A86: GrayScale PutSprite

To: assembly-86@lists.ticalc.org
Subject: A86: GrayScale PutSprite
From: Dux Gregis <assets@eden.rutgers.edu>
Date: Mon, 13 Jul 1998 12:46:21 -0600
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-86@lists.ticalc.org


;Input: bc = x,y; ix = 8x8 sprite location: video mem layer, graph mem
layer
;Output: sprite drawn; ix points to next sprite (if your sprites follow
;    in sequence); hl and af and de destroyed

PutSprite:
 ld h,63                           ;shifted to $fc with add hl,hl
 ld a,c
 add a,a                           ;a*4
 add a,a
 ld l,a
 add hl,hl                       ;hl*4 (what was c has been mlt by 16)
 add hl,hl
 ld a,b                           ;a/8
 rra
 rra
 rra
 or l                                ;add to more significant bytes
 ld l,a
 ld a,7                           ;use bottom 7 bits for counter
 and b
 ld d,a                               ;save counter copy in d
 push bc
 push hl
 call copy_sprite
 ld bc,$32                       ;memory difference
 pop hl
 sbc hl,bc                       ;_plotSScreen offset (carry already
reset)
 call copy_sprite
 pop bc
 ret

copy_sprite:
 ld e,8                           ;8 rows
ps_loop:
 ld b,d                              ;get saved bit offset in b
 ld a,(ix)                   ;get this byte of the sprite in a
 inc ix                           ;point ix to the next byte of the
sprite
 ld c,0
 call bit_shift
 xor (hl)                      ;change this to or if you want
 ld (hl),a
 inc l
 ld a,(hl)
 xor c                       ;also changable to or (if you changed the
first)
 ld (hl),a
 ld a,15                       ;add 15 to hl (now ready for next row)
 call add_hl_a
 dec e                       ;counter (8 rows)
 jr nz,ps_loop
 ret

add_hl_a:                               ;add hl,a
 add a,l
 ld l,a
 ret nc
 inc h
 ret

bit_shift:                           ;while(b=<0)
 dec b                               ; a>>c
 ret m
 srl a
 rr c
 jr bit_shift

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Re: A86: GrayScale PutSprite

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