[stella] Updated missile.bin -- TWO missiles! :^)

[Ruffin Bailey <rufbo1@xxxxxxxxxxx>]

Welp, between Kirk's recent message and Manuel's Beta Demo I finally broke
out DAsm and did my biannual night's worth of 2600 hacking.  Added another
missile to the missile.bin code that's moved by player two's joystick (at
least it works in MacStella 0.7), but I'm left with a couple of questions.

The first is pretty easy, I think.  When the two "missiles" (16 scans high
right now to make them easier to see, so to speak) are on the same scan
line, give or take, they change height.  Is that because of timing issues
regarding when I push Y into ENAM0 and ENAM1?  Forgive me; I'm not up on
timing issues just yet other than staying < 76 (?).  Time to pull back out
the timing guide and relearn my "weenie instructions".

Second... in the code I open up initializing $80 and $81, the variables
where I'm storing M0's y-position and M1's y-position, respectively, to
#$40, yet the variables start out at zero when the app starts up.  I'm
storing $80 in GRP0 to debug and view the value, so to speak, and it's sure
nuff zero to start.  What's re-/un-initializing this value?

Welp, a fun night's work while watching a movie, and a good excuse to pull
OS 9 out of the closet for a while on the iBook.  In 2004, players and
collisions!

Thanks in advance, and watch out for Mac line breaks.

Ruffin Bailey

Attachment: 2missiles.asm
Description: application/applefile

;  ------------------------------------------------------------------------
;   * Subject: [stella] Distella --> DAsm problem
;   * From: Ruffin Bailey <rufbo@xxxxxxxxxxxxx>
;   * Date: Fri, 21 Aug 98 13:55:03 -0000
;  ------------------------------------------------------------------------

; See original message post for details
;   http://www.biglist.com/lists/stella/archives/9808/msg00065.html
; dasm source.s -f3 -osource.bin

; Disassembly of missile.bin aka How to move a missile around your screen.
; Disassembled Sat Aug 15 11:32:54 1998
; Using DiStella v2.0 on a Mac, no less!
;
; Command Line: distella -pafs missile.bin
;
        processor 6502
VSYNC   =  $00
VBLANK  =  $01
WSYNC   =  $02
COLUP0  =  $06
COLUP1  =  $07
COLUPF  =  $08
COLUBK  =  $09
CTRLPF  =  $0A
PF0     =  $0D
PF1     =  $0E
GRP0    =  $1B
GRP1    =  $1C
ENAM0   =  $1D
ENAM1   =  $1E
ENABL   =  $1F
HMM0    =  $22
HMM1    =  $23
HMOVE   =  $2A
CXCLR   =  $2C
SWCHA   =  $0280
INTIM   =  $0284
TIM64T  =  $0296

       ORG $F000

START:
       SEI            ;2
       CLD            ;2
       LDA    #$40    ;2
       STA    $80     ;3	$80 is holding the value where missle zero should be shown (the "y-value")
	   				  ;		starting at $40 (64 decimal)
       STA    $81     ;3	$81 is holding the value where missle one should be shown (the "y-value")
	   				  ;		also starting at $40 (64 decimal)

       LDX    #$FF    ;2
       TXS            ;2
       LDA    #$00    ;2
LF00B: STA    VSYNC,X ;4
       DEX            ;2
       BNE    LF00B   ;2
       JSR    LF0D8   ;6
LF013: JSR    LF025   ;6
       JSR    LF03F   ;6
       JSR    LF044   ;6
       JSR    LF07D   ;6
       JSR    LF0D0   ;6
       JMP    LF013   ;3
LF025: LDX    #$00    ;2
       LDA    #$02    ;2
       STA    WSYNC   ;3
       STA    WSYNC   ;3
       STA    WSYNC   ;3
       STA    VSYNC   ;3
       STA    WSYNC   ;3
       STA    WSYNC   ;3
       LDA    #$2C    ;2
       STA    TIM64T  ;4
       STA    WSYNC   ;3
       STA    VSYNC   ;3
       RTS            ;6

LF03F: LDA    #$00    ;2
       STA    COLUBK  ;3
       RTS            ;6



LF044: LDA    #$88    ;2  setting up the colors
       STA    COLUP0  ;3  P0 is blue
       LDA    #$36    ;2
       STA    COLUPF  ;3  PF redish (won't see that here, though)
       LDA    #$D8    ;2
       STA    COLUP1  ;3  P1 yellow (Sir Not Pictured in this film)
       LDA    #$00    ;2
       STA    COLUBK  ;3  BK black
       LDA    #$00    ;2
       STA    CTRLPF  ;3

       LDA    #$00    ;2
       STA    HMM0    	;3	if there's no joystick move, m0 goes nowhere
       sta HMM1			;	set missile one's move to nothing as well

       LDA    SWCHA   ;4  SWCHA dissection
       BMI    LF065   ;2  Player 0       | Player 1
       LDY    #$F0    ;2  ===============|===============
       STY    HMM0    ;3  D7  D6  D5  D4 | D3  D2  D1  D0
LF065: ROL            ;2  rt  lt  dn  up | rt  lt  dn  up
       BMI    LF06C   ;2
       LDY    #$10    ;2  I'm using BMI to read D7 of SWCHA
       STY    HMM0    ;3  (which has been read into the accumulator)
LF06C: ROL            ;2  Then rolling the byte to the left and reading the
       BMI    LF073   ;2  next bit (D6,5,4...) with BMI since the next
       INC    $80     ;5  bit would now be D7.
       INC    $80     ;5
LF073: ROL            ;2  $80 holds the scan line that the missile
       BMI    MISSLE1CHECK   ;2  will appear on, and since I'm counting up from 1
       DEC    $80     ;5  in the screen drawing loop, I decrease $80 to move
       DEC    $80     ;5  the missile up and increase $80 to go down.

; we're going to do the same thing now with missile 1
; SWCHA's got that too!  Keep rolling left
MISSLE1CHECK

       rol	; grab the next bit      
       BMI    M1LEFT   ;2  
       LDY    #$F0    ;2  
       STY    HMM1    ;3  
M1LEFT: ROL            ;2  
       BMI    M1DOWN   ;2
       LDY    #$10    ;2 
       STY    HMM1    ;3 
M1DOWN: ROL            ;2 
       BMI    M1UP   ;2 
       INC    $81     ;5 
       INC    $81     ;5
M1UP: ROL            ;2 
       BMI    JOYDONE   ;2 
       DEC    $81     ;5 
       DEC    $81     ;5 



JOYDONE: STA    CXCLR   ;3	Clear the collision latches.




; see what's in $80 by sticking it in P1's graphic
	lda $80
	sta GRP1

       RTS            ;6  I assume the HMM0 commands are self-explanatory!  ;)


; SCREEN DRAW
LF07D: LDA    INTIM   ;4  Here's the screen draw routine.
       BNE    LF07D   ;2
       STA    WSYNC   ;3
       STA    VBLANK  ;3
       LDA    #$02    ;2
       STA    CTRLPF  ;3
       LDX    #$01    ;2
       STA    HMOVE   ;3 DON'T FORGET TO HIT HMOVE!! or the object won't move
	   				  ;  horizontally.  I might have forgotten that for a while,
					  ;  causing nearly unbearable psychological pain.


LF08E: STA    WSYNC   ;3 
       INX            ;2 	Increase the line counter
       BEQ    endScreen   ;2


LF0B2: INX            ;2
       
	   ldy #$00
	   txa	; get the line count in the accum
	   sbc $80
	   adc #$10
	   bcc nextCheck
	   ldy #$02
nextCheck
       sty ENAM0
	   ldy #$00
	   txa
	   sbc $81
	   adc #$10
	   bcc beyondThis
	   ldy #$02
beyondThis
       sty ENAM1
	   
	   CPX    #$C1    ;2
       BEQ endScreen
	   STA WSYNC	;3 looks like I was missing this line
	   JMP LF0B2   ;2


; Clean everything out and skip on out of the
endScreen: LDA    #$02    ;2
       STA    WSYNC   ;3
       STA    VBLANK  ;3
       LDY    #$00    ;2
       STY    PF0     ;3
       STY    PF1     ;3
       STY    PF1     ;3
       STY    GRP0    ;3
       STY    GRP1    ;3
       STY    ENAM0   ;3
       STY    ENAM1   ;3
       STY    ENABL   ;3
       RTS            ;6

LF0D0: LDX    #$1E    ;2
LF0D2: STA    WSYNC   ;3
       DEX            ;2
       BNE    LF0D2   ;2
       RTS            ;6

LF0D8: LDA    #$00    ;2
       STA    $90     ;3
       RTS            ;6

        org $FFFC
        .word START
        .word START

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