Fix T51931: VBO not updating when UVs are added to shader node tree

UVs need specific data in the VBO, which is not computed unless the
shaders assigned to the mesh actually use UVs. When adding UVs to the
shader, the VBOs were not being recomputed to include the required data.

This adds a DEG relation between the shader and the mesh, and recomputes
the required data if the shader changed.

Thanks Sergey, for all the DEG stuff...

source/blender/blenkernel/BKE_mesh.h

@@ -406,6 +406,7 @@ enum {
 	BKE_MESH_BATCH_DIRTY_ALL = 0,
 	BKE_MESH_BATCH_DIRTY_SELECT,
 	BKE_MESH_BATCH_DIRTY_NOCHECK,
+	BKE_MESH_BATCH_DIRTY_SHADING,
 };
 void BKE_mesh_batch_cache_dirty(struct Mesh *me, int mode);
 void BKE_mesh_batch_cache_free(struct Mesh *me);

source/blender/blenkernel/BKE_object.h

@@ -200,6 +200,8 @@ void BKE_object_eval_cloth(struct EvaluationContext *eval_ctx,
                            struct Scene *scene,
                            struct Object *object);
 
+void BKE_object_eval_update_shading(struct EvaluationContext *eval_ctx,
+                                    struct Object *object);
 
 void BKE_object_handle_data_update(struct EvaluationContext *eval_ctx,
                                    struct Scene *scene,

source/blender/blenkernel/intern/object_update.c

@@ -401,3 +401,11 @@ void BKE_object_eval_cloth(EvaluationContext *UNUSED(eval_ctx), Scene *scene, Ob
 	DEBUG_PRINT("%s on %s\n", __func__, object->id.name);
 	BKE_ptcache_object_reset(scene, object, PTCACHE_RESET_DEPSGRAPH);
 }
+
+void BKE_object_eval_update_shading(EvaluationContext *UNUSED(eval_ctx), Object *object)
+{
+	DEBUG_PRINT("%s on %s\n", __func__, object->id.name);
+	if (object->type == OB_MESH) {
+		BKE_mesh_batch_cache_dirty(object->data, BKE_MESH_BATCH_DIRTY_SHADING);
+	}
+}

source/blender/depsgraph/intern/builder/deg_builder_nodes.cc

@@ -781,10 +781,19 @@ void DepsgraphNodeBuilder::build_obdata_geom(Scene *scene, Object *ob)
 	}
 
 	/* materials */
-	for (int a = 1; a <= ob->totcol; a++) {
-		Material *ma = give_current_material(ob, a);
-		if (ma != NULL) {
-			build_material(ma);
+	if (ob->totcol != 0) {
+		if (ob->type == OB_MESH) {
+			add_operation_node(&ob->id,
+			                   DEG_NODE_TYPE_SHADING,
+			                   function_bind(BKE_object_eval_update_shading, _1, ob),
+			                   DEG_OPCODE_SHADING);
+		}
+
+		for (int a = 1; a <= ob->totcol; a++) {
+			Material *ma = give_current_material(ob, a);
+			if (ma != NULL) {
+				build_material(ma);
+			}
 		}
 	}
 

source/blender/depsgraph/intern/builder/deg_builder_relations.cc

@@ -1448,6 +1448,15 @@ void DepsgraphRelationBuilder::build_obdata_geom(Main *bmain, Scene *scene, Obje
 			Material *ma = give_current_material(ob, a);
 			if (ma != NULL) {
 				build_material(ma);
+
+				if (ob->type == OB_MESH) {
+					OperationKey material_key(&ma->id,
+					                          DEG_NODE_TYPE_SHADING,
+					                          DEG_OPCODE_PLACEHOLDER,
+					                          "Material Update");
+					OperationKey shading_key(&ob->id, DEG_NODE_TYPE_SHADING, DEG_OPCODE_SHADING);
+					add_relation(material_key, shading_key, "Material Update");
+				}
 			}
 		}
 	}

source/blender/depsgraph/intern/depsgraph_type_defines.cc

@@ -129,6 +129,8 @@ static const char *stringify_opcode(eDepsOperation_Code opcode)
 
 		STRINGIFY_OPCODE(COPY_ON_WRITE);
 
+		STRINGIFY_OPCODE(SHADING);
+
 		case DEG_NUM_OPCODES: return "SpecialCase";
 #undef STRINGIFY_OPCODE
 	}

source/blender/depsgraph/intern/depsgraph_types.h

@@ -217,6 +217,9 @@ typedef enum eDepsOperation_Code {
 	/* Copy on Write ------------------------- */
 	DEG_OPCODE_COPY_ON_WRITE,
 
+	/* Shading operations  ------------------------- */
+	DEG_OPCODE_SHADING,
+
 	DEG_NUM_OPCODES,
 } eDepsOperation_Code;
 

source/blender/depsgraph/intern/nodes/deg_node.cc

@@ -239,6 +239,14 @@ void IDDepsNode::tag_update(Depsgraph *graph)
 				do_component_tag = true;
 			}
 		}
+		else if (comp_node->type == DEG_NODE_TYPE_SHADING) {
+			/* TODO(sergey): For until we properly handle granular flags for DEG_id_tag_update()
+			 * we skip flushing here to keep Luca happy.
+			 */
+			if (GS(id_orig->name) != ID_MA) {
+				do_component_tag = false;
+			}
+		}
 		if (do_component_tag) {
 			comp_node->tag_update(graph);
 		}

source/blender/draw/intern/draw_cache_impl_mesh.c

@@ -1598,6 +1598,16 @@ void DRW_mesh_batch_cache_dirty(Mesh *me, int mode)
 		case BKE_MESH_BATCH_DIRTY_NOCHECK:
 			cache->is_really_dirty = true;
 			break;
+		case BKE_MESH_BATCH_DIRTY_SHADING:
+			GWN_VERTBUF_DISCARD_SAFE(cache->shaded_triangles_data);
+			if (cache->shaded_triangles) {
+				for (int i = 0; i < cache->mat_len; ++i) {
+					GWN_BATCH_DISCARD_SAFE(cache->shaded_triangles[i]);
+				}
+			}
+
+			MEM_SAFE_FREE(cache->shaded_triangles);
+			break;
 		default:
 			BLI_assert(0);
 	}