Framebuffer Objects - Praise for OpenGL ES 30 Programming Guide - page 331

Note that glGenRenderbuffers is not required to assign a renderbuffer
object name before it is bound using glBindRenderbuffer . Although
it is a good practice to call glGenRenderbuffers , many applications
specify compile-time constants for their buffers. An application can
specify an unused renderbuffer object name to glBindRenderbuffer .
However, we do recommend that OpenGL ES applications call
glGenRenderbuffers and use renderbuffer object names returned
by glGenRenderbuffers instead of specifying their own buffer
object names.
The first time the renderbuffer object name is bound by calling
glBindRenderbuffer , the renderbuffer object is allocated with the
appropriate default state. If this allocation is successful, the allocated
object will become the newly bound renderbuffer object.
The following state and default values are associated with a renderbuffer
object:
• Width and height in pixels—The default value is zero.
• Internal format—This describes the format of the pixels stored in the
renderbuffer. It must be a color-, depth-, or stencil-renderable format.
• Color bit-depth—This is valid only if the internal format is a color-
renderable format. The default value is zero.
• Depth bit-depth—This is valid only if the internal format is a depth-
renderable format. The default value is zero.
• Stencil bit-depth—This is valid only if the internal format is a stencil-
renderable format. The default value is zero.
glBindRenderbuffer can also be used to bind to an existing renderbuffer
object (i.e., an object that has been assigned and used before and,
therefore, has a valid state associated with it). No changes to the state of
the newly bound renderbuffer object are made by the bind command.
Once a renderbuffer object is bound, we can specify the
dimensions and format of the image stored in the renderbuffer. The
glRenderbufferStorage command can be used for this purpose.
glRenderbufferStorage looks very similar to glTexImage2D , except
that no image data is supplied. You can also create a multisample
renderbuffer by using the glRenderbufferStorageMultisample
command. glRenderbufferStorage is equivalent to
glRenderStorageMultisample with samples set to zero. The width
and height of the renderbuffer are specified in pixels and must