frame interp: fix obj_fchain

include/d/actor/d_a_obj_fchain.h

@@ -31,6 +31,10 @@ public:
     csXyz* getAngle() { return field_0x8a4; }
     J3DModelData* getModelData() { return mModelData; }
 
+#if TARGET_PC
+    void onInterpCallback();
+#endif
+
 private:
     /* 0x568 */ request_of_phase_process_class mPhase;
     /* 0x570 */ J3DModelData* mModelData;
@@ -42,6 +46,14 @@ private:
     /* 0x694 */ cXyz field_0x694[22];
     /* 0x79C */ cXyz field_0x79c[22];
     /* 0x8A4 */ csXyz field_0x8a4[22];
+
+#if TARGET_PC
+    static const int CHAIN_COUNT = 22;
+    cXyz mChainInterpPrev[CHAIN_COUNT];
+    cXyz mChainInterpCurr[CHAIN_COUNT];
+    bool mChainInterpPrevValid;
+    bool mChainInterpCurrValid;
+#endif
 };
 
 STATIC_ASSERT(sizeof(daObjFchain_c) == 0x928);