(C++) Am I on the right track with using framebuffers in OpenGL? - c++

Question

My current issues are;
I am unsure at which point I can render to the frame buffer, glBindFramebuffer(GL_FRAMEBUFFER, fbo); , I am assuming this is done after I have bound the frame buffer. (Where can I render to the framebuffer?)
I am unsure how I can get the texture I have rendered to use later as a texture. (How will I be accessing the texture after rendering to it?)
Here is my code so far;
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB);
glutInitWindowPosition(100,100);
glutInitWindowSize(400,400);
glutCreateWindow("Main Window");
glutDisplayFunc(display);
GLuint fbo;
glGenFramebuffers(1, &fbo);
glBindFramebuffer(GL_FRAMEBUFFER, fbo);
//Draw stuff here?
GLuint tex;
glBindTexture(GL_TEXTURE_2D, tex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 800, 600, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex, 0);
GLuint rbo;
glGenRenderbuffers(1, &rbo);
glBindRenderbuffer(GL_RENDERBUFFER, rbo);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, 800, 600);
glBindRenderbuffer(GL_RENDERBUFFER, 0);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo);
if(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE) cout << "FB setup: Complete" << endl;
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glDeleteFramebuffers(1, &fbo);
// use texture here?
// i.e. draw quad with texture, where is the texture?
glutMainLoop();
return 0;
}

Answer 1

You can render to the framebuffer as soon as it is bound and has all necessary textures and renderbuffers attached (i.e. it must be "complete").
You can use the texture as soon as you've finished rendering to the framebuffer and unbound it. Note that you cannot use a texture of a framebuffer while drawing into the same framebuffer.
As scicyb pointed out, you also can't delete the framebuffer while you're still using it. The texture is not part of the framebuffer, so you can use the texture after deleting the framebuffer, but you can't use the framebuffer after deleting the framebuffer. The framebuffer is used to draw things and the texture is where the pixels end up when you draw them.