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

Provided by: opengl-4-man-doc_1.0~svn22917-1_all

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