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.

5 files changed, 56 insertions, 0 deletions

diff --git a/source/blender/windowmanager/CMakeLists.txt b/source/blender/windowmanager/CMakeLists.txt
index 0da45202730..234491a2186 100644
--- a/source/blender/windowmanager/CMakeLists.txt
+++ b/source/blender/windowmanager/CMakeLists.txt
@@ -35,6 +35,7 @@ set(INC
 	../compositor
 	../depsgraph
 	../editors/include
+	../draw
 	../gpu
 	../imbuf
 	../makesdna
diff --git a/source/blender/windowmanager/WM_api.h b/source/blender/windowmanager/WM_api.h
index 4449736d2a5..bf894b2ad03 100644
--- a/source/blender/windowmanager/WM_api.h
+++ b/source/blender/windowmanager/WM_api.h
@@ -119,6 +119,11 @@ struct bScreen *WM_window_get_active_screen(const struct wmWindow *win) ATTR_NON
 void            WM_window_set_active_screen(struct wmWindow *win, struct WorkSpace *workspace, struct bScreen *screen) ATTR_NONNULL(1);
 bool WM_window_is_temp_screen(const struct wmWindow *win) ATTR_WARN_UNUSED_RESULT;
 
+void *WM_opengl_context_create(void);
+void WM_opengl_context_dispose(void *context);
+void WM_opengl_context_activate(void *context);
+void WM_opengl_context_release(void *context);
+
 /* defines for 'type' WM_window_open_temp */
 enum {
 	WM_WINDOW_RENDER = 1,
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();
diff --git a/source/blender/windowmanager/intern/wm_window.c b/source/blender/windowmanager/intern/wm_window.c
index 103f8d580c1..278a70b9c9d 100644
--- a/source/blender/windowmanager/intern/wm_window.c
+++ b/source/blender/windowmanager/intern/wm_window.c
@@ -1038,6 +1038,26 @@ void wm_window_make_drawable(wmWindowManager *wm, wmWindow *win)
 	}
 }
 
+/* Reset active the current window opengl drawing context. */
+void wm_window_reset_drawable(void)
+{
+	BLI_assert(BLI_thread_is_main());
+	wmWindowManager *wm = G.main->wm.first;
+
+	if (wm == NULL)
+		return;
+
+	wmWindow *win = wm->windrawable;
+
+	if (win && win->ghostwin) {
+		gpu_batch_presets_reset();
+		immDeactivate();
+		GHOST_ActivateWindowDrawingContext(win->ghostwin);
+		GWN_context_active_set(win->gwnctx);
+		immActivate();
+	}
+}
+
 /* called by ghost, here we handle events for windows themselves or send to event system */
 /* mouse coordinate converversion happens here */
 static int ghost_event_proc(GHOST_EventHandle evt, GHOST_TUserDataPtr C_void_ptr)
@@ -2044,3 +2064,25 @@ void wm_window_IME_end(wmWindow *win)
 	win->ime_data = NULL;
 }
 #endif  /* WITH_INPUT_IME */
+
+/* ****** direct opengl context management ****** */
+
+void *WM_opengl_context_create(void)
+{
+	return GHOST_CreateOpenGLContext(g_system);
+}
+
+void WM_opengl_context_dispose(void *context)
+{
+	GHOST_DisposeOpenGLContext(g_system, (GHOST_ContextHandle)context);
+}
+
+void WM_opengl_context_activate(void *context)
+{
+	GHOST_ActivateOpenGLContext((GHOST_ContextHandle)context);
+}
+
+void WM_opengl_context_release(void *context)
+{
+	GHOST_ReleaseOpenGLContext((GHOST_ContextHandle)context);
+}
diff --git a/source/blender/windowmanager/wm_window.h b/source/blender/windowmanager/wm_window.h
index 0264955a4c5..652cefb1a54 100644
--- a/source/blender/windowmanager/wm_window.h
+++ b/source/blender/windowmanager/wm_window.h
@@ -58,6 +58,7 @@ void		wm_window_process_events	(const bContext *C);
 void		wm_window_process_events_nosleep(void);
 
 void		wm_window_make_drawable(wmWindowManager *wm, wmWindow *win);
+void		wm_window_reset_drawable(void);
 
 void		wm_window_raise			(wmWindow *win);
 void		wm_window_lower			(wmWindow *win);