horizontal scrolling in basic

[777]

hi,

i want to know how to do horizontal scrolling in basic. i know it has something to do with the 'to' statement using the print statement, which i read somehwere. also i would like to know how to scroll whole screens, not just single lines. thank you.

[1024MAK]

Hello and Welcome to our forum

Is this a question intended for a ZX80, a ZX81 or a ZX Spectrum?

Mark

[777]

zx spectrum

[RWAP]

I have moved this to the Spectrum section

[Shaun_B]

Whole screen scrolling in BASIC? Err... it's possible but not quickly.

At a guess, you would need a variable to represent each line of the screen that you want to scroll, here's a simple example using three string variables for speed

Code: Select all

 1 LET a$="01234567890123456789012345678901": LET b$=a$(2 TO )+a$(1): LET c$=b$(2 TO )+b$(1)
 2 LET a$=a$(2 TO )+a$(1): LET b$=b$(2 TO )+b$(1): LET c$=c$(2 TO )+c$(1)
 3 PRINT AT 0,0;a$;b$;c$;b$;a$;b$;c$;b$;a$;b$;c$;b$;a$;b$;c$;b$;a$;b$;c$;b$;a$;
 4 GO TO 2

Now the more variables you represent by each line you want to scroll, the slower your BASIC listing will go.

Regards,

Shaun.

[Shaun_B]

As an aside to the above listing, I believe that it's only possible to get a limited number of redefined characters using pure Sinclair ZX Spectrum BASIC; the limit is around 26 I think. Everything else you scroll must therefore be within the pre-defined character set.

Regards,

Shaun.

[1024MAK]

Yes, but it is also possible to redirect (POKE) a system variable so it points to your own custom character set. Best to do this as the final stage of development, as it makes the listing rather hard to read if you redefine A-Z, a-z and 0 to 9 etc to graphic characters

Mark

[Shaun_B]

Yes, but it is also possible to redirect (POKE) a system variable so it points to your own custom character set. Best to do this as the final stage of development, as it makes the listing rather hard to read if you redefine A-Z, a-z and 0 to 9 etc to graphic characters

Mark

Good point. So we're getting towards "achieve good results with assembly" type answer.

Unless the person asking the question is thinking of Speccy Next BASIC running at 28Mhz?

Is there a limit on the string var length on the Speccy, or is it a case of "keep going until there is no RAM left"?

Regards,

Shaun.

[1024MAK]

The string size for the ZX Spectrum BASIC is held as a two byte value. So string size is not a problem
Certainly if you want, you can hold all the text for a screen in a single string variable if you want.

Try this:

String test

IMG_5126.JPG (251.62 KiB) Viewed 20124 times

How many times did you have to press Y to scroll?...

Mark

[1024MAK]

Not that this has much practical value, as you have to keep writing to the display, but it's a bit of fun...

Bit of fun

IMG_5129.JPG (158.46 KiB) Viewed 20113 times

Mark