Vertex Attributes, Vertex Arrays, and Buffer Objects - Praise for OpenGL ES 30 Programming Guide - page 159

GL_TRANSFORM_FEEDBACK_BUFFER
GL_UNIFORM_BUFFER

offset offset in bytes from the beginning of the mapped buffer

length number of bytes of the buffer from offset to flush

If an application maps with GL_MAP_FLUSH_EXPLICIT_BIT but does not
explicitly flush a modified region with glFlushMappedBufferRange ,
its contents will be undefined.

Copying Buffer Objects

So far, we have shown how to load buffer objects with data using
glBufferData , glBufferSubData , and glMapBufferRange . All of these
techniques involve transferring data from the application to the device. It
is also possible with OpenGL ES 3.0 to copy data from one buffer object
to another entirely on the device. This can be done using the function
glCopyBufferSubData .

void glCopyBufferSubData (GLenum readtarget ,
GLenum writetarget ,
GLintptr readoffset ,
GLintptr writeoffset ,
GLsizeiptr size )

readtarget the buffer object target to read from.

writetarget the buffer object target to write to. Both readtarget

and writetarget can be set to any of the following
targets (although they must not be the same target):
GL_ARRAY_BUFFER
GL_ELEMENT_ARRAY_BUFFER
GL_COPY_READ_BUFFER
GL_COPY_WRITE_BUFFER
GL_PIXEL_PACK_BUFFER
GL_PIXEL_UNPACK_BUFFER
GL_TRANSFORM_FEEDBACK_BUFFER
GL_UNIFORM_BUFFER

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