Frame Buffer Object (FBO) is not working. What is the right way to use?

Question

I am trying to use FBO but i am living some problems. I will show you my steps but first i will show my running screen ,so we can compare them. Like before fbo after fbo.

My running screen and Draw() function code:

glClearColor(0.5,0.5,0.5,1.0);
glLoadIdentity();
glTranslatef(0.0,0.0,-3.0);
glRotatef(0,0.0,1.0,0.0);
glUniform3f(glGetUniformLocation(mainShader->getProgramId(),"lightPos"),0,1,2); 
mainShader->useShader();    
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    scene->draw(mainShader->getProgramId());    
mainShader->delShader();

After I tried to add FBO :

Create FBO texture function:

unsigned int createTexture(int w,int h,bool isDepth=false)
{
    unsigned int textureId;
    glGenTextures(1,&textureId);
    glBindTexture(GL_TEXTURE_2D,textureId);
    glTexImage2D(GL_TEXTURE_2D,0,(!isDepth ? GL_RGBA8 : GL_DEPTH_COMPONENT),w,h,0,isDepth ? GL_DEPTH_COMPONENT : GL_RGBA,GL_FLOAT,NULL);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_CLAMP_TO_EDGE);

    int i;
    i=glGetError();
    if(i!=0)
    {
        std::cout << "Error happened while loading the texture: " << i << std::endl;
    }
    glBindTexture(GL_TEXTURE_2D,0);
    return textureId;
}

Init() function :

void init()
{
    glClearColor(0,0,0,1);
    glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluPerspective(50,640.0/480.0,1,1000);
    glMatrixMode(GL_MODELVIEW);
    glEnable(GL_DEPTH_TEST);
    mainShader=new shader("vertex.vs","fragment.frag");
    quadRenderShader=new shader("quadRender.vs","quadRender.frag");
    scene=new meshLoader("test.blend");

    renderTexture=createTexture(640,480);
    depthTexture=createTexture(640,480,true);
    glGenFramebuffers(1,&FBO);
    glBindFramebuffer(GL_FRAMEBUFFER,FBO);
    //GL_COLOR_ATTACHMENT0
    //GL_DEPTH_ATTACHMENT
    glFramebufferTexture2D(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,GL_TEXTURE_2D,renderTexture,0);

    glFramebufferTexture2D(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,GL_TEXTURE_2D,depthTexture,0);


    int i=glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if(i!=GL_FRAMEBUFFER_COMPLETE)
    {
        std::cout << "Framebuffer is not OK, status=" << i << std::endl;
    }
    glBindFramebuffer(GL_FRAMEBUFFER,0);

}

And Draw() function:

void display()
{
    //rendering to texture...
    glClearColor(0.5,0.5,0.5,1.0);
    glLoadIdentity();
    glTranslatef(0.0,0.0,-3.0);
    glRotatef(0,0.0,1.0,0.0);
    glUniform3f(glGetUniformLocation(mainShader->getProgramId(),"lightPos"),0,1,2);     
    mainShader->useShader();
    glBindFramebuffer(GL_FRAMEBUFFER,FBO);
        glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
        scene->draw(mainShader->getProgramId());
    glBindFramebuffer(GL_FRAMEBUFFER,0);
    mainShader->delShader();




    glClearColor(0.0,0.0,0.0,1.0);
    //render texture to screen
    glLoadIdentity();       
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    quadRenderShader->useShader();
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D,depthTexture);
    glUniform1i(glGetUniformLocation(quadRenderShader->getProgramId(),"texture"),0);
    quad->draw(quadRenderShader->getProgramId());
    quadRenderShader->delShader();

}

and Result only drawing last setup color (glClearColor) so black :

Result should be like in tutorial :

Note: I know tutorial monkey is purple but it is not problem.

Answer 1

I ran into this problem and fixed it by clearing BOTH the framebuffer quads contents which happens after it is bound, and since the quad is drawn to the screen, the screen needs to be cleared too:

while(!glfwWindowShouldClose(window))
{
    // clear quad from screen
    glClear(GL_COLOR_BUFFER_BIT);
    glClear(GL_DEPTH_BUFFER_BIT);
    glBindFramebuffer(GL_FRAMEBUFFER,FBO);
    // clear fbo contents
    glClear(GL_COLOR_BUFFER_BIT);
    glClear(GL_DEPTH_BUFFER_BIT);
    ...
    glBindFramebuffer(GL_FRAMEBUFFER,0);

}

Answer 2

What happens if you change your:

glBindFramebuffer(GL_FRAMEBUFFER,FBO);
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    scene->draw(mainShader->getProgramId());

to the first line of your display function? Try to compare your code to this of mine: https://github.com/felipunky/LearnOpenGL-master/tree/master/LearnOpenGL I use frameBuffers there the only difference is that I need to reference the shaders to themselves, so I have:

glBindTexture( GL_TEXTURE_2D, even ? textureColourBufferOne : textureColourBuffer );

You would just have something like:

glBindTexture( GL_TEXTURE_2D, textureColourBufferOne );