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.

2 files changed, 8 insertions, 9 deletions

diff --git a/source/blender/editors/render/render_internal.c b/source/blender/editors/render/render_internal.c
index 0130b93babf..98d37eedb1b 100644
--- a/source/blender/editors/render/render_internal.c
+++ b/source/blender/editors/render/render_internal.c
@@ -869,15 +869,6 @@ static int screen_render_invoke(bContext *C, wmOperator *op, const wmEvent *even
 		return OPERATOR_CANCELLED;
 	}
 
-	/* XXX FIXME If engine is an OpenGL engine do not run modal.
-	 * This is a problem for animation rendering since you cannot abort them.
-	 * This also does not open an image editor space. */
-	if (RE_engine_is_opengl(re_type)) {
-		/* ensure at least 1 area shows result */
-		render_view_open(C, event->x, event->y, op->reports);
-		return screen_render_exec(C, op);
-	}
-	
 	/* only one render job at a time */
 	if (WM_jobs_test(CTX_wm_manager(C), scene, WM_JOB_TYPE_RENDER))
 		return OPERATOR_CANCELLED;
diff --git a/source/blender/editors/render/render_opengl.c b/source/blender/editors/render/render_opengl.c
index 8eb9283790b..1f9894b3b9f 100644
--- a/source/blender/editors/render/render_opengl.c
+++ b/source/blender/editors/render/render_opengl.c
@@ -57,6 +57,8 @@
 
 #include "DEG_depsgraph.h"
 
+#include "DRW_engine.h"
+
 #include "WM_api.h"
 #include "WM_types.h"
 
@@ -323,6 +325,7 @@ static void screen_opengl_render_doit(const bContext *C, OGLRender *oglrender, R
 			unsigned char *gp_rect;
 			unsigned char *render_rect = (unsigned char *)RE_RenderViewGetById(rr, oglrender->view_id)->rect32;
 
+			DRW_opengl_context_enable();
 			GPU_offscreen_bind(oglrender->ofs, true);
 
 			glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
@@ -342,6 +345,7 @@ static void screen_opengl_render_doit(const bContext *C, OGLRender *oglrender, R
 				blend_color_mix_byte(&render_rect[i], &render_rect[i], &gp_rect[i]);
 			}
 			GPU_offscreen_unbind(oglrender->ofs, true);
+			DRW_opengl_context_disable();
 
 			MEM_freeN(gp_rect);
 		}
@@ -652,7 +656,9 @@ static bool screen_opengl_render_init(bContext *C, wmOperator *op)
 	sizey = (scene->r.size * scene->r.ysch) / 100;
 
 	/* corrects render size with actual size, not every card supports non-power-of-two dimensions */
+	DRW_opengl_context_enable(); /* Offscreen creation needs to be done in DRW context. */
 	ofs = GPU_offscreen_create(sizex, sizey, full_samples ? 0 : samples, true, true, err_out);
+	DRW_opengl_context_disable();
 
 	if (!ofs) {
 		BKE_reportf(op->reports, RPT_ERROR, "Failed to create OpenGL off-screen buffer, %s", err_out);
@@ -841,7 +847,9 @@ static void screen_opengl_render_end(bContext *C, OGLRender *oglrender)
 	if (oglrender->fx)
 		GPU_fx_compositor_destroy(oglrender->fx);
 
+	DRW_opengl_context_enable();
 	GPU_offscreen_free(oglrender->ofs);
+	DRW_opengl_context_disable();
 
 	if (oglrender->is_sequencer) {
 		MEM_freeN(oglrender->seq_data.ibufs_arr);