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glMapBuffer — map a buffer object's data store
void * glMapBuffer( | GLenum | target, |
| GLenum | access); |
target
Specifies the target buffer object being mapped.
The symbolic constant must be
GL_ARRAY_BUFFER,
GL_ELEMENT_ARRAY_BUFFER,
GL_PIXEL_PACK_BUFFER, or
GL_PIXEL_UNPACK_BUFFER.
access
Specifies the access policy, indicating whether it will be possible to read from, write to,
or both read from and write to the buffer object's mapped data store. The symbolic constant must be
GL_READ_ONLY, GL_WRITE_ONLY, or GL_READ_WRITE.
GLboolean glUnmapBuffer(GLenum target);
target
Specifies the target buffer object being unmapped.
The symbolic constant must be
GL_ARRAY_BUFFER,
GL_ELEMENT_ARRAY_BUFFER,
GL_PIXEL_PACK_BUFFER, or
GL_PIXEL_UNPACK_BUFFER.
glMapBuffer maps to the client's address space the entire data store of the buffer object
currently bound to target. The data can then be directly read and/or written relative to
the returned pointer, depending on the specified access policy. If the GL is unable to
map the buffer object's data store, glMapBuffer generates an error and returns
NULL. This may occur for system-specific reasons, such as low virtual memory availability.
If a mapped data store is accessed in a way inconsistent with the specified access policy,
no error is generated, but performance may be negatively impacted and system errors, including program
termination, may result. Unlike the usage parameter of glBufferData,
access is not a hint, and does in fact constrain the usage of the mapped data store on
some GL implementations. In order to achieve the highest performance available, a buffer object's data store
should be used in ways consistent with both its specified usage and
access parameters.
A mapped data store must be unmapped with glUnmapBuffer before its buffer object is used.
Otherwise an error will be generated by any GL command that attempts to dereference the buffer object's data store.
When a data store is unmapped, the pointer to its data store becomes invalid. glUnmapBuffer
returns GL_TRUE unless the data store contents have become corrupt during the time
the data store was mapped. This can occur for system-specific reasons that affect the availability of graphics
memory, such as screen mode changes. In such situations, GL_FALSE is returned and the
data store contents are undefined. An application must detect this rare condition and reinitialize the data store.
A buffer object's mapped data store is automatically unmapped when the buffer object is deleted or its data store
is recreated with glBufferData.
If an error is generated, glMapBuffer returns NULL, and
glUnmapBuffer returns GL_FALSE.
glMapBuffer and glUnmapBuffer are available only if the GL version is 1.5 or greater.
GL_PIXEL_PACK_BUFFER and GL_PIXEL_UNPACK_BUFFER are
available only if the GL version is 2.1 or greater.
Parameter values passed to GL commands may not be sourced from the returned pointer. No error will be generated, but results will be undefined and will likely vary across GL implementations.
GL_INVALID_ENUM is generated if target is not
GL_ARRAY_BUFFER, GL_ELEMENT_ARRAY_BUFFER,
GL_PIXEL_PACK_BUFFER, or GL_PIXEL_UNPACK_BUFFER.
GL_INVALID_ENUM is generated if access is not
GL_READ_ONLY, GL_WRITE_ONLY, or GL_READ_WRITE.
GL_OUT_OF_MEMORY is generated when glMapBuffer is executed
if the GL is unable to map the buffer object's data store. This may occur for a variety of system-specific
reasons, such as the absence of sufficient remaining virtual memory.
GL_INVALID_OPERATION is generated if the reserved buffer object name 0 is bound to target.
GL_INVALID_OPERATION is generated if glMapBuffer is executed for
a buffer object whose data store is already mapped.
GL_INVALID_OPERATION is generated if glUnmapBuffer is executed for
a buffer object whose data store is not currently mapped.
GL_INVALID_OPERATION is generated if glMapBuffer or glUnmapBuffer is executed
between the execution of glBegin and the corresponding
execution of glEnd.
glGetBufferPointerv with argument GL_BUFFER_MAP_POINTER
glGetBufferParameteriv with argument GL_BUFFER_MAPPED, GL_BUFFER_ACCESS, or GL_BUFFER_USAGE
Copyright © 2005 Addison-Wesley. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.