRAW_FRAMEBUFFER.