## Name

glMapBuffer, glMapNamedBuffer — map all of a buffer object's data store into the client's address space

## C Specification

`void *glMapBuffer(` | GLenum target,
| GLenum access`)`;

`void *glMapNamedBuffer(` | GLuint buffer,
| GLenum access`)`;

## Parameters

`target`

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

  Buffer Binding Target | Purpose
  --- | ---
  `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 `glMapNamedBuffer`.

`access`

  Specifies the access policy for `glMapBuffer` and `glMapNamedBuffer`, indicating whether it will be possible to read from, write to, or both read from and write to the buffer object's mapped data store. The symbolic constant must be `GL_READ_ONLY`, `GL_WRITE_ONLY`, or `GL_READ_WRITE`.

## Description

`glMapBuffer` and `glMapNamedBuffer` map the entire data store of a specified buffer object into the client's address space. The data can then be directly read and/or written relative to the returned pointer, depending on the specified `access` policy.

A pointer to the beginning of the mapped range is returned once all pending operations on that buffer object have completed, and may be used to modify and/or query the corresponding range of the data store according to the value of `access`:

- `GL_READ_ONLY` indicates that the returned pointer may be used to read buffer object data.

- `GL_WRITE_ONLY` indicates that the returned pointer may be used to modify buffer object data.

- `GL_READ_WRITE` indicates that the returned pointer may be used to read and to modify buffer object data.

If an error is generated, 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.

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.

No GL error is generated if the returned pointer is accessed in a way inconsistent with `access` (e.g. used to read from a mapping made with `access` `GL_WRITE_ONLY` or write to a mapping made with `access` `GL_READ_ONLY`), but the result is undefined and system errors (possibly including program termination) may occur.

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.

## 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 available 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.

## Errors

`GL_INVALID_ENUM` is generated by `glMapBuffer` if `target` is not one of the buffer binding targets listed above.

`GL_INVALID_OPERATION` is generated by `glMapBuffer` if zero is bound to `target`.

`GL_INVALID_OPERATION` is generated by `glMapNamedBuffer` if `buffer` is not the name of an existing buffer object.

`GL_INVALID_ENUM` is generated if `access` is not `GL_READ_ONLY`, `GL_WRITE_ONLY`, or `GL_READ_WRITE`.

`GL_OUT_OF_MEMORY` is generated if the GL is unable to map the buffer object's data store. This may occur for a variety of system-specific reasons, such as the absence of sufficient remaining virtual memory.

`GL_INVALID_OPERATION` is generated if the buffer object is in a mapped state.

## Associated Gets

glGetBufferPointerv with argument `GL_BUFFER_MAP_POINTER`

glGetBufferParameter with argument `GL_BUFFER_MAPPED`, `GL_BUFFER_ACCESS`, or `GL_BUFFER_USAGE`

glGet with `pname` `GL_MIN_MAP_BUFFER_ALIGNMENT`. The value must be a power of two that is at least 64.

## Version Support

| OpenGL Version
--- | ---
Function / Feature Name | 2.0 | 2.1 | 3.0 | 3.1 | 3.2 | 3.3 | 4.0 | 4.1 | 4.2 | 4.3 | 4.4 | 4.5
`glMapBuffer` | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔
`glMapNamedBuffer` | - | - | - | - | - | - | - | - | - | - | - | ✔

## See Also

glBindBuffer, glBindBufferBase, glBindBufferRange, glBufferData, glBufferSubData, glDeleteBuffers, glMapBufferRange, glUnmapBuffer

## Copyright

Copyright © 2005 Addison-Wesley. 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/.