glMapBuffer man page on Oracle
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GLMAPBUFFER(3G) OpenGL Manual GLMAPBUFFER(3G)
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_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.
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
opengl.org 04/29/2014 GLMAPBUFFER(3G)
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