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docs.GL

glMapBuffer

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 GL_BUFFER_USAGE (see glGet*BufferParameter and usage of glBufferData) 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 - - - - - - - - - - - ✔
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