>Wongck at 14:18, 13 October 2011

2011-10-13T14:18:28Z

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>Tompee: categorise

2006-10-15T11:57:00Z

categorise

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>Zorro 2 at 14:51, 11 September 2006

2006-09-11T14:51:37Z

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>Zorro 2 at 15:37, 3 July 2006

2006-07-03T15:37:57Z

New page

<pre>
BUGS & TRICKS in GFA BASIC

By Corsair of The Giants.

This is an article about stupid BUGS in GFA BASIC. If you want to see a
little bit of the power(?) of GFA-BASIC, please reboot the intro of
this mag. (It's written in it)

There are a lot bugs especially in GFA BASIC 3.6 TT! Try this in that
version (interpreter): SDPOKE &HFF8241,&H777. Wham! Bombs, no basic
error, just bombs!
I advice you to use a lower version of GFA BASIC, but v3.6 has extra
commands. (See Maggie issue V)

Well, enough talked about v3.6, I shall now give you some useful
information with some examples about GFA BASIC in general. Don't blame
me if I do not talk good English!

The first trick to know is the RESERVE trick. If you use this command,
you can set free some memory for using it for your own data like
pictures, samples, executing programs etc. Without this command you are
hopeless! I will give you the old and bad example (don't use this):

RESERVE 30000 !Reserve all memory exept for 30000 bytes
start%=HIMEM !Find start free memory
BLOAD "THING.DAT",start% !Load data to start%
... Rest of program
RESERVE !Set memory back

This example works perfectly till the program reaches the last line
(RESERVE) and there appears an error: ERROR WHILE RESERVE. GFA BASIC
gives an error and you have lost all your memory exept 30000 bytes!
This is the way to prevent it: (use this method!)

mem%=FRE()-30000 !Better way to reserve memory
RESERVE FRE()-mem% !Reserve it
start%=HIMEM !Find start free memory
BLOAD "THING.DAT",start% !Load data to start%
... Rest of program
RESERVE !Wow, no bombs

The next point is HIMEM. I'm against it because I've bad experience
with using this command. The best way is to MALLOC it and later (when
leaving the program) to free it with VOID MFREE(adres%). Something like
this:

mem%=FRE()-30000 !Better way to reserve memory
RESERVE FRE()-mem% !Reserve it
start%=MALLOC(50000) !"Lock" 50000 bytes memory
BLOAD "THING.DAT",start% !Load data to start% (max. 50000 bytes)
... Rest of program
VOID MFREE(start%) !Set memory free
RESERVE

Use always a%=MALLOC(32000) instead of a$=STRING$(32000,0) because when
a VOID FRE(0) appears (=memory garbage), the pointer to a$ could be
changed!

Now I will you give my own logbase and physbase routine. I have tried
some variations of this routine but this one works nice:

PROCEDURE init_screens
RESERVE FRE()-(64512+256) !Reserve memory (512 bytes waste!)
screen%=MALLOC(64512) !Allocate memory
screen1%=XBIOS(3) !Save original screen
screen2%=screen%-(screen% MOD 256)
screen3%=screen2%+32000
' Clean screens:
scrncln$=STRING$(32000,0) !I use it only for a while...
BMOVE V:scrncln$,screen2% !Clean screen A
BMOVE V:scrncln$,screen3% !Clean screen B
CLR scrncln$ !Erase scrncln$ (erased after VOID FRE() )
RETURN
PROCEDURE exit_screens
set_screen(screen1%,screen1%)!Screens back to original (important)
VOID MFREE(screen%)
RESERVE
RETURN
PROCEDURE set_screen(log%,phys%)
VOID XBIOS(5,L:log%,L:phys%,W:-1)
RETURN
PROCEDURE swap_screen
SWAP screen2%,screen3%
VOID XBIOS(5,L:screen2%,L:screen3%,W:-1)
RETURN

How to use it:

init_screens !Initiale screens
set_screen(screen2%,screen3%) !Work on scr. 2, see scr. 3
PBOX 0,0,100,100 !Wow, a BOX!! (and it's filled)
swap_screen !Now we see it
VOID INP(2) !Wait for a key
exit_screens !Deactivate screens

This was a short example for using this screenrout. Of course you can
do it better but this is the structure. Never forget to GOSUB
exit_screens or else you lose memory and your screens are still
activated....

Well, I stop this article here and hope you can use it. I'm sure you
will find more articles in future! If you have questions or other
things (legal!) than you can write to me:

CORSAIR of the (still cool) GIANTS
Wildschutweg 33
1456 AD Neck
The Netherlands

P.S.: If people think this text is lame 'coz all is common knowledge,
they've to f*ck off because I try to help people. If all the coders
learn from eachother, you automatically get better productions. (Yo
Bonus, I hope the previous sentence wasn't to rude for the mag)

P.S. 2: Please use the option to contact me, I haven't written this
text for "the sake of the walls". Else I'm beginning to feel a little
bit angry at the DO-NO-RESPOND-'COZ-IT-COSTS-TOO-MUCH-MONEY-people. If
I receive a few letters (do it!) I will "reveal" some more GFA-BASIC
tricks (vertical rasters? no problem). (I will send them to this mag)

</pre>

Bugs and Tricks - Revision history

>Wongck at 14:18, 13 October 2011

>Tompee: categorise

>Zorro 2 at 14:51, 11 September 2006

>Zorro 2 at 15:37, 3 July 2006