A truly Mind Boggling issue,

[Cobalt]

Mysterious value changing, WHY?
the values in Location_Checker are being changed with in the SUB but I can't find where I am changing them!?
Just walk straight left when you run the program, it will try to enter the town, that when the numbers get changed

Code: QB64: [Select]

1. 'World of Palma; Exploration demo
2. '5/12/2021
3. 'Collision checking OFF version
4. 'Cobalt
5. TYPE WorldTiles
6.  Id AS _UNSIGNED _BYTE
7.  Is_Walkable AS _BYTE
8.  Is_Animated AS _BYTE
9.  Encounter_Group AS _BYTE 'what types of creature encounters possible
10.  Is_Village AS _BYTE
11.  Is_Cave AS _BYTE 'Covers all Cave-like locations
12.  Display_Layer AS _BYTE 'for tiles that the player can walk under
13. END TYPE
14. TYPE TownTiles
15.  Id AS _UNSIGNED _BYTE
16.  Is_Walkable AS _BYTE
17.  Is_Animated AS _BYTE
18.  Is_NPC_Location AS _BYTE 'where the NPCs stand
19.  Is_Building AS _BYTE 'covers shops and houses
20.  Is_Exit AS _BYTE
21. END TYPE
22. TYPE PlayerTemp
23.  Wx AS INTEGER
24.  Wy AS INTEGER
25.  Tx AS _BYTE
26.  Ty AS _BYTE
27.  Fr AS _BYTE
28.  Is_Intown AS _BYTE
29. END TYPE
30. TYPE TownData
31.  Start_X AS INTEGER 'When entering a town player start here
32.  Start_Y AS INTEGER
33.  Exit_X AS INTEGER 'When leaving a town player starts in world here
34.  Exit_Y AS INTEGER
35. END TYPE
36. TYPE StartData
37.  X AS INTEGER
38.  Y AS INTEGER
39.  Map AS _BYTE
40. END TYPE
41. TYPE ExitData
42.  X AS INTEGER
43.  Y AS INTEGER
44.  Map AS _BYTE
45. END TYPE
46.  
47. SCREEN _NEWIMAGE(700, 480, 32)
48. DIM SHARED Map(128, 96) AS WorldTiles, TownMap(9, 50, 39) AS TownTiles, P AS PlayerTemp
49. DIM SHARED char&, MapAni&, TileX2&, frame%, FPSC%, g.facing AS _BYTE, g.moving AS _BYTE
50. DIM SHARED Conv&, AlisAnim(4) AS _BYTE
51. DIM SHARED AnimationOrder(3, 8) '8 frames for sync between Waves\marsh and Shore animations
52. DIM SHARED Enter(10) AS StartData
53. DIM SHARED Exits(10) AS ExitData
54. 'time for the layer system
55. DIM SHARED Layer(26) AS LONG
56. Layer(0) = _DISPLAY
57. Layer(1) = _NEWIMAGE(640, 480, 32)
58. Layer(2) = _NEWIMAGE(640, 480, 32)
59.  
60. MFI_Loader "PS_Overworld_Test.MFI"
61.  
62. _CLEARCOLOR _RGB32(62), char&
63. 'place the conveyor system in corect world location
64. CONST Conveyor_1_Pos_X = 32 * 82
65. CONST Conveyor_1_Pos_Y = 32 * 53 + 8
66. CONST Conveyor_2_Pos_X = 32 * 79 + 8
67. CONST Conveyor_2_Pos_Y = 32 * 56
68. CONST Conveyor_Frame_Speed = 2
69. '--------------------------------------------------
70. DATA 0,1,2,3,4,4,1,0: 'shore animation order
71. FOR i%% = 0 TO 7
72.  READ AnimationOrder(1, i%%)
73. NEXT i%%
74. DATA 0,1,2,1: 'animation frame order
75. FOR i%% = 0 TO 3
76.  READ AlisAnim(i%%)
77. NEXT i%%
78. DATA 36,18,0
79. DATA 85,47,-1
80. READ Enter(1).X, Enter(1).Y, Enter(1).Map
81. READ Exits(1).X, Exits(1).Y, Exits(1).Map
82. 'Enter Camineet from over world
83. Map(82, 46).Is_Village = 1
84. Map(83, 46).Is_Village = 1
85. Map(82, 47).Is_Village = 1
86. Map(83, 47).Is_Village = 1
87. '------------------------------
88. 'Exit Camineet to over world
89. TownMap(0, 39, 18).Is_Exit = 1
90. TownMap(0, 38, 18).Is_Exit = 1
91. TownMap(0, 21, 27).Is_Exit = 1
92. TownMap(0, 20, 27).Is_Exit = 1
93. 'Exit Camineet to Space port(if player has roadpass
94. TownMap(0, 11, 19).Is_Exit = 2
95. TownMap(0, 11, 20).Is_Exit = 2
96. '------------------------------
97. CONST TRUE = -1, FALSE = NOT TRUE
98. CONST Default_Key_Right = 19712, Default_Key_Left = 19200, Default_Key_Up = 18432, Default_Key_Down = 20480
99. CONST Default_A_Button = 32, Default_B_Button = 13, Default_Start_Button = 65, Default_Select_Button = 66
100. CONST down = 0, up = 1, right = 2, left = 3
101. _SCREENMOVE 10, 10
102.  
103. T2! = _FREETIMER
104. ON TIMER(T2!, 1) FPS
105.  
106. 'TIMER(T2!) ON
107. P.Wx = Exits(1).X
108. P.Wy = Exits(1).Y
109. P.Is_Intown = -1
110. _DEST Layer(2)
111.  
112. DO
113.  IF CheckFlag%% THEN Location_Checker P.Is_Intown, P.Wx, P.Wy: CheckFlag%% = FALSE
114.  IF P.Is_Intown > -1 THEN
115.   TownMap_Tile_loader P.Wx, P.Wy, P.Tx, P.Ty 'Mapx%, Mapy%, Playrx%, Playry%
116.   _PRINTSTRING (640, 45), "ID-" + STR$(TownMap(P.Is_Intown, P.Wx, P.Wy).Id), Layer(0)
117.   _PRINTSTRING (640, 60), "UP-" + STR$(TownMap(P.Is_Intown, P.Wx, P.Wy - 1).Id) + " ", Layer(0)
118.   _PRINTSTRING (640, 75), "DN-" + STR$(TownMap(P.Is_Intown, P.Wx, P.Wy + 1).Id) + " ", Layer(0)
119.   _PRINTSTRING (640, 90), "LT-" + STR$(TownMap(P.Is_Intown, P.Wx - 1, P.Wy).Id) + " ", Layer(0)
120.   _PRINTSTRING (640, 105), "RT-" + STR$(TownMap(P.Is_Intown, P.Wx + 1, P.Wy).Id) + " ", Layer(0)
121.   _PRINTSTRING (640, 120), "XT-" + STR$(TownMap(P.Is_Intown, P.Wx + 1, P.Wy).Is_Exit) + " ", Layer(0)
122.   _PRINTSTRING (640, 135), "TwN-" + STR$(P.Is_Intown) + " ", Layer(0)
123.  ELSE
124.   Map_Loader_tiled_Base P.Wx, P.Wy, P.Tx, P.Ty 'Mapx%, Mapy%, Playrx%, Playry%
125.   _PRINTSTRING (640, 45), "ID-" + STR$(Map(P.Wx, P.Wy).Id), Layer(0)
126.   _PRINTSTRING (640, 60), "UP-" + STR$(Map(P.Wx, P.Wy - 1).Id) + " ", Layer(0)
127.   _PRINTSTRING (640, 75), "DN-" + STR$(Map(P.Wx, P.Wy + 1).Id) + " ", Layer(0)
128.   _PRINTSTRING (640, 90), "LT-" + STR$(Map(P.Wx - 1, P.Wy).Id) + " ", Layer(0)
129.   _PRINTSTRING (640, 105), "RT-" + STR$(Map(P.Wx + 1, P.Wy).Id) + " ", Layer(0)
130.  END IF
131.  _PRINTSTRING (640, 0), "FPS-" + STR$(FPSC%), Layer(0)
132.  _PRINTSTRING (640, 15), "X-" + STR$(P.Wx), Layer(0)
133.  _PRINTSTRING (640, 30), "Y-" + STR$(P.Wy), Layer(0)
134.  Place_Alis
135.  _PUTIMAGE , Layer(2), Layer(1)
136.  CLS , 0
137.  _PUTIMAGE (0, 0), Layer(1), _DISPLAY
138.  frame% = frame% + 1
139.  '-----------------Controls------------------
140.  IF _KEYDOWN(Default_Key_Up) AND (NOT g.moving) THEN g.facing = up: g.moving = TRUE
141.  IF _KEYDOWN(Default_Key_Left) AND (NOT g.moving) THEN g.facing = left: g.moving = TRUE
142.  IF _KEYDOWN(Default_Key_Right) AND (NOT g.moving) THEN g.facing = right: g.moving = TRUE
143.  IF _KEYDOWN(Default_Key_Down) AND (NOT g.moving) THEN g.facing = down: g.moving = TRUE
144.  IF _KEYDOWN(27) THEN exitflag%% = -1
145.  SELECT CASE g.facing
146.   CASE up
147.    IF Collision(P.Wx, P.Wy - 1) THEN g.moving = FALSE
148.   CASE down
149.    IF Collision(P.Wx, P.Wy + 1) THEN g.moving = FALSE
150.   CASE left
151.    IF Collision(P.Wx - 1, P.Wy) THEN g.moving = FALSE
152.   CASE right
153.    IF Collision(P.Wx + 1, P.Wy) THEN g.moving = FALSE
154.  
155.  END SELECT
156.  '--------------------------------------------
157.  '----------------Movement--------------------
158.  IF g.moving THEN
159.   SELECT CASE g.facing
160.    CASE up
161.     P.Ty = P.Ty + 2
162.     IF (ABS(P.Ty) MOD 32) = 0 THEN g.moving = FALSE: P.Wy = P.Wy - 1: P.Ty = 0: CheckFlag%% = TRUE
163.     IF NOT _KEYDOWN(Default_Key_Up) THEN Ft%% = 0: P.Fr = 0 ELSE g.moving = TRUE
164.    CASE down
165.     P.Ty = P.Ty - 2
166.     IF (P.Ty MOD 32) = 0 THEN g.moving = FALSE: P.Wy = P.Wy + 1: P.Ty = 0: CheckFlag%% = TRUE
167.     IF NOT _KEYDOWN(Default_Key_Down) THEN Ft%% = 0: P.Fr = 0 ELSE g.moving = TRUE
168.    CASE left
169.     P.Tx = P.Tx + 2
170.     IF (ABS(P.Tx) MOD 32) = 0 THEN g.moving = FALSE: P.Wx = P.Wx - 1: P.Tx = 0: CheckFlag%% = TRUE
171.     IF NOT _KEYDOWN(Default_Key_Left) THEN Ft%% = 0: P.Fr = 0 ELSE g.moving = TRUE
172.    CASE right
173.     P.Tx = P.Tx - 2
174.     IF (P.Tx MOD 32) = 0 THEN g.moving = FALSE: P.Wx = P.Wx + 1: P.Tx = 0: CheckFlag%% = TRUE
175.     IF NOT _KEYDOWN(Default_Key_Right) THEN Ft%% = 0: P.Fr = 0 ELSE g.moving = TRUE
176.   END SELECT
177.  END IF
178.  IF g.moving THEN Ft%% = Ft%% + 1
179.  IF Ft%% = 8 THEN P.Fr = P.Fr + 1: Ft%% = 0
180.  IF P.Fr = 4 THEN P.Fr = 0
181.  'Correct for map wrap
182.  IF P.Wx = 128 THEN P.Wx = 0
183.  IF P.Wx = -1 THEN P.Wx = 127
184.  IF P.Wy = 96 THEN P.Wy = 0
185.  IF P.Wy = -1 THEN P.Wy = 95
186.  '--------------------
187.  IF Enter(1).Y = 0 THEN END
188.  
189.  _LIMIT 60
190. LOOP UNTIL exitflag%%
191. TIMER(T2!) OFF
192. _DEST Layer(0)
193.  
194. FUNCTION Collision (X1%, Y1%)
195.  Result%% = TRUE 'always assume collision
196.  IF P.Is_Intown > -1 THEN
197.   IF TownMap(P.Is_Intown, X1%, Y1%).Is_Walkable THEN Result%% = FALSE
198.  ELSE
199.   IF Map(X1%, Y1%).Is_Walkable THEN Result%% = FALSE
200.  END IF
201.  Collision = Result%%
202. END FUNCTION
203.  
204. SUB Map_Loader_tiled_Base (X1%, Y1%, Sx%, Sy%)
205.  STATIC SubFrame(3) AS _BYTE, MainFrame(3) AS _BYTE, Triggered%%
206.  FOR x% = -1 TO 20
207.   FOR y% = -1 TO 15
208.    mx% = X1% + x% - 9 '-9 to center on player character
209.    my% = Y1% + y% - 7 '-7 to center(ish) on player character
210.    '------Adjust for map wrap around------
211.    IF mx% < 0 THEN mx% = 128 + mx% 'use addition cause mx% is a negative
212.    IF mx% > 127 THEN mx% = mx% - 128
213.    IF my% < 0 THEN my% = 96 + my% 'use addition cause my% is a negative
214.    IF my% > 95 THEN my% = my% - 96
215.    '--------------------------------------
216.    'main map tiles
217.    _PUTIMAGE (Sx% + x% * 32, Sy% + y% * 32)-STEP(31, 31), TileX2&, Layer(Map(mx%, my%).Display_Layer), (0 + Map(mx%, my%).Id * 34, 0)-STEP(31, 31)
218.    'animated map tiles
219.    IF Map(mx%, my%).Is_Animated THEN
220.     SELECT CASE Map(mx%, my%).Id
221.      CASE 1 TO 4 'waves
222.       _PUTIMAGE (Sx% + x% * 32, Sy% + y% * 32)-STEP(31, 31), MapAni&, Layer(1), (544 + MainFrame(1) * 34, 0)-STEP(31, 31)
223.      CASE 21 TO 25 'marsh
224.       _PUTIMAGE (Sx% + x% * 32, Sy% + y% * 32)-STEP(31, 31), MapAni&, Layer(1), (544 + (Map(mx%, my%).Id - 21) * 34, 34 + MainFrame(1) * 34)-STEP(31, 31)
225.      CASE 5 TO 20 'shore
226.       _PUTIMAGE (Sx% + x% * 32, Sy% + y% * 32)-STEP(31, 31), MapAni&, Layer(1), ((Map(mx%, my%).Id - 5) * 34, AnimationOrder(1, MainFrame(2)) * 34)-STEP(31, 31)
227.     END SELECT
228.    END IF
229.   NEXT y%
230.  NEXT x%
231.  'Horizontal conveyor
232.  _PUTIMAGE (Sx% + Conveyor_1_Pos_X - (X1% * 32), Sy% + Conveyor_1_Pos_Y - (Y1% * 32)), Conv&, Layer(2), (0, 0 + (MainFrame(0) * 34))-STEP(255, 31)
233.  'vertical conveyor
234.  _PUTIMAGE (Sx% + Conveyor_2_Pos_X - (X1% * 32), Sy% + Conveyor_2_Pos_Y - (Y1% * 32)), Conv&, Layer(2), (257 + (MainFrame(0) * 34), 0)-STEP(31, 223)
235.  FOR i%% = 0 TO 2
236.   SubFrame(i%%) = SubFrame(i%%) + 1
237.   IF SubFrame(0) = 5 + Conveyor_Frame_Speed THEN MainFrame(0) = MainFrame(0) + Conveyor_Frame_Speed: SubFrame(0) = 0
238.   IF SubFrame(1) = 16 THEN MainFrame(1) = MainFrame(1) + 1: SubFrame(1) = 0
239.   IF SubFrame(2) = 24 THEN MainFrame(2) = MainFrame(2) + 1: SubFrame(2) = 0
240.  NEXT i%%
241.  IF MainFrame(0) = 8 THEN MainFrame(0) = 0
242.  IF MainFrame(1) = 4 THEN MainFrame(1) = 0
243.  IF MainFrame(2) = 8 THEN MainFrame(2) = 0
244. END SUB
245.  
246. SUB TownMap_Tile_loader (X1%, Y1%, Sx%, Sy%)
247.  FOR x% = -1 TO 20
248.   FOR y% = -1 TO 15
249.    mx% = X1% + x% - 9 '-9 to center on player character
250.    my% = Y1% + y% - 7 '-7 to center(ish) on player character
251.    'town map tiles
252.    _PRINTSTRING (0, 0), STR$(P.Is_Intown) + STR$(mx%) + STR$(my%), Layer(0)
253.    _PUTIMAGE (Sx% + x% * 32, Sy% + y% * 32)-STEP(31, 31), Layer(3), Layer(1), (0 + TownMap(P.Is_Intown, mx%, my%).Id * 34, 0)-STEP(31, 31)
254.   NEXT
255.  NEXT
256. END SUB
257.  
258. SUB FPS
259.  ' STATIC LastCount%
260.  FPSC% = frame%
261.  frame% = 0
262. END SUB
263.  
264. SUB Place_Alis
265.  IF NOT g.moving THEN
266.   _PUTIMAGE (290, 210)-STEP(31, 45), char&, Layer(1), (0 + 17 * g.facing, 120)-STEP(15, 22)
267.  ELSE
268.   _PUTIMAGE (290, 210)-STEP(31, 45), char&, Layer(1), (68 + 51 * g.facing + AlisAnim(P.Fr) * 17, 120)-STEP(15, 22)
269.  END IF
270. END SUB
271.  
272. SUB Location_Checker (Map%%, X%, Y%)
273.  _PRINTSTRING (0, 0), STR$(Map%%) + STR$(X%) + STR$(Y%), Layer(0)
274.  IF P.Is_Intown > -1 THEN
275.  
276.   IF TownMap(Map%%, X%, Y%).Is_Exit THEN
277.    P.Is_Intown = Exits(TownMap(Map%%, X%, Y%).Is_Exit).Map
278.    P.Wx = Exits(TownMap(Map%%, X%, Y%).Is_Exit).X
279.    P.Wy = Exits(TownMap(Map%%, X%, Y%).Is_Exit).Y
280.   END IF
281.  ELSE
282.   IF Map(X%, Y%).Is_Village THEN
283.    P.Is_Intown = Enter(Map(X%, Y%).Is_Village).Map
284.    P.Wx = Enter(Map(X%, Y%).Is_Village).X
285.    P.Wy = Enter(Map(X%, Y%).Is_Village).Y
286.    _PRINTSTRING (0, 16), STR$(P.Is_Intown) + STR$(P.Wx) + STR$(P.Wy), Layer(0)
287.    _PRINTSTRING (0, 32), STR$(Enter(1).Map) + STR$(Enter(1).X) + STR$(Enter(1).Y), Layer(0)
288.    _PRINTSTRING (0, 48), STR$(Map%%) + STR$(X%) + STR$(Y%), Layer(0)
289.    _PRINTSTRING (0, 64), STR$(Map(X%, Y%).Is_Village), Layer(0)
290.  
291.    END
292.   END IF
293.  END IF
294. END SUB
295.  
296.  
297. SUB MFI_Loader (FN$)
298.  DIM Size(128) AS LONG, FOffset(128) AS LONG
299.  OPEN FN$ FOR BINARY AS #1
300.  GET #1, , c~%% 'retrieve number of files
301.  FOR I~%% = 1 TO c~%%
302.   GET #1, , FOffset(I~%%)
303.   GET #1, , Size(I~%%)
304.   FOffset&(I~%%) = FOffset&(I~%%) + 1
305.  NEXT I~%%
306.  
307.  TileX2& = LoadGFX(FOffset(1), Size(1)) ' _LOADIMAGE("gfx\maps\PalmaTiles2x2.bmp", 32) '_NEWIMAGE(640, 480, 32)
308.  Conv& = LoadGFX(FOffset(2), Size(2)) '_LOADIMAGE("gfx\maps\conveyoranim.bmp", 32) 'Conveyor
309.  MapAni& = LoadGFX(FOffset(3), Size(3)) '_LOADIMAGE("gfx\maps\mapanimation.bmp", 32) 'Water, shore, and marsh frames
310.  char& = LoadGFX(FOffset(4), Size(4)) '_LOADIMAGE("gfx\CharacterSheetC.png", 32) '
311.  Layer(3) = LoadGFX(FOffset(6), Size(6))
312.  LoadData FOffset(5), Size(5)
313.  F1 = FREEFILE
314.  OPEN "temp.dat" FOR BINARY AS #F1
315.  GET #F1, , Map()
316.  CLOSE #F1
317.  IF _FILEEXISTS("temp.dat") THEN KILL "temp.dat"
318.  LoadData FOffset(7), Size(7)
319.  F1 = FREEFILE
320.  OPEN "temp.dat" FOR BINARY AS #F1
321.  GET #F1, , TownMap()
322.  CLOSE #F1
323.  
324.  CLOSE #1
325.  IF _FILEEXISTS("temp.dat") THEN KILL "temp.dat"
326. END SUB
327.  
328. SUB LoadData (Foff&, Size&)
329.  IF _FILEEXISTS("temp.dat") THEN KILL "temp.dat"
330.  OPEN "temp.dat" FOR BINARY AS #3
331.  dat$ = SPACE$(Size&)
332.  GET #1, Foff&, dat$
333.  PUT #3, , dat$
334.  CLOSE #3
335. END SUB
336.  
337. REM '$include:'MFI_Loader2.bi'
338.  
339. FUNCTION LoadGFX& (Foff&, Size&)
340.  IF _FILEEXISTS("temp.dat") THEN KILL "temp.dat"
341.  OPEN "temp.dat" FOR BINARY AS #3
342.  dat$ = SPACE$(Size&)
343.  GET #1, Foff&, dat$
344.  PUT #3, , dat$
345.  CLOSE #3
346.  LoadGFX& = _LOADIMAGE("temp.dat", 32)
347. END FUNCTION
348.  
349. FUNCTION LoadFFX& (Foff&, Size&, Fize%%)
350.  IF _FILEEXISTS("temp.dat") THEN KILL "temp.dat"
351.  OPEN "temp.dat" FOR BINARY AS #3
352.  dat$ = SPACE$(Size&)
353.  GET #1, Foff&, dat$
354.  PUT #3, , dat$
355.  CLOSE #3
356.  LoadFFX& = _LOADFONT("temp.dat", Fize%%, "monospace")
357. END FUNCTION
358.  
359. FUNCTION LoadSFX& (Foff&, Size&)
360.  IF _FILEEXISTS("temp.dat") THEN KILL "temp.dat"
361.  OPEN "temp.dat" FOR BINARY AS #3
362.  dat$ = SPACE$(Size&)
363.  GET #1, Foff&, dat$
364.  PUT #3, , dat$
365.  CLOSE #3
366.  LoadSFX& = _SNDOPEN("temp.dat")
367. END FUNCTION
368.  

[TempodiBasic]

Hi Cobalt
I have given a look at code and it seems too linear the code into SUB checker...

If your goal is to PRESERVE the values of parameters passed to the SUB the solution is easy
put each of parameters into brackets passing them for value and not for reference.

Code: QB64: [Select]

1.     If CheckFlag%% Then Location_Checker (P.Is_Intown), (P.Wx), (P.Wy)

and this is the result
  [ You are not allowed to view this attachment ]  

it needs a closer reasearch to find where the global variable are changed.

[SMcNeill]

Change:

SUB Location_Checker (Map%%, X%, Y%)


To:

SUB Location_Checker (tempMap%%, tempX%, tempY%)
Map%% = tempMap%%: X% = tempX%: Y% = tempY%

[SMcNeill]

Hi Cobalt
I have given a look at code and it seems too linear the code into SUB checker...

If your goal is to PRESERVE the values of parameters passed to the SUB the solution is easy
put each of parameters into brackets passing them for value and not for reference.

Code: QB64: [Select]

1.     If CheckFlag%% Then Location_Checker (P.Is_Intown), (P.Wx), (P.Wy)

This is a bad habit to fall into, as QB64 doesn’t always allow passing via reference like this.  There’s a few cases where this habit will kill your program completely, with no warning and no message.  (I think it’s from a Windows unregistered seg fault.)  I don’t remember the quirk off the top of my head to cause the issue now —  passing strings via parentheses?  Passing arrays? — but it’s happened to me enough, and it’s such a PITA to sort out and debug, that this method goes high into my list of Things Steve Says Not To Do(tm).

[TempodiBasic]

@SMcNeill
Hi Steve
Yes I Agree that passing by value is not well checked and it can bring you to a mess. But IF you project a SUB to not give back parameters changed the mess disappears.

Moreover yes String and Arrays cannot be passed by value but only by reference.

this your solution is a good universal solution

SUB Location_Checker (tempMap%%, tempX%, tempY%)
Map%% = tempMap%%: X% = tempX%: Y% = tempY%

but in the specific code Map% X% Y% are parameters that bring lobal shared variables so the code will become

Code: QB64: [Select]

1. Sub Location_Checker ' (Map%%, X%, Y%)
2. ' this stores values of global shared variables while the SUB does its work  
3.   PI = P.Is_Intown
4.     PX = P.Wx
5.     PY = P.Wy
6.     _PrintString (0, 0), Str$(PI) + Str$(PX) + Str$(PY), Layer(0)
7.     If P.Is_Intown > -1 Then
8.         ' e' in citta'
9.         If TownMap(PI, PX, PY).Is_Exit Then ' se esce segna l'uscita
10.         ' here global shared variables are changed at this istant  so...
11.     P.Is_Intown = Exits(TownMap(PI, PX, PY).Is_Exit).Map  ' here variables are the same of at entry sub time
12.             P.Wx = Exits(TownMap(PI, PX, PY).Is_Exit).X   ' here P.Is_InTown is already changed
13.             P.Wy = Exits(TownMap(PI, PX, PY).Is_Exit).Y   ' here both P.Is_Intown both P.Wx are already changed
14.         End If
15.         _PrintString (10, 100), Str$(PI) + Str$(PX) + Str$(PY) + Str$(PI), Layer(0)
16.         '      _Delay .5
17.     Else
18.         _PrintString (10, 120), Str$(PI) + Str$(PX) + Str$(PY) + Str$(PI), Layer(0)
19.         '       _Delay 0.5
20.         If Map(PX, PY).Is_Village Then ' se e' villaggio   ' segna l'ingresso in villaggio
21.         ' here global shared variables are changed at this istant  so...
22.             P.Is_Intown = Enter(Map(PX, PY).Is_Village).Map   ' here variables are the same of at entry sub time
23.             P.Wx = Enter(Map(PX, PY).Is_Village).X  ' here P.Is_InTown is already changed but it doesn't matter
24.             P.Wy = Enter(Map(PX, PY).Is_Village).Y  ' here both P.Is_Intown both P.Wx are already changed and the second variable changes the results
25.             _PrintString (0, 16), Str$(P.Is_Intown) + Str$(P.Wx) + Str$(P.Wy), Layer(0)
26.             _PrintString (0, 32), Str$(Enter(1).Map) + Str$(Enter(1).X) + Str$(Enter(1).Y), Layer(0)
27.             _PrintString (0, 48), Str$(PI) + Str$(PX) + Str$(PY), Layer(0)
28.             _PrintString (0, 64), Str$(Map(PX, PY).Is_Village), Layer(0)
29.            ' End
30.         End If
31.     End If
32. End Sub
33.  
34.  

@Cobalt
as you see from my comments to your code the issue is that you're changing  global shared variables during a work with them!
the use of the parameters has hidden  this event to your eyes.

[Cobalt]

see in my primative little monkey brain this seems like :

Code: QB64: [Select]

1. Var1 = 4
2. Var2 = 5
3. Var3 = 6
4.  
5. A = Var1
6. B = Var2
7. C = Var3
8.  
9. Var1 = Var1 + 1
10. Var2 = Var2 + 1
11. Var3 = Var3 + 1
12.  
13. PRINT A, B, C
14.  

And getting an output of  5  6  7

I will have to look at the Dragon Warrior code again, cause I used the exact same method to move the player every time they used stairs in a dungeon and it didn't do this there.