dos33fsprogs/games/lemm/hgr_hlin.s

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;=================================
; Simple Horizontal LINE
;=================================
; line from (x,a) to (x+y,a)
; todo: use Carry to say if X>255
hgr_hlin:
; get ROW into (GBASL)
sty xrun_save
stx x1_save
; X1 already in X
; Y1 already in A ; Y1 into A
;ldy #0 ; always 0
;jsr HPOSN ; (Y,X),(A) (values stores in HGRX,XH,Y)
; important part is row is in GBASL/GBASH
; HPOSN also shifts color odd/even for us
; HPOSN also puts X1/7 into Y
tay ; get row info for Y1 into GBASL/GBASH
lda hposn_high,Y
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; eor #$00 draws on page2
; eor #$60 draws on page1
hgr_hlin_page_smc:
eor #$00
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sta GBASH
lda hposn_low,Y
sta GBASL
lda div7_table,X ; put X1/7 into Y
tay
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; reset color bits
ldx HGR_COLOR
lda hgr_colortbl,X
sta HGR_BITS
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and #$1 ; only shift if in odd column?
beq hlin_no_shift_colors
jsr shift_colors
hlin_no_shift_colors:
; check if narrow corner case where begin and end same block
; if RX%7 + XRUN < 7
ldx x1_save
lda mod7_table,X
clc
adc xrun_save
cmp #7
bcs not_same_block
;====================================
; special case if all in one block
same_block:
; want to use MASK of left_mask (MOD7) ANDed with ~left_mask (MOD7+XRUN)
lda mod7_table,X ; get x1%7
tax ; put in X
lda left_masks,X ; get left mask
sta same_block_mask_smc+1
txa ; x1%7
clc
adc xrun_save ; (x1%7)+xrun
tax
lda left_masks,X ; get left mask
eor #$7f
and same_block_mask_smc+1
sta same_block_mask_smc+1
lda (GBASL),Y
eor HGR_BITS
same_block_mask_smc:
and #$dd
eor (GBASL),Y
sta (GBASL),Y
rts
not_same_block:
; see if not starting on boundary
; X still has X1 in it
lda mod7_table,X
beq draw_run
; handle not full left border
handle_ragged_left:
tax
lda (GBASL),Y
eor HGR_BITS
and left_masks,X
eor (GBASL),Y
sta (GBASL),Y
iny ; move to next
; adjust RUN length by 7- mod7
txa ; load mod7
eor #$ff
sec
adc #7
eor #$ff
sec
adc xrun_save
sta xrun_save
jsr shift_colors
; draw run of same values
draw_run:
lda xrun_save
tax
lda mod7_table,X ; get right partial value
sta right_mask_smc+1
lda div7_table,X ; get run length
tax
; cmp #7
; bcc draw_right ; blt
draw_run_loop:
beq draw_right
lda HGR_BITS ; get color
sta (GBASL),Y ; store out
iny ; move to next block
jsr shift_colors
dex
jmp draw_run_loop
; draw rightmost
draw_right:
right_mask_smc:
ldx #$dd
beq done_hgr_hlin
; see if not starting on boundary
; ldx xrun_save
; tax
lda (GBASL),Y
eor HGR_BITS
;right_mask_smc:
; and #$dd
and right_masks,X
eor (GBASL),Y
sta (GBASL),Y
done_hgr_hlin:
rts
x1_save: .byte $00
xrun_save: .byte $00
;right_masks:
; .byte $80,$81,$83,$87, $8F,$9F,$BF
;left_masks:
; .byte $FF,$FE,$FC,$F8, $F0,$E0,$C0
;==========================
; shift colors
;==========================
; 00000000 and 10000000 => no change (black)
; 01111111 and 11111111 => no change? (white)
; 01010101 => invert 00101010
shift_colors:
lda HGR_BITS
asl
cmp #$C0
bpl done_shift_colors
lda HGR_BITS
eor #$7f
sta HGR_BITS
done_shift_colors:
rts
;==========================
; set color
;==========================
; color in X
set_hcolor:
lda hgr_colortbl,X
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sta HGR_BITS
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rts
; lives at $F6F6 in Applesoft ROM
hgr_colortbl:
.byte $00,$2A,$55,$7F
.byte $80,$AA,$D5,$FF
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hgr_hlin_page_toggle:
lda hgr_hlin_page_smc+1
eor #$60
sta hgr_hlin_page_smc+1
rts
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; notes
; 4+3
; 0000 CCCC 0000 1111
; 0000 000C 0000 0001
; 4000 = 80 80
; 4400 = 81 81
; 4800 = 83 83
; 4C00 = 87 87
; 5000 = 8F 8F
; 5400 = 9F 9F
; 5800 = BF BF
;----
; 5C00 = FF FF
; 4080 = ff 81 FF 81
; 4480 = ff 83
; 4880 = ff 87
; 4c80 = ff 8F
; 5080 = ff 9f
; 5480 = ff bf
;-----------
; 5880 = ff ff
; 5c80 = ff ff 81