glMapNamedBuffer

glMapBuffer: man4/glMapBuffer.xml

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 :

1. GL_READ_ONLY indicates that the returned pointer may be used to read buffer object data.
2. GL_WRITE_ONLY indicates that the returned pointer may be used to modify buffer object data.
3. 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.

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.