mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-11-01 01:06:33 +00:00
47 lines
841 B
ArmAsm
47 lines
841 B
ArmAsm
;================================
|
|
; scrn routine
|
|
;================================
|
|
; Xcoord in XPOS
|
|
; Ycoord in YPOS
|
|
; color returned in A
|
|
; assume reading from $c00
|
|
|
|
scrn:
|
|
lda YPOS ; 3
|
|
|
|
and #$fe ; make even ; 2
|
|
tay ; 2
|
|
|
|
lda gr_offsets,Y ; lookup low-res memory address ; 4
|
|
clc ; 2
|
|
adc XPOS ; 3
|
|
sta GBASL ; 3
|
|
|
|
lda gr_offsets+1,Y ; 4
|
|
adc #$8 ; assume reading from $c0 ; 3
|
|
sta GBASH ; 3
|
|
|
|
ldy #0 ; 2
|
|
|
|
lda YPOS ; 3
|
|
lsr ; 2
|
|
bcs scrn_adjust_even ;2nt/3t
|
|
|
|
scrn_adjust_odd:
|
|
lda (GBASL),Y ; top/bottom color ; 5+
|
|
jmp scrn_done ; 3
|
|
|
|
scrn_adjust_even:
|
|
lda (GBASL),Y ; top/bottom color ; 5+
|
|
|
|
lsr ; 2
|
|
lsr ; 2
|
|
lsr ; 2
|
|
lsr ; 2
|
|
|
|
scrn_done:
|
|
|
|
and #$f ; 2
|
|
|
|
rts ; 6
|