Draw Manager: Prevent misuse of static draw context

This is supposed to help catch bugs if referrencing stack data out of
the draw loop context.

No change is suppose to happen for users (specially because the changes
here happens mostly on debug).

It includes a change in the logic for render loop, to make sure DST is
not accessed before we enter it - contribution by Campbell Barton.

2 files changed, 38 insertions, 11 deletions

diff --git a/source/blender/draw/DRW_engine.h b/source/blender/draw/DRW_engine.h
index 0aca41a970d..b780e86b9ec 100644
--- a/source/blender/draw/DRW_engine.h
+++ b/source/blender/draw/DRW_engine.h
@@ -65,6 +65,10 @@ void DRW_engine_viewport_data_size_get(
 
 void DRW_draw_view(const struct bContext *C);
 
+void DRW_draw_render_loop_ex(
+        struct Depsgraph *graph,
+        struct ARegion *ar, struct View3D *v3d,
+        const struct bContext *evil_C);
 void DRW_draw_render_loop(
         struct Depsgraph *graph,
         struct ARegion *ar, struct View3D *v3d);
diff --git a/source/blender/draw/intern/draw_manager.c b/source/blender/draw/intern/draw_manager.c
index 9d3110d9091..de89f22649f 100644
--- a/source/blender/draw/intern/draw_manager.c
+++ b/source/blender/draw/intern/draw_manager.c
@@ -2825,22 +2825,26 @@ void DRW_draw_view(const bContext *C)
 	ARegion *ar = CTX_wm_region(C);
 	View3D *v3d = CTX_wm_view3d(C);
 
-	DST.draw_ctx.evil_C = C;
-
-	DRW_draw_render_loop(graph, ar, v3d);
+	DRW_draw_render_loop_ex(graph, ar, v3d, C);
 }
 
 /**
  * Used for both regular and off-screen drawing.
  */
-void DRW_draw_render_loop(
+void DRW_draw_render_loop_ex(
         struct Depsgraph *graph,
-        ARegion *ar, View3D *v3d)
+        ARegion *ar, View3D *v3d,
+        const bContext *evil_C)
 {
 	Scene *scene = DEG_get_scene(graph);
 	SceneLayer *sl = DEG_get_scene_layer(graph);
 	RegionView3D *rv3d = ar->regiondata;
 
+	/* Reset before using it. */
+	memset(&DST, 0x0, sizeof(DST));
+
+	DST.draw_ctx.evil_C = evil_C;
+
 	bool cache_is_dirty;
 	DST.viewport = rv3d->viewport;
 	v3d->zbuf = true;
@@ -2919,8 +2923,17 @@ void DRW_draw_render_loop(
 	DRW_state_reset();
 	DRW_engines_disable();
 
-	/* avoid accidental reuse */
-	memset(&DST, 0x0, sizeof(DST));
+#ifdef DEBUG
+	/* Avoid accidental reuse. */
+	memset(&DST, 0xFF, sizeof(DST));
+#endif
+}
+
+void DRW_draw_render_loop(
+        struct Depsgraph *graph,
+        ARegion *ar, View3D *v3d)
+{
+	DRW_draw_render_loop_ex(graph, ar, v3d, NULL);
 }
 
 void DRW_draw_render_loop_offscreen(
@@ -2969,6 +2982,9 @@ void DRW_draw_select_loop(
 #else
 	RegionView3D *rv3d = ar->regiondata;
 
+	/* Reset before using it. */
+	memset(&DST, 0x0, sizeof(DST));
+
 	/* backup (_never_ use rv3d->viewport) */
 	void *backup_viewport = rv3d->viewport;
 	rv3d->viewport = NULL;
@@ -3056,8 +3072,10 @@ void DRW_draw_select_loop(
 	DRW_state_reset();
 	DRW_engines_disable();
 
-	/* avoid accidental reuse */
-	memset(&DST, 0x0, sizeof(DST));
+#ifdef DEBUG
+	/* Avoid accidental reuse. */
+	memset(&DST, 0xFF, sizeof(DST));
+#endif
 
 	/* Cleanup for selection state */
 	GPU_viewport_free(viewport);
@@ -3083,6 +3101,9 @@ void DRW_draw_depth_loop(
 	void *backup_viewport = rv3d->viewport;
 	rv3d->viewport = NULL;
 
+	/* Reset before using it. */
+	memset(&DST, 0x0, sizeof(DST));
+
 	struct GPUViewport *viewport = GPU_viewport_create();
 	GPU_viewport_size_set(viewport, (const int[2]){ar->winx, ar->winy});
 
@@ -3139,8 +3160,10 @@ void DRW_draw_depth_loop(
 	DRW_state_reset();
 	DRW_engines_disable();
 
-	/* avoid accidental reuse */
-	memset(&DST, 0x0, sizeof(DST));
+#ifdef DEBUG
+	/* Avoid accidental reuse. */
+	memset(&DST, 0xFF, sizeof(DST));
+#endif
 
 	/* Cleanup for selection state */
 	GPU_viewport_free(viewport);