GLMAPINVALIDATERANGEBIT

GL_MAP_INVALIDATE_RANGE_BIT is a bit flag used in OpenGL as part of the glMapBufferRange API. It indicates that the contents of the specified range of a buffer’s data store may be discarded when the mapping occurs, allowing the implementation to avoid preserving or reading the previous data for that range.

When mapping a buffer, this flag is typically combined with other map options such as GL_MAP_WRITE_BIT. The effect is that the driver may invalidate the contents of the mapped range, enabling more efficient data updates by reducing memory traffic. Importantly, the flag only permits discarding the previous contents; it does not force the data to be zero-filled. After mapping with this flag, the application should not rely on any prior values in the mapped range until new writes have completed.

Usage considerations include ensuring that the mapped range is entirely within the bounds of the buffer, and understanding that invalidation applies only to the specified range. The behavior is most beneficial when the application intends to overwrite the region completely and does not need the old data. The flag can be combined with GL_MAP_INVALIDATE_BUFFER_BIT to discard the entire buffer, though that affects all contents rather than just a sub-range.

Compatibility and origin: GL_MAP_INVALIDATE_RANGE_BIT is part of the ARB_map_buffer_range extension and is supported in OpenGL core profiles since the ARB_map_buffer_range introduction. It is commonly used in performance-critical scenarios where buffers are re-written in place, such as streaming vertex data or dynamic uniform blocks.

Example: glMapBufferRange(GL_ARRAY_BUFFER, offset, length, GL_MAP_WRITE_BIT | GL_MAP_INVALIDATE_RANGE_BIT); followed by writes to the returned pointer, and glUnmapBuffer(GL_ARRAY_BUFFER).