So, I got yesterday's little move-a-missile into a "move a happy
face sprite" (that looks left/right depending on which way it's
moving)
And man, I'm feeling the pain of how tight a kernel has to be...
Here's what I came up with:
(using Y forthe line counter, starting at 191
YPosFromBot is how far from the bottom it is)
--snip--
ScanLoop
STA WSYNC
; here the idea is that VisiblePlayerLine
; is zero if the line isn't being drawn now,
; otherwise it's however many lines we have to go
;if scanline counter is at YPosFromBot,
;activate the player
CheckActivatePlayer
CPY YPosFromBot
BNE SkipActivatePlayer
LDA #8
STA VisiblePlayerLine
SkipActivatePlayer
;turn player off then see if it should be on
LDA #00
STA GRP0
;
;if the VisiblePlayerLine is non zero,
;we're drawing it
;
LDX VisiblePlayerLine
BEQ FinishPlayer
IsPlayerOn
LDA BigHeadGraphic-1,X
STA GRP0
DEC VisiblePlayerLine
FinishPlayer
DEY
BNE ScanLoop
--snip--
that's it. When it's moving over to the left, the top line
(and only the top line) gets cut off; I think my kernel isn't
fitting in HBLANK in the case where it's having to set
VisiblePlayerLine.
And man, this is for one lonely sprite! Any reccomendations
for cleaning it up?
Full listing follows...
thanks for any advice, I think I'll head to the library and
see if I can find any 6502 books...the computer books section
looked suitably aged.
-
KirkIsrael@xxxxxxxxxxxxx http://kisrael.com
"Without music, life would be a mistake. ...I would only believe
in a God that knew how to dance." --Friedrich Nietzsche
--snip--
; yet another moving dot by Kirk Israel
processor 6502
include vcs.h
org $F000
YPosFromBot = $80;
VisiblePlayerLine = $81;
;generic start up stuff...
Start
SEI
CLD
TXS
LDX #$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 %00000000
; 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 movement will be zero
LDX #$00
LDA #$40 ;Left?
BIT SWCHA
BNE SkipMoveLeft
LDX #$10
LDA %00001000
STA REFP0
SkipMoveLeft
LDA #$80 ;Right?
BIT SWCHA
BNE SkipMoveRight
LDX #$F0
LDA %00000000
STA REFP0
SkipMoveRight
STX HMP0 ;set horiz movement for player 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 VisiblePlayerLine
; is zero if the line isn't being drawn now,
; otherwise it's however many lines we have to go
CheckActivatePlayer
CPY YPosFromBot
BNE SkipActivatePlayer
LDA #8
STA VisiblePlayerLine
SkipActivatePlayer
;turn player off then see if it should be on
LDA #00
STA GRP0
;
;if the VisiblePlayerLine is non zero,
;we're drawing it
;
LDX VisiblePlayerLine
BEQ FinishPlayer
IsPlayerOn
LDA BigHeadGraphic-1,X
STA GRP0
DEC VisiblePlayerLine
FinishPlayer
DEY
BNE ScanLoop
LDA #2
STA WSYNC
STA VBLANK
LDX #30
OverScanWait
STA WSYNC
DEX
BNE OverScanWait
JMP MainLoop
org $FF00
BigHeadGraphic
.byte %00111100
.byte %01111110
.byte %11000001
.byte %10111111
.byte %11111111
.byte %11101011
.byte %01111110
.byte %00111100
org $FFFC
.word Start
.word Start
--snip--
----------------------------------------------------------------------------------------------
Archives (includes files) at http://www.biglist.com/lists/stella/archives/
Unsub & more at http://www.biglist.com/lists/stella/
