Re: Apple II Graphics Programming (Assembly)

[paulrsm <paul.rsm@att.net>]

On Jul 7, 7:40 pm, cerebral_monkey <berkleycame...@gmail.com> wrote:
> Am I doing something wrong here? The screen is still filled with
> random data after execution. (I wrote a subroutine to clear the
> screen, but the built-in version is probably much faster)

My standard way of clearing the hi-res screen is:

 LDA #0 ;FILL BYTE
 LDY #PAGE ;PAGE=$20, $40, or $60
 STY PTR+1
 LDY #0 ;INIT INDEX
 STY PTR
 LDX #$20 ;PAGE COUNT
a STA (PTR),Y
 INY
 BNE a
 INC PTR+1
 DEX
 BNE a
 RTS

If I need speed, then I use

; clear hi-res page 1
 LDA #0 ;FILL BYTE
 LDY #0 ;INIT INDEX
a STA $2000,Y
 STA $2100,Y
 STA $2200,Y
 STA $2300,Y
 ...
 STA $3E00,Y
 STA $3F00,Y
 INY
 BNE a
 RTS

--
Paul Santa Maria
Maumee, Ohio USA