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_COPY_READ_BUFFER,
GL_COPY_WRITE_BUFFER, GL_ELEMENT_ARRAY_BUFFER,
GL_PIXEL_PACK_BUFFER, GL_PIXEL_UNPACK_BUFFER,
GL_TEXTURE_BUFFER, GL_TRANSFORM_FEEDBACK_BUFFER, or
GL_UNIFORM_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.
If an error occurs, glMapBufferRange returns a NULL
pointer.
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.
GL_OUT_OF_MEMORY is generated if glMapBufferRange
fails because memory for the mapping could not be obtained.
glMapBuffer(), glFlushMappedBufferRange(),
glBindBuffer()
Copyright © 2010 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/.