GLMAPBUFFERRANGE
Section: [FIXME: manual] (3G)
Updated: 01/26/2021
Page Index
NAME
glMapBufferRange, glMapNamedBufferRange - map all or part of a buffer object's data store into the client's address space
C SPECIFICATION
-
void *glMapBufferRange(GLenum target, GLintptr offset, GLsizeiptr length, GLbitfield access);
-
void *glMapNamedBufferRange(GLuint buffer, GLintptr offset, GLsizeiptr length, GLbitfield access);
PARAMETERS
target
-
- Specifies the target to which the buffer object is bound for
glMapBufferRange, which must be one of the buffer binding targets in the following table:
|
Buffer Binding Target
|
Purpose
|
|
GL_ARRAY_BUFFER
|
Vertex attributes
|
|
GL_ATOMIC_COUNTER_BUFFER
|
Atomic counter storage
|
|
GL_COPY_READ_BUFFER
|
Buffer copy source
|
|
GL_COPY_WRITE_BUFFER
|
Buffer copy destination
|
|
GL_DISPATCH_INDIRECT_BUFFER
|
Indirect compute dispatch commands
|
|
GL_DRAW_INDIRECT_BUFFER
|
Indirect command arguments
|
|
GL_ELEMENT_ARRAY_BUFFER
|
Vertex array indices
|
|
GL_PIXEL_PACK_BUFFER
|
Pixel read target
|
|
GL_PIXEL_UNPACK_BUFFER
|
Texture data source
|
|
GL_QUERY_BUFFER
|
Query result buffer
|
|
GL_SHADER_STORAGE_BUFFER
|
Read-write storage for shaders
|
|
GL_TEXTURE_BUFFER
|
Texture data buffer
|
|
GL_TRANSFORM_FEEDBACK_BUFFER
|
Transform feedback buffer
|
|
GL_UNIFORM_BUFFER
|
Uniform block storage
|
buffer
-
Specifies the name of the buffer object for
glMapNamedBufferRange.
offset
-
Specifies the starting offset within the buffer of the range to be mapped.
length
-
Specifies the length of the range to be mapped.
access
-
Specifies a combination of access flags indicating the desired access to the mapped range.
DESCRIPTION
glMapBufferRange
and
glMapNamedBufferRange
map all or part of the data store of a specified buffer object into the client's address space.
offset
and
length
indicate the range of data in the buffer object that is to be mapped, in terms of basic machine units.
access
is a bitfield containing flags which describe the requested mapping. These flags are described below.
A pointer to the beginning of the mapped range is returned once all pending operations on the buffer object have completed, and may be used to modify and/or query the corresponding range of the data store according to the following flag bits set in
access:
-
•
GL_MAP_READ_BIT
indicates that the returned pointer may be used to read buffer object data. No GL error is generated if the pointer is used to query a mapping which excludes this flag, but the result is undefined and system errors (possibly including program termination) may occur.
-
•
GL_MAP_WRITE_BIT
indicates that the returned pointer may be used to modify buffer object data. No GL error is generated if the pointer is used to modify a mapping which excludes this flag, but the result is undefined and system errors (possibly including program termination) may occur.
-
•
GL_MAP_PERSISTENT_BIT
indicates that the mapping is to be made in a persistent fassion and that the client intends to hold and use the returned pointer during subsequent GL operation. It is not an error to call drawing commands (render) while buffers are mapped using this flag. It is an error to specify this flag if the buffer's data store was not allocated through a call to the
glBufferStorage()
command in which the
GL_MAP_PERSISTENT_BIT
was also set.
-
•
GL_MAP_COHERENT_BIT
indicates that a persistent mapping is also to be coherent. Coherent maps guarantee that the effect of writes to a buffer's data store by either the client or server will eventually become visible to the other without further intervention from the application. In the absence of this bit, persistent mappings are not coherent and modified ranges of the buffer store must be explicitly communicated to the GL, either by unmapping the buffer, or through a call to
glFlushMappedBufferRange()
or
glMemoryBarrier().
The following
optional
flag bits in
access
may be used to modify the mapping:
-
•
GL_MAP_INVALIDATE_RANGE_BIT
indicates that the previous contents of the specified range may be discarded. Data within this range are undefined with the exception of subsequently written data. No GL error is generated if subsequent GL operations access unwritten data, but the result is undefined and system errors (possibly including program termination) may occur. This flag may not be used in combination with
GL_MAP_READ_BIT.
-
•
GL_MAP_INVALIDATE_BUFFER_BIT
indicates that the previous contents of the entire buffer may be discarded. Data within the entire buffer are undefined with the exception of subsequently written data. No GL error is generated if subsequent GL operations access unwritten data, but the result is undefined and system errors (possibly including program termination) may occur. This flag may not be used in combination with
GL_MAP_READ_BIT.
-
•
GL_MAP_FLUSH_EXPLICIT_BIT
indicates that one or more discrete subranges of the mapping may be modified. When this flag is set, modifications to each subrange must be explicitly flushed by calling
glFlushMappedBufferRange(). No GL error is set if a subrange of the mapping is modified and not flushed, but data within the corresponding subrange of the buffer are undefined. This flag may only be used in conjunction with
GL_MAP_WRITE_BIT. When this option is selected, flushing is strictly limited to regions that are explicitly indicated with calls to
glFlushMappedBufferRange()
prior to unmap; if this option is not selected
glUnmapBuffer()
will automatically flush the entire mapped range when called.
-
•
GL_MAP_UNSYNCHRONIZED_BIT
indicates that the GL should not attempt to synchronize pending operations on the buffer prior to returning from
glMapBufferRange
or
glMapNamedBufferRange. No GL error is generated if pending operations which source or modify the buffer overlap the mapped region, but the result of such previous and any subsequent operations is undefined.
If an error occurs, a
NULL
pointer is returned.
If no error occurs, the returned pointer will reflect an allocation aligned to the value of
GL_MIN_MAP_BUFFER_ALIGNMENT
basic machine units. Subtracting
offset
from this returned pointer will always produce a multiple of the value of
GL_MIN_MAP_BUFFER_ALIGNMENT.
The returned pointer values may not be passed as parameter values to GL commands. For example, they may not be used to specify array pointers, or to specify or query pixel or texture image data; such actions produce undefined results, although implementations may not check for such behavior for performance reasons.
Mappings to the data stores of buffer objects may have nonstandard performance characteristics. For example, such mappings may be marked as uncacheable regions of memory, and in such cases reading from them may be very slow. To ensure optimal performance, the client should use the mapping in a fashion consistent with the values of
GL_BUFFER_USAGE
for the buffer object and of
access. Using a mapping in a fashion inconsistent with these values is liable to be multiple orders of magnitude slower than using normal memory.
NOTES
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 accepted 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.
The
GL_MAP_PERSISTENT_BIT
and
GL_MAP_COHERENT_BIT
flags are available only if the GL version is 4.4 or greater.
ERRORS
GL_INVALID_ENUM
is generated by
glMapBufferRange
if
target
is not one of the buffer binding targets listed above.
GL_INVALID_OPERATION
is generated by
glMapBufferRange
if zero is bound to
target.
GL_INVALID_OPERATION
is generated by
glMapNamedBufferRange
if
buffer
is not the name of an existing buffer object.
GL_INVALID_VALUE
is generated if
offset
or
length
is negative, if $offset + length$ is greater than the value of
GL_BUFFER_SIZE
for the buffer object, or if
access
has any bits set other than those defined above.
GL_INVALID_OPERATION
is generated for any of the following conditions:
-
•
length
is zero.
-
•
The buffer object is already in a mapped state.
-
•
Neither
GL_MAP_READ_BIT
nor
GL_MAP_WRITE_BIT
is set.
-
•
GL_MAP_READ_BIT
is set and any of
GL_MAP_INVALIDATE_RANGE_BIT,
GL_MAP_INVALIDATE_BUFFER_BIT
or
GL_MAP_UNSYNCHRONIZED_BIT
is set.
-
•
GL_MAP_FLUSH_EXPLICIT_BIT
is set and
GL_MAP_WRITE_BIT
is not set.
-
•
Any of
GL_MAP_READ_BIT,
GL_MAP_WRITE_BIT,
GL_MAP_PERSISTENT_BIT, or
GL_MAP_COHERENT_BIT
are set, but the same bit is not included in the buffer's storage flags.
No error is generated if memory outside the mapped range is modified or queried, but the result is undefined and system errors (possibly including program termination) may occur.
ASSOCIATED GETS
glGet()
with
pname
GL_MIN_MAP_BUFFER_ALIGNMENT. The value must be a power of two that is at least 64.
VERSION SUPPORT
|
|
OpenGL Version
|
|
Function / Feature Name
|
2.0
|
2.1
|
3.0
|
3.1
|
3.2
|
3.3
|
4.0
|
4.1
|
4.2
|
4.3
|
4.4
|
4.5
|
|
glMapBufferRange
|
-
|
-
|
✔
|
✔
|
✔
|
✔
|
✔
|
✔
|
✔
|
✔
|
✔
|
✔
|
|
glMapNamedBufferRange
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
✔
|
SEE ALSO
glMapBuffer(),
glUnmapBuffer(),
glFlushMappedBufferRange(),
glBindBuffer(),
glBufferStorage()
COPYRIGHT
Copyright
©
2010-2014 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.
m[blue]http://opencontent.org/openpub/m[].
COPYRIGHT
Copyright © 2014 Khronos Group