glMapBuffer

glMapBuffer is an OpenGL API function that maps the data store of a bound buffer object into the client's address space. By obtaining a pointer to the buffer’s memory, applications can read or modify the buffer contents directly without issuing subdata calls. The mapping is performed for the entire data store of the bound buffer object.

To use glMapBuffer, a buffer object must be bound to a target such as GL_ARRAY_BUFFER, GL_ELEMENT_ARRAY_BUFFER, or other buffer targets that support mapping. The access parameter indicates how the mapped memory will be used by the client; common values are GL_READ_ONLY for read access and GL_WRITE_ONLY for write access. In practice, if both read and write access are needed, glMapBufferRange with appropriate flags is often preferred.

The function returns a pointer to the mapped memory. If mapping fails, a NULL pointer is returned, and no memory is mapped. After the client is finished accessing the data, glUnmapBuffer must be called with the same target. If the buffer contents are modified, the unmapping step ensures the changes are visible to the GPU. Some implementations may require synchronization or may stall the CPU if the GPU is actively using the buffer.

glMapBuffer is related to glMapBufferRange, which provides more granular control by allowing mapping of a subrange of a buffer and supports additional flags to influence behavior and performance, such as invalidation or flushing ranges.

Notes and caveats: mapping can incur performance costs due to synchronization with the GPU, and the mapped pointer becomes invalid after unmapping or buffer data changes. Access permissions and availability can vary by OpenGL version and extensions.