SW: Add the oangdiff field to USER struct as suggested by Hendricks,

and use it in MovePoints. This will be used for interpolating
the angles of sprites carried by SOs soon.

source/sw/src/game.h

@@ -1594,6 +1594,8 @@ typedef struct
     short Vis;              // Shading upgrade, for shooting, etc...
     SWBOOL DidAlert;          // Has actor done his alert noise before?
 
+    int16_t oangdiff;      // Used for interpolating sprite angles
+
     uint8_t filler;
 } USER,*USERp;
 

source/sw/src/track.cpp

@@ -1892,6 +1892,7 @@ PlayerPart:
             }
         }
 
+        int16_t oldang = sp->ang;
         sp->ang = u->sang;
 
         if (TEST(u->Flags, SPR_ON_SO_SECTOR))
@@ -1931,6 +1932,8 @@ PlayerPart:
                 setspritez(sop->sp_num[i], (vec3_t *)sp);
         }
 
+        u->oangdiff += GetDeltaAngle(sp->ang, oldang);
+
         if (TEST(sp->extra, SPRX_BLADE))
         {
             DoBladeDamage(sop->sp_num[i]);