GLMAPCOHERENTBIT

GLMAPCOHERENTBIT is a flag used in graphics API terminology to indicate that a mapped region of memory is coherent between the host (CPU) and the device (GPU). The concept is closely related to the OpenGL GL_MAP_COHERENT_BIT, and in some bindings or documentation it is presented as an alias or explanatory name for the same capability. The flag is typically combined with other mapping flags to control how memory is accessed and synchronized.

In practice, GLMAPCOHERENTBIT is set when creating a persistent, mapped buffer or texture so that writes performed by the host are visible to the device without explicit synchronization operations after mapping. It is commonly used with persistent mapping flags such as GL_MAP_PERSISTENT_BIT and access flags like GL_MAP_WRITE_BIT. When this bit is enabled, the implementation guarantees coherence between host caches and device memory, reducing the need for manual flushes or barriers in many scenarios.

Semantics and trade-offs: enabling coherence simplifies programming for dynamic resources but can impose performance and resource costs. Coherent mappings may constrain certain caching strategies or increase hardware overhead to maintain live synchronization. As a result, developers use GLMAPCOHERENTBIT selectively for resources that are frequently updated by the CPU and read by the GPU, such as dynamic vertex data or streaming textures.

Limitations: support for coherence is hardware- and driver-dependent. Not all devices provide persistent coherent mappings, and the performance benefits vary with workload. Developers should consult the relevant API specifications and driver documentation for exact behavior and guarantees.

See also: GL_MAP_COHERENT_BIT, GL_MAP_PERSISTENT_BIT, GL_MAP_WRITE_BIT, GL_MAP_READ_BIT, OpenGL.