So I revamped thin red line, and got myself a missile
that (gasp) isn't the height of the screen! And you can
move it where ever you want with the joystick! I'm so
happpy. It actually came together pretty well, and my
kernal is somewhat reminiscent of a real kernel, in keeping
track of the height of the missile and all.
So any suggestions re: blatant inefficiencies are welcome.
Also, how do you do a logical NOT?
I'm a little worried I'm playing a little fast and loose
with what I'm putting in VBLANK, but the controller still
seems to work...
--snip--
; yet another moving dot by Kirk Israel
processor 6502
include vcs.h
org $F000
YPosFromBot = $80;
VisibleMissileLine = $81;
;generic start up stuff...
Start
SEI
CLD
TXS
LDX #$FF
LDA #0
ClearMem
STA 0,X
DEX
BNE ClearMem
LDA #$00
STA COLUBK
LDA #33
STA COLUP0
LDA #80
STA YPosFromBot ;Initial Y Position
LDA #$20
STA NUSIZ0 ;Quad Width
;VSYNC time
MainLoop
LDA #2
STA VSYNC
STA WSYNC
STA WSYNC
STA WSYNC
LDA #43
STA TIM64T
LDA #0
STA VSYNC
;Main Computations; check down, up, left, right
;general idea is to do a BIT compare to see if
;a certain direction is pressed, and skip the value
;change if so
LDA #$10 ;Down?
BIT SWCHA
BNE SkipMoveDown
INC YPosFromBot
SkipMoveDown
LDA #$20 ;Up?
BIT SWCHA
BNE SkipMoveUp
DEC YPosFromBot
SkipMoveUp
;assum horiz position will be zero
LDX #$00
LDA #$40 ;Left?
BIT SWCHA
BNE SkipMoveLeft
LDX #$10
SkipMoveLeft
LDA #$80 ;Right?
BIT SWCHA
BNE SkipMoveRight
LDX #$F0
SkipMoveRight
STX HMM0 ;set the move for missile 0
WaitForVblankEnd
LDA INTIM
BNE WaitForVblankEnd
LDY #191
STA VBLANK
STA WSYNC
STA HMOVE
;main scanline loop...
ScanLoop
STA WSYNC
; 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 YPosFromBot
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
IsMissileOn
LDA #2
STA ENAM0
DEC VisibleMissileLine
FinishMissile
DEY
BNE ScanLoop
LDA #2
STA WSYNC
STA VBLANK
LDX #30
OverScanWait
STA WSYNC
DEX
BNE OverScanWait
JMP MainLoop
org $FFFC
.word Start
.word Start
--snip--
--
KirkIsrael@xxxxxxxxxxxxx http://kisrael.com
"If anyone disagrees with anything I say, I am quite prepared not only to
retract it, but also to deny under oath that I ever said it." --T. Lehrer
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