Petit Computer Journal #22

5. Loop with Player input + background process

Last post, we were dealing with idle loop and how we process the button inputs and the corresponding code handlers. This time, I'm going to show you a clearer form to handle player input.

One of the most asked question is how to move the player sprite UDLR, and shoot. I'm going to show you how you should structure your code and divide it into two parts:

1. Process Input
2. Act on Input

While we are processing input, we want it very, very quick. This means that we do not act on any of the input at all. We simply store the information and that's it.

Later on, depending on the variables set, we can process the data. I'm using an extra variable to determine whether or not the player is shooting, and whether or not the bullet is being shot.

This is a very simple structure. If you can use array for directions, then I suggest that you use it. Even loading array using DATA statements is preferable to hand-coding it, like I'm doing here. Even though it doesn't take much time at all, copying and pasting, using array is the neater and better solution. Easier to maintain, too.

We'll take a look at multi-threading process next.

1. ACLS
2. SPSET 1,68,0,0,0,0
3. SPOFS 1,128,96
4. SPSET 10,40,0,0,0,0
5. SPANIM 10,2,6
6. SPOFS 10,-50,-50
7. 
   
8. 
   
9. @INIT
10. PD=0:'PD=PLAYER DIRECTION. 0=STOP.1234=UDLR
11. BB=0
12. 
    
13. @LOOP
14. ' PROCESS INPUT
15. VSYNC 1:TX=TCHX:TY=TCHY:TS=TCHST:TT=TCHTIME
16. B=BUTTON(0)
17. SPREAD(1),PX,PY
18. 
    
19. IF (B AND 1) THEN PD=1
20. IF (B AND 2) THEN PD=2
21. IF (B AND 4) THEN PD=3
22. IF (B AND 8) THEN PD=4
23. IF (B AND 16) THEN PA=1 ELSE PA=0:'PLAYER ACTION: SHOOT
24. 
    
25. 'ACT ON INPUT
26. 'THIS SECTION IS THE IDLE SECTION
27. IF (SPCHK(1) AND 1) GOTO @LOOP ELSE GOSUB @PMOVE
28. IF (SPCHK(10) AND 1) THEN BB=1 ELSE BB=0
29. 
    
30. IF !BB THEN SPOFS 10,-50,-50
31. IF PA AND !BB THEN GOSUB @PSHOOT:PD=0
32. GOTO @LOOP
33. 
    
34. @PMOVE
35. IF PD>4 OR PD<0 THEN PD=0
36. ON PD GOTO @MSTOP,@MUP,@MDOWN,@MLEFT,@MRIGHT
37. @MSTOP
38. SPCHR 1,68
39. SPANIM 1,1,0
40. RETURN
41. @MUP
42. SPCHR 1,76
43. SPANIM 1,4,15
44. SPOFS 1,PX,PY-16,60
45. RETURN
46. @MDOWN
47. SPCHR 1,68
48. SPANIM 1,4,15
49. SPOFS 1,PX,PY+16,60
50. RETURN
51. @MLEFT
52. SPCHR 1,72
53. SPANIM 1,4,15
54. SPOFS 1,PX-16,PY,60
55. RETURN
56. @MRIGHT
57. SPCHR 1,64
58. SPANIM 1,4,15
59. SPOFS 1,PX+16,PY,60
60. RETURN
61. 
    
62. @PSHOOT
63. IF PD>4 OR PD<0 THEN RETURN
64. ON PD GOTO @PSTOP,@PUP,@PDOWN,@PLEFT,@PRIGHT
65. @PSTOP
66. GOTO @PDOWN
67. RETURN
68. @PUP
69. SPCHR 10,46
70. SPOFS 10,PX,PY,0
71. SPOFS 10,PX,PY-160,160
72. RETURN
73. @PDOWN
74. SPCHR 10,42
75. SPOFS 10,PX,PY,0
76. SPOFS 10,PX,PY+160,160
77. RETURN
78. @PLEFT
79. SPCHR 10,44
80. SPOFS 10,PX,PY,0
81. SPOFS 10,PX-160,PY,160
82. RETURN
83. @PRIGHT
84. SPCHR 10,40
85. SPOFS 10,PX,PY,0
86. SPOFS 10,PX+160,PY,160
87. RETURN