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.

source/blender/draw/DRW_engine.h

@@ -125,4 +125,9 @@ void EDIT_ARMATURE_collection_settings_create(struct IDProperty *properties);
 void PAINT_WEIGHT_collection_settings_create(struct IDProperty *properties);
 void PAINT_VERTEX_collection_settings_create(struct IDProperty *properties);
 
+void DRW_opengl_context_create(void);
+void DRW_opengl_context_destroy(void);
+void DRW_opengl_context_enable(void);
+void DRW_opengl_context_disable(void);
+
 #endif /* __DRW_ENGINE_H__ */

source/blender/draw/intern/draw_cache.c

@@ -45,6 +45,7 @@ static struct DRWShapeCache {
 	Gwn_Batch *drw_single_vertice;
 	Gwn_Batch *drw_fullscreen_quad;
 	Gwn_Batch *drw_quad;
+	Gwn_Batch *drw_sphere;
 	Gwn_Batch *drw_screenspace_circle;
 	Gwn_Batch *drw_plain_axes;
 	Gwn_Batch *drw_single_arrow;
@@ -266,7 +267,6 @@ Gwn_Batch *DRW_cache_fullscreen_quad_get(void)
 Gwn_Batch *DRW_cache_quad_get(void)
 {
 	if (!SHC.drw_quad) {
-		/* Use a triangle instead of a real quad */
 		float pos[4][2] = {{-1.0f, -1.0f}, { 1.0f, -1.0f}, {1.0f,  1.0f}, {-1.0f,  1.0f}};
 		float uvs[4][2] = {{ 0.0f,  0.0f}, { 1.0f,  0.0f}, {1.0f,  1.0f}, { 0.0f,  1.0f}};
 
@@ -294,7 +294,10 @@ Gwn_Batch *DRW_cache_quad_get(void)
 /* Sphere */
 Gwn_Batch *DRW_cache_sphere_get(void)
 {
-	return GPU_batch_preset_sphere(2);
+	if (!SHC.drw_sphere) {
+		SHC.drw_sphere = gpu_batch_sphere(32, 24);
+	}
+	return SHC.drw_sphere;
 }
 
 /** \} */

source/blender/draw/intern/draw_manager.c

@@ -30,6 +30,7 @@
 #include "BLI_rect.h"
 #include "BLI_string.h"
 #include "BLI_string_utils.h"
+#include "BLI_threads.h"
 
 #include "BIF_glutil.h"
 
@@ -82,6 +83,7 @@
 
 #include "WM_api.h"
 #include "WM_types.h"
+#include "wm_window.h"
 
 #include "draw_manager_text.h"
 #include "draw_manager_profiling.h"
@@ -97,6 +99,8 @@
 #include "engines/basic/basic_engine.h"
 #include "engines/external/external_engine.h"
 
+#include "../../../intern/gawain/gawain/gwn_context.h"
+
 #include "DEG_depsgraph.h"
 #include "DEG_depsgraph_query.h"
 
@@ -369,6 +373,13 @@ static struct DRWMatrixOveride {
 
 ListBase DRW_engines = {NULL, NULL};
 
+/* Unique ghost context used by the draw manager. */
+static void *g_ogl_context = NULL;
+static Gwn_Context *g_gwn_context = NULL;
+
+/* Mutex to lock the drw manager and avoid concurent context usage. */
+static ThreadMutex g_ogl_context_mutex = BLI_MUTEX_INITIALIZER;
+
 #ifdef USE_GPU_SELECT
 static unsigned int g_DRW_select_id = (unsigned int)-1;
 
@@ -3440,6 +3451,7 @@ void DRW_draw_render_loop_ex(
         ARegion *ar, View3D *v3d, const eObjectMode object_mode,
         const bContext *evil_C)
 {
+
 	Scene *scene = DEG_get_evaluated_scene(depsgraph);
 	ViewLayer *view_layer = DEG_get_evaluated_view_layer(depsgraph);
 	RegionView3D *rv3d = ar->regiondata;
@@ -3626,6 +3638,11 @@ void DRW_render_to_image(RenderEngine *engine, struct Depsgraph *depsgraph)
 	RenderData *r = &scene->r;
 	Render *render = engine->re;
 	const EvaluationContext *eval_ctx = RE_GetEvalCtx(render);
+	/* Changing Context */
+	DRW_opengl_context_enable();
+	/* IMPORTANT: We dont support immediate mode in render mode!
+	 * This shall remain in effect until immediate mode supports
+	 * multiple threads. */
 
 	/* Reset before using it. */
 	memset(&DST, 0x0, sizeof(DST));
@@ -3705,6 +3722,9 @@ void DRW_render_to_image(RenderEngine *engine, struct Depsgraph *depsgraph)
 	glEnable(GL_SCISSOR_TEST);
 	GPU_framebuffer_restore();
 
+	/* Changing Context */
+	DRW_opengl_context_disable();
+
 #ifdef DEBUG
 	/* Avoid accidental reuse. */
 	memset(&DST, 0xFF, sizeof(DST));
@@ -3722,6 +3742,37 @@ void DRW_render_object_iter(
 	DEG_OBJECT_ITER_FOR_RENDER_ENGINE_END
 }
 
+static struct DRWSelectBuffer {
+	struct GPUFrameBuffer *framebuffer;
+	struct GPUTexture *texture_depth;
+} g_select_buffer = {NULL};
+
+static void draw_select_framebuffer_setup(const rcti *rect)
+{
+	if (g_select_buffer.framebuffer == NULL) {
+		g_select_buffer.framebuffer = GPU_framebuffer_create();
+	}
+
+	/* If size mismatch recreate the texture. */
+	if ((g_select_buffer.texture_depth != NULL) &&
+		((GPU_texture_width(g_select_buffer.texture_depth) != BLI_rcti_size_x(rect)) ||
+		(GPU_texture_height(g_select_buffer.texture_depth) != BLI_rcti_size_y(rect))))
+	{
+		GPU_texture_free(g_select_buffer.texture_depth);
+		g_select_buffer.texture_depth = NULL;
+	}
+
+	if (g_select_buffer.texture_depth == NULL) {
+		g_select_buffer.texture_depth = GPU_texture_create_depth(BLI_rcti_size_x(rect), BLI_rcti_size_y(rect), NULL);
+
+		GPU_framebuffer_texture_attach(g_select_buffer.framebuffer, g_select_buffer.texture_depth, 0, 0);
+
+		if (!GPU_framebuffer_check_valid(g_select_buffer.framebuffer, NULL)) {
+			printf("Error invalid selection framebuffer\n");
+		}
+	}
+}
+
 /* Must run after all instance datas have been added. */
 void DRW_render_instance_buffer_finish(void)
 {
@@ -3767,13 +3818,20 @@ void DRW_draw_select_loop(
 		}
 	}
 
+	gpuPushAttrib(GPU_ENABLE_BIT | GPU_VIEWPORT_BIT);
+	glDisable(GL_SCISSOR_TEST);
+
 	struct GPUViewport *viewport = GPU_viewport_create();
 	GPU_viewport_size_set(viewport, (const int[2]){BLI_rcti_size_x(rect), BLI_rcti_size_y(rect)});
 
-	bool cache_is_dirty;
 	DST.viewport = viewport;
 	v3d->zbuf = true;
 
+	/* Setup framebuffer */
+	draw_select_framebuffer_setup(rect);
+	GPU_framebuffer_bind(g_select_buffer.framebuffer);
+	DRW_framebuffer_clear(false, true, false, NULL, 1.0f);
+
 	DST.options.is_select = true;
 
 	/* Get list of enabled engines */
@@ -3786,7 +3844,6 @@ void DRW_draw_select_loop(
 	}
 
 	/* Setup viewport */
-	cache_is_dirty = true;
 
 	/* Instead of 'DRW_context_state_init(C, &DST.draw_ctx)', assign from args */
 	DST.draw_ctx = (DRWContextState){
@@ -3802,10 +3859,7 @@ void DRW_draw_select_loop(
 	/* Init engines */
 	drw_engines_init();
 
-	/* TODO : tag to refresh by the dependency graph */
-	/* ideally only refresh when objects are added/removed */
-	/* or render properties / materials change */
-	if (cache_is_dirty) {
+	{
 		drw_engines_cache_init();
 
 		if (use_obedit) {
@@ -3843,16 +3897,57 @@ void DRW_draw_select_loop(
 	/* Avoid accidental reuse. */
 	memset(&DST, 0xFF, sizeof(DST));
 #endif
+	GPU_framebuffer_restore();
 
 	/* Cleanup for selection state */
 	GPU_viewport_free(viewport);
 	MEM_freeN(viewport);
 
+	/* Restore Drawing area. */
+	gpuPopAttrib();
+	glEnable(GL_SCISSOR_TEST);
+
 	/* restore */
 	rv3d->viewport = backup_viewport;
 #endif  /* USE_GPU_SELECT */
 }
 
+static void draw_depth_texture_to_screen(GPUTexture *texture)
+{
+	const float w = (float)GPU_texture_width(texture);
+	const float h = (float)GPU_texture_height(texture);
+
+	Gwn_VertFormat *format = immVertexFormat();
+	unsigned int texcoord = GWN_vertformat_attr_add(format, "texCoord", GWN_COMP_F32, 2, GWN_FETCH_FLOAT);
+	unsigned int pos = GWN_vertformat_attr_add(format, "pos", GWN_COMP_F32, 2, GWN_FETCH_FLOAT);
+
+	immBindBuiltinProgram(GPU_SHADER_3D_IMAGE_DEPTH_COPY);
+
+	GPU_texture_bind(texture, 0);
+
+	immUniform1i("image", 0); /* default GL_TEXTURE0 unit */
+
+	immBegin(GWN_PRIM_TRI_STRIP, 4);
+
+	immAttrib2f(texcoord, 0.0f, 0.0f);
+	immVertex2f(pos, 0.0f, 0.0f);
+
+	immAttrib2f(texcoord, 1.0f, 0.0f);
+	immVertex2f(pos, w, 0.0f);
+
+	immAttrib2f(texcoord, 0.0f, 1.0f);
+	immVertex2f(pos, 0.0f, h);
+
+	immAttrib2f(texcoord, 1.0f, 1.0f);
+	immVertex2f(pos, w, h);
+
+	immEnd();
+
+	GPU_texture_unbind(texture);
+
+	immUnbindProgram();
+}
+
 /**
  * object mode select-loop, see: ED_view3d_draw_depth_loop (legacy drawing).
  */
@@ -3865,6 +3960,8 @@ void DRW_draw_depth_loop(
 	ViewLayer *view_layer = DEG_get_evaluated_view_layer(depsgraph);
 	RegionView3D *rv3d = ar->regiondata;
 
+	DRW_opengl_context_enable();
+
 	/* backup (_never_ use rv3d->viewport) */
 	void *backup_viewport = rv3d->viewport;
 	rv3d->viewport = NULL;
@@ -3872,9 +3969,17 @@ void DRW_draw_depth_loop(
 	/* Reset before using it. */
 	memset(&DST, 0x0, sizeof(DST));
 
+	gpuPushAttrib(GPU_ENABLE_BIT | GPU_VIEWPORT_BIT);
+	glDisable(GL_SCISSOR_TEST);
+
 	struct GPUViewport *viewport = GPU_viewport_create();
 	GPU_viewport_size_set(viewport, (const int[2]){ar->winx, ar->winy});
 
+	/* Setup framebuffer */
+	draw_select_framebuffer_setup(&ar->winrct);
+	GPU_framebuffer_bind(g_select_buffer.framebuffer);
+	DRW_framebuffer_clear(false, true, false, NULL, 1.0f);
+
 	bool cache_is_dirty;
 	DST.viewport = viewport;
 	v3d->zbuf = true;
@@ -3935,10 +4040,35 @@ void DRW_draw_depth_loop(
 	memset(&DST, 0xFF, sizeof(DST));
 #endif
 
+	/* TODO: Reading depth for operators should be done here. */
+
+	GPU_framebuffer_restore();
+
 	/* Cleanup for selection state */
 	GPU_viewport_free(viewport);
 	MEM_freeN(viewport);
 
+	/* Restore Drawing area. */
+	gpuPopAttrib();
+	glEnable(GL_SCISSOR_TEST);
+
+	/* Changin context */
+	DRW_opengl_context_disable();
+
+	/* XXX Drawing the resulting buffer to the BACK_BUFFER */
+	gpuPushMatrix();
+	gpuPushProjectionMatrix();
+	wmOrtho2_region_pixelspace(ar);
+	gpuLoadIdentity();
+
+	glEnable(GL_DEPTH_TEST); /* Cannot write to depth buffer without testing */
+	glDepthFunc(GL_ALWAYS);
+	draw_depth_texture_to_screen(g_select_buffer.texture_depth);
+	glDepthFunc(GL_LEQUAL);
+
+	gpuPopMatrix();
+	gpuPopProjectionMatrix();
+
 	/* restore */
 	rv3d->viewport = backup_viewport;
 }
@@ -4139,6 +4269,11 @@ extern struct GPUUniformBuffer *globals_ubo; /* draw_common.c */
 extern struct GPUTexture *globals_ramp; /* draw_common.c */
 void DRW_engines_free(void)
 {
+	DRW_opengl_context_enable();
+
+	DRW_TEXTURE_FREE_SAFE(g_select_buffer.texture_depth);
+	DRW_FRAMEBUFFER_FREE_SAFE(g_select_buffer.framebuffer);
+
 	DRW_shape_cache_free();
 	DRW_stats_free();
 	DRW_globals_free();
@@ -4164,9 +4299,86 @@ void DRW_engines_free(void)
 	MEM_SAFE_FREE(RST.bound_texs);
 	MEM_SAFE_FREE(RST.bound_tex_slots);
 
+	DRW_opengl_context_disable();
+
 #ifdef WITH_CLAY_ENGINE
 	BLI_remlink(&R_engines, &DRW_engine_viewport_clay_type);
 #endif
 }
 
 /** \} */
+
+/** \name Init/Exit (DRW_opengl_ctx)
+ * \{ */
+
+void DRW_opengl_context_create(void)
+{
+	BLI_assert(g_ogl_context == NULL); /* Ensure it's called once */
+	BLI_assert(BLI_thread_is_main());
+
+	BLI_mutex_init(&g_ogl_context_mutex);
+
+	immDeactivate();
+	/* This changes the active context. */
+	g_ogl_context = WM_opengl_context_create();
+	/* Be sure to create gawain.context too. */
+	g_gwn_context = GWN_context_create();
+	immActivate();
+	/* Set default Blender OpenGL state */
+	GPU_state_init();
+	/* So we activate the window's one afterwards. */
+	wm_window_reset_drawable();
+}
+
+void DRW_opengl_context_destroy(void)
+{
+	BLI_assert(BLI_thread_is_main());
+	if (g_ogl_context != NULL) {
+		WM_opengl_context_activate(g_ogl_context);
+		GWN_context_active_set(g_gwn_context);
+		GWN_context_discard(g_gwn_context);
+		WM_opengl_context_dispose(g_ogl_context);
+		BLI_mutex_end(&g_ogl_context_mutex);
+	}
+}
+
+void DRW_opengl_context_enable(void)
+{
+	if (g_ogl_context != NULL) {
+		/* IMPORTANT: We dont support immediate mode in render mode!
+		 * This shall remain in effect until immediate mode supports
+		 * multiple threads. */
+		BLI_mutex_lock(&g_ogl_context_mutex);
+		if (BLI_thread_is_main()) {
+			immDeactivate();
+		}
+		WM_opengl_context_activate(g_ogl_context);
+		GWN_context_active_set(g_gwn_context);
+		if (BLI_thread_is_main()) {
+			immActivate();
+		}
+	}
+}
+
+void DRW_opengl_context_disable(void)
+{
+	if (g_ogl_context != NULL) {
+#ifdef __APPLE__
+		/* Need to flush before disabling draw context, otherwise it does not
+		 * always finish drawing and viewport can be empty or partially drawn */
+		glFlush();
+#endif
+
+		if (BLI_thread_is_main()) {
+			wm_window_reset_drawable();
+		}
+		else {
+			WM_opengl_context_release(g_ogl_context);
+			GWN_context_active_set(NULL);
+		}
+
+		BLI_mutex_unlock(&g_ogl_context_mutex);
+	}
+}
+
+/** \} */

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;

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);

source/blender/editors/space_view3d/space_view3d.c

@@ -65,6 +65,8 @@
 #include "GPU_viewport.h"
 #include "GPU_matrix.h"
 
+#include "DRW_engine.h"
+
 #include "WM_api.h"
 #include "WM_types.h"
 #include "WM_message.h"
@@ -572,7 +574,9 @@ static void view3d_main_region_exit(wmWindowManager *wm, ARegion *ar)
 	}
 
 	if (rv3d->viewport) {
+		DRW_opengl_context_enable();
 		GPU_viewport_free(rv3d->viewport);
+		DRW_opengl_context_disable();
 		MEM_freeN(rv3d->viewport);
 		rv3d->viewport = NULL;
 	}
@@ -757,7 +761,9 @@ static void view3d_main_region_free(ARegion *ar)
 			GPU_fx_compositor_destroy(rv3d->compositor);
 		}
 		if (rv3d->viewport) {
+			DRW_opengl_context_enable();
 			GPU_viewport_free(rv3d->viewport);
+			DRW_opengl_context_disable();
 			MEM_freeN(rv3d->viewport);
 		}
 

source/blender/editors/space_view3d/view3d_draw.c

@@ -2131,11 +2131,13 @@ ImBuf *ED_view3d_draw_offscreen_imbuf(
 	}
 
 	const bool own_ofs = (ofs == NULL);
+	DRW_opengl_context_enable();
 
 	if (own_ofs) {
 		/* bind */
 		ofs = GPU_offscreen_create(sizex, sizey, use_full_sample ? 0 : samples, true, false, err_out);
 		if (ofs == NULL) {
+			DRW_opengl_context_disable();
 			return NULL;
 		}
 	}
@@ -2267,6 +2269,8 @@ ImBuf *ED_view3d_draw_offscreen_imbuf(
 		GPU_offscreen_free(ofs);
 	}
 
+	DRW_opengl_context_disable();
+
 	if (ibuf->rect_float && ibuf->rect)
 		IMB_rect_from_float(ibuf);
 

source/blender/editors/space_view3d/view3d_view.c

@@ -922,6 +922,11 @@ int view3d_opengl_select(
 	UI_Theme_Store(&theme_state);
 	UI_SetTheme(SPACE_VIEW3D, RGN_TYPE_WINDOW);
 
+#ifndef WITH_OPENGL_LEGACY
+	/* All of the queries need to be perform on the drawing context. */
+	DRW_opengl_context_enable();
+#endif
+
 	/* Re-use cache (rect must be smaller then the cached)
 	 * other context is assumed to be unchanged */
 	if (GPU_select_is_cached()) {
@@ -941,7 +946,7 @@ int view3d_opengl_select(
 		v3d->zbuf = true;
 		glEnable(GL_DEPTH_TEST);
 	}
-	
+
 	if (vc->rv3d->rflag & RV3D_CLIPPING)
 		ED_view3d_clipping_set(vc->rv3d);
 	
@@ -994,6 +999,11 @@ int view3d_opengl_select(
 		ED_view3d_clipping_disable();
 
 finally:
+
+#ifndef WITH_OPENGL_LEGACY
+	DRW_opengl_context_disable();
+#endif
+
 	if (hits < 0) printf("Too many objects in select buffer\n");  /* XXX make error message */
 
 	UI_Theme_Restore(&theme_state);

source/blender/gpu/CMakeLists.txt

@@ -150,6 +150,7 @@ data_to_c_simple(shaders/gpu_shader_image_modulate_alpha_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_image_alpha_color_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_image_color_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_image_depth_linear_frag.glsl SRC)
+data_to_c_simple(shaders/gpu_shader_image_depth_copy_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_image_interlace_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_image_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_vert.glsl SRC)

source/blender/gpu/GPU_batch.h

@@ -58,6 +58,8 @@ void gpu_batch_init(void);
 void gpu_batch_exit(void);
 
 /* gpu_batch_presets.c */
+/* Only use by draw manager. Use the presets function instead for interface. */
+Gwn_Batch *gpu_batch_sphere(int lat_res, int lon_res) ATTR_WARN_UNUSED_RESULT;
 /* Replacement for gluSphere */
 Gwn_Batch *GPU_batch_preset_sphere(int lod) ATTR_WARN_UNUSED_RESULT;
 Gwn_Batch *GPU_batch_preset_sphere_wire(int lod) ATTR_WARN_UNUSED_RESULT;

source/blender/gpu/GPU_shader.h

@@ -134,6 +134,7 @@ typedef enum GPUBuiltinShader {
 	GPU_SHADER_2D_IMAGE_MASK_UNIFORM_COLOR,
 	GPU_SHADER_3D_IMAGE_MODULATE_ALPHA,
 	GPU_SHADER_3D_IMAGE_DEPTH,
+	GPU_SHADER_3D_IMAGE_DEPTH_COPY,
 	/* stereo 3d */
 	GPU_SHADER_2D_IMAGE_INTERLACE,
 	/* points */

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);

source/blender/gpu/intern/gpu_shader.c

@@ -77,6 +77,7 @@ extern char datatoc_gpu_shader_image_interlace_frag_glsl[];
 extern char datatoc_gpu_shader_image_mask_uniform_color_frag_glsl[];
 extern char datatoc_gpu_shader_image_modulate_alpha_frag_glsl[];
 extern char datatoc_gpu_shader_image_depth_linear_frag_glsl[];
+extern char datatoc_gpu_shader_image_depth_copy_frag_glsl[];
 extern char datatoc_gpu_shader_3D_vert_glsl[];
 extern char datatoc_gpu_shader_3D_normal_vert_glsl[];
 extern char datatoc_gpu_shader_3D_flat_color_vert_glsl[];
@@ -712,6 +713,8 @@ GPUShader *GPU_shader_get_builtin_shader(GPUBuiltinShader shader)
 		                                         datatoc_gpu_shader_image_modulate_alpha_frag_glsl },
 		[GPU_SHADER_3D_IMAGE_DEPTH] = { datatoc_gpu_shader_3D_image_vert_glsl,
 		                                datatoc_gpu_shader_image_depth_linear_frag_glsl },
+		[GPU_SHADER_3D_IMAGE_DEPTH_COPY] = { datatoc_gpu_shader_3D_image_vert_glsl,
+		                                     datatoc_gpu_shader_image_depth_copy_frag_glsl },
 
 		[GPU_SHADER_2D_IMAGE_INTERLACE] = { datatoc_gpu_shader_2D_image_vert_glsl,
 		                                    datatoc_gpu_shader_image_interlace_frag_glsl },

source/blender/gpu/intern/gpu_viewport.c

@@ -345,6 +345,8 @@ void GPU_viewport_bind(GPUViewport *viewport, const rcti *rect)
 	int rect_w = BLI_rcti_size_x(rect) + 1;
 	int rect_h = BLI_rcti_size_y(rect) + 1;
 
+	DRW_opengl_context_enable();
+
 	if (dfbl->default_fb) {
 		if (rect_w != viewport->size[0] || rect_h != viewport->size[1] || U.ogl_multisamples != viewport->samples) {
 			gpu_viewport_buffers_free(
@@ -465,6 +467,7 @@ cleanup:
 		if (!ok) {
 			GPU_viewport_free(viewport);
 			MEM_freeN(viewport);
+			DRW_opengl_context_disable();
 			return;
 		}
 
@@ -523,7 +526,11 @@ void GPU_viewport_unbind(GPUViewport *viewport)
 	if (dfbl->default_fb) {
 		GPU_framebuffer_texture_unbind(NULL, NULL);
 		GPU_framebuffer_restore();
+	}
 
+	DRW_opengl_context_disable();
+
+	if (dfbl->default_fb) {
 		glEnable(GL_SCISSOR_TEST);
 		glDisable(GL_DEPTH_TEST);
 	}
@@ -581,6 +588,7 @@ static void gpu_viewport_passes_free(PassList *psl, int psl_len)
 	}
 }
 
+/* Must be executed inside Drawmanager Opengl Context. */
 void GPU_viewport_free(GPUViewport *viewport)
 {
 	gpu_viewport_engines_data_free(viewport);

source/blender/gpu/shaders/gpu_shader_image_depth_copy_frag.glsl

@@ -0,0 +1,12 @@
+
+in vec2 texCoord_interp;
+out vec4 fragColor;
+
+uniform sampler2D image;
+
+void main()
+{
+	float depth = texture(image, texCoord_interp).r;
+	fragColor = vec4(depth);
+	gl_FragDepth = depth;
+}

source/blender/windowmanager/CMakeLists.txt

@@ -35,6 +35,7 @@ set(INC
 	../compositor
 	../depsgraph
 	../editors/include
+	../draw
 	../gpu
 	../imbuf
 	../makesdna

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,

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();

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);
+}

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);