This separate context allows two things: - It allows viewports in multi-windows configuration. - F12 render can use this context in a separate thread and do a non-blocking render. The downside is that the context cannot be used while rendering so a request to refresh a viewport will lock the UI. This is something that will be adressed in the future. Under the hood what does that mean: - Not adding more mess with VAOs management in gawain. - Doing depth only draw for operators / selection needs to be done in an offscreen buffer. - The 3D cursor "autodis" operator is still reading the backbuffer so we need to copy the result to it. - All FBOs needed by the drawmanager must to be created/destroyed with its context active. - We cannot use batches created for UI in the DRW context and vice-versa. There is a clear separation of resources that enables the use of safe multi-threading.