WM: new offscreen window draw method to replace all existing methods.

For Blender 2.8 we had to be compatible with very old OpenGL versions, and
triple buffer was designed to work without offscreen rendering, by copying
the the backbuffer to a texture right before swapping. This way we could
avoid redrawing unchanged regions by copying them from this texture on the
next redraws. Triple buffer used to suffer from poor performance and driver
bugs on specific cards, so alternative draw methods remained available.

Now that we require newer OpenGL, we can have just a single draw method
that draw each region into an offscreen buffer, and then draws those to
the screen. This has some advantages:

* Poor 3D view performance when using Region Overlap should be solved now,
  since we can also cache overlapping regions in offscreen buffers.
* Page flip, anaglyph and interlace stereo drawing can be a little faster
  by avoiding a copy to an intermediate texture.
* The new 3D view drawing already writes to an offscreen buffer, which we
  can draw from directly instead of duplicating it to another buffer.
* Eventually we will be able to remove depth and stencil buffers from the
  window and save memory, though at the moment there are still some tools
  using it so it's not possible yet.
* This also fixes a bug with Eevee sampling not progressing with stereo
  drawing in the 3D viewport.

Differential Revision: https://developer.blender.org/D3061

2 files changed, 76 insertions, 87 deletions

diff --git a/source/blender/draw/DRW_engine.h b/source/blender/draw/DRW_engine.h
index cf76bfdeef5..13bf5426a5d 100644
--- a/source/blender/draw/DRW_engine.h
+++ b/source/blender/draw/DRW_engine.h
@@ -102,10 +102,12 @@ void DRW_draw_render_loop_ex(
         struct Depsgraph *depsgraph,
         struct RenderEngineType *engine_type,
         struct ARegion *ar, struct View3D *v3d,
+        struct GPUViewport *viewport,
         const struct bContext *evil_C);
 void DRW_draw_render_loop(
         struct Depsgraph *depsgraph,
-        struct ARegion *ar, struct View3D *v3d);
+        struct ARegion *ar, struct View3D *v3d,
+        struct GPUViewport *viewport);
 void DRW_draw_render_loop_offscreen(
         struct Depsgraph *depsgraph,
         struct RenderEngineType *engine_type,
diff --git a/source/blender/draw/intern/draw_manager.c b/source/blender/draw/intern/draw_manager.c
index 6550fa19105..6e8f9d50aae 100644
--- a/source/blender/draw/intern/draw_manager.c
+++ b/source/blender/draw/intern/draw_manager.c
@@ -1041,42 +1041,46 @@ void DRW_notify_view_update(const DRWUpdateContext *update_ctx)
 	Scene *scene = update_ctx->scene;
 	ViewLayer *view_layer = update_ctx->view_layer;
 
-	if (rv3d->viewport == NULL) {
-		return;
-	}
+	/* Separate update for each stereo view. */
+	for (int view = 0; view < 2; view++) {
+		GPUViewport *viewport = WM_draw_region_get_viewport(ar, view);
+		if (!viewport) {
+			continue;
+		}
 
-	/* XXX Really nasty locking. But else this could
-	 * be executed by the material previews thread
-	 * while rendering a viewport. */
-	BLI_mutex_lock(&DST.ogl_context_mutex);
+		/* XXX Really nasty locking. But else this could
+		 * be executed by the material previews thread
+		 * while rendering a viewport. */
+		BLI_mutex_lock(&DST.ogl_context_mutex);
 
-	/* Reset before using it. */
-	drw_state_prepare_clean_for_draw(&DST);
+		/* Reset before using it. */
+		drw_state_prepare_clean_for_draw(&DST);
 
-	DST.viewport = rv3d->viewport;
-	DST.draw_ctx = (DRWContextState){
-		.ar = ar, .rv3d = rv3d, .v3d = v3d,
-		.scene = scene, .view_layer = view_layer, .obact = OBACT(view_layer),
-		.engine_type = engine_type,
-		.depsgraph = depsgraph, .object_mode = OB_MODE_OBJECT,
-	};
+		DST.viewport = viewport;
+		DST.draw_ctx = (DRWContextState){
+			.ar = ar, .rv3d = rv3d, .v3d = v3d,
+			.scene = scene, .view_layer = view_layer, .obact = OBACT(view_layer),
+			.engine_type = engine_type,
+			.depsgraph = depsgraph, .object_mode = OB_MODE_OBJECT,
+		};
 
-	drw_engines_enable(view_layer, engine_type);
+		drw_engines_enable(view_layer, engine_type);
 
-	for (LinkData *link = DST.enabled_engines.first; link; link = link->next) {
-		DrawEngineType *draw_engine = link->data;
-		ViewportEngineData *data = drw_viewport_engine_data_ensure(draw_engine);
+		for (LinkData *link = DST.enabled_engines.first; link; link = link->next) {
+			DrawEngineType *draw_engine = link->data;
+			ViewportEngineData *data = drw_viewport_engine_data_ensure(draw_engine);
 
-		if (draw_engine->view_update) {
-			draw_engine->view_update(data);
+			if (draw_engine->view_update) {
+				draw_engine->view_update(data);
+			}
 		}
-	}
 
-	DST.viewport = NULL;
+		DST.viewport = NULL;
 
-	drw_engines_disable();
+		drw_engines_disable();
 
-	BLI_mutex_unlock(&DST.ogl_context_mutex);
+		BLI_mutex_unlock(&DST.ogl_context_mutex);
+	}
 }
 
 /** \} */
@@ -1099,28 +1103,34 @@ void DRW_notify_id_update(const DRWUpdateContext *update_ctx, ID *id)
 	Depsgraph *depsgraph = update_ctx->depsgraph;
 	Scene *scene = update_ctx->scene;
 	ViewLayer *view_layer = update_ctx->view_layer;
-	if (rv3d->viewport == NULL) {
-		return;
-	}
-	/* Reset before using it. */
-	drw_state_prepare_clean_for_draw(&DST);
-	DST.viewport = rv3d->viewport;
-	DST.draw_ctx = (DRWContextState){
-		.ar = ar, .rv3d = rv3d, .v3d = v3d,
-		.scene = scene, .view_layer = view_layer, .obact = OBACT(view_layer),
-		.engine_type = engine_type,
-		.depsgraph = depsgraph, .object_mode = OB_MODE_OBJECT,
-	};
-	drw_engines_enable(view_layer, engine_type);
-	for (LinkData *link = DST.enabled_engines.first; link; link = link->next) {
-		DrawEngineType *draw_engine = link->data;
-		ViewportEngineData *data = drw_viewport_engine_data_ensure(draw_engine);
-		if (draw_engine->id_update) {
-			draw_engine->id_update(data, id);
+
+	/* Separate update for each stereo view. */
+	for (int view = 0; view < 2; view++) {
+		GPUViewport *viewport = WM_draw_region_get_viewport(ar, view);
+		if (!viewport) {
+			continue;
+		}
+
+		/* Reset before using it. */
+		drw_state_prepare_clean_for_draw(&DST);
+		DST.viewport = viewport;
+		DST.draw_ctx = (DRWContextState){
+			.ar = ar, .rv3d = rv3d, .v3d = v3d,
+			.scene = scene, .view_layer = view_layer, .obact = OBACT(view_layer),
+			.engine_type = engine_type,
+			.depsgraph = depsgraph, .object_mode = OB_MODE_OBJECT,
+		};
+		drw_engines_enable(view_layer, engine_type);
+		for (LinkData *link = DST.enabled_engines.first; link; link = link->next) {
+			DrawEngineType *draw_engine = link->data;
+			ViewportEngineData *data = drw_viewport_engine_data_ensure(draw_engine);
+			if (draw_engine->id_update) {
+				draw_engine->id_update(data, id);
+			}
 		}
+		DST.viewport = NULL;
+		drw_engines_disable();
 	}
-	DST.viewport = NULL;
-	drw_engines_disable();
 }
 
 /** \} */
@@ -1140,10 +1150,11 @@ void DRW_draw_view(const bContext *C)
 	View3D *v3d = CTX_wm_view3d(C);
 	Scene *scene = DEG_get_evaluated_scene(depsgraph);
 	RenderEngineType *engine_type = ED_view3d_engine_type(scene, v3d->drawtype);
+	GPUViewport *viewport = WM_draw_region_get_bound_viewport(ar);
 
 	/* Reset before using it. */
 	drw_state_prepare_clean_for_draw(&DST);
-	DRW_draw_render_loop_ex(depsgraph, engine_type, ar, v3d, C);
+	DRW_draw_render_loop_ex(depsgraph, engine_type, ar, v3d, viewport, C);
 }
 
 /**
@@ -1154,6 +1165,7 @@ void DRW_draw_render_loop_ex(
         struct Depsgraph *depsgraph,
         RenderEngineType *engine_type,
         ARegion *ar, View3D *v3d,
+        GPUViewport *viewport,
         const bContext *evil_C)
 {
 
@@ -1163,7 +1175,7 @@ void DRW_draw_render_loop_ex(
 
 	DST.draw_ctx.evil_C = evil_C;
 
-	DST.viewport = rv3d->viewport;
+	DST.viewport = viewport;
 	v3d->zbuf = true;
 
 	/* Setup viewport */
@@ -1298,7 +1310,8 @@ void DRW_draw_render_loop_ex(
 
 void DRW_draw_render_loop(
         struct Depsgraph *depsgraph,
-        ARegion *ar, View3D *v3d)
+        ARegion *ar, View3D *v3d,
+        GPUViewport *viewport)
 {
 	/* Reset before using it. */
 	drw_state_prepare_clean_for_draw(&DST);
@@ -1306,7 +1319,7 @@ void DRW_draw_render_loop(
 	Scene *scene = DEG_get_evaluated_scene(depsgraph);
 	RenderEngineType *engine_type = ED_view3d_engine_type(scene, v3d->drawtype);
 
-	DRW_draw_render_loop_ex(depsgraph, engine_type, ar, v3d, NULL);
+	DRW_draw_render_loop_ex(depsgraph, engine_type, ar, v3d, viewport, NULL);
 }
 
 /* @viewport CAN be NULL, in this case we create one. */
@@ -1316,18 +1329,10 @@ void DRW_draw_render_loop_offscreen(
         const bool draw_background, GPUOffScreen *ofs,
         GPUViewport *viewport)
 {
-	RegionView3D *rv3d = ar->regiondata;
-
-	/* backup */
-	void *backup_viewport = rv3d->viewport;
-	{
-		/* backup (_never_ use rv3d->viewport) */
-		if (viewport == NULL) {
-			rv3d->viewport = GPU_viewport_create_from_offscreen(ofs);
-		}
-		else {
-			rv3d->viewport = viewport;
-		}
+	/* Create temporary viewport if needed. */
+	GPUViewport *render_viewport = viewport;
+	if (viewport == NULL) {
+		render_viewport = GPU_viewport_create_from_offscreen(ofs);
 	}
 
 	GPU_framebuffer_restore();
@@ -1336,17 +1341,13 @@ void DRW_draw_render_loop_offscreen(
 	drw_state_prepare_clean_for_draw(&DST);
 	DST.options.is_image_render = true;
 	DST.options.draw_background = draw_background;
-	DRW_draw_render_loop_ex(depsgraph, engine_type, ar, v3d, NULL);
-
-	/* restore */
-	{
-		if (viewport == NULL) {
-			/* don't free data owned by 'ofs' */
-			GPU_viewport_clear_from_offscreen(rv3d->viewport);
-			GPU_viewport_free(rv3d->viewport);
-		}
+	DRW_draw_render_loop_ex(depsgraph, engine_type, ar, v3d, render_viewport, NULL);
 
-		rv3d->viewport = backup_viewport;
+	/* Free temporary viewport. */
+	if (viewport == NULL) {
+		/* don't free data owned by 'ofs' */
+		GPU_viewport_clear_from_offscreen(render_viewport);
+		GPU_viewport_free(render_viewport);
 	}
 
 	/* we need to re-bind (annoying!) */
@@ -1516,10 +1517,6 @@ void DRW_draw_select_loop(
 	/* Reset before using it. */
 	drw_state_prepare_clean_for_draw(&DST);
 
-	/* backup (_never_ use rv3d->viewport) */
-	void *backup_viewport = rv3d->viewport;
-	rv3d->viewport = NULL;
-
 	bool use_obedit = false;
 	int obedit_mode = 0;
 	if (obedit != NULL) {
@@ -1646,9 +1643,6 @@ void DRW_draw_select_loop(
 
 	/* Cleanup for selection state */
 	GPU_viewport_free(viewport);
-
-	/* restore */
-	rv3d->viewport = backup_viewport;
 #endif  /* USE_GPU_SELECT */
 }
 
@@ -1702,10 +1696,6 @@ void DRW_draw_depth_loop(
 
 	DRW_opengl_context_enable();
 
-	/* backup (_never_ use rv3d->viewport) */
-	void *backup_viewport = rv3d->viewport;
-	rv3d->viewport = NULL;
-
 	/* Reset before using it. */
 	drw_state_prepare_clean_for_draw(&DST);
 
@@ -1802,9 +1792,6 @@ void DRW_draw_depth_loop(
 
 	gpuPopMatrix();
 	gpuPopProjectionMatrix();
-
-	/* restore */
-	rv3d->viewport = backup_viewport;
 }
 
 /** \} */