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GLMAPBUFFERRANGE(3G)			  OpenGL Manual 		     GLMAPBUFFERRANGE(3G)

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_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:

       o   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.

       o   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:

       o   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.

       o   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.

       o   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.

       o   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. 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.

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:

       o   The buffer is already in a mapped state.

       o   Neither GL_MAP_READ_BIT or GL_MAP_WRITE_BIT is set.

       o   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.

       o   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.

SEE ALSO
       glMapBuffer(), glFlushMappedBufferRange(), glBindBuffer()

COPYRIGHT
       Copyright (C) 2010-2012 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				    06/10/2014			     GLMAPBUFFERRANGE(3G)
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