Petit Computer Journal #20

IdleLoop

I'm going to do something different this time around. Usually I would make a new program, illustrating a new concept. However, this time, I won't be doing something new and exciting. I'll be doing something that is old and boring: idle loop.

What is idle loop? Well, you know the main loop on the program that goes like this:

1. @MAINLOOP
2. 'get player input
3. 'process player input
4. GOTO @MAINLOOP

That's it. Idle loop is so called because if the player has no input, it'll just wait around doing nothing. In other words, being idle.

So, you're probably wondering why I want to show that here. Shouldn't that process be known to everybody? Yes, it should. But not to everybody. Just like loop, there are various situations that you have to watch out for. For example, where would you want to put the @INIT function?

INIT function deals with initial state of the program. This is where default values come into play. Also, I like to put in @QUIT function, where the program does clean up when it exits. I don't put it in all my programs, especially simple ones, but for completeness, I want my programs to clean up after itself. It's just good programming practice.

So, the structure would be

1. Global settings, DIM, and such
2. INIT function
3. MAIN function
4. END/QUIT/CLEANUP function

There is a difference between Global Settings and INIT. In Global Settings, you allocate memory to the variables, and load any static resource needed. Fortunately, Petit Computer takes care most of it for you. Very little needed to be here. Some programming language requires you to load modules/libraries here as well.

INIT function deals with initializing the variables to start-up state. That means loading any custom screens if any. Backgrounds, Icons, and the like. This function gets called whenever the player quit to the title screen. It basically start fresh. If you have game states then you load that separately from this function. And yes, you want to have that special loading function, so you can override default graphics and provide the player with custom sprites and skin.

QUIT function basically says good-bye. There's not much here for Petit Computer. If you don't need anything, just leave it out, or just put out a good-bye message to the player.

The MAIN function will handle several types of cases:

1. Infinite Loop
2. Loop with Timer
3. Loop with VSYNC
4. Loop with Player input (wait)
5. Loop with Player input (no wait)
6. Loop with Player input + background process
7. Loop with Player input + multi-thread

1. Infinite Loop

The first case is the simplest. You want the program to run forever, like in showing demo.

1. @LOOP
2. ?"Hello World"
3. GOTO @LOOP

2. Loop with Timer

Sometimes, you want to have the program run for a certain length of time. Say, like a Timer. You can do it like this:

1. 'TIMER PROGRAM BY HARRY HARDJONO
2. SPSET 1,156,0,0,0,0
3. SPOFS 1,-50,-50
4. SPANIM 1,4,15
5. SPSCALE 1,200
6. 
   
7. @INIT
8. CLS
9. ?"HOW MANY SECONDS?"
10. INPUT T
11. IF 0>=T GOTO @END
12. SPOFS 1,0,48,0
13. SPOFS 1,224,48,T*60
14. 
    
15. @LOOP
16. IF (SPCHK(1) AND 1)==0 GOTO @END
17. BEEP 28:WAIT 60
18. GOTO @LOOP
19. 
    
20. @END
21. ?"TIME'S UP!"
22. SPCLR 1
23. BEEP 50
24. WAIT 300

And that's it. The code before the INIT creates and sets the sprite. INIT is used to send the sprite across the screen, timed according to T variable. The loop then simply waits for the sprite to stop moving, and gave a "ding" sound when it's done. Also, sprite clean up is done at the END.

3. Loop with Player input (wait)

Let's modify the program a bit. We want to have a player input, and we want it to wait for each input. Let's say A to start the timer, B to set the timer, and X to end the program.

1. @INIT
2. CLS
3. ?"HOW MANY SECONDS?"
4. INPUT T
5. IF 0>=T GOTO @END
6. ?"A STARTS TIMER"
7. ?"B SETS NEW TIME"
8. ?"X EXIT"
9. 
   
10. @LOOP
11. VSYNC 1:B=BTRIG()
12. IF (B AND 16) GOTO @TICK
13. IF (B AND 32) GOTO @INIT
14. IF (B AND 64) GOTO @END
15. GOTO @LOOP
16. @TICK
17. SPOFS 1,0,48,0
18. SPOFS 1,224,48,T*60
19. @TOCK
20. LOCATE 0,4:SPREAD(1),X,Y:?"TIME LEFT: ";FLOOR((224-X)*T/224);"   "
21. IF (SPCHK(1) AND 1) THEN BEEP 28:WAIT 60:GOTO @TOCK
22. ?"TIME'S UP!":SPOFS 1,-50,-50:BEEP 50
23. GOTO @LOOP
24. 
    
25. @END
26. ?"GOODBYE!"
27. SPCLR 1:WAIT 300

If you notice, there's TICK and TOCK. Normally, I would put these on separate subroutine, but since I'm showing you how to do LOOP while waiting for user input, I simply group it all at once. Does it look like spaghetti code to you?

4. Loop with Player input (no wait)

Let's do one more improvement, and this time, we're going to do player input without waiting. Let's implement a PAUSE button. The truth is, it's very simple. Petit Computer, by default, does not wait for user input.

Here, we simply check if the sprite is moving. If so, then we stop it. Else, we start it.

1. 'TIMER PROGRAM BY HARRY HARDJONO
2. SPSET 1,156,0,0,0,0
3. SPOFS 1,-50,-50
4. SPANIM 1,4,15
5. SPSCALE 1,200
6. 
   
7. @INIT
8. CLS
9. ?"HOW MANY SECONDS?"
10. INPUT T
11. IF 0>=T GOTO @END
12. ?"A STARTS TIMER"
13. ?"B SETS NEW TIME"
14. ?"X EXIT"
15. ?"Y PAUSE"
16. 
    
17. @LOOP
18. VSYNC 1:B=BTRIG()
19. IF (B AND 16) GOTO @TICK
20. IF (B AND 32) GOTO @INIT
21. IF (B AND 64) GOTO @END
22. GOTO @LOOP
23. @TICK
24. SPOFS 1,0,48,0
25. SPOFS 1,224,48,T*60
26. @TOCK
27. LOCATE 0,8:SPREAD(1),X,Y:?"TIME LEFT: ";FLOOR((224-X)*T/224);"   "
28. IF (BUTTON(0) AND 128) GOTO @PAUSE
29. IF (SPCHK(1) AND 1) THEN BEEP 28:WAIT 60:GOTO @TOCK
30. ?"TIME'S UP!":SPOFS 1,-50,-50:BEEP 50
31. GOTO @LOOP
32. 
    
33. @PAUSE
34. IF (SPCHK(1) AND 1) THEN SPOFS 1,X,Y,0 
35. IF (BUTTON(0) AND 16) THEN SPOFS 1,224,48,FLOOR((224-X)*T/224)*60:GOTO @TOCK
36. IF (BUTTON(0) AND 32) GOTO @INIT
37. IF (BUTTON(0) AND 64) GOTO @END
38. GOTO @PAUSE
39. 
    
40. @END
41. ?"GOODBYE!"
42. SPCLR 1:WAIT 300

Simple as that. We simply use the variable values from TIME LEFT to stop the sprite where it stands, and starts it in according to TIME LEFT. There's a trick here, that we use BUTTON(0) instead of BTRIG. We do that because of WAIT 60 that we have will cause BTRIG signal to get lost. BUTTON(0) will read the input continuously. Press A to restart the timer.

Petit Computer Programming can be so easy! Next, we'll examine loops with background processes.