Signature
Parameters
| Variables | Description |
|---|---|
| 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 |
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
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
Version Support
| glMapBufferRange | |
| glMapNamedBufferRange |
See Also
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.
http://opencontent.org/openpub/
.