Ubuntu Manpage: glMapBufferRange - map a section of a buffer object's data store

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NAME

       glMapBufferRange - map a section of a buffer object's data store

C SPECIFICATION


       void *glMapBufferRange(GLenum target, GLintptr offset, GLsizeiptr length, GLbitfield access);

PARAMETERS

       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.

DESCRIPTION

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.

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_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

       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/.

AUTHORS

       opengl.org

opengl.org                                         10/22/2013                               GLMAPBUFFERRANGE(3G)