mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-11-30 06:50:39 +00:00
568 lines
15 KiB
PHP
568 lines
15 KiB
PHP
|
|
|
|
; MULTISPRITE LIBRARY
|
|
|
|
; 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.
|
|
|
|
; There are two separate multisprite kernels:
|
|
|
|
; MSpriteDraw1 - Single-line sprites, no playfield.
|
|
; This kernel requires TIMER_TABLE_SETUP at the 0th
|
|
; scanline, as it uses the timer to figure out the
|
|
; current scanline. No vertical clipping is performed.
|
|
; In fact, if sprites go past the bottom, it will
|
|
; mess up the vertical sync.
|
|
|
|
; MSpriteDraw2 - Double-line sprites with playfield.
|
|
; The playfield is updated and the sprites are positioned
|
|
; in 8-scanline segments.
|
|
; This kernel uses the timer internally, but does not
|
|
; use the timer table or TIMER_TABLE_SETUP.
|
|
; Sprites are clipped on the bottom edge, but disappear
|
|
; off the top edge.
|
|
|
|
; Your program must call MSpriteInit when it starts,
|
|
; and MSpriteFrame between every frame.
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
seg.u Variables
|
|
|
|
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
|
|
Shape0 ds NSprites ; shape index
|
|
Flags0 ds NSprites ; NUSIZ and reflection flags
|
|
Sorted0 ds NSprites ; sorted list of sprite indices
|
|
Priority0 ds NSprites ; sprite priority list, if missed
|
|
|
|
;MinYDist equ 0 ; min. Y distance to consider sprite (not used)
|
|
;MinYPos equ 1 ; TODO???
|
|
MinYDist equ 6 ; min. Y distance to consider sprite
|
|
MinYPos equ 2+MinYDist
|
|
|
|
PF0Ptr word ; pointer to playfield data
|
|
PF1Ptr word ; pointer to playfield data
|
|
PF2Ptr word ; pointer to playfield data
|
|
PFIndex byte ; offset into playfield array
|
|
PFCount byte ; lines left in this playfield segment
|
|
|
|
; temporary values for kernel
|
|
; TODO: share with global temporaries
|
|
Temp byte
|
|
Colp0 byte
|
|
Colp1 byte
|
|
tmpPF0 byte
|
|
tmpPF1 byte
|
|
tmpPF2 byte
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
seg Code
|
|
|
|
; call at start of program
|
|
MSpriteInit subroutine
|
|
; Initialize initial sort order
|
|
ldx #0
|
|
.loop
|
|
txa
|
|
sta Sorted0,x
|
|
inx
|
|
cpx #NSprites
|
|
bne .loop
|
|
rts
|
|
|
|
; call between frames
|
|
MSpriteFrame subroutine
|
|
; 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
|
|
jsr ResetCounters
|
|
stx CurIndex
|
|
rts
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
; SINGLE-LINE KERNEL
|
|
|
|
MSpriteDraw1 subroutine
|
|
.NextFindSprite
|
|
; Try to schedule sprites to both players
|
|
jsr FindAnotherSprite
|
|
; Apply fine offsets
|
|
sta WSYNC ; start next scanline
|
|
sta HMOVE ; apply the previous fine position(s)
|
|
sta HMCLR ; clear motion registers
|
|
ldx #0
|
|
stx VDELP0 ; set vertical delay off
|
|
stx VDELP1 ; set vertical delay off
|
|
; See if time to draw
|
|
jsr DrawSprites1
|
|
; Repeat until all scanlines drawn
|
|
lda INTIM
|
|
cmp #$1f
|
|
bcs .NextFindSprite
|
|
lda #191
|
|
jmp WaitForScanline
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
; DOUBLE-LINE KERNEL WITH BACKGROUND
|
|
|
|
MSpritePrefill2 subroutine
|
|
lda #0
|
|
sta Scanline
|
|
jsr FindAnotherSprite2
|
|
jsr FindAnotherSprite2
|
|
sta WSYNC
|
|
sta HMOVE ; apply the previous fine position(s)
|
|
sta HMCLR ; clear motion registers
|
|
rts
|
|
|
|
MSpriteDraw2 subroutine
|
|
sta WSYNC
|
|
sta PFIndex ; 24 * 4 scanlines = 96 2xlines
|
|
lda #0
|
|
sta PFCount
|
|
sta VDELP1
|
|
lda #1
|
|
sta VDELP0 ; updates to GRP0 will be delayed
|
|
jmp .NewSprites
|
|
.Draw8Lines
|
|
; Phase 0: Fetch PF0 byte
|
|
jsr DrawSprites2
|
|
ldy PFIndex
|
|
lda (PF0Ptr),y ; load PF0
|
|
sta tmpPF0
|
|
; Phase 1: Fetch PF1 byte
|
|
jsr DrawSprites2
|
|
ldy PFIndex
|
|
lda (PF1Ptr),y ; load PF1
|
|
sta tmpPF1
|
|
; Phase 2: Fetch PF2 byte
|
|
jsr DrawSprites2
|
|
ldy PFIndex
|
|
lda (PF2Ptr),y ; load PF2
|
|
sty PFIndex
|
|
sta tmpPF2
|
|
; Phase 3: Write PF0/PF1/PF2 registers
|
|
jsr DrawSprites2
|
|
lda tmpPF0
|
|
sta PF0
|
|
lda tmpPF1
|
|
sta PF1
|
|
lda tmpPF2
|
|
sta PF2
|
|
; Go to next scanline, unless playfield is done
|
|
; or unless this segment is done
|
|
dec PFIndex
|
|
bmi .NoMoreLines ; playfield done
|
|
dec PFCount
|
|
bpl .Draw8Lines ; keep drawing
|
|
; done drawing, reset player counters
|
|
jsr ResetCounters
|
|
.NewSprites
|
|
lda PFIndex
|
|
asl
|
|
asl
|
|
eor #$7f
|
|
sbc #34
|
|
sta Scanline ; Scanlines = 127 - PFIndex*4
|
|
; Set up 0-2 player objects taking up to 8 scanlines
|
|
TIMER_SETUP 7
|
|
jsr FindAnotherSprite2
|
|
jsr CalcSpriteEnd
|
|
; Update playfield
|
|
ldy PFIndex
|
|
lda (PF0Ptr),y ; load PF0 -> X
|
|
tax
|
|
lda (PF1Ptr),y ; load PF1 -> tmp
|
|
sta tmpPF1
|
|
lda (PF2Ptr),y ; load PF2 -> Y
|
|
tay
|
|
; Apply fine offsets
|
|
TIMER_WAIT ; wait for 8th scanlines and WSYNC
|
|
sta HMOVE ; apply the previous fine position(s)
|
|
sta HMCLR ; clear motion registers
|
|
; Store playfield registers
|
|
stx PF0
|
|
lda tmpPF1
|
|
sta PF1
|
|
sty PF2
|
|
dec PFIndex ; no more playfield?
|
|
bmi .NoMoreLines
|
|
lda PFCount
|
|
bne .Draw8Lines
|
|
sta WSYNC ; one more line
|
|
beq .NewSprites
|
|
.NoMoreLines
|
|
rts
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
; SPRITE DRAWING ROUTINES
|
|
; used by kernels
|
|
; need to set SIndx0/1, SSize0/1, PData0/1, PColr0/1
|
|
; all players must already be setup
|
|
|
|
; called by single-line kernel
|
|
DrawSprites1 subroutine
|
|
; Wait for next precise scanline
|
|
lda #0 ; 0 = wait for next
|
|
.AnotherScanline
|
|
jsr WaitForScanline
|
|
lda Timer2Scanline,y ; lookup scanline #
|
|
beq .AnotherScanline ; not if zero!
|
|
sta Scanline ; save it
|
|
DrawSprites1a
|
|
; 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
|
|
DrawSprites1b
|
|
.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
|
|
jsr ResetCounters
|
|
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
|
|
|
|
; called by 2-line kernel
|
|
DrawSprites2 subroutine
|
|
; Fetch sprite 0 values
|
|
lda SSize0 ; height in 2xlines
|
|
sec
|
|
isb SIndx0 ; INC yp0, then SBC yp0
|
|
bcs DoDraw0 ; inside bounds?
|
|
lda #0 ; no, load the padding offset (0)
|
|
DoDraw0
|
|
tay ; -> Y
|
|
lda (PColr0),y ; color for both lines
|
|
sta Colp0 ; -> colp0
|
|
lda (PData0),y ; bitmap for first line
|
|
sta GRP0 ; -> [GRP0] (delayed due to VDEL)
|
|
; Fetch sprite 1 values
|
|
lda SSize1 ; height in 2xlines
|
|
sec
|
|
isb SIndx1 ; INC yp0, then SBC yp0
|
|
bcs DoDraw1 ; inside bounds?
|
|
lda #0 ; no, load the padding offset (0)
|
|
DoDraw1
|
|
tay ; -> Y
|
|
lda (PColr1),y ; color for both lines
|
|
tax
|
|
lda (PData1),y ; bitmap for first line
|
|
tay
|
|
; WSYNC and store sprite values
|
|
lda Colp0
|
|
; still have about 30 cycles left...
|
|
sta WSYNC
|
|
sty GRP1 ; GRP0 is also updated due to VDELP0 flag
|
|
stx COLUP1
|
|
sta COLUP0
|
|
; Return to caller
|
|
rts
|
|
|
|
CalcSpriteEnd subroutine
|
|
; Calculate # of lines to draw for each sprite
|
|
; SIndx = 255 - ypos + scanline
|
|
lda SIndx0
|
|
beq .zero0
|
|
sec
|
|
sbc Scanline
|
|
eor #$ff
|
|
sta SIndx0
|
|
sec
|
|
sbc SSize0
|
|
.zero0
|
|
sta Temp
|
|
lda SIndx1
|
|
beq .zero1
|
|
sec
|
|
sbc Scanline
|
|
eor #$ff
|
|
sta SIndx1
|
|
sec
|
|
sbc SSize1
|
|
cmp Temp
|
|
bmi .cmp1 ; sindx0 < sindx1?
|
|
.zero1
|
|
lda Temp ; load higher number
|
|
.cmp1
|
|
; Compute the number of 8x lines in this section
|
|
eor #$ff
|
|
clc
|
|
adc #1
|
|
lsr
|
|
lsr
|
|
sta PFCount
|
|
rts
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
; COMMON ROUTINES
|
|
|
|
ResetCounters subroutine
|
|
ldx #0
|
|
stx SSize0
|
|
stx SSize1
|
|
stx SIndx0
|
|
stx SIndx1
|
|
rts
|
|
|
|
; 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
|
|
FindAnotherSprite2 ; alternate entry point when scanline known
|
|
; 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.
|
|
; TODO: disable for 2-line sprite kernel
|
|
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
|
|
; Set player 1 reflection/number/size flags
|
|
lda Flags0,y
|
|
sta REFP1 ; reflection flag
|
|
sta NUSIZ1 ; number-size
|
|
; Get index into SpriteDataMap (index * 4)
|
|
lda Shape0,y
|
|
asl
|
|
asl
|
|
tax
|
|
; 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
|
|
inc SSize1 ; +1 to height
|
|
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
|
|
lda Flags0,y
|
|
sta REFP0 ; reflection flag
|
|
sta NUSIZ0 ; number-size
|
|
lda Shape0,y
|
|
asl
|
|
asl
|
|
tax
|
|
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
|
|
inc SSize0 ; +1 to height
|
|
.SetupDone
|
|
inc CurIndex ; go to next sprite in sort order
|
|
.NoNearSprite
|
|
rts
|
|
|
|
; 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
|
|
|