I want to do post processing effects so I was thinking If I could just make custom framebuffer in cocos2dx like OpenGL and render the ALL SCENES objects in it. I want a single frame buffer for all scenes. Is there any way? Thanks.
Framebuffers will be your friend. You can create as many as you wish with
glCreateFramebuffers(). Here is a documentation page, which lists all handy functions for doing that in "raw" OpenGL. Documentation
cocos2d has the
RenderTexture class, which will fit also your needs. Here is a quick overview click me
Here is some theory and practise on framebuffers:https://learnopengl.com/#!Advanced-OpenGL/Framebuffers it also explaines how to implement some very simple post-processing effects