mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-11-26 10:49:17 +00:00
581 lines
15 KiB
Plaintext
581 lines
15 KiB
Plaintext
processor 6502
|
|
include "vcs.h"
|
|
include "macro.h"
|
|
include "xmacro.h"
|
|
|
|
; For lots of games, we'd like to display more than two sprites.
|
|
; There are lots of different ways to tackle this on the VCS,
|
|
; but we're going to try for a generalized approach that lets
|
|
; use have N different sprites at any X-Y coordinate, each with
|
|
; its own bitmap and color table. This is tricky because we can
|
|
; only do so much on each scanline.
|
|
|
|
; Our approach is to separate the problem into three phases.
|
|
; In the sort phase, we sort all sprites by Y coordinate.
|
|
; We do one sort pass per frame, so it may take several frames
|
|
; for the sort to stabilize.
|
|
; In the positioning phase, we look at the sprites in Y-sorted
|
|
; order, looking several lines ahead to see if a sprite is
|
|
; coming up. We then allocate it to one of the two player
|
|
; objects in hardware and set its position using the SetHorizPos
|
|
; method. We can set one or both of the player objects this way.
|
|
|
|
; In the display phase, we display the objects which we previously
|
|
; assigned and positioned. First we figure out how many scanlines are
|
|
; required. If only one object is scheduled, we just use its height.
|
|
; If two objects are scheduled, we go until the bottommost line has
|
|
; been displayed. We then loop through, fetching pixels and colors
|
|
; for one or both objects (up to four lookup tables) and setting
|
|
; registers at the appropriate time. We don't have time to do much
|
|
; else, so we don't look for any new objects to schedule until
|
|
; we're done with this loop.
|
|
|
|
; This scheme can only display up to two objects on a given
|
|
; scanline, so if the system tries to schedule a third, it will
|
|
; be ignored. Also, the positioning routine takes a few scanlines
|
|
; to complete, so if the top of a sprite is too close to the
|
|
; bottom of another sprite, the latter may not be displayed.
|
|
;
|
|
; To mitigate this, we increment a priority counter when a
|
|
; sprite entry is missed. In the sort phase, we move those sprites
|
|
; ahead of lower priority sprites in the sort order. This makes
|
|
; overlapping sprites flicker instead of randomly disappear.
|
|
|
|
seg.u Variables
|
|
org $80
|
|
|
|
Scanline byte ; current scanline
|
|
CurIndex byte ; current sprite # to try to schedule
|
|
|
|
PData0 word ; pointer (lo/hi) to player 0 bitmap data
|
|
PData1 word ; pointer to player 1 bitmap data
|
|
PColr0 word ; pointer to player 0 color data
|
|
PColr1 word ; pointer to player 1 color data
|
|
SIndx0 byte ; next y-position to draw player 0
|
|
; or during draw, index into sprite
|
|
; zero means not assigned
|
|
SIndx1 byte ; ... for player 1
|
|
SSize0 byte ; sprite size for player 0
|
|
SSize1 byte ; sprite size for player 1
|
|
|
|
NSprites equ 8 ; max # of sprites
|
|
XPos0 ds NSprites ; x coord for each sprite
|
|
YPos0 ds NSprites ; y coord for each sprite
|
|
Sorted0 ds NSprites ; sorted list of sprite indices
|
|
Priority0 ds NSprites ; sprite priority list, if missed
|
|
|
|
MinYDist equ 7 ; min. Y distance to consider sprite
|
|
|
|
; Fetchs the approximate scanline (could be off by +/- 1)
|
|
; into A. Takes 11 or 14 cycles.
|
|
MAC GET_APPROX_SCANLINE
|
|
ldy INTIM
|
|
lda Timer2Scanline,y
|
|
bne .Ok
|
|
lda Timer2Scanline-1,y
|
|
.Ok
|
|
ENDM
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
seg Code
|
|
org $f000
|
|
|
|
; Initialize and set initial X and Y offsets of objects.
|
|
Start
|
|
CLEAN_START
|
|
ldx #0
|
|
lda #10
|
|
ldy #40
|
|
InitLoop
|
|
sty XPos0,x
|
|
sta YPos0,x
|
|
clc
|
|
adc #19
|
|
iny
|
|
iny
|
|
iny
|
|
iny
|
|
iny
|
|
iny
|
|
inx
|
|
cpx #NSprites
|
|
bne InitLoop
|
|
; Initialize initial sort order
|
|
ldx #0
|
|
InitLoop2
|
|
txa
|
|
sta Sorted0,x
|
|
inx
|
|
cpx #NSprites
|
|
bne InitLoop2
|
|
|
|
; Next frame loop
|
|
NextFrame
|
|
; VSYNC and VBLANK periods
|
|
VERTICAL_SYNC
|
|
TIMER_SETUP 24
|
|
; Do joystick movement
|
|
jsr MoveJoystick
|
|
; Do one iteration of bubble sort on sprite indices
|
|
ldx #NSprites-2
|
|
SortLoop
|
|
jsr SwapSprites
|
|
dex
|
|
bpl SortLoop ; loop until <= 0
|
|
; Reset scanline counter and sprite objects
|
|
ldx #0
|
|
stx CurIndex
|
|
stx SIndx0
|
|
stx SIndx1
|
|
stx SSize0
|
|
stx SSize1
|
|
TIMER_WAIT
|
|
; end of VBLANK
|
|
|
|
; Scanline loop
|
|
TIMER_SETUP 216 ; timer <- #$ff
|
|
lda #$90
|
|
sta COLUBK
|
|
NextFindSprite
|
|
; Try to schedule sprites to both players
|
|
jsr FindAnotherSprite
|
|
jsr FindAnotherSprite
|
|
; Apply fine offsets
|
|
sta WSYNC ; start next scanline
|
|
sta HMOVE ; apply the previous fine position(s)
|
|
; See if time to draw
|
|
jsr DrawSprites
|
|
; Repeat until all scanlines drawn
|
|
sta HMCLR ; reset the old horizontal position(s)
|
|
lda INTIM
|
|
cmp #$14 ; scanline 198
|
|
bcs NextFindSprite
|
|
lda #201 ; + 9 lines, end exactly
|
|
jsr WaitForScanline
|
|
; end of Scanline loop
|
|
|
|
NoMoreScanlines
|
|
; Clear all colors to black before overscan
|
|
ldx #0
|
|
stx COLUBK
|
|
stx COLUP0
|
|
stx COLUP1
|
|
stx COLUPF
|
|
; 30-2 lines of overscan
|
|
TIMER_SETUP 28
|
|
TIMER_WAIT
|
|
; Go to next frame
|
|
jmp NextFrame
|
|
|
|
; We were too late to display a sprite.
|
|
; Put it earlier in the sort order and try next frame.
|
|
; X = sort index
|
|
.MissedSprite subroutine
|
|
; Have we already looked at all the sprites?
|
|
; Increment priority for this sort entry
|
|
inc Priority0,x
|
|
; Go to next sort index, until we get to the end
|
|
inx
|
|
stx CurIndex
|
|
.OutOfSprites
|
|
rts
|
|
; Try to assign the next sprite in the sort order into
|
|
; one of the two player slots.
|
|
; If sprite found, uses at least 3 scanlines for SetHorizPos.
|
|
FindAnotherSprite ; subroutine entry point
|
|
; Get the approximate scanline
|
|
GET_APPROX_SCANLINE
|
|
clc
|
|
adc #MinYDist
|
|
sta Scanline
|
|
; Calculate the distance to next sprite
|
|
ldx CurIndex
|
|
cpx #NSprites
|
|
bcs .OutOfSprites
|
|
ldy Sorted0,x ; get sprite index # in Y-sorted order
|
|
lda YPos0,y ; get Y position of sprite
|
|
cmp Scanline ; SpriteY - Scanline
|
|
; Don't schedule the sprite if it's too soon or its scanline
|
|
; has already passed -- mark it missed
|
|
bmi .MissedSprite ; passed it? (or > 127 lines away)
|
|
; A sprite is starting soon, now we need to schedule it
|
|
; to either one of the player objects
|
|
lda XPos0,y
|
|
; Is player 1 available?
|
|
ldx SIndx1
|
|
bne .Plyr1NotReady
|
|
; Due to timing issues, we have artifacts if player 1 is
|
|
; too close to the left edge of the screen. So we'd prefer to
|
|
; put those sprites in the player 0 slot.
|
|
cmp #34 ; X < 34
|
|
bcc .Plyr1NotReady
|
|
; First let's set its horizontal offset
|
|
ldx #1
|
|
jsr SetHorizPos ; set horizontal position (does WSYNC)
|
|
; Assign the sprite's Y position to player 1
|
|
lda YPos0,y
|
|
sta SIndx1
|
|
; Get index into SpriteDataMap (index * 4)
|
|
ldx MultBy4,y
|
|
; Copy addresses of pixel/color maps to player 1
|
|
lda SpriteDataMap,x
|
|
sta PData1
|
|
lda SpriteDataMap+1,x
|
|
sta PData1+1
|
|
lda SpriteDataMap+2,x
|
|
sta PColr1
|
|
lda SpriteDataMap+3,x
|
|
sta PColr1+1
|
|
; Get the sprite height as the first byte of the color map
|
|
ldy #0
|
|
lda (PColr1),y
|
|
sta SSize1
|
|
jmp .SetupDone
|
|
.Plyr1NotReady
|
|
ldx SIndx0
|
|
bne .NoNearSprite ; both players in use
|
|
; Player 0 is available
|
|
; This is essentially the same as the player 1 routine
|
|
ldx #0
|
|
jsr SetHorizPos
|
|
lda YPos0,y
|
|
sta SIndx0
|
|
ldx MultBy4,y
|
|
lda SpriteDataMap,x
|
|
sta PData0
|
|
lda SpriteDataMap+1,x
|
|
sta PData0+1
|
|
lda SpriteDataMap+2,x
|
|
sta PColr0
|
|
lda SpriteDataMap+3,x
|
|
sta PColr0+1
|
|
ldy #0
|
|
lda (PColr0),y
|
|
sta SSize0
|
|
.SetupDone
|
|
inc CurIndex ; go to next sprite in sort order
|
|
.NoNearSprite
|
|
rts
|
|
|
|
; Draw any scheduled sprites.
|
|
DrawSprites subroutine
|
|
; Wait for next precise scanline
|
|
lda #0 ; 0 = wait for next
|
|
jsr WaitForScanline
|
|
lda Timer2Scanline,y ; lookup scanline #
|
|
sta Scanline ; save it
|
|
; Calculate # of lines to draw for each sprite
|
|
; Sprite Y - current scanline + sprite height
|
|
lda SIndx0
|
|
beq .Empty0 ; sprite 0 is inactive?
|
|
sec
|
|
sbc Scanline
|
|
clc
|
|
adc SSize0
|
|
sta SIndx0 ; SIndx0 += SSize0 - Scanline
|
|
.Empty0
|
|
lda SIndx1
|
|
beq .Empty1 ; sprite 1 is inactive?
|
|
sec
|
|
sbc Scanline
|
|
clc
|
|
adc SSize1
|
|
sta SIndx1 ; SIndx1 += SSize1 - Scanline
|
|
.Empty1
|
|
; Find out the maximum # of lines to draw
|
|
; by taking the maximum of the two sprite heights
|
|
cmp SIndx0
|
|
bpl .Cmp1 ; sindx0 < sindx1?
|
|
lda SIndx0
|
|
.Cmp1
|
|
tax ; X = # of lines left to draw
|
|
beq .NoSprites ; X = 0? we're done
|
|
sta WSYNC ; next scanline
|
|
.DrawNextScanline
|
|
; Make sure player 0 index is within bounds
|
|
ldy SIndx0
|
|
cpy SSize0
|
|
bcs .Inactive0 ; index >= size? (or index < 0)
|
|
; Lookup pixels for player 0
|
|
lda (PData0),y
|
|
; Do WSYNC and then quickly store pixels for player 0
|
|
sta WSYNC
|
|
sta GRP0
|
|
; Lookup/store colors for player 0
|
|
lda (PColr0),y
|
|
sta COLUP0
|
|
.DrawSprite1
|
|
; Make sure player 1 index is within bounds
|
|
ldy SIndx1
|
|
cpy SSize1
|
|
bcs .Inactive1 ; index >= size? (or index < 0)
|
|
; Lookup/store pixels and colors for player 1
|
|
; Note that we are already 30-40 pixels into the scanline
|
|
; by this point...
|
|
lda (PData1),y
|
|
sta GRP1
|
|
lda (PColr1),y
|
|
sta COLUP1
|
|
.Inactive1
|
|
; Decrement the two sprite indices
|
|
dey
|
|
sty SIndx1
|
|
dec SIndx0
|
|
; Repeat until we've drawn all the scanlines for this job
|
|
dex
|
|
bne .DrawNextScanline
|
|
; Free up both player objects by zeroing them out
|
|
stx SIndx0
|
|
stx SIndx1
|
|
stx SSize0
|
|
stx SSize1
|
|
sta WSYNC
|
|
stx GRP0
|
|
stx GRP1
|
|
; No sprites were drawn; just exit
|
|
.NoSprites
|
|
rts
|
|
.Inactive0
|
|
; Alternate player 0 path when it is inactive
|
|
sta WSYNC
|
|
lda #0
|
|
sta GRP0
|
|
sta COLUP0
|
|
beq .DrawSprite1 ; always taken due to lda #0
|
|
|
|
; Perform one sort iteration
|
|
; X register contains sort index (0 to NSprites-1)
|
|
SwapSprites subroutine
|
|
; First compare Priority[i] and Priority[i+1]
|
|
lda Priority0,x
|
|
cmp Priority0+1,x
|
|
bcs .CompareYPos
|
|
; If Priority[i] < Priority[i+1], do the swap
|
|
; anyway after resetting priorities
|
|
lda #0
|
|
sta Priority0,x
|
|
sta Priority0+1,x ; reset
|
|
ldy Sorted0+1,x
|
|
bcc .DoSwap ; swap due to priority
|
|
.CompareYPos
|
|
; Compare Y[i] and Y[i+1]
|
|
ldy Sorted0,x
|
|
lda YPos0,y
|
|
ldy Sorted0+1,x
|
|
cmp YPos0,y
|
|
bcc .NoSwap ; Y[i] < Y[i+1]? don't swap
|
|
.DoSwap
|
|
; Swap Sorted[i] and Sorted[i+1]
|
|
lda Sorted0,x ; A <- Sorted[i]
|
|
sty Sorted0,x ; Y -> Sorted[i]
|
|
sta Sorted0+1,x ; A -> Sorted[i+1]
|
|
.NoSwap
|
|
rts
|
|
|
|
; Read joystick movement and apply to object 0
|
|
MoveJoystick subroutine
|
|
; Move vertically
|
|
ldx YPos0
|
|
lda #%00010000 ;Up?
|
|
bit SWCHA
|
|
bne .SkipMoveUp
|
|
cpx #8
|
|
bcc .SkipMoveUp
|
|
dex
|
|
.SkipMoveUp
|
|
lda #%00100000 ;Down?
|
|
bit SWCHA
|
|
bne .SkipMoveDown
|
|
cpx #170
|
|
bcs .SkipMoveDown
|
|
inx
|
|
.SkipMoveDown
|
|
stx YPos0
|
|
; Move horizontally
|
|
ldx XPos0
|
|
lda #%01000000 ;Left?
|
|
bit SWCHA
|
|
bne .SkipMoveLeft
|
|
cpx #5
|
|
bcc .SkipMoveLeft
|
|
dex
|
|
.SkipMoveLeft
|
|
lda #%10000000 ;Right?
|
|
bit SWCHA
|
|
bne .SkipMoveRight
|
|
cpx #140
|
|
bcs .SkipMoveRight
|
|
inx
|
|
.SkipMoveRight
|
|
stx XPos0
|
|
rts
|
|
|
|
|
|
; SetHorizPos - Sets the horizontal position of an object.
|
|
; The X register contains the index of the desired object:
|
|
; X=0: player 0
|
|
; X=1: player 1
|
|
; X=2: missile 0
|
|
; X=3: missile 1
|
|
; X=4: ball
|
|
; NOTE: This version of the routine does a NEWLINE after executing
|
|
; because when the beam is at the far right side of the screen
|
|
; there is little time to do so before wrapping to the next line.
|
|
; It does NOT do a HMOVE and HCLR.
|
|
SetHorizPos subroutine
|
|
sta WSYNC ; start a new line
|
|
sec ; set carry flag
|
|
.DivideLoop
|
|
sbc #15 ; subtract 15
|
|
bcs .DivideLoop ; branch until negative
|
|
eor #7 ; calculate fine offset
|
|
asl
|
|
asl
|
|
asl
|
|
asl
|
|
sta HMP0,x ; set fine offset
|
|
sta RESP0,x ; fix coarse position
|
|
rts ; return to caller
|
|
|
|
; Pass: A = desired scanline
|
|
; Returns: Y = timer value - 1
|
|
align $10
|
|
WaitForScanline subroutine
|
|
ldy INTIM ; Fetch timer value
|
|
.Wait
|
|
cpy INTIM
|
|
beq .Wait ; Wait for it to change
|
|
sta WSYNC ; Sync with scan line
|
|
cmp Timer2Scanline,y ; lookup scanline
|
|
bcs WaitForScanline ; repeat until >=
|
|
rts
|
|
|
|
; Bitmap data "standing" position
|
|
Frame0
|
|
.byte #0
|
|
.byte #%01101100;$F6
|
|
.byte #%00101000;$86
|
|
.byte #%00101000;$86
|
|
.byte #%00111000;$86
|
|
.byte #%10111010;$C2
|
|
.byte #%10111010;$C2
|
|
.byte #%01111100;$C2
|
|
.byte #%00111000;$C2
|
|
.byte #%00111000;$16
|
|
.byte #%01000100;$16
|
|
.byte #%01111100;$16
|
|
.byte #%01111100;$18
|
|
.byte #%01010100;$18
|
|
.byte #%01111100;$18
|
|
.byte #%11111110;$F2
|
|
.byte #%00111000;$F4
|
|
|
|
; Bitmap data "throwing" position
|
|
Frame1
|
|
.byte #0
|
|
.byte #%01101100;$F6
|
|
.byte #%01000100;$86
|
|
.byte #%00101000;$86
|
|
.byte #%00111000;$86
|
|
.byte #%10111010;$C2
|
|
.byte #%10111101;$C2
|
|
.byte #%01111101;$C2
|
|
.byte #%00111001;$C2
|
|
.byte #%00111000;$16
|
|
.byte #%01101100;$16
|
|
.byte #%01111100;$16
|
|
.byte #%01111100;$18
|
|
.byte #%01010100;$18
|
|
.byte #%01111100;$18
|
|
.byte #%11111110;$F2
|
|
.byte #%00111000;$F4
|
|
|
|
; Color data for each line of sprite
|
|
ColorFrame0
|
|
.byte #17 ; height
|
|
.byte #$F6;
|
|
.byte #$86;
|
|
.byte #$86;
|
|
.byte #$86;
|
|
.byte #$C2;
|
|
.byte #$C2;
|
|
.byte #$C2;
|
|
.byte #$C2;
|
|
.byte #$16;
|
|
.byte #$16;
|
|
.byte #$16;
|
|
.byte #$18;
|
|
.byte #$18;
|
|
.byte #$18;
|
|
.byte #$F2;
|
|
.byte #$F4;
|
|
|
|
; Enemy cat-head graphics data
|
|
EnemyFrame0
|
|
.byte #0
|
|
.byte #%00111100;$AE
|
|
.byte #%01000010;$AE
|
|
.byte #%11100111;$AE
|
|
.byte #%11111111;$AC
|
|
.byte #%10011001;$8E
|
|
.byte #%01111110;$8E
|
|
.byte #%11000011;$98
|
|
.byte #%10000001;$98
|
|
|
|
; Enemy cat-head color data
|
|
EnemyColorFrame0
|
|
.byte #9 ; height
|
|
.byte #$AE;
|
|
.byte #$AC;
|
|
.byte #$A8;
|
|
.byte #$AC;
|
|
.byte #$8E;
|
|
.byte #$8E;
|
|
.byte #$98;
|
|
.byte #$94;
|
|
|
|
; Mapping of sprite objects (0-7) to sprite data
|
|
SpriteDataMap
|
|
.word Frame0,ColorFrame0
|
|
.word EnemyFrame0,EnemyColorFrame0
|
|
.word EnemyFrame0,EnemyColorFrame0
|
|
.word EnemyFrame0,EnemyColorFrame0
|
|
.word EnemyFrame0,EnemyColorFrame0
|
|
.word EnemyFrame0,EnemyColorFrame0
|
|
.word EnemyFrame0,EnemyColorFrame0
|
|
.word Frame1,ColorFrame0
|
|
|
|
; Multiplication by 4 table
|
|
; faster than tya/asl/asl/tay
|
|
MultBy4
|
|
.byte #$00,#$04,#$08,#$0c
|
|
.byte #$10,#$14,#$18,#$1c
|
|
.byte #$20,#$24,#$28,#$2c
|
|
.byte #$30,#$34,#$38,#$3c
|
|
|
|
; Timer -> Scanline table
|
|
align $100
|
|
Timer2Scanline
|
|
.byte 215, 0,214,213,212,211,210, 0,209,208,207,206,205,204, 0,203
|
|
.byte 202,201,200,199, 0,198,197,196,195,194, 0,193,192,191,190,189
|
|
.byte 188, 0,187,186,185,184,183, 0,182,181,180,179,178, 0,177,176
|
|
.byte 175,174,173,172, 0,171,170,169,168,167, 0,166,165,164,163,162
|
|
.byte 0,161,160,159,158,157,156, 0,155,154,153,152,151, 0,150,149
|
|
.byte 148,147,146, 0,145,144,143,142,141,140, 0,139,138,137,136,135
|
|
.byte 0,134,133,132,131,130, 0,129,128,127,126,125,124, 0,123,122
|
|
.byte 121,120,119, 0,118,117,116,115,114, 0,113,112,111,110,109,108
|
|
.byte 0,107,106,105,104,103, 0,102,101,100, 99, 98, 0, 97, 96, 95
|
|
.byte 94, 93, 92, 0, 91, 90, 89, 88, 87, 0, 86, 85, 84, 83, 82, 0
|
|
.byte 81, 80, 79, 78, 77, 76, 0, 75, 74, 73, 72, 71, 0, 70, 69, 68
|
|
.byte 67, 66, 0, 65, 64, 63, 62, 61, 60, 0, 59, 58, 57, 56, 55, 0
|
|
.byte 54, 53, 52, 51, 50, 0, 49, 48, 47, 46, 45, 44, 0, 43, 42, 41
|
|
.byte 40, 39, 0, 38, 37, 36, 35, 34, 0, 33, 32, 31, 30, 29, 28, 0
|
|
.byte 27, 26, 25, 24, 23, 0, 22, 21, 20, 19, 18, 0, 17, 16, 15, 14
|
|
.byte 13, 12, 0, 11, 10, 9, 8, 7, 0, 6, 5, 4, 3, 2, 0, 1
|
|
|
|
; Epilogue
|
|
org $fffc
|
|
.word Start
|
|
.word Start
|