dos33fsprogs/music/cd/horiz_bot.s
2022-09-06 00:30:11 -04:00

202 lines
3.0 KiB
ArmAsm

; horizontal star wipe
; initial code = 164 bytes
; 163 bytes = jmp to bra
; 158 bytes = cleanup initialization
; 156 bytes = BIT trick
; 154 bytes = set offsets properly
; 151 bytes = redo init
; 145 bytes = leave OFFSET_POINTER in X
; 136 bytes = get rid of end offsets
GBASL = $26
GBASH = $27
BASL = $28
BASH = $29
OFFSET_POINTER = $FE
LINE = $FF
SET_GR = $C050
SET_TEXT = $C051
FULLGR = $C052
TEXTGR = $C053
PAGE1 = $C054
PAGE2 = $C055
LORES = $C056 ; Enable LORES graphics
HIRES = $C057 ; Enable HIRES graphics
HGR2 = $F3D8
SETTXT = $FB36
SETGR = $FB40
BASCALC = $FBC1 ; Y-Coord in A, address in BASL/H, X,Y preserved
WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
;================================
; Clear screen and setup graphics
;================================
horiz:
jsr SETGR ; set lo-res 40x40 mode, PAGE1
bit FULLGR ; show full screen
lda #3 ; count down from 3 to 0 each subline
sta LINE
forever_loop:
lda #$0
tax ; X = OFFSET_POINTER into length pointers
; A = screen line, 0..24
big_loop:
pha ; save screen line on stack
jsr BASCALC ; calculate address of line in BASL/BASH
ldy #39 ; draw 40 pixels on screen
hlin:
tya
; if signed (y>offset) && (y<endoffset) draw
; if signed (y<=offset) || (y>endoffset) don't draw
clc
sbc offsets,X
bvs gurg
eor #$80
gurg:
bpl skip_pixel ; neg if A<=offset
tya
clc
sbc offsets,X
sbc #30
bvs gurg2
eor #$80
gurg2:
bmi skip_pixel ; neg if A<=endoffset
color_smc:
lda #$3b
.byte $2c ; bit trick, skips next two bytes
skip_pixel:
lda #$0 ; color black otherwise
blah:
sta (BASL),Y ; write out pixel
dey ; decrement Xcoord
bpl hlin ; loop until done all 40 pixels
lda #$bb ; force color to all-pink
sta color_smc+1
;==========================================
; draw star at beginning of line
lda offsets,X ; only draw if on-screen
bmi skip_star
clc ; modify x-coord
lda BASL
adc offsets,X
sta BASL
ldy LINE ; which line of bitmap to use
lda star_bitmap-1,Y ; get low bit of bitmap into carry
ldy #7 ; 8-bits wide
draw_line_loop:
lsr
pha
bcc its_transparent
lda #$ff ; white
sta (BASL),Y ; draw on screen
its_transparent:
pla
dey
bpl draw_line_loop
skip_star:
; see if new offset (meaning, we've gone three lines)
dec LINE
bne not3
;======================
; new line
;======================
lda #$b3
sta color_smc+1 ; add shadow to (top?) of line
dec offsets,X ; scroll the line length
; lda offsets,X
; and #$7f
; sta offsets,X
inx ; point to next set of offsets
lda #3 ; reset line vlue
sta LINE
not3:
;==========================
pla ; restore line count
clc
adc #1 ; increment
cmp #24 ; see if reached bottom
bne big_loop
; ideally we'd page flip, no room though
lda #80 ; delay a bit
jsr WAIT
beq forever_loop
offsets:
.byte 30,29,31,38,31,34,32,35
;endoffsets:
; .byte 60,50,61,68,61,64,62,65
; 76543210
; @
; @@@@@
; @ @
star_bitmap:
.byte $50
.byte $f8
.byte $20
; for bot
jmp horiz