Fix change ship class edgecases

code/decals/decals.cpp

@@ -185,6 +185,10 @@ Decal::Decal() {
 	vm_vec_make(&scale, 1.f, 1.f, 1.f);
 }
 
+void Decal::markForDeletion() {
+	orig_obj_type = OBJ_NONE;
+}
+
 bool Decal::isValid() const  {
 	if (!object.isValid()) {
 		return false;
@@ -193,6 +197,11 @@ bool Decal::isValid() const  {
 		return false;
 	}
 
+	if (orig_obj_type == OBJ_NONE) {
+		//Decal should be cleared
+		return false;
+	}
+
 	if (orig_obj_type != object.objp()->type) {
 		mprintf(("Decal object type for object %d has changed from %s to %s. Please let m!m know about this\n",
 				object.objnum, Object_type_names[orig_obj_type], Object_type_names[object.objp()->type]));
@@ -536,4 +545,13 @@ void addSingleFrameDecal(Decal&& info) {
 	active_single_frame_decals.push_back(info);
 }
 
+void invalidateForShip(const ship* shipp) {
+	int objnum = shipp->objnum;
+	for (Decal& decal : active_decals) {
+		if (decal.object.objnum == objnum) {
+			decal.markForDeletion();
+		}
+	}
+}
+
 }

code/decals/decals.h

@@ -66,6 +66,8 @@ struct Decal {
 
 	Decal();
 
+	void markForDeletion();
+
 	bool isValid() const;
 };
 
@@ -160,4 +162,6 @@ void addDecal(creation_info& info,
 
 void addSingleFrameDecal(Decal&& info);
 
+void invalidateForShip(const ship* shipp);
+
 }

code/ship/ship.cpp

@@ -11766,10 +11766,18 @@ static void ship_model_change(int n, int ship_type)
 	}
 
 	model_delete_instance(sp->model_instance_num);
+	if (sp->cockpit_model_instance >= 0) {
+		model_delete_instance(sp->cockpit_model_instance);
+	}
 
 	// create new model instance data
 	// note: this is needed for both subsystem stuff and submodel animation stuff
 	sp->model_instance_num = model_create_instance(OBJ_INDEX(objp), sip->model_num);
+	if (sip->cockpit_model_num >= 0)
+		sp->cockpit_model_instance = model_create_instance(model_objnum_special::OBJNUM_COCKPIT, sip->cockpit_model_num);
+	else
+		sp->cockpit_model_instance = -1;
+
 	pmi = model_get_instance(sp->model_instance_num);
 
 	// Goober5000 - deal with texture replacement by re-applying the same code we used during parsing
@@ -12069,6 +12077,8 @@ void change_ship_type(int n, int ship_type, int by_sexp)
 	Assertion(weapon_turret_matches.empty(), "Failed to find matches for every turret a projectile was fired from on ship %s in change_ship_type(); get a coder!\n", sp->ship_name);
 	Assertion(last_targeted_matches.empty(), "Somehow failed to find every subsystem a player was previously targeting on ship %s in change_ship_type(); get a coder!\n", sp->ship_name);
 
+	decals::invalidateForShip(sp);
+
 	// point to new ship data
 	ship_model_change(n, ship_type);
 	sp->ship_info_index = ship_type;