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, 4 deletions

diff --git a/source/blender/gpu/intern/gpu_batch_presets.c b/source/blender/gpu/intern/gpu_batch_presets.c
index 9db04832a51..21d6906083a 100644
--- a/source/blender/gpu/intern/gpu_batch_presets.c
+++ b/source/blender/gpu/intern/gpu_batch_presets.c
@@ -31,6 +31,7 @@
 
 #include "BLI_utildefines.h"
 #include "BLI_math.h"
+#include "BLI_threads.h"
 
 #include "GPU_batch.h"
 #include "gpu_shader_private.h"
@@ -71,7 +72,7 @@ static void batch_sphere_lat_lon_vert(
 }
 
 /* Replacement for gluSphere */
-static Gwn_Batch *batch_sphere(int lat_res, int lon_res)
+Gwn_Batch *gpu_batch_sphere(int lat_res, int lon_res)
 {
 	const float lon_inc = 2 * M_PI / lon_res;
 	const float lat_inc = M_PI / lat_res;
@@ -146,6 +147,7 @@ static Gwn_Batch *batch_sphere_wire(int lat_res, int lon_res)
 Gwn_Batch *GPU_batch_preset_sphere(int lod)
 {
 	BLI_assert(lod >= 0 && lod <= 2);
+	BLI_assert(BLI_thread_is_main());
 
 	if (lod == 0) {
 		return g_presets_3d.batch.sphere_low;
@@ -161,6 +163,7 @@ Gwn_Batch *GPU_batch_preset_sphere(int lod)
 Gwn_Batch *GPU_batch_preset_sphere_wire(int lod)
 {
 	BLI_assert(lod >= 0 && lod <= 1);
+	BLI_assert(BLI_thread_is_main());
 
 	if (lod == 0) {
 		return g_presets_3d.batch.sphere_wire_low;
@@ -182,9 +185,9 @@ void gpu_batch_presets_init(void)
 	}
 
 	/* Hard coded resolution */
-	g_presets_3d.batch.sphere_low = batch_sphere(8, 16);
-	g_presets_3d.batch.sphere_med = batch_sphere(16, 10);
-	g_presets_3d.batch.sphere_high = batch_sphere(32, 24);
+	g_presets_3d.batch.sphere_low = gpu_batch_sphere(8, 16);
+	g_presets_3d.batch.sphere_med = gpu_batch_sphere(16, 10);
+	g_presets_3d.batch.sphere_high = gpu_batch_sphere(32, 24);
 
 	g_presets_3d.batch.sphere_wire_low = batch_sphere_wire(6, 8);
 	g_presets_3d.batch.sphere_wire_med = batch_sphere_wire(8, 16);