NAME

       glMapBuffer - map a buffer object's data store

C SPECIFICATION

       void * glMapBuffer(GLenum target, GLenum access);

PARAMETERS

       target
           Specifies the target buffer object being mapped. The symbolic constant must be
           GL_ARRAY_BUFFER, GL_ATOMIC_COUNTER_BUFFER, GL_COPY_READ_BUFFER, GL_COPY_WRITE_BUFFER,
           GL_DRAW_INDIRECT_BUFFER, GL_DISPATCH_INDIRECT_BUFFER, GL_ELEMENT_ARRAY_BUFFER,
           GL_PIXEL_PACK_BUFFER, GL_PIXEL_UNPACK_BUFFER, GL_QUERY_BUFFER,
           GL_SHADER_STORAGE_BUFFER, GL_TEXTURE_BUFFER, GL_TRANSFORM_FEEDBACK_BUFFER or
           GL_UNIFORM_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.

C SPECIFICATION

       GLboolean glUnmapBuffer(GLenum target);

PARAMETERS

       target
           Specifies the target buffer object being unmapped. The symbolic constant must be
           GL_ARRAY_BUFFER, GL_ATOMIC_COUNTER_BUFFER, GL_COPY_READ_BUFFER, GL_COPY_WRITE_BUFFER,
           GL_DRAW_INDIRECT_BUFFER, GL_DISPATCH_INDIRECT_BUFFER, GL_ELEMENT_ARRAY_BUFFER,
           GL_PIXEL_PACK_BUFFER, GL_PIXEL_UNPACK_BUFFER, GL_SHADER_STORAGE_BUFFER,
           GL_TEXTURE_BUFFER, GL_TRANSFORM_FEEDBACK_BUFFER or GL_UNIFORM_BUFFER.

DESCRIPTION

       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 no error
       occurs, the returned pointer will have an alignment of at least
       GL_MIN_MAP_BUFFER_ALIGNMENT basic machine units. The value of GL_MIN_MAP_BUFFER_ALIGNMENT
       can be retrieved by calling glGet() with pname set to GL_MIN_MAP_BUFFER_ALIGNMENT and must
       be a power of two that is at least 64.

       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.

NOTES

       If an error is generated, glMapBuffer returns NULL, and glUnmapBuffer returns GL_FALSE.

       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.

       Alignment of the returned pointer is guaranteed only if the version of the GL version is
       4.2 or greater. Also, the GL_ATOMIC_COUNTER_BUFFER target is accepted only if the GL
       version is 4.2 or greater.

       The GL_DISPATCH_INDIRECT_BUFFER and GL_SHADER_STORAGE_BUFFER targets are available only if
       the GL version is 4.3 or greater.

       The GL_QUERY_BUFFER target is available only if the GL version is 4.4 or greater.

ERRORS

       GL_INVALID_ENUM is generated if target is not one of the accepted targets.

       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.

ASSOCIATED GETS

       glGetBufferPointerv() with argument GL_BUFFER_MAP_POINTER

       glGetBufferParameter() with argument GL_BUFFER_MAPPED, GL_BUFFER_ACCESS, or
       GL_BUFFER_USAGE

SEE ALSO

       glBindBuffer(), glBindBufferBase(), glBindBufferRange(), glBufferData(),
       glBufferSubData(), glDeleteBuffers()

COPYRIGHT

       Copyright © 2005 Addison-Wesley. Copyright © 2010-2011 Khronos Group. 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/.

AUTHORS

       opengl.org