GLMAPBUFFERRANGE(3G)

📦
version 1.1 · 7 versions
, in centos-stream 9

okay so bestie, we're deep in glMapBufferRange(3G) territory and it's literally about mapping all or part of a buffer object's data store into the client's address space. no cap, this is the whole vibe.

💖 NAME 💖

glMapBufferRange, glMapNamedBufferRange — map all or part of a buffer object's data store into the client's address space. periodt.

🌸 C SPECIFICATION 🌸

void *glMapBufferRange(GLenum target, GLintptr offset,
                       GLsizeiptr length, GLbitfield access);

void *glMapNamedBufferRange(GLuint buffer, GLintptr offset,
                            GLsizeiptr length, GLbitfield access);

🎀 PARAMETERS 🎀

target

Specifies the target to which the buffer object is bound for glMapBufferRange, which must be one of the buffer binding targets in the following list:

  • GL_ARRAY_BUFFER — vertex attributes
  • GL_ATOMIC_COUNTER_BUFFER — atomic counter storage
  • GL_COPY_READ_BUFFER — buffer copy source
  • GL_COPY_WRITE_BUFFER — buffer copy destination
  • GL_DISPATCH_INDIRECT_BUFFER — indirect compute dispatch commands
  • GL_DRAW_INDIRECT_BUFFER — indirect command arguments
  • GL_ELEMENT_ARRAY_BUFFER — vertex array indices
  • GL_PIXEL_PACK_BUFFER — pixel read target
  • GL_PIXEL_UNPACK_BUFFER — texture data source
  • GL_QUERY_BUFFER — query result buffer
  • GL_SHADER_STORAGE_BUFFER — read-write storage for shaders
  • GL_TEXTURE_BUFFER — texture data buffer
  • GL_TRANSFORM_FEEDBACK_BUFFER — transform feedback buffer
  • GL_UNIFORM_BUFFER — uniform block storage

buffer

Specifies the name of the buffer object for glMapNamedBufferRange. iykyk.

offset

Specifies the starting offset within the buffer of the range to be mapped.

length

Specifies the length of the range to be mapped.

access

Specifies a combination of access flags indicating the desired access to the mapped range. this is the bitfield bestie, pay attention 💅

🌈 DESCRIPTION 🌈

glMapBufferRange and glMapNamedBufferRange map all or part of the data store of a specified buffer object into the client's address space. offset and length indicate the range of data in the buffer object that 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.

A pointer to the beginning of the mapped range is returned once all pending operations on the buffer object have completed, and may be used to modify and/or query the corresponding range of the data store 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. like, do not test this at home 😭
  • 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. same energy, bestie: undefined is not your friend 💀
  • 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. so slay, but only if you set it up right ✨
  • 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(). the way that coherence matters… iconic honestly 🫶

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 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. okay so this one is giving "throw it away, I'll write new stuff" 🙈
  • 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. whole-buffer chaos, but make it deliberate 💅
  • 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. so either you flush by hand or the unmap does it for you, no in-between bestie 🎀
  • GL_MAP_UNSYNCHRONIZED_BIT — indicates that the GL should not attempt to synchronize pending operations on the buffer prior to returning from glMapBufferRange or glMapNamedBufferRange. 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. highkey risky vibe, but okay 👀

If an error occurs, a NULL pointer is returned.

If no error occurs, the returned pointer will reflect an allocation aligned to the value of GL_MIN_MAP_BUFFER_ALIGNMENT basic machine units. Subtracting offset from this returned pointer will always produce a multiple of the value of GL_MIN_MAP_BUFFER_ALIGNMENT. alignment math, but make it glam ✨

The returned pointer values may not be passed as parameter values to GL commands. For example, they may not be used to specify array pointers, or to specify or query pixel or texture image data; such actions produce undefined results, although implementations may not check for such behavior for performance reasons. literally do not pass these pointers around like candy, bestie 💀

Mappings to the data stores of buffer objects may have nonstandard performance characteristics. For example, such mappings may be marked as uncacheable regions of memory, and in such cases reading from them may be very slow. To ensure optimal performance, the client should use the mapping in a fashion consistent with the values of GL_BUFFER_USAGE for the buffer object and of access. Using a mapping in a fashion inconsistent with these values is liable to be multiple orders of magnitude slower than using normal memory. not me warning you about the slow lane 😭💅

🌸 NOTES 🌸

okay so real talk bestie — the returned pointer is guaranteed to be aligned only if the version of GL is 4.2 or greater. like, don’t come for the alignment unless you’re on 4.2+. also, the GL_ATOMIC_COUNTER_BUFFER target is accepted only if the GL version is 4.2 or greater. periodt. ✨

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. 🦋

and the GL_MAP_PERSISTENT_BIT and GL_MAP_COHERENT_BIT flags are available only if the GL version is 4.4 or greater. no cap. 💅

💀 ERRORS 💀

  • GL_INVALID_ENUM is generated by glMapBufferRange if target is not one of the buffer binding targets listed above. 🚩
  • GL_INVALID_OPERATION is generated by glMapBufferRange if zero is bound to target.
  • GL_INVALID_OPERATION is generated by glMapNamedBufferRange if buffer is not the name of an existing buffer object.
  • GL_INVALID_VALUE is generated if offset or length is negative, if $offset + length$ is greater than the value of GL_BUFFER_SIZE for the buffer object, or if access has any bits set other than those defined above.

GL_INVALID_OPERATION is generated for any of the following conditions:

  • length is zero.
  • The buffer object is already in a mapped state.
  • Neither GL_MAP_READ_BIT nor 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 set, but the same bit is not included in the buffer’s storage flags.
also important, bestie: no error is generated if memory outside the mapped range is modified or queried, but the result is undefined and system errors — possibly including program termination 😭 — may occur. so like… please don’t. that’s giving “chaos gremlin” energy and not the cute kind.

🔍 ASSOCIATED GETS 🔍

glGet() with pname GL_MIN_MAP_BUFFER_ALIGNMENT. the value must be a power of two that is at least 64. that’s the whole vibe. ✨

👑 VERSION SUPPORT 👑

here’s the OpenGL version vibe check, bestie:

  • glMapBufferRange — 2.0: -; 2.1: -; 3.0: ✔; 3.1: ✔; 3.2: ✔; 3.3: ✔; 4.0: ✔; 4.1: ✔; 4.2: ✔; 4.3: ✔; 4.4: ✔; 4.5: ✔.
  • glMapNamedBufferRange — 2.0: -; 2.1: -; 3.0: -; 3.1: -; 3.2: -; 3.3: -; 4.0: -; 4.1: -; 4.2: -; 4.3: -; 4.4: -; 4.5: ✔.

🫶 SEE ALSO 🫶

go read these too, iykyk:

  • glMapBuffer()
  • glUnmapBuffer()
  • glFlushMappedBufferRange()
  • glBindBuffer()
  • glBufferStorage()

Copyright © 2010-2014 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/.

Copyright © 2014 Khronos Group

okay that’s the page, bestie! it says it comes from [FIXME: source], dated 08/09/2021, and it’s filed under GLMAPBUFFERRANGE(3G). mwah 💋🎀

📦 where this page comes from