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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:

       ·   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. 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:

       ·   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.

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

COPYRIGHT
       Copyright © 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			  04/29/2014		  GLMAPBUFFERRANGE(3G)

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