Hi there!
I wrote:
>Now I'm thinking of alternatives. Does anybody have an
>idea?
So I spent the last two hours analyzing how other
Starfields are made, which was quite disappointing.
Star Ship: Uhm... well ;-)
SW-TAG: Re-Using two particles à four times -> 15Hz
flicker.
Gyruss: Now that is interesting. The whole Starfield is
generated using only 1 particle most of the time and
should flicker extrem. I wonder why it doesn't seem to
be too annoying...
Star Voyager: I had some hope for a special Imagic trick
here, but they're cooking with water only, too :-) Just
like Starmaster it's using the ball, wasting a complete
scannline to reposition it.
Star Raiders: It's using all three particles, plus it
divided the screnn into an upper and a lower region. Due
to a midscreen repositioning it can display six
particles at once, which is resulting in 12 stars with
only 30Hz flicker. Quite clever, though I think it
dosn't look too good, when the sprites are *trapped* in
their part of the screen.
Most promising right now look indeed solutions based on
Pauls suggestion, that is a more realistic starfield,
like the ones utilized in 'Earth Dies Screaming' and
'Solaris'. I'll yet have to analyze their code for
hidden trapdors, though ;-)
I'll soon report on my further progress.
Following at the bottom is my 10 minutes worth of
reverse-engineering Star Voyager.
Strange programming style... :-)
Greetings,
Manuel
------> Part of the Star Voyager kernel <-------
; Stop vertical blank
STX VBLANK ; X->0
DEX ; X->FF
STX PF2 ;
STA WSYNC ;
STX PF0 ;
STX PF1 ;
; Position first star:
LDA $F3 ;
STA HMBL ; Fine Movement
LDY $E8 ;
NOP ;
L10CA: DEY ;
BPL L10CA ;
STA RESBL ;
STA WSYNC ;
STA HMOVE ;
STA WSYNC ;3
LDY $83 ;3
BEQ L10E1 ;2
DEY ;2
LDA ($95),Y ;5
STA GRP1 ;3
JMP L10E4 ;3
L10E1: JSR L1AC5 ; Waste 12 cycles
L10E4: LDY $84 ;3
BEQ L10F0 ;2
DEY ;2
LDA ($93),Y ;5
STA GRP0 ;3
JMP L10F3 ;3
L10F0: JSR L1AC5 ; Waste 12 cycles
L10F3: PHA ;
PLA ; Waste 7 cycles
INX ; X->0
STA RESM1 ;3
LDY $83 ;3
NOP ;2
STX $8E ;3
LDA $DD ;3
STA $90 ;3
TXA ; A->0
STA HMCLR ;3
STA PF2 ;3
STA PF1 ;3
BEQ L1117 ; Jump always
; Reposition Star / Waste a scannline
L110A: LDA #$00 ;2
STA $8F ;3
LDY $91 ;3
L1110: DEY ;2
BPL L1110 ;2
STA RESBL ;3
Nextline
STA WSYNC ;3
L1117: STX HMOVE ;3
LDY $83 ;3
CPX $A8 ;3
BCC L1126 ;2
CPX $AA ;3
BCS L1126 ;2
LDA ($95),Y ;5
INY ;2
L1126: STA GRP1 ;3
STY $83 ;3
; Do the crosshair
LDA #$00 ;
CPX #$28 ; Reached line $28?
BNE L1132 ; N: Skip
LDA #$40 ; Y: Draw Crosshair
L1132: STA PF2 ;
----------------------------------------------------------------------------------------------
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