Qbasic key repeat

[mickster9]

Im making a game in qb where the arrow keys control a sprite on screen. I currently use: k$ = INKEY$. Then check k$ to change to x/y coordinates of the sprite by +/- 10.
The problem is that when any direction is held down the sprite will move very quickly in that direction. I want it so that when an arrow key is pressed, the sprite will move once, then the key must be released for it to move againn in that direction.

[BC_Programmer]

you'll need to create a "flag" variable, such as "LASTKEY", you would set this variable to the value of K$ at the end of the game loop (or equivalent). When your comparing the values of K$ to determine which direction to move, you make sure that the current value of LASTKEY is "", which would mean that this is the first time the key was held down.

[mickster9]

Ive tried but i still cant get it to work.
Heres how the main loop of the game is structured:

Code: [Select]

DO
...
...
...
 k$ = INKEY$

 IF k$ = CHR$(27) THEN END
 IF k$ = CHR$(0) + CHR$(72) THEN y = y - 10
 IF k$ = CHR$(0) + CHR$(80) THEN y = y + 10
 IF k$ = CHR$(0) + CHR$(75) THEN x = x - 10
 IF k$ = CHR$(0) + CHR$(77) THEN x = x + 10
...
...
...
LOOP
Can anyone show me how exactly to get it to work with this code.

[BC_Programmer]

basically, you only want to handle a keystroke if the previously detected key was "" (or no key)
That is- as long as they push a key, it will not continue with the symptoms you describe.


try this- LASTKEY$ holds the key from the previous iteration.

Code: [Select]

DO
...
...
...
 k$ = INKEY$
 IF LASTKEY$="" THEN
 IF k$ = CHR$(27) THEN END
 IF k$ = CHR$(0) + CHR$(72) THEN y = y - 10
 IF k$ = CHR$(0) + CHR$(80) THEN y = y + 10
 IF k$ = CHR$(0) + CHR$(75) THEN x = x - 10
 IF k$ = CHR$(0) + CHR$(77) THEN x = x + 10
END IF

LASTKEY$=K$
...
...
...
LOOP


I'm a little rusty with QuickBasic, but I'm pretty sure INKEY$ returns an empty string when no key is pressed.

[mickster9]

Thankyou I was correct in understanding the first time after all but it doesn't work.
Any clue as to why?
And according to the help file: INKEY$ returns a null string if there is no character to return.

[BC_Programmer]

null string and "" are the same thing. Looks like I'm gonna have to fire up my old laptop and figure this out.

[BC_Programmer]

I tried to get it to work, but for some reason, it doesn't work. Maybe a Null String is different then an empty one in QB.


One possible solution would be to use "ON KEY" events.

[mickster9]

Thanks for trying anyway. ill just have to keep trying and maybe i could use 'on key'

[BC_Programmer]

Oh wait a second- is this QBASIC, or QuickBasic?

[mickster9]

I am using qbasic 1.1 now but i may also have quickbasic 4.5 to use if it helps

[BC_Programmer]

I don't know about QBASIC having ON KEY, I haven't used that in a VERY long time- QuickBasic 4.5 likely has it, however.

Generally, you have ON KEY (keycode) GOTO (label)

and then you have the code for that keycode- I believe the exact syntax is presented in the online help.

On the other hand, Now that I think about it- there is no way to perform the flag testing I mentioned beforehand, so I'm not sure how that would work...


I just did, however, recently recall what a "null string" means in QB- Instead of comparing to an empty string "" as I did, I believe one would have to use VarPtr or StrPtr or a similiar function, to determine that it's pointer isn't 0.


I apologize for my vagueness, I haven't done QB very much in over 3 or 4 years. If I get time I might check this out myself, but I'm almost positive there will be some use of a Pointer-type function.

[mickster9]

I still havent got sorted yet...
From what i can find out searching the internet a null string in qbasic/quickbasic is the same as an empty string or ""
Ive investigated VarPtr and it seems that it returns the memory offset of a variable which remains the same regardless of the value of the variable. ie i cannot use it to check when the string is null as it will not change.
I dont know of any pointer functions and could not find anything else in the help index. I also think ON KEY events will not help because it does not solve the problem only provides another way of retrieving the input..

[BC_Programmer]

This seems like such a simple problem. We must be overlooking something obvious here.

Your definitely right about the ON KEY only providing a different method of input-


In the interim, what you could do is programmatically change the typematic rate for the duration of your program- it won't stop the repeat, but you can greatly reduce it.

[alexskywalker]

I used the method of solving this problem as stated at the beginning of the thread, and it worked just fine for me. my program does not work, however, this is due to graphics issues.

[mickster9]

wow i was suprised to see this resurrected.
I gave up with qbasic a long time ago but i'm still interested...

Could you show me at least part of your code if it works for you.
Also which program version are you running and on what system?

I'm also happy to help with your graphics issues if you need it.