2 files changed, 25 insertions, 21 deletions

diff --git a/src/newgrf_spritegroup.cpp b/src/newgrf_spritegroup.cpp
index 2c3d19ff1..451cd59be 100644
--- a/src/newgrf_spritegroup.cpp
+++ b/src/newgrf_spritegroup.cpp
@@ -17,6 +17,25 @@
 SpriteGroupPool _spritegroup_pool("SpriteGroup");
 INSTANTIATE_POOL_METHODS(SpriteGroup)
 
+TemporaryStorageArray<int32, 0x110> _temp_store;
+
+
+/**
+ * ResolverObject (re)entry point.
+ * This cannot be made a call to a virtual function because virtual functions
+ * do not like NULL and checking for NULL *everywhere* is more cumbersome than
+ * this little helper function.
+ * @param group the group to resolve for
+ * @param object information needed to resolve the group
+ * @param top_level true if this is a top-level SpriteGroup, false if used nested in another SpriteGroup.
+ * @return the resolved group
+ */
+/* static */ const SpriteGroup *SpriteGroup::Resolve(const SpriteGroup *group, ResolverObject &object, bool top_level)
+{
+	if (group == NULL) return NULL;
+	return group->Resolve(object);
+}
+
 RealSpriteGroup::~RealSpriteGroup()
 {
 	free(this->loaded);
@@ -34,9 +53,6 @@ RandomizedSpriteGroup::~RandomizedSpriteGroup()
 	free(this->groups);
 }
 
-TemporaryStorageArray<int32, 0x110> _temp_store;
-
-
 static inline uint32 GetVariable(const ResolverObject &object, ScopeResolver *scope, byte variable, uint32 parameter, bool *available)
 {
 	/* First handle variables common with Action7/9/D */
@@ -230,7 +246,7 @@ const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) con
 		/* Try to get the variable. We shall assume it is available, unless told otherwise. */
 		bool available = true;
 		if (adjust->variable == 0x7E) {
-			const SpriteGroup *subgroup = SpriteGroup::Resolve(adjust->subroutine, object);
+			const SpriteGroup *subgroup = SpriteGroup::Resolve(adjust->subroutine, object, false);
 			if (subgroup == NULL) {
 				value = CALLBACK_FAILED;
 			} else {
@@ -247,7 +263,7 @@ const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) con
 		if (!available) {
 			/* Unsupported variable: skip further processing and return either
 			 * the group from the first range or the default group. */
-			return SpriteGroup::Resolve(this->num_ranges > 0 ? this->ranges[0].group : this->default_group, object);
+			return SpriteGroup::Resolve(this->num_ranges > 0 ? this->ranges[0].group : this->default_group, object, false);
 		}
 
 		switch (this->size) {
@@ -271,11 +287,11 @@ const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) con
 
 	for (i = 0; i < this->num_ranges; i++) {
 		if (this->ranges[i].low <= value && value <= this->ranges[i].high) {
-			return SpriteGroup::Resolve(this->ranges[i].group, object);
+			return SpriteGroup::Resolve(this->ranges[i].group, object, false);
 		}
 	}
 
-	return SpriteGroup::Resolve(this->default_group, object);
+	return SpriteGroup::Resolve(this->default_group, object, false);
 }
 
 
@@ -302,7 +318,7 @@ const SpriteGroup *RandomizedSpriteGroup::Resolve(ResolverObject &object) const
 	uint32 mask  = (this->num_groups - 1) << this->lowest_randbit;
 	byte index = (scope->GetRandomBits() & mask) >> this->lowest_randbit;
 
-	return SpriteGroup::Resolve(this->groups[index], object);
+	return SpriteGroup::Resolve(this->groups[index], object, false);
 }
 
 
diff --git a/src/newgrf_spritegroup.h b/src/newgrf_spritegroup.h
index da26c1a0e..e6eb4fbcb 100644
--- a/src/newgrf_spritegroup.h
+++ b/src/newgrf_spritegroup.h
@@ -81,19 +81,7 @@ public:
 	virtual byte GetNumResults() const { return 0; }
 	virtual uint16 GetCallbackResult() const { return CALLBACK_FAILED; }
 
-	/**
-	 * ResolverObject (re)entry point.
-	 * This cannot be made a call to a virtual function because virtual functions
-	 * do not like NULL and checking for NULL *everywhere* is more cumbersome than
-	 * this little helper function.
-	 * @param group the group to resolve for
-	 * @param object information needed to resolve the group
-	 * @return the resolved group
-	 */
-	static const SpriteGroup *Resolve(const SpriteGroup *group, ResolverObject &object)
-	{
-		return group == NULL ? NULL : group->Resolve(object);
-	}
+	static const SpriteGroup *Resolve(const SpriteGroup *group, ResolverObject &object, bool top_level = true);
 };