mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-11-30 06:50:39 +00:00
574 lines
14 KiB
Plaintext
574 lines
14 KiB
Plaintext
processor 6502
|
|
include "vcs.h"
|
|
include "macro.h"
|
|
include "xmacro.h"
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
;
|
|
; This example draws a pseudo-3D road using the two missiles
|
|
; and ball objects. With these, we'll draw the two shoulders
|
|
; of the road, and also the dashed center line.
|
|
;
|
|
; Our plan is this: The two missiles and ball all start at the
|
|
; same position on the horizon. As we go down the screen, we'll
|
|
; move the three objects slightly based on the curve of the road.
|
|
; The left shoulder of the road will be biased a little more to
|
|
; the left, and the right shoulder will bias a little more right.
|
|
; We can use the HMOVE registers for movement, since each object
|
|
; will not need to move more than seven pixels on any given
|
|
; scanline.
|
|
;
|
|
; It'd be easier if the scanlines went from bottom to top,
|
|
; because we could just start at the horizontal center of the
|
|
; screen and follow the road curve to the horizon, ending up
|
|
; wherever the road takes us. But scanlines go top to bottom,
|
|
; so we have to also do some preprocessing before the frame begins
|
|
; to figure out where the road ends up.
|
|
;
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
seg.u Variables
|
|
org $80
|
|
|
|
TrackFrac .byte ; fractional position along track
|
|
Speed .byte ; speed of car
|
|
TimeOfDay .word ; 16-bit time of day counter
|
|
; Variables for preprocessing step
|
|
XPos .word ; 16-bit X position
|
|
XVel .word ; 16-bit X velocity
|
|
TPos .word ; 16-bit track position
|
|
TrackLookahead .byte ; current fractional track increment
|
|
; Variables for track generation
|
|
Random .byte ; random counter
|
|
GenTarget .byte ; target of current curve
|
|
GenDelta .byte ; curve increment
|
|
GenCur .byte ; current curve value
|
|
|
|
ZOfs .byte ; counter to draw striped center line
|
|
Weather .byte ; bitmask for weather
|
|
|
|
NumRoadSegments equ 28
|
|
|
|
; Preprocessing result: X positions for all track segments
|
|
RoadX0 REPEAT NumRoadSegments
|
|
.byte
|
|
REPEND
|
|
|
|
; Generated track curve data
|
|
TrackLen equ 5
|
|
TrackData REPEAT TrackLen
|
|
.byte
|
|
REPEND
|
|
|
|
InitialSpeed equ 10 ; starting speed
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
seg Code
|
|
org $f000
|
|
|
|
Start
|
|
CLEAN_START
|
|
lda #1
|
|
sta Random
|
|
lda #InitialSpeed
|
|
sta Speed
|
|
lda #0
|
|
sta TimeOfDay+1
|
|
lda #0
|
|
sta Weather
|
|
|
|
NextFrame
|
|
|
|
VERTICAL_SYNC
|
|
|
|
; Set up some values for road curve computation,
|
|
; since we have some scanline left over.
|
|
lda #0
|
|
sta XVel
|
|
sta XVel+1
|
|
sta XPos
|
|
lda #70 ; approx. center of screen
|
|
sta XPos+1
|
|
lda TrackFrac
|
|
sta TPos
|
|
lda #0
|
|
sta TPos+1
|
|
lda #10 ; initial lookahead
|
|
sta TrackLookahead
|
|
|
|
; VSYNC+37+198+23 = 4+258 = 262 lines
|
|
|
|
TIMER_SETUP 37
|
|
|
|
; Initialize array with X road positions
|
|
jsr PreprocessCurve
|
|
|
|
TIMER_WAIT
|
|
|
|
; Now draw the main frame
|
|
TIMER_SETUP 198
|
|
|
|
jsr DrawSky
|
|
jsr SetupRoadComponents
|
|
jsr DrawRoad ; draw the road
|
|
|
|
TIMER_WAIT
|
|
|
|
TIMER_SETUP 23
|
|
; Advance position on track
|
|
; TrackFrac += Speed
|
|
lda TrackFrac
|
|
clc
|
|
adc Speed
|
|
sta TrackFrac
|
|
bcc .NoGenTrack ; addition overflowed?
|
|
jsr GenTrack ; yes, generate new track segment
|
|
.NoGenTrack
|
|
; TimeOfDay += 1
|
|
inc TimeOfDay
|
|
bne .NoTODInc
|
|
inc TimeOfDay+1
|
|
lda TimeOfDay+1
|
|
; See if it's nighttime yet, and if the stars come out
|
|
clc
|
|
adc #8
|
|
and #$3f
|
|
cmp #$35
|
|
ror
|
|
sta Weather
|
|
.NoTODInc
|
|
|
|
TIMER_WAIT
|
|
jmp NextFrame
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
; Compute road curve from bottom of screen to horizon.
|
|
PreprocessCurve subroutine
|
|
ldx #NumRoadSegments-1
|
|
.CurveLoop
|
|
; Modify X position
|
|
; XPos += XVel (16 bit add)
|
|
lda XPos
|
|
clc
|
|
adc XVel
|
|
sta XPos
|
|
lda XPos+1
|
|
adc XVel+1
|
|
sta XPos+1
|
|
sta RoadX0,x ; store in RoadX0 array
|
|
; Modify X velocity (slope)
|
|
; XVel += TrackData[TPos]
|
|
ldy TPos+1
|
|
lda TrackData,y
|
|
clc ; clear carry for ADC
|
|
bmi .CurveLeft ; track slope negative?
|
|
adc XVel
|
|
sta XVel
|
|
lda XVel+1
|
|
adc #0 ; carry +1
|
|
jmp .NoCurveLeft
|
|
.CurveLeft
|
|
adc XVel
|
|
sta XVel
|
|
lda XVel+1
|
|
sbc #0 ; carry -1
|
|
nop ; make the branch timings are the same
|
|
.NoCurveLeft
|
|
sta XVel+1
|
|
; Advance TPos (TrackData index)
|
|
; TPos += TrackLookahead
|
|
lda TPos
|
|
clc
|
|
adc TrackLookahead
|
|
sta TPos
|
|
lda TPos+1
|
|
adc #0
|
|
sta TPos+1
|
|
; Go to next segment
|
|
inc TrackLookahead ; see further along track
|
|
dex
|
|
bpl .CurveLoop
|
|
rts
|
|
|
|
; Set road component X positions and enable registers
|
|
SetupRoadComponents subroutine
|
|
lda RoadX0
|
|
sta HMCLR ; clear HMOVE registers
|
|
sec
|
|
sta WSYNC
|
|
.DivideLoop
|
|
sbc #15 ; subtract 15
|
|
bcs .DivideLoop ; branch while carry still set
|
|
adc #15
|
|
tay
|
|
lda HMoveTable,y ; lookup HMOVE value
|
|
sta HMM0 ; set missile 0 fine pos
|
|
sta HMBL ; set ball fine pos
|
|
sta HMM1 ; set missile 1 fine pos
|
|
sta RESM0 ; set missile 0 position
|
|
sta RESBL ; set ball position
|
|
sta RESM1 ; set missile 1 position
|
|
sta WSYNC
|
|
sta HMOVE
|
|
; Make road components converge at horizon
|
|
; This will require an additional HMOVE
|
|
lda #$90 ; right 7 pixels
|
|
ldy #$70 ; left 7 pixels
|
|
ldx #$00 ; no movement
|
|
SLEEP 14 ; wait until safe to set regs
|
|
sta HMM0
|
|
sty HMM1
|
|
stx HMBL
|
|
sta WSYNC
|
|
sta HMOVE
|
|
rts
|
|
|
|
; Draw the sky, adding clouds and time-of-day colors.
|
|
DrawDaytime subroutine
|
|
lda TimeOfDay+1 ; offset into sunset color table
|
|
and #$3f
|
|
tay
|
|
lda #16 ; initial height of sky segment
|
|
.SkyLoop2
|
|
tax ; height -> X
|
|
pha ; push original height
|
|
.SkyLoop
|
|
lda SunsetColors,y ; get sunset color
|
|
sta WSYNC ; start scanline
|
|
sta COLUBK ; set background color
|
|
lda SunsetColors+2,y ; get cloud color
|
|
sta COLUPF ; set foreground color
|
|
lda CloudPFData0,x ; load clouds -> playfield
|
|
sta PF0
|
|
lda CloudPFData1,x
|
|
sta PF1
|
|
lda CloudPFData2,x
|
|
sta PF2
|
|
dex
|
|
bne .SkyLoop ; repeat until sky segment done
|
|
iny ; next sky color
|
|
tya
|
|
and #$3f ; keep sky color in range 0-63
|
|
tay ; sky color -> Y
|
|
pla ; restore original segment height
|
|
sec
|
|
sbc #2 ; segment height - 2
|
|
cmp #2 ; done with segments?
|
|
bcs .SkyLoop2 ; no, repeat
|
|
; Draw mountains
|
|
; First, load mountain color
|
|
lda TimeOfDay+1
|
|
lsr
|
|
lsr ; divide time-of-day by 4
|
|
and #$f ; keep in range 0-15
|
|
tax ; -> Y
|
|
lda MountainColors,x ; load mountain color
|
|
sta COLUPF ; set foreground
|
|
lda GroundColors,x ; load ground color
|
|
pha ; save it for later
|
|
ldx #0
|
|
stx PF0
|
|
stx PF1 ; to avoid artifacts, we have to
|
|
stx PF2 ; clear previous clouds
|
|
.MtnLoop
|
|
lda SunsetColors,y ; get sunset color
|
|
sta WSYNC ; start scanline
|
|
sta COLUBK ; set background color
|
|
lda MtnPFData0,x ; load mountains -> playfield
|
|
sta PF0
|
|
lda MtnPFData1,x
|
|
sta PF1
|
|
lda MtnPFData2,x
|
|
sta PF2
|
|
iny ; next sky color
|
|
tya
|
|
and #$3f ; keep sky color in range 0-63
|
|
tay ; sky color -> Y
|
|
inx
|
|
cpx #7 ; only 7 scanlines for the mountains
|
|
bne .MtnLoop
|
|
; Setup colors and enable road components
|
|
pla ; restore ground color
|
|
sta COLUBK ; set background
|
|
lda #0
|
|
sta PF0
|
|
sta PF1
|
|
sta PF2
|
|
rts
|
|
|
|
DrawSky
|
|
bit Weather
|
|
bmi DrawNight
|
|
jmp DrawDaytime
|
|
|
|
; Draw the night sky, with stars.
|
|
DrawNight subroutine
|
|
lda #6
|
|
sta ENABL
|
|
sta COLUPF
|
|
ldy #0
|
|
.MoreStars
|
|
sta RESBL ; strobe the ball to display a star
|
|
adc Start,y ; "randomize" the A register
|
|
bmi .Delay1
|
|
.Delay1
|
|
ror
|
|
bcc .Delay2
|
|
.Delay2
|
|
ror
|
|
bcs .Delay3
|
|
.Delay3
|
|
ror
|
|
bcs .Delay4
|
|
.Delay4
|
|
iny
|
|
ldx INTIM
|
|
cpx #$89 ; timer says we're done?
|
|
bcs .MoreStars ; nope, make more stars
|
|
lda #0
|
|
sta ENABL ; disable ball
|
|
rts
|
|
|
|
DrawRoad subroutine
|
|
lda #2
|
|
sta ENAM0
|
|
sta ENAM1 ; enable missiles
|
|
sta COLUPF
|
|
sta COLUP0
|
|
sta COLUP1 ; set their colors too
|
|
; Draw road
|
|
lda TrackFrac
|
|
asl
|
|
sta WSYNC ; WSYNC so scanline starts at same place each time
|
|
asl ; TrackFrac * 4
|
|
sta ZOfs ; -> counter for animated stripe
|
|
ldx #0 ; 0 is farthest segment
|
|
.RoadLoop
|
|
lda RoadColors,x ; color of sides and center line
|
|
sta COLUP0
|
|
sta COLUP1
|
|
sta COLUPF
|
|
lda RoadX0+1,x ; get next X coordinate
|
|
sec
|
|
sbc RoadX0,x ; subtract this X coordinate
|
|
clc
|
|
adc #7 ; add 7
|
|
tay ; -> Y
|
|
lda HMoveTable-3,y ; left side biased left
|
|
sta HMM0
|
|
lda HMoveTable,y ; center line
|
|
sta HMBL
|
|
lda HMoveTable+3,y ; right side biased right
|
|
sta HMM1
|
|
sta WSYNC
|
|
sta HMOVE
|
|
sta WSYNC
|
|
; Make dashed road stripe by using a counter
|
|
; initialized to the fractional track position,
|
|
; then subracting the PIA timer as an approximation
|
|
; to Z value.
|
|
lda ZOfs
|
|
sec
|
|
sbc INTIM
|
|
sta ZOfs ; ZOfs -= timer
|
|
rol
|
|
rol
|
|
rol ; shift left by 3
|
|
sta ENABL ; enable ball (bit 2)
|
|
sta WSYNC
|
|
lda RoadWidths,x ; lookup register for missile size
|
|
sta NUSIZ0 ; store missile 0 size
|
|
sta NUSIZ1 ; store missile 1 size
|
|
sta WSYNC
|
|
inx
|
|
cpx #NumRoadSegments-1
|
|
bne .RoadLoop ; repeat until all segments done
|
|
; Clean up road objects
|
|
lda #0
|
|
sta ENAM0
|
|
sta ENAM1
|
|
sta ENABL
|
|
sta COLUBK
|
|
sta NUSIZ0
|
|
sta NUSIZ1
|
|
rts
|
|
|
|
; Get next random number
|
|
NextRandom subroutine
|
|
lda Random
|
|
lsr
|
|
bcc .NoEor
|
|
eor #$d4
|
|
.NoEor:
|
|
sta Random
|
|
rts
|
|
|
|
; Generate next track byte
|
|
GenTrack subroutine
|
|
; Shift the existing track data one byte up
|
|
; (a[i] = a[i+1])
|
|
ldx #0
|
|
.ShiftTrackLoop
|
|
lda TrackData+1,x
|
|
sta TrackData,x
|
|
inx
|
|
cpx #TrackLen-1
|
|
bne .ShiftTrackLoop
|
|
; Modify our current track value and
|
|
; see if it intersects the target value
|
|
lda GenCur
|
|
clc
|
|
adc GenDelta
|
|
cmp GenTarget
|
|
beq .ChangeTarget ; target == cur?
|
|
bit GenTarget ; we need the sign flag
|
|
bmi .TargetNeg ; target<0?
|
|
bcs .ChangeTarget ; target>=0 && cur>=target?
|
|
bcc .NoChangeTarget ; branch always taken
|
|
.TargetNeg
|
|
bcs .NoChangeTarget ; target<0 && cur<target?
|
|
; Generate a new target value and increment value,
|
|
; and make sure the increment value is positive if
|
|
; the target is above the current value, and negative
|
|
; otherwise
|
|
.ChangeTarget
|
|
jsr NextRandom ; get a random value
|
|
and #$3f ; range 0..63
|
|
sec
|
|
sbc #$1f ; range -31..32
|
|
sta GenTarget ; -> target
|
|
cmp GenCur
|
|
bmi .TargetBelow ; current > target?
|
|
jsr NextRandom ; get a random value
|
|
and #$f ; mask to 0..15
|
|
jmp .TargetAbove
|
|
.TargetBelow
|
|
jsr NextRandom
|
|
ora #$f0 ; mask to -16..0
|
|
.TargetAbove
|
|
ora #1 ; to avoid 0 values
|
|
sta GenDelta ; -> delta
|
|
lda GenCur
|
|
.NoChangeTarget
|
|
; Store the value in GenCur, and also
|
|
; at the end of the TrackData array
|
|
sta GenCur
|
|
sta TrackData+TrackLen-1
|
|
rts
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
; HMOVE table from -7 to +8
|
|
HMoveTable
|
|
hex 7060504030201000f0e0d0c0b0a09080
|
|
|
|
; Sunset table
|
|
SunsetColors
|
|
hex 00000000a07060504446383efc0c9f9f
|
|
hex aeaeaeaeaeaeaeaeaeaeaeaeaeaeaeae
|
|
hex 9f9f9f0cfc3e384644506070a0000000
|
|
hex 00000000000000000000000000000000
|
|
hex 0000 ; for overflow
|
|
|
|
MountainColors
|
|
hex 00021012f4f6e6264604020000000000
|
|
GroundColors
|
|
hex 00c0c2c4c6c8c8e6e4e2e00000000000
|
|
|
|
RoadColors
|
|
hex 020202
|
|
hex 040404
|
|
hex 060606
|
|
hex 08080808
|
|
hex 0a0a0a0a0a
|
|
hex 0c0c0c0c0c0c
|
|
hex 0e0e0e0e0e0e0e0e0e
|
|
|
|
RoadWidths
|
|
hex 000000000000
|
|
hex 10101010
|
|
hex 1010101010
|
|
hex 202020202020
|
|
hex 202020202020202020
|
|
|
|
; Cloud data
|
|
CloudPFData0
|
|
.byte #%10000000
|
|
.byte #%11100000
|
|
.byte #%10000000
|
|
.byte #%00000000
|
|
.byte #%00000000
|
|
.byte #%10000000
|
|
.byte #%11100000
|
|
.byte #%00000000
|
|
|
|
CloudPFData1
|
|
.byte #%11000000
|
|
.byte #%11110000
|
|
.byte #%11100001
|
|
.byte #%00000011
|
|
.byte #%00000111
|
|
.byte #%11000000
|
|
.byte #%00000000
|
|
.byte #%00011000
|
|
|
|
CloudPFData2
|
|
.byte #%00000000
|
|
.byte #%00001110
|
|
.byte #%00011111
|
|
.byte #%00000111
|
|
.byte #%01100000
|
|
.byte #%11000000
|
|
.byte #%00000110
|
|
.byte #%00000000
|
|
|
|
; Mountain data
|
|
MtnPFData0
|
|
.byte #%00000000
|
|
.byte #%00000000
|
|
.byte #%00000000
|
|
.byte #%00000000
|
|
.byte #%00000000
|
|
.byte #%10000000
|
|
.byte #%11100000
|
|
|
|
MtnPFData1
|
|
.byte #%00000000
|
|
.byte #%00010000
|
|
.byte #%00110000
|
|
.byte #%01111000
|
|
.byte #%11111100
|
|
.byte #%11111110
|
|
.byte #%11111110
|
|
|
|
MtnPFData2
|
|
.byte #%00000000
|
|
.byte #%00000000
|
|
.byte #%00000000
|
|
.byte #%00000100
|
|
.byte #%00101110
|
|
.byte #%01111111
|
|
.byte #%11111111
|
|
|
|
CarSprite
|
|
.byte 0
|
|
.byte #%10000001;--
|
|
.byte #%10111101;--
|
|
.byte #%11111111;--
|
|
.byte #%10000001;--
|
|
.byte #%10111101;--
|
|
.byte #%01011010;--
|
|
.byte #%01011010;--
|
|
.byte #%01011010;--
|
|
.byte #%00100100;--
|
|
.byte #%11111111;--
|
|
.byte #%10111101;--
|
|
.byte #%00111100;--
|
|
|
|
; Epilogue
|
|
org $fffc
|
|
.word Start
|
|
.word Start
|