GLMAPWRITEBIT

GL_MAP_WRITE_BIT is a constant used in OpenGL to indicate write access when mapping the storage of a buffer object. It is part of a set of map access flags that control how a mapped region of memory may be used by the client application. The flag is typically used with the glMapBufferRange function, which accepts a bitwise combination of mapping access flags.

When used, GL_MAP_WRITE_BIT signals that the client will write data into the mapped memory region. This enables the driver to apply appropriate synchronization and caching rules to ensure that writes are visible to subsequent GL operations. GL_MAP_WRITE_BIT is commonly combined with other flags, such as GL_MAP_READ_BIT (if reading is also allowed) or GL_MAP_INVALIDATE_RANGE_BIT (to indicate that previous contents may be discarded in the mapped range).

Usage context and cautions: glMapBufferRange(target, offset, length, GL_MAP_WRITE_BIT) maps a portion of a buffer for writing, returning a pointer to writeable memory. After writing, the application must call glUnmapBuffer to complete the operation and make the changes visible to the GPU. The exact ordering and visibility of writes can depend on the driver and the device’s memory model, so developers should follow the OpenGL specification for synchronization pitfalls and ensure proper unmapping.

Relation to other flags: GL_MAP_WRITE_BIT is one of several mapping flags, including GL_MAP_READ_BIT, GL_MAP_INVALIDATE_RANGE_BIT, GL_MAP_INVALIDATE_BUFFER_BIT, and GL_MAP_UNSYNCHRONIZED_BIT. These flags can be combined to convey precise intent and optimize performance, particularly with modern buffer mapping techniques and persistent mapping.

See also: GL_MAP_READ_BIT, GL_MAP_INVALIDATE_RANGE_BIT, GL_MAP_INVALIDATE_BUFFER_BIT, GL_MAP_UNSYNCHRONIZED_BIT, glMapBufferRange, glUnmapBuffer.