GLAPI/glMapBufferRange

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glMapBufferRange
Core in version 4.4
Core since version 3.0

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

Function Definition

 void *glMapBufferRange(GLenum target​, GLintptr offset​, GLsizeiptr length​, GLbitfield access​);
target
Specifies the target buffer object. The symbolic constant must be 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_SHADER_STORAGE_BUFFER​, GL_TEXTURE_BUFFER​, GL_TRANSFORM_FEEDBACK_BUFFER​, or GL_UNIFORM_BUFFER​.
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. 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 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 fashion 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.

See Also

glBindBuffer, glBufferData, glUnmapBuffer, glMapBuffer, glFlushMappedBufferRange

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/.