glreadpixels with FBO attachment - c++

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.