glMapBufferRange — map a section of a buffer object's data store
void *glMapBufferRange( | GLenum target, |
GLintptr offset, | |
GLsizeiptr length, | |
GLbitfield access) ; |
target
Specifies a binding to which the target buffer is bound.
offset
Specifies a the starting offset within the buffer of the range to be mapped.
length
Specifies a length of the range to be mapped.
access
Specifies a combination of access flags indicating the desired access to the range.
glMapBufferRange
maps all or part of the data store of a buffer object into the client's address
space. target
specifies the target to which the buffer is bound and must be one of 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_TEXTURE_BUFFER
,
GL_TRANSFORM_FEEDBACK_BUFFER
, GL_UNIFORM_BUFFER
or GL_SHADER_STORAGE_BUFFER
. offset
and
length
indicate the range of data in the buffer object htat 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.
If no error occurs, a pointer to the beginning of the mapped range is returned once all pending operations on that buffer have
completed, and may be used to modify and/or query the corresponding range of the buffer, 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.
Furthermore, 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 sub-
sequent 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
.
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.
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.
If an error occurs, glMapBufferRange
returns a NULL
pointer.
If no error occurs, the returned pointer will reflect 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. Subtracting offset
from this returned pointed will always produce a multiple of GL_MIN_MAP_BUFFER_ALINMENT
.
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.
GL_INVALID_VALUE
is generated if either of offset
or length
is negative,
or if offset
+ length
is greater than the value of GL_BUFFER_SIZE
.
GL_INVALID_VALUE
is generated if access
has any bits set other than those defined above.
GL_INVALID_OPERATION
is generated for any of the following conditions:
The buffer is already in a mapped state.
Neither GL_MAP_READ_BIT
or 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 included in access
, but the same bit
is not included in the buffer's storage flags.
GL_OUT_OF_MEMORY
is generated if glMapBufferRange
fails because memory for the
mapping could not be obtained.
Copyright © 2010-2013 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/.