14 replies to this topic

[Primordial Ooze]

I'm trying to get a missile to fire from the player 0 when the fire button is pressed. I managed to get the missile to appear when the player presses the fire button, but it doesn't appear where expected at the front of player 0. Additionally if player 0 moves the missile doesn't fire at player 0's new position. Any ideas?

	; First we have to tell DASM that we're 
	; coding to the 6502:

		processor 6502

	; Then we have to include the "vcs.h" file
	; that includes all the "convenience names"
	; for all the special atari memory locations...

		include "vcs.h"

		include "macro.h"

	;**************************************************************************

		SEG.U vars; tells dasm that the proceding instructions are variable declarations
				
		ORG $80; tells dasm to start placing our variables in memory location 0080

player0x = $80; player0's x position

player0y = $81; player0's y position

shotfired = $82

visibleplayer0line = $83; current visible line for player 0

player0buffer = $84; player buffer for holding the line to draw for the player graphic

missile0x = $85; missile 0's x position

missile0y = $86; missile 0's y position

visiblemissileline = $87; line where missile is drawn

lives = $88; player lives

score = $89; game score

		SEG code

	; tell DASM where in the memory to place
	; all the code that follows...$F000 is the preferred
	; spot where it goes to make an atari program

		ORG $F000

	; we'll call the start of our program "Start".
Start

		SEI	; Disable Any Interrupts
		CLD	  ; Clear BCD math bit.
		LDX #$FF; put X to the top...
		TXS	; ...and use it reset the stack pointer

	; Clear RAM and all TIA registers

		lda #0	;Put Zero into A, X is at $FF

Clear		   sta 0,x	;Now, this doesn't mean what you think...

		dex	;decrement X (decrease X by one)

		bne Clear;if the last command resulted in something 
			 ;that's "N"ot "Equal" to Zero, branch back
			 ;to "Clear"

	;---------------------
	; One Time Initiations

		lda #$FA

		sta COLUBK; set the background color to sandy brown

		lda #$04

		sta COLUP0; set the player color to silver

		lda #$B8

		sta COLUPF; set the playfield color to ooze green

	;---------------------
	; Start New Game

StartNewGame	lda #105

		sta player0x; player0's initial x position

		lda #40

		sta player0y; player0's initial y position

		lda #0

		sta shotfired; set shotfired inital value to 0

		lda #0

		sta missile0x; missile 0's initial x position

		lda #0

		sta missile0y; missile 0's initial y position

		lda #3

		sta lives; start the player with 3 lives

		lda #0

		sta score; set high bit of score inital value to 0

		lda #0

		sta score+1; set nibble bit of score inital value to 0

		lda #0

		sta score+2; low bit of score inital value to 0

GameLoop

	;*********************** VERTICAL SYNC HANDLER

		lda  #2

		sta VSYNC; Sync it up you damn dirty television!
			; and that vsync on needs to be held for three scanlines...
			; count with me here,
		sta WSYNC; one... (our program waited for the first scanline to finish...)

		sta WSYNC; two...

		sta WSYNC; three...

		lda  #43;load 43 (decimal) in the accumulator

		sta  TIM64T;and store that in the timer

		lda #0	; Zero out the VSYNC
		sta  VSYNC ; cause that time is over

	;*********************** Joystick Input
	; Here we check for left and right
	; joystick input

		lda #%01000000; a 0 in bit D6 means the joystick was pushed left

		bit SWCHA; was the joystick moved left?

		bne SkipPlayer0MoveLeft; if bit D6 isn't equal to 0 then jump to SkipPlayer0MoveLeft

		dec player0x; otherwise the player moved the joystick left so deincrement the players position by one

SkipPlayer0MoveLeft
	
		lda #%10000000; a 0 in bit D7 means the joystick was pushed right

		bit SWCHA ; was the joystick moved right?

		bne SkipPlayer0MoveRight;if bit D6 isn't equal to 0 then jump to SkipPlayer0MoveRight

		inc player0x;otherwise the player moved the joystick right so increment the players position by one

SkipPlayer0MoveRight

		ldx player0x; load the players position into the x register

		jsr PositionSprite; jump to our Position Sprite Subroutine to position the player

		lda #0		; zero out the buffer

		sta player0buffer; just in case

		lda INPT4; read button input

		bmi ButtonNotPressed; skip if button not pressed

		lda #1	; must be pressed, set accumulator to 1 (true)

		sta shotfired; shotFired to true from value in acumulator

		lda player0x; load player 0's x position

		sta missile0x; and set it to the missile 0's x position

		lda player0y; load player 0's y position

		sta missile0y; and set it to missile 0's y position

		lda #2	; set the acumulator to 2

		sed	; set decimal mode

		clc	; clear carry status

		adc missile0y; set missile 0's position just above player 0

		cld	; clear decimal mode 

ButtonNotPressed


	;*********************** VERTICAL BLANK WAIT-ER
WaitForVblankEnd
	
		lda INTIM;load timer...

		BNE WaitForVblankEnd;killing time if the timer's not yet zero

		ldy #191 ;Y is going to hold how many lines we have to do
			;...we're going to count scanlines here. theoretically
			; since this example is ass simple, we could just repeat
			; the timer trick, but often its important to know 
			; just what scan line we're at.

		sta WSYNC;We do a WSYNC just before that so we don't turn on

		sta VBLANK;End the VBLANK period with the zero

	;*********************** Scan line Loop
ScanLoop

		sta WSYNC ;Wait for the previous line to finish

		lda player0buffer;buffer was set during last scanline

		sta GRP0		;put it as graphics now

		cpy player0y; compare the player's y position

		bne SkipActivatePlayer0; if it isn't 0 then jump to SkipActivePlayer0

		lda #5	; otherwise load our accumulatior with the number of lines to draw

		sta visibleplayer0line; and store it 

SkipActivatePlayer0

	;set player buffer to all zeros for this line, and then see if 
	;we need to load it with graphic data

		lda #0		

		sta player0buffer  ;set buffer, not GRP0

	;if the VisiblePlayerLine is non zero,
	;we're drawing it next line

		ldx visibleplayer0line;check the visible player line...

		beq FinishPlayer;skip the drawing if its zero...

		lda player0-1,X	;otherwise, load the correct line from player0
				;section below... it's off by 1 though, since at zero
				;we stop drawing
		sta player0buffer;put that line as player graphic for the next line

		dec visibleplayer0line;and decrement the line count

FinishPlayer

	; here the idea is that VisibleMissileLine
	; is zero if the line isn't being drawn now,
	; otherwise it's however many lines we have to go

CheckActivateMissile

		cpy missile0y

		bne SkipActivateMissile

		lda #8

		sta visiblemissileline

SkipActivateMissile

	;turn missile off then see if it's turned on

		lda #0	

		sta ENAM0

	;if the VisibleMissileLine is non zero,
	;we're drawing it

		lda visiblemissileline

		beq FinishMissile
	
		lda #2		

		sta ENAM0

		dec visiblemissileline

		inc missile0y
 
FinishMissile

		dey	;subtract one off the line counter thingy

		bne ScanLoop;and repeat if we're not finished with all the scanlines.

		lda #2	;#2 for the VBLANK...

		sta WSYNC  ;Finish this final scanline.

		sta VBLANK ; Make TIA output invisible for the overscan, 
			; (and keep it that way for the vsync and vblank)

	;***************************** OVERSCAN CALCULATIONS
	;I'm just gonna count off the 30 lines of the overscan.
	;You could do more program code if you wanted to.

		ldx #30	;store 30

OverScanWait

		sta WSYNC

		dex

		bne OverScanWait

		jmp  GameLoop	 ;Continue this loop forver! Back to the code for the vsync etc

Divide15

.POS	SET 0			; start our counter at 0

		REPEAT 256	; repeat this loop 256 times

		.byte (.POS / 15) + 1; put that counter value / 15 in the ROM

.POS	SET .POS + 1		; increment our counter by one

		REPEND		; repeat the loop if neccessary

PositionSprite

		sta WSYNC	; wait for vsync

	; Pass X register holding desired X position of sprite!

		lda Divide15,x; xPosition / 15

		tax	; transfer the value in the accumulator to the x register

SimpleLoop	dex	; deincrement x by 1

		bne SimpleLoop; continue looping if the x register isn't 0

		sta RESP0; start drawing the sprite

		rts	; return from the subroutine

		; here's the actual player0 graphic

player0
			.byte #%00011000
			.byte #%00111100
			.byte #%11111111
			.byte #%00111100
			.byte #%00011000

update_low_score_digits

		sed 	; set decimal mode

		clc 	; clear carry status

		adc score ; add accumulator to score's low digits w/carry.

		sta score; store the updated low digits.

	;NOTE: Here's where a triple-NOP comes into play.  We need
	;a seperate entrypoint to this subroutine for cases where the
	;low digits are ignored (like adding 100, for example).  But
	;carry status and BCD mode need to have been setup.  So,
	;place the triple-NOP opcode here to skip over them...
	;with A reset at zero so that only carry affects the score:

		lda #0 	; reset the accumulator...

		.byte $0C ; ...and skip over the next 2 bytes

update_middle_score_digits

		sed 	; set decimal mode

		clc; clear carry status

		adc score+1 ; add accumulator to score's middle digits w/carry.

		sta score+1 ; store the updated middle digits

	;Here we do the same thing (in case the game needs to add 10,000...
	;or 100,000 increments to a score (ignoring all the lower ones)
	;Again, A is reset at zero so that only carry affects the score:

		lda #0	; reset the accumulator...

		.byte $0C; ...and skip over the next 2 bytes

update_high_score_digits

		sed	; set decimal mode

		clc	; clear carry status

		adc score+1; add accumulator to score's high digits w/carry.

		sta score+2; store the last 2 digits

	;With the score updated, clear BCD mode and exit via RTS:

		cld	; clear decimal mode

		rts	; and return to the program line that called this routine.

	;*************************************************************************
	; Interrupt Vectors

		ORG $FFFA

InterruptVectors

		.word Start		 ; NMI

		.word Start		 ; RESET

		.word Start		 ; IRQ

		END

[Rybags]

I'm not up to scratch on the 2600, but...

  lda player0y; load player 0's y position
  sta missile0y; and set it to missile 0's y position
  lda #2   ; set the acumulator to 2
  sed   ; set decimal mode
  clc   ; clear carry status
  adc missile0y; set missile 0's position just above player 0
  cld   ; clear decimal mode 
ButtonNotPressed
   ;*********************** VERTICAL BLANK WAIT-ER
WaitForVblankEnd
			lda INTIM;load timer...

Why are you using Decimal mode for calculating Y postition?
Also, you're doing the add, but not storing it anywhere.

Another unrelated hint... with flags, rather than testing them by doing a LDA... BEQ - it's useful to just use the top 2 bits of a byte to signify things, then you can just test with the BIT instruction, without having to lose contents of a register.

[Primordial Ooze]

Thanks, i fixed the code and now i got it to appear above the player sprite. However for some reason it doesn't fire from player 0's x position and instead fires from the same exact location every time. I have posted the code for reference.

	; First we have to tell DASM that we're 
	; coding to the 6502:

		processor 6502

	; Then we have to include the "vcs.h" file
	; that includes all the "convenience names"
	; for all the special atari memory locations...

		include "vcs.h"

		include "macro.h"

	;**************************************************************************

		SEG.U vars; tells dasm that the proceding instructions are variable declarations
				
		ORG $80; tells dasm to start placing our variables in memory location 0080

player0x = $80; player0's x position

player0y = $81; player0's y position

visibleplayer0line = $82; current visible line for player 0

player0buffer = $83; player buffer for holding the line to draw for the player graphic

missile0x = $84; missile 0's x position

missile0y = $85; missile 0's y position

visiblemissile0line = $86; line where missile is drawn

lives = $87; player lives

score = $88; game score

		SEG code

	; tell DASM where in the memory to place
	; all the code that follows...$F000 is the preferred
	; spot where it goes to make an atari program

		ORG $F000

	; we'll call the start of our program "Start".
Start

		SEI	; Disable Any Interrupts
		CLD	  ; Clear BCD math bit.
		LDX #$FF; put X to the top...
		TXS	; ...and use it reset the stack pointer

	; Clear RAM and all TIA registers

		lda #0	;Put Zero into A, X is at $FF

Clear		   sta 0,x	;Now, this doesn't mean what you think...

		dex	;decrement X (decrease X by one)

		bne Clear;if the last command resulted in something 
			 ;that's "N"ot "Equal" to Zero, branch back
			 ;to "Clear"

	;---------------------
	; One Time Initiations

		lda #$FA

		sta COLUBK; set the background color to sandy brown

		lda #$04

		sta COLUP0; set the player color to silver

		lda #$B8

		sta COLUPF; set the playfield color to ooze green

	;---------------------
	; Start New Game

StartNewGame	lda #105

		sta player0x; player0's initial x position

		lda #40

		sta player0y; player0's initial y position

		lda #0

		sta missile0x; missile 0's initial x position

		lda #0

		sta missile0y; missile 0's initial y position

		lda #3

		sta lives; start the player with 3 lives

		lda #0

		sta score; set high bit of score inital value to 0

		lda #0

		sta score+1; set nibble bit of score inital value to 0

		lda #0

		sta score+2; low bit of score inital value to 0

GameLoop

	;*********************** VERTICAL SYNC HANDLER

		lda  #2

		sta VSYNC; Sync it up you damn dirty television!
			; and that vsync on needs to be held for three scanlines...
			; count with me here,
		sta WSYNC; one... (our program waited for the first scanline to finish...)

		sta WSYNC; two...

		sta WSYNC; three...

		lda  #43;load 43 (decimal) in the accumulator

		sta  TIM64T;and store that in the timer

		lda #0	; Zero out the VSYNC
		sta  VSYNC ; cause that time is over

	;*********************** Joystick Input
	; Here we check for left and right
	; joystick input

		lda #%01000000; a 0 in bit D6 means the joystick was pushed left

		bit SWCHA; was the joystick moved left?

		bne SkipPlayer0MoveLeft; if bit D6 isn't equal to 0 then jump to SkipPlayer0MoveLeft

		dec player0x; otherwise the player moved the joystick left so deincrement the players position by one

SkipPlayer0MoveLeft
	
		lda #%10000000; a 0 in bit D7 means the joystick was pushed right

		bit SWCHA ; was the joystick moved right?

		bne SkipPlayer0MoveRight;if bit D6 isn't equal to 0 then jump to SkipPlayer0MoveRight

		inc player0x;otherwise the player moved the joystick right so increment the players position by one

SkipPlayer0MoveRight

		ldx player0x; load the players position into the x register

		jsr PositionSprite; jump to our Position Sprite Subroutine to position the player

		lda #0		; zero out the buffer

		sta player0buffer; just in case

		lda INPT4; read button input

		bmi ButtonNotPressed; skip if button not pressed

		lda player0x; load player 0's x position

		sta missile0x; and set it to the missile 0's x position

		lda player0y; load player 0's y position

		sta missile0y; and set it to missile 0's y position

		lda #8	; set the acumulator to 8

		clc	; clear carry status

		adc missile0y; add 2 to missile 0's y position so it's above player 0

		sta missile0y; and set it to missile 0's y position

ButtonNotPressed


	;*********************** VERTICAL BLANK WAIT-ER
WaitForVblankEnd
	
		lda INTIM;load timer...

		BNE WaitForVblankEnd;killing time if the timer's not yet zero

		ldy #191 ;Y is going to hold how many lines we have to do
			;...we're going to count scanlines here. theoretically
			; since this example is ass simple, we could just repeat
			; the timer trick, but often its important to know 
			; just what scan line we're at.

		sta WSYNC;We do a WSYNC just before that so we don't turn on

		sta VBLANK;End the VBLANK period with the zero

	;*********************** Scan line Loop
ScanLoop

		sta WSYNC ;Wait for the previous line to finish

		lda player0buffer;buffer was set during last scanline

		sta GRP0		;put it as graphics now

		cpy player0y; compare the player's y position

		bne SkipActivatePlayer0; if it isn't 0 then jump to SkipActivePlayer0

		lda #5	; otherwise load our accumulatior with the number of lines to draw

		sta visibleplayer0line; and store it 

SkipActivatePlayer0

	;set player buffer to all zeros for this line, and then see if 
	;we need to load it with graphic data

		lda #0		

		sta player0buffer  ;set buffer, not GRP0

	;if the VisiblePlayerLine is non zero,
	;we're drawing it next line

		ldx visibleplayer0line;check the visible player line...

		beq FinishPlayer;skip the drawing if its zero...

		lda player0-1,X	;otherwise, load the correct line from player0
				;section below... it's off by 1 though, since at zero
				;we stop drawing
		sta player0buffer;put that line as player graphic for the next line

		dec visibleplayer0line;and decrement the line count

FinishPlayer

	; here the idea is that visiblemissile0line
	; is zero if the line isn't being drawn now,
	; otherwise it's however many lines we have to go

CheckActivateMissile

		cpy missile0y; is missile 0's y position the same as the current scanline?

		bne SkipActivateMissile; if it isn't then don't set missle 0's visible lines

		lda #8		; otherwise set the missiles visible lines to 8

		sta visiblemissile0line; and store it in the visiblemissileline

SkipActivateMissile

	;turn missile off then see if it's turned on

		lda #0

		sta ENAM0; disable the missile

	;if the visiblemissile0line is non zero,
	;we're drawing it

		lda visiblemissile0line; if the visiblemissle line is zero

		beq FinishMissile; don't draw the missile
	
		lda #2		; otherwise set the accumulator to 2		

		sta ENAM0	; and draw the missile

		dec visiblemissile0line; and decrement the visiblemissileline by 1

		inc missile0y	; increment missle 0's y position by 1
 
FinishMissile

		dey	;subtract one off the line counter thingy

		bne ScanLoop;and repeat if we're not finished with all the scanlines.

		lda #2	;#2 for the VBLANK...

		sta WSYNC  ;Finish this final scanline.

		sta VBLANK ; Make TIA output invisible for the overscan, 
			; (and keep it that way for the vsync and vblank)

	;***************************** OVERSCAN CALCULATIONS
	;I'm just gonna count off the 30 lines of the overscan.
	;You could do more program code if you wanted to.

		ldx #30	;store 30

OverScanWait

		sta WSYNC

		dex

		bne OverScanWait

		jmp  GameLoop	 ;Continue this loop forver! Back to the code for the vsync etc

Divide15

.POS	SET 0			; start our counter at 0

		REPEAT 256	; repeat this loop 256 times

		.byte (.POS / 15) + 1; put that counter value / 15 in the ROM

.POS	SET .POS + 1		; increment our counter by one

		REPEND		; repeat the loop if neccessary

PositionSprite

		sta WSYNC	; wait for vsync

	; Pass X register holding desired X position of sprite!

		lda Divide15,x; xPosition / 15

		tax	; transfer the value in the accumulator to the x register

SimpleLoop	dex	; deincrement x by 1

		bne SimpleLoop; continue looping if the x register isn't 0

		sta RESP0; start drawing the sprite

		rts	; return from the subroutine

		; here's the actual player0 graphic

player0
			.byte #%00011000
			.byte #%00111100
			.byte #%11111111
			.byte #%00111100
			.byte #%00011000

update_low_score_digits

		sed 	; set decimal mode

		clc 	; clear carry status

		adc score ; add accumulator to score's low digits w/carry.

		sta score; store the updated low digits.

	;NOTE: Here's where a triple-NOP comes into play.  We need
	;a seperate entrypoint to this subroutine for cases where the
	;low digits are ignored (like adding 100, for example).  But
	;carry status and BCD mode need to have been setup.  So,
	;place the triple-NOP opcode here to skip over them...
	;with A reset at zero so that only carry affects the score:

		lda #0 	; reset the accumulator...

		.byte $0C ; ...and skip over the next 2 bytes

update_middle_score_digits

		sed 	; set decimal mode

		clc; clear carry status

		adc score+1 ; add accumulator to score's middle digits w/carry.

		sta score+1 ; store the updated middle digits

	;Here we do the same thing (in case the game needs to add 10,000...
	;or 100,000 increments to a score (ignoring all the lower ones)
	;Again, A is reset at zero so that only carry affects the score:

		lda #0	; reset the accumulator...

		.byte $0C; ...and skip over the next 2 bytes

update_high_score_digits

		sed	; set decimal mode

		clc	; clear carry status

		adc score+1; add accumulator to score's high digits w/carry.

		sta score+2; store the last 2 digits

	;With the score updated, clear BCD mode and exit via RTS:

		cld	; clear decimal mode

		rts	; and return to the program line that called this routine.

	;*************************************************************************
	; Interrupt Vectors

		ORG $FFFA

InterruptVectors

		.word Start		 ; NMI

		.word Start		 ; RESET

		.word Start		 ; IRQ

		END

Sincerely,

Primordial Ooze

Edited by Primordial Ooze, Sun Feb 22, 2009 7:11 PM.

[Wickeycolumbus]

Your problem is that you never reposition the missile. No matter what you store in missile x, it will never move horizontally. You should probably get write/find a universal horizontal positioning routine.

this is the one I use:

PositionSprites
		sta HMCLR
		sec
		sta WSYNC		 
PositionSpriteLoop
		sbc	#15
		bcs	PositionSpriteLoop 

		eor	#7		 
		asl
		asl
		asl
		asl			   

		sta.wx HMP0,X	 
		sta	RESP0,X   
		sta	WSYNC	  
		sta	HMOVE	 
		rts

all you do is load the horizontal position to the accumulator, load the sprite # in X (0 for P0, 1 for P1, 2 for M0, 3 for M1, 4 for BL), and jsr PositionSprites. it takes 2 lines, and you have to put a WSYNC write in between calls like this:

	lda player0x
	ldx #0
	jsr PositionSprites

	sta WSYNC

	lda missile0x
	ldx #2
	jsr PositionSprites

the WSYNC write is required because of a hardware bug of the TIA that requires a 24 cycle delay after an HMOVE before HMxx writes. It will work fine on an emulator without the WSYNC write, but there will be unpredictable results on the real thing.

Edited by Wickeycolumbus, Sun Feb 22, 2009 7:32 PM.

[Primordial Ooze]

Thanks, but it still doesn't quite work. If you hold the fire button down and move the player towards the left after you reach the middle left you will notice missile 0 will "cave in" into player 0's sprite and if you continue moving left the missile will be almost completely merged with player 0's sprite and stops working altogether. If you move towards the right, everything works as normal. Any ideas?

; First we have to tell DASM that we're 
; coding to the 6502:

		processor 6502

; Then we have to include the "vcs.h" file
; that includes all the "convenience names"
; for all the special atari memory locations...

		include "vcs.h"

		include "macro.h"

;**************************************************************************

		SEG.U vars; tells dasm that the proceding instructions are variable declarations
				
		ORG $80; tells dasm to start placing our variables in memory location 0080

player0x = $80; player0's x position

player0y = $81; player0's y position

visibleplayer0line = $82; current visible line for player 0

player0buffer = $83; player buffer for holding the line to draw for the player graphic

missile0x = $84; missile 0's x position

missile0y = $85; missile 0's y position

visiblemissile0line = $86; line where missile is drawn

lives = $87; player lives

score = $88; game score

		SEG code

; tell DASM where in the memory to place
; all the code that follows...$F000 is the preferred
; spot where it goes to make an atari program

		ORG $F000

; we'll call the start of our program "Start".
Start

		SEI; Disable Any Interrupts
		CLD	; Clear BCD math bit.
		LDX #$FF; put X to the top...
		TXS; ...and use it reset the stack pointer

; Clear RAM and all TIA registers

		lda #0;Put Zero into A, X is at $FF

Clear		   sta 0,x;Now, this doesn't mean what you think...

		dex;decrement X (decrease X by one)

		bne Clear;if the last command resulted in something 
		;that's "N"ot "Equal" to Zero, branch back
		;to "Clear"

;---------------------
; One Time Initiations

		lda #$FA

		sta COLUBK; set the background color to sandy brown

		lda #$04

		sta COLUP0; set the player color to silver

		lda #$B8

		sta COLUPF; set the playfield color to ooze green

;---------------------
; Start New Game

StartNewGame	lda #105

		sta player0x; player0's initial x position

		lda #40

		sta player0y; player0's initial y position

		lda #0

		sta missile0x; missile 0's initial x position

		lda #0

		sta missile0y; missile 0's initial y position

		lda #3

		sta lives; start the player with 3 lives

		lda #0

		sta score; set high bit of score inital value to 0

		lda #0

		sta score+1; set nibble bit of score inital value to 0

		lda #0

		sta score+2; low bit of score inital value to 0

GameLoop

;*********************** VERTICAL SYNC HANDLER

		lda  #2

		sta VSYNC; Sync it up you damn dirty television!
	; and that vsync on needs to be held for three scanlines...
	; count with me here,
		sta WSYNC; one... (our program waited for the first scanline to finish...)

		sta WSYNC; two...

		sta WSYNC; three...

		lda  #43;load 43 (decimal) in the accumulator

		sta  TIM64T;and store that in the timer

		lda #0; Zero out the VSYNC
		sta  VSYNC; cause that time is over

;*********************** Joystick Input
; Here we check for left and right
; joystick input

		lda #%01000000; a 0 in bit D6 means the joystick was pushed left

		bit SWCHA; was the joystick moved left?

		bne SkipPlayer0MoveLeft; if bit D6 isn't equal to 0 then jump to SkipPlayer0MoveLeft

		dec player0x; otherwise the player moved the joystick left so deincrement the players position by one

SkipPlayer0MoveLeft
	
		lda #%10000000; a 0 in bit D7 means the joystick was pushed right

		bit SWCHA; was the joystick moved right?

		bne SkipPlayer0MoveRight;if bit D6 isn't equal to 0 then jump to SkipPlayer0MoveRight

		inc player0x;otherwise the player moved the joystick right so increment the players position by one

SkipPlayer0MoveRight

		lda player0x; load the players position into the accumulator

		ldx #0; set the sprite to be positioned as player 0

		jsr PositionSprite; jump to our Position Sprite Subroutine to position player 0

		sta WSYNC; wait for sync

		lda #0; zero out the buffer

		sta player0buffer; just in case

		lda INPT4; read button input

		bmi ButtonNotPressed; skip if button not pressed

		lda player0x; load player 0's x position

		sta missile0x; and set it to the missile 0's x position

		lda #4; set the acumulator to 4

		clc; clear carry status

		adc missile0x; add 4 to missile 0's x position so it's centered at player 0

		sta missile0x; and set it to missile 0's x position

		lda player0y; load player 0's y position

		sta missile0y; and set it to missile 0's y position

		lda #8; set the acumulator to 8

		clc; clear carry status

		adc missile0y; add 8 to missile 0's y position so it's above player 0

		sta missile0y; and set it to missile 0's y position

		lda missile0x; load missile 0's x position into the accumulator

		ldx #2; set the sprite to be positioned to missile 0

		jsr PositionSprite; jump to our Position Sprite Subroutine to position missile 0


ButtonNotPressed


;*********************** VERTICAL BLANK WAIT-ER
WaitForVblankEnd
	
		lda INTIM;load timer...

		BNE WaitForVblankEnd;killing time if the timer's not yet zero

		ldy #191;Y is going to hold how many lines we have to do
	;...we're going to count scanlines here. theoretically
	; since this example is ass simple, we could just repeat
	; the timer trick, but often its important to know 
	; just what scan line we're at.

		sta WSYNC;We do a WSYNC just before that so we don't turn on

		sta VBLANK;End the VBLANK period with the zero

;*********************** Scan line Loop
ScanLoop

		sta WSYNC;Wait for the previous line to finish

		lda player0buffer;buffer was set during last scanline

		sta GRP0;put it as graphics now

		cpy player0y; compare the player's y position

		bne SkipActivatePlayer0; if it isn't 0 then jump to SkipActivePlayer0

		lda #5; otherwise load our accumulatior with the number of lines to draw

		sta visibleplayer0line; and store it 

SkipActivatePlayer0

;set player buffer to all zeros for this line, and then see if 
;we need to load it with graphic data

		lda #0		

		sta player0buffer;set buffer, not GRP0

;if the VisiblePlayerLine is non zero,
;we're drawing it next line

		ldx visibleplayer0line;check the visible player line...

		beq FinishPlayer;skip the drawing if its zero...

		lda player0-1,X;otherwise, load the correct line from player0
		;section below... it's off by 1 though, since at zero
		;we stop drawing
		sta player0buffer;put that line as player graphic for the next line

		dec visibleplayer0line;and decrement the line count

FinishPlayer

; here the idea is that visiblemissile0line
; is zero if the line isn't being drawn now,
; otherwise it's however many lines we have to go

CheckActivateMissile

		cpy missile0y; is missile 0's y position the same as the current scanline?

		bne SkipActivateMissile; if it isn't then don't set missle 0's visible lines

		lda #8; otherwise set the missiles visible lines to 8

		sta visiblemissile0line; and store it in the visiblemissileline

SkipActivateMissile

;turn missile off then see if it's turned on

		lda #0

		sta ENAM0; disable the missile

;if the visiblemissile0line is non zero,
;we're drawing it

		lda visiblemissile0line; if the visiblemissle line is zero

		beq FinishMissile; don't draw the missile
	
		lda #2; otherwise set the accumulator to 2		

		sta ENAM0; and draw the missile

		dec visiblemissile0line; and decrement the visiblemissileline by 1

		inc missile0y; increment missle 0's y position by 1
 
FinishMissile

		dey;subtract one off the line counter thingy

		bne ScanLoop;and repeat if we're not finished with all the scanlines.

		lda #2;#2 for the VBLANK...

		sta WSYNC;Finish this final scanline.

		sta VBLANK; Make TIA output invisible for the overscan, 
	; (and keep it that way for the vsync and vblank)

;***************************** OVERSCAN CALCULATIONS
;I'm just gonna count off the 30 lines of the overscan.
;You could do more program code if you wanted to.

		ldx #30;store 30

OverScanWait

		sta WSYNC

		dex

		bne OverScanWait

		jmp  GameLoop;Continue this loop forver! Back to the code for the vsync etc

PositionSprite

	sta HMCLR

	sec

	sta WSYNC
		
PositionSpriteLoop

	sbc	#15

	bcs	PositionSpriteLoop

	eor	#7

	asl

	asl

	asl

	asl			  

	sta.wx HMP0,X	

	sta	RESP0,X  

	sta	WSYNC	  

	sta	HMOVE	

	rts

; here's the actual player0 graphic

player0
			.byte #%00011000
			.byte #%00111100
			.byte #%11111111
			.byte #%00111100
			.byte #%00011000

update_low_score_digits

		sed; set decimal mode

		clc; clear carry status

		adc score; add accumulator to score's low digits w/carry.

		sta score; store the updated low digits.

;NOTE: Here's where a triple-NOP comes into play.  We need
;a seperate entrypoint to this subroutine for cases where the
;low digits are ignored (like adding 100, for example).  But
;carry status and BCD mode need to have been setup.  So,
;place the triple-NOP opcode here to skip over them...
;with A reset at zero so that only carry affects the score:

		lda #0; reset the accumulator...

		.byte $0C; ...and skip over the next 2 bytes

update_middle_score_digits

		sed; set decimal mode

		clc; clear carry status

		adc score+1; add accumulator to score's middle digits w/carry.

		sta score+1; store the updated middle digits

;Here we do the same thing (in case the game needs to add 10,000...
;or 100,000 increments to a score (ignoring all the lower ones)
;Again, A is reset at zero so that only carry affects the score:

		lda #0; reset the accumulator...

		.byte $0C; ...and skip over the next 2 bytes

update_high_score_digits

		sed; set decimal mode

		clc; clear carry status

		adc score+1; add accumulator to score's high digits w/carry.

		sta score+2; store the last 2 digits

;With the score updated, clear BCD mode and exit via RTS:

		cld; clear decimal mode

		rts; and return to the program line that called this routine.

;*************************************************************************
; Interrupt Vectors

		ORG $FFFA

InterruptVectors

		.word Start	; NMI

		.word Start	; RESET

		.word Start	; IRQ

		END

Sincerely,

Primordial Ooze

Attached Files

•  PrimordialOoze.bin   4K   88 downloads

Edited by Primordial Ooze, Sun Feb 22, 2009 8:09 PM.

[Omegamatrix]

Primordial Ooze, you can also save some bytes like this:

StartNewGame
	   lda #105
	   sta player0x; player0's initial x position
	   lda #40
	   sta player0y; player0's initial y position
	   lda #3
	   sta lives; start the player with 3 lives
	   lda #0
	   sta missile0x; missile 0's initial x position
	   sta missile0y; missile 0's initial y position
	   sta score; set high bit of score inital value to 0
	   sta score+1; set nibble bit of score inital value to 0
	   sta score+2; low bit of score inital value to 0

Because you don't need to reload the accumulator with #0 every time. You can also move all the registers you need to zero out beside each other and put it in a loop:

	ldx	#5			  ; number of times through loop
	lda	#0			  ; value to be stored
.loopClearRam
	sta	missile0x,X	; all the regsiters have been lined up in ram before hand
	dex				   ; decrease X
	bne	.loopClearRam  ; this loop is taken until X = 0

I presume later on StartNewGame will be used when the reset switch is hit. As it is right now though registers have already been cleared in the intial clear ram and all TIA registers. There are certain ram locations that are more beneficial to link side by side then others, particularly the ones that hold your position values.

[Primordial Ooze]

Omegamatrix, on Sun Feb 22, 2009 9:11 PM, said:

Primordial Ooze, you can also save some bytes like this:

StartNewGame
	   lda #105
	   sta player0x; player0's initial x position
	   lda #40
	   sta player0y; player0's initial y position
	   lda #3
	   sta lives; start the player with 3 lives
	   lda #0
	   sta missile0x; missile 0's initial x position
	   sta missile0y; missile 0's initial y position
	   sta score; set high bit of score inital value to 0
	   sta score+1; set nibble bit of score inital value to 0
	   sta score+2; low bit of score inital value to 0

Because you don't need to reload the accumulator with #0 every time. You can also move all the registers you need to zero out beside each other and put it in a loop:

	ldx	#5			 ; number of times through loop
	lda	#0			 ; value to be stored
.loopClearRam
	sta	missile0x,X; all the regsiters have been lined up in ram before hand
	dex				  ; decrease X
	bne	.loopClearRam ; this loop is taken until X = 0

I presume later on StartNewGame will be used when the reset switch is hit. As it is right now though registers have already been cleared in the intial clear ram and all TIA registers. There are certain ram locations that are more beneficial to link side by side then others, particularly the ones that hold your position values.

Thanks, i will do that. Any solutions to my problem?

Sincerely,

Primordial Ooze

[Rybags]

I believe you also need a flag to test if a missile is already onscreen.

Otherwise, your code might keep initiating the missile fire because the button is held.

You might try using the Missile X-Pos. Just have it set at 0 to signify that no missile is onscreen.

Then all you need to do is test the X-Pos before your button checking code.
If X-Pos is non-zero, then skip the button check.

Of course, you'll need to set Missile X-Pos back to 0 once it's no longer needed.

[Primordial Ooze]

Rybags, on Mon Feb 23, 2009 12:42 AM, said:

I believe you also need a flag to test if a missile is already onscreen.

Otherwise, your code might keep initiating the missile fire because the button is held.

You might try using the Missile X-Pos. Just have it set at 0 to signify that no missile is onscreen.

Then all you need to do is test the X-Pos before your button checking code.
If X-Pos is non-zero, then skip the button check.

Of course, you'll need to set Missile X-Pos back to 0 once it's no longer needed.

Actually i can do it using missile0y, as as soon as missile0y hits 0 it stops moving and being drawn. The other problem i am having is the missile "caving in" and merging with the player sprite when you move the player towards the left. Any ideas on why this is happening?

Sincerely,

Primordial Ooze

[Primordial Ooze]

I still haven't found a problem with my missile merging with the player sprite and i have tried everything. Any ideas?

Sincerely,

Primordial Ooze

[Devin]

You could explicitly align all the players and missiles during vertical blank. Here is some excellent assembly code that I found on these boards a while ago. I don't know the original authors name.

This subroutine will position any of the graphical objects on the screen in the specified column. You just need to assign the registers and JSR.

Just note that the HMOVE is not cleared after the call. You need to clear it after horizontal blank is over.

;---------------------------------------------------------------
; Subroutine: PosSprite
;
; In	   : a = position.
;			x = sprite (0 = player 0, 1 = player 1, 
;						2 = missile 0, 3 = missile 1, 4 = ball)
;
; Out	  : None
;
; Destroyed: A
;---------------------------------------------------------------

PosSprite
	STA   HMCLR
	SEC
	STA   WSYNC	;					  begin line 1

PosSpriteLoop
	SBC	#15
	BCS	PosSpriteLoop ;+4/5	4/ 9.../54

	EOR	#7			;+2	  6/11.../56
	ASL
	ASL
	ASL
	ASL				  ;+8	 14/19.../64

	STA.wx HMP0,X		;+5	 19/24.../69
	STA	RESP0,X	;+4	 23/28/33/38/43/48/53/58/63/68/73
	STA	WSYNC		 ;+3	 0			  begin line 2
	STA	HMOVE		 ;+3
	RTS				  ;+6	 9

[Wickeycolumbus]

Your problem is that in your kernel, you enable the missile too late in the line, so on the left side of the screen, the missile wont move vertically. Here is a fixed source and binary.

Attached Files

•  ooze.zip   4.62K   85 downloads

[Primordial Ooze]

Wickeycolumbus, on Wed Feb 25, 2009 8:16 PM, said:

Your problem is that in your kernel, you enable the missile too late in the line, so on the left side of the screen, the missile wont move vertically. Here is a fixed source and binary.

Thanks for fixing my code. What i don't understand is what you mean by drawing it "late on the scanline". I'm using modified code from the joystick example in Atari 2600 Programming 101 and couldn't figure out what i did wrong. Could you please explain it?

Sincerely,

Primordial Ooze

Edited by Primordial Ooze, Wed Feb 25, 2009 11:11 PM.

[Wickeycolumbus]

Primordial Ooze, on Wed Feb 25, 2009 11:59 PM, said:

Wickeycolumbus, on Wed Feb 25, 2009 8:16 PM, said:

Your problem is that in your kernel, you enable the missile too late in the line, so on the left side of the screen, the missile wont move vertically. Here is a fixed source and binary.

Thanks for fixing my code. What i don't understand is what you mean by drawing it "late on the scanline". I'm using modified code from the joystick example in Atari 2600 Programming 101 and couldn't figure out what i did wrong. Could you please explain it?

Sincerely,

Primordial Ooze

In a 2600 kernel, you are storing to the graphics registers just cycles before they are drawn on the screen. Your kernel was attempting to enable the Missile sprite on a pixel that had already been drawn by the time your kernel enabled it. Hope that makes more sense.

-Rick

[Primordial Ooze]

Wickeycolumbus, on Thu Feb 26, 2009 4:14 PM, said:

Primordial Ooze, on Wed Feb 25, 2009 11:59 PM, said:

Wickeycolumbus, on Wed Feb 25, 2009 8:16 PM, said:

Your problem is that in your kernel, you enable the missile too late in the line, so on the left side of the screen, the missile wont move vertically. Here is a fixed source and binary.

Thanks for fixing my code. What i don't understand is what you mean by drawing it "late on the scanline". I'm using modified code from the joystick example in Atari 2600 Programming 101 and couldn't figure out what i did wrong. Could you please explain it?

Sincerely,

Primordial Ooze

In a 2600 kernel, you are storing to the graphics registers just cycles before they are drawn on the screen. Your kernel was attempting to enable the Missile sprite on a pixel that had already been drawn by the time your kernel enabled it. Hope that makes more sense.

-Rick

Now that i looked at my code and your code side by side, i see what you mean. In my game missile0 always had a higher scanline then player0, however in my game code it always drew player0 first and then the missile which the scanline was already passed through. So to fix my code you just moved my missile code to the beginning of the scanline loop so missile0 is drawn first and then then player0 like it should. Thanks for the explaination, it makes alot of sense!

Sincerely,

Primordial Ooze