dos33fsprogs/seasons/seasons.s
2020-05-19 12:19:50 -04:00

270 lines
5.9 KiB
ArmAsm

; Apple II Seasons -=DESiRE=- 128B Demo for Outline 2020
; based on the code in Hellmood's 64B x86 demo "Autumn"
; by deater (Vince Weaver) <vince@deater.net>
; DOS version is 64 bytes
; original Apple II 6502 port was 167 bytes
; I got it down to 126 bytes
; qkumba got it down to 116
; color-cycling brought it back up to 127 bytes
; To save space, runs from the zero page starting at $50
; need to avoid $E0-$E5 used by the hgr/hplot routines
; Zero Page Addresses
XCOORDL = $F3
XCOORDH = $F4
YCOORDL = $F5
YCOORDH = $F6
EBP1 = $F7
EBP2 = $F8
EBP3 = $F9
EBP4 = $FA
COLORL = $FB
COLORH = $FC
SOUND = $FD
FRAMEL = $FE
FRAMEH = $FF
; Soft Switches
KEYPRESS= $C000
KEYRESET= $C010
SPEAKER = $C030
; ROM routines
; Some of these are in the Applesoft ROMs so need at least an Apple II+
; or later to run
TEXT = $FB36 ; Set text mode
HGR2 = $F3D8 ; Set full-screen hi-res mode using page 2 ($4000)
; 280x192 6-colors
HPLOT0 = $F457 ; Plot point, (Y,X) = Horizontal, (A=Vertical)
HCOLOR = $F6EC ; Set color in X, must be 0..7
; use zero-page addressing to save space
.zeropage
seasons:
;===================
; init screen ; Instruction Length
jsr HGR2 ; 3
; init vars to zero. Apple II doesn't clear RAM
; some of these might be necessary?
; should we make this a loop?
; ldx #0 ; 2
; stx XCOORDL ; 2
; stx YCOORDL ; 2
; stx XCOORDH ; 2
; stx YCOORDH ; 2
; stx EBP1 ; 2
; stx EBP2 ; 2
; stx EBP3 ; 2
; stx EBP4 ; 2
; stx COLORH ; 2
seasons_forever:
; save old Xcoord value to X/Y for later
; push/pop is 1 byte each but have to get
; value into accumulator first
ldx XCOORDL ; 2
ldy XCOORDH ; 2
; 16-bit subtraction x=x-y
; need to set carry before subtraction on 6502
txa ; 1 (xcoordl in X)
sec ; 1
sbc YCOORDL ; 2
sta XCOORDL ; 2
tya ; 1 (xcoordh in Y)
sbc YCOORDH ; 2
; 16-bit arithmatic shift right of X
; 6502 has no asr instruction
; cmp #$80 sets carry if high bit set
cmp #$80 ; 2 ; XCOORDH still in A from before
ror ; 1
sta XCOORDH ; 2
ror XCOORDL ; 2
; 16-bit add, ycoord=ycoord+oldx
clc ; 1
txa ; 1
adc YCOORDL ; 2
sta YCOORDL ; 2
tya ; 1
adc YCOORDH ; 2
; 16-bit arithmatic shift right of y-coord
cmp #$80 ; 2 ; YCOORDH still in A from before
ror ; 1
sta YCOORDH ; 2
ror YCOORDL ; 2
; 32 bit rotate of low bit shifted out of Y-coordinate
ror EBP1 ; 2
ror EBP2 ; 2
ror EBP3 ; 2
ror EBP4 ; 2
; branch if carry set
bcs label_11f ; 2
; 16-bit increment of color
inc COLORL ; 2
bne no_oflo ; 2
inc COLORH ; 2
no_oflo:
; 16-bit add of X-coord by 0x80
; this keeps the drawing roughly to the 280x192 screen
; carry should still be clear (inc doesn't set it)
lda XCOORDL ; 2
adc #$80 ; 2
sta XCOORDL ; 2
bcc no_oflo2 ; 2
inc XCOORDH ; 2
no_oflo2:
; 16-bit negate of Y-coord
sec ; 1
lda #0 ; 2
sbc YCOORDL ; 2
sta YCOORDL ; 2
lda #0 ; 2
sbc YCOORDH ; 2
sta YCOORDH ; 2
label_11f:
; skipping the color manipulation done here by original
; mix colors a bit?
; 16-bit shift of color
; 2nd is a rotate as asl doesn't shift in cary
lda COLORL ; 2
asl ; 1 ; shl %ax
rol COLORH ; 2
eor COLORH ; 2
sta COLORL ; 2
; get color mapping
; using a color lookup table looks best but too many bytes
; you can approximate something close to the lookup with
; two extra instructions
and #$7 ; 2
smc:
ora #$2 ; 2
tax ; 1
; if using color lookup table
; tay ; 1
; ldx color_lookup,Y ; 3 (could be 2 if we run in zero page)
; if ycoord negative, loop
lda YCOORDH ; 2
bmi seasons_forever ; 2
; if top bits of xcoord, loop
lda XCOORDH ; 2
and #$f0 ; 2
bne seasons_forever ; 2
put_pixel:
; actually set the color
jsr HCOLOR ; 3 ; color is in X
; set up paramaters for HPLOT ROM call
ldx XCOORDL ; 2 ; x coord in (y:x)
ldy XCOORDH ; 2
lda YCOORDL ; 2 ; y coord in A
jsr HPLOT0 ; 3
; flip palettes when color at $4200 (roughly 0,32 on screen)
; changes. This is sort of arbitrary, but having a 16-bit counter
; takes too many instructions and Apple II doesn't have a
; programmable timer
lda $4200 ; 3 ; check colors at 0,32
bmi seasons_forever ; 2
; flip between blue/purple and orange/green palettes
; with self-modifying code. 2 bytes are saved when
; we execute in the zero page
lda smc+1 ; 2
eor #$3 ; 2
sta smc+1 ; 2
; the adc/sbc in HPLOT0 leave the V flag clear
; so we can save a byte (over jump) by using bvc
bvc seasons_forever ; 2
; Thankfully not necessary for a 128B demo?
; lda KEYPRESS ; 3 ; see if key pressed
; bpl seasons_forever ; 2 ; loop if not
; bit KEYRESET
exit_to_prompt:
; jsr TEXT ; 3 ; return to text mode
; jmp $3D0 ; 3 ; return to Applesoft prompt
;========================================================
;========================================================
; color lookup tables used when testing
; some of them look better, but make the executable bigger
; than the AND/OR version of setting colors
; Apple II Hi-Res Colors
; It's all NTSC artifacting and complex
; There can be color-clash at a 3.5 pixel level
; Adjacent on pixels make white, adjacent off make black
; Simplistic summary, you can have these 8 colors (6 unique)
; 0 = Black0
; 1 = Green
; 2 = Purple
; 3 = White0
; 4 = Black1
; 5 = Orange
; 6 = Blue
; 7 = White2
color_lookup:
; colorful palette
; .byte $01,$01,$02,$03, $05,$05,$06,$07
; blue and purple palette
; .byte $02,$02,$03,$06, $06,$06,$02,$07
; qkumba ora2 white/blue/purple
; .byte $02,$03,$02,$03, $06,$07,$06,$07
; ora1 white/orange/green
; .byte $01,$01,$03,$03, $05,$05,$07,$07
; better mixed orange/green/white
; .byte $01,$03,$03,$03, $05,$05,$07,$07
; orange and green palette
; .byte $01,$01,$03,$05, $05,$05,$01,$07
; .byte $01,$00,$01,$00, $05,$00,$05,$00
; "Leaf" Locations
; TOP-LEFT ?? CENTER-TOP TOP-RIGHT LEFT ?? CENTER-BOTTOM ??