渲染动态立方体贴图（OpenGL）

Question

I'm trying to render a scene 6 times and put them on the sides of a cubemap. I'd like to do this properly first before moving onto learning Geometry shaders which would allow this to be done in one pass. Here goes the code:

    void Scene::setupFBO()
    {
        glGenTextures(1, &cubemap);
        glBindTexture(GL_TEXTURE_CUBE_MAP,cubemap);
        glActiveTexture(GL_TEXTURE0);           
        const int size = 128;           
            // create the fbo
        glGenFramebuffers(1, &fbo);
        glBindFramebuffer(GL_FRAMEBUFFER, fbo);

        for(int i=0;i<6;i++)
        {
            glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_RGB,
                size, size, 0, GL_RGB, GL_UNSIGNED_BYTE, 0);

        }
        glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER,
        GL_LINEAR);
        glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER,
        GL_LINEAR);
        glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S,
        GL_CLAMP_TO_EDGE);
        glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T,
        GL_CLAMP_TO_EDGE);
        glTexParameterf(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R,
        GL_CLAMP_TO_EDGE);

        // create the uniform depth buffer
        glGenRenderbuffers(1, &depthbuff);
        glBindRenderbuffer(GL_RENDERBUFFER, depthbuff);
        glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, size, size);
        //glBindRenderbuffer(GL_RENDERBUFFER, 0);
        GLenum drawBufs[] = {GL_COLOR_ATTACHMENT0};
        // attach it
        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, fbo);
        //glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_CUBE_MAP_POSITIVE_X, cubemap, 0);
        glDrawBuffers(1, drawBufs);

        glBindFramebuffer(GL_FRAMEBUFFER, 0);    
        glBindTexture(GL_TEXTURE_CUBE_MAP, 0);

    }

---

    void Scene::pass1()
    {
        GLuint p = glGetSubroutineIndex(program->id,GL_FRAGMENT_SHADER,"pass1");
        glUniformSubroutinesuiv(GL_FRAGMENT_SHADER,1,&p);

        mat4 view;
        glBindFramebuffer(GL_FRAMEBUFFER, fbo);
        for(int i=0;i<6;i++)
        {
            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
            glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, cubemap, 0);
            if(i==0) //X+
                cam->Update(vec3(0),vec3(10,0,0)); // position, target
            else if(i==1) //X-
                cam->Update(vec3(0),vec3(-10,0,0));
            else if(i==2) //Y+
                cam->Update(vec3(0),vec3(0,10,0));
            else if(i == 3) //....
                cam->Update(vec3(0),vec3(0,-10,0));
            else if(i == 4)
                cam->Update(vec3(0),vec3(0,0,10));
            else if(i == 5)
                cam->Update(vec3(0),vec3(0,0,-10));

            view = cam->getViewMat();
            for(int ii=1;ii<SHAPE_COUNT;ii++){
                shapes[ii]->setViewMat(view);
                shapes[ii]->Draw();
            }

        }
    }

---

    void Scene::pass2()
    {
        GLuint p = glGetSubroutineIndex(program->id,GL_FRAGMENT_SHADER,"pass2");
        glUniformSubroutinesuiv(GL_FRAGMENT_SHADER,1,&p);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glBindFramebuffer(GL_FRAMEBUFFER, 0);
        cam->Update(vec3(0,0,10),vec3(0));
        mat4 view = cam->getViewMat();
        for(int i=0;i<SHAPE_COUNT;i++){
            shapes[i]->setViewMat(view);
            (*shapes[i]).Draw();
        }
    }

---

void Scene::Draw(){
    pass1(); // Create the cubemap
    pass2(); // Draw the scene normally
}

I've modified the code from my previous project that implemented a static cubemap that was used for IBL and reflection/refraction. I'll provide the shaders codes if you think it's necessary. At this stage there's only gibberish being rendered.

End result

The actual scene

Update The big square was the result of a bug in my setViewMat function which didn't apply the stacked transformations. It now only renders the scene, the texture is black. I've used AMD gDEBugger to see the resulting cubemap which is just black. So I think it's either my initial fbo binding or how I render each side in the first pass that's at fault.

Answer 1

OK, I finally got it working. In setupFBO I shouldn't have unbound the cubemap. I've posted the updated pass1,2 code anyways. Though the rendering works I have trouble ordering the sides as it seems the sides are not mapped as I had anticipated, X+, X- , ....

 void Scene::pass1()
  {
    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
    GLuint p = glGetSubroutineIndex(program->id,GL_FRAGMENT_SHADER,"pass1");
    glUniformSubroutinesuiv(GL_FRAGMENT_SHADER,1,&p);
    glViewport(0,0,512,512);
    mat4 view, proj;
    proj = glm::perspective(90.0f, 1.0f, 1.0f, 500.0f);
    for(int i=0;i<6;i++)
    {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
       if(i==0)
          view = Camera::Update(vec3(0),vec3(1,0,0),vec3(0,1,0));// pos, target, up
       else if(i==1)
          view =  Camera::Update(vec3(0),vec3(-1,0,0),vec3(0,1,0));
       else if(i==2)
         view =  Camera::Update(vec3(0),vec3(0,1,0),vec3(0,0,1));
       else if(i == 3)
         view =  Camera::Update(vec3(0),vec3(0,-1,0),vec3(0,0,-1));
       else if(i == 4)
         view =  Camera::Update(vec3(0),vec3(0,0,1),vec3(0,1,0));
       else if(i == 5)
         view =  Camera::Update(vec3(0),vec3(0,0,-1),vec3(0,1,0));
        for(int ii=1;ii<SHAPE_COUNT;ii++){
            shapes[ii]->setProjMat(proj);
            shapes[ii]->setViewMatAndUpdate(view); // Empties the transformation stack, pushes the new view matrix and applies all the transformations again
            shapes[ii]->Draw();
                    //Reverts back to the original stack
            shapes[ii]->setViewMatAndUpdate(cam->getViewMat());
        }
        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
            GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, cubemap,0);
     }
   }

---

void Scene::pass2()
{
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    GLuint p = glGetSubroutineIndex(program->id,GL_FRAGMENT_SHADER,"pass2");
    glUniformSubroutinesuiv(GL_FRAGMENT_SHADER,1,&p);
    glViewport(0,0,Constants::Instance()->gWidth,Constants::Instance()->gHeight);
    float  aspectRatio = 8.0f/6.0f;
    mat4 proj = cam->getProjMat();
    for(int i=0;i<SHAPE_COUNT;i++){
        shapes[i]->setProjMat(proj);
        (*shapes[i]).Draw();
    }
}

---

OK, I figured out the ordering by color coding each side of the cube, not sure why it is this way.

if(i==1)
    view = Camera::Update(vec3(0),vec3(1,0,0),vec3(0,1,0));
else if(i==2)
    view =  Camera::Update(vec3(0),vec3(-1,0,0),vec3(0,1,0));
else if(i==4)
    view =  Camera::Update(vec3(0),vec3(0,1,0),vec3(0,0,1));
else if(i == 3)
    view =  Camera::Update(vec3(0),vec3(0,-1,0),vec3(0,0,-1));
else if(i == 0)
    view =  Camera::Update(vec3(0),vec3(0,0,1),vec3(0,1,0));
else if(i == 5)
    view =  Camera::Update(vec3(0),vec3(0,0,-1),vec3(0,1,0));