The OpenGL Graphics System: A Specification

2.9. BUFFER OBJECTS 36
Name Value
BUFFER SIZE size
BUFFER USAGE usage
BUFFER ACCESS READ WRITE
BUFFER MAPPED FALSE
BUFFER MAP POINTER NULL
Table 2.7: Buffer object initial state.
Clients must align data elements consistent with the requirements of the client
platform, with an additional base-level requirement that an offset within a buffer to
a datum comprising N basic machine units be a multiple of N.
If the GL is unable to create a data store of the requested size, the error
OUT OF MEMORY is generated.
To modify some or all of the data contained in a buffer object’s data store, the
client may use the command
void BufferSubData( enum target, intptr offset,
sizeiptr size, const void *data );
with target set to ARRAY BUFFER. offset and size indicate the range of data in the
buffer object that is to be replaced, in terms of basic machine units. data specifies a
region of client memory size basic machine units in length, containing the data that
replace the specified buffer range. An INVALID VALUE error is generated if offset
or size is less than zero, or if offset + size is greater than the value of BUFFER SIZE.
The entire data store of a buffer object can be mapped into the client’s address
space by calling
void *MapBuffer( enum target, enum access );
with target set to ARRAY BUFFER. If the GL is able to map the buffer object’s
data store into the client’s address space, MapBuffer returns the pointer value
to the data store. If the buffer data store is already in the mapped state, Map-
Buffer returns NULL, and an INVALID OPERATION error is generated. Otherwise
MapBuffer returns NULL, and the error OUT OF MEMORY is generated. access is
specified as one of READ ONLY, WRITE ONLY, or READ WRITE, indicating the operations
that the client may perform on the data store through the pointer while the
data store is mapped.
MapBuffer sets buffer object state values as shown in table 2.8.
Version 2.0 - October 22, 2004