DRW: Add new Draw Manager OpenGL Context.

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.

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/windowmanager/intern/wm_init_exit.c b/source/blender/windowmanager/intern/wm_init_exit.c
index 43e4f7757f5..a2f5f1b1e10 100644
--- a/source/blender/windowmanager/intern/wm_init_exit.c
+++ b/source/blender/windowmanager/intern/wm_init_exit.c
@@ -125,6 +125,8 @@
 
 #include "DEG_depsgraph.h"
 
+#include "DRW_engine.h"
+
 #ifdef WITH_OPENSUBDIV
 #  include "BKE_subsurf.h"
 #endif
@@ -207,6 +209,7 @@ void WM_init(bContext *C, int argc, const char **argv)
 		/* sets 3D mouse deadzone */
 		WM_ndof_deadzone_set(U.ndof_deadzone);
 #endif
+		DRW_opengl_context_create();
 
 		GPU_init();
 
@@ -549,6 +552,10 @@ void WM_exit_ext(bContext *C, const bool do_python)
 
 	BLF_exit();
 
+	if (!G.background) {
+		DRW_opengl_context_destroy();
+	}
+
 #ifdef WITH_INTERNATIONAL
 	BLF_free_unifont();
 	BLF_free_unifont_mono();