Godot engine, set render target to opengl-es framebuffer

Recently, I am focus on playing with godot. And I got a problem when I try to set render target to a opengl-es framebuffer. I tried RasterizerGLES2::set_base_framebuffer but it does not work.

My sample code:

// create framebuffer and attach texture
glGenFramebuffers(1, &my_target_framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, my_target_framebuffer);

glGenTextures(1, &my_target_texture);
glBindTexture(GL_TEXTURE_2D, my_target_texture);
glTexParameteri(...);
glTexImage2D(...);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, my_target_texture, 0);
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);

// clear to RED
glClearColor(1, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glBindFramebuffer(GL_FRAMEBUFFER, 0);

// then call set_base_framebuffer, something like:
RasterizerGLES2::set_base_framebuffer(my_target_framebuffer, 
Vector2(my_target_width, my_target_height));

It does not work at all, and my_target_framebuffer is always RED (does not draw to my_target_framebuffer), and screen flicker.

plz help!

BTW, I use godot 2.1