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Trifox
Account closed
Registered: Mar 2006
Posts: 108 |
*newbie* Raster Bars ....
Hi all, i am wondering how to implement as nice
raster bar algorithm, i started with:
http://www.ffd2.com/fridge/vic/stableraster.txt
for a stable entry point, how do i now change raster bar color in each subsequent line ? i was fiddling around with after the irq3 exits, it calls irq1 with a subsequent line, and then start it over, the problem is, when initiating the interrupt routine more than once in a it shifts abit to the right so the starting position of the change of color is visible on screen ... any hints to fill subsequent lines at allways the same x-position ?! |
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WVL
Registered: Mar 2002
Posts: 886 |
you have to count the number of cpu cycles in your loop, and match this to the number of cycles the cpu has available each rasterline. If there are too many cycles each loop, the position where you change will slowly drift 'to the right', if there are too few cycles in your loop, it will 'drift to the left'. On normal rasterlines, there are 63 cycles available for the cpu. However, there are also lines called 'bad lines', which have less. Also using sprites on a certain rasterline means less cycles available for the cpu.
For further reference, I suggest you pick up the 'Vic Article' :) google for it. |
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Trifox
Account closed
Registered: Mar 2006
Posts: 108 |
puh, ok, i have implemented a bunch of this ... ;)
here are some results, if you like watch'em:
http://www.digitalgott.de/c64/sines-raster.asm
and
http://www.digitalgott.de/c64/sines-raster.prg
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Wanderer
Account closed
Registered: Apr 2003
Posts: 478 |
It works great in PAL. I see that you're using $d020 only.
See the other thread for a way to do it using $d020/$d021 which allows you to have text on the screen.
Looks nice though.
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Trifox
Account closed
Registered: Mar 2006
Posts: 108 |
at the moment i am just playing around with the copper-like effects ... ;) next time i watch how to display a sprite logo or some scrolltext, or a sprite scrolltext,
if you like you can watch another raster bar example,
this time more like a 1d dotflag .. ;)
http://www.digitalgott.de/c64/sinus_raster_flag.prg
and the source
http://www.digitalgott.de/c64/sinus_raster_flag.asm |
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Oswald
Registered: Apr 2002
Posts: 5031 |
btw you dont need any flicker fix for a rasterbar routine, you _dont_ need to be cycle exact at all. Max is about 8 cycle jitter, which can be placed on a screen area (right and left border of the screen) that will be never visible.
cycle exact timings were invented for hi tech stuff, like opening the side borders.
simpleirqsetup:
sei
lda #$7f ;disable default cia #1 timer interrupts
sta $dc0d ;which is used by kernal to flash cursor, etc.
lda #$01
sta $d01a ;ask for raster interrupts from vic
lda #$40
sta $d012 ;at rasterline $40
lda $d011
and #%01111111
sta $d011 ;0 into 9th bit of requested rasterline
lda $dc0d ;acknowledge any pending cia #1
lda $dd0d ;cia #2
lsr $d019 ;or raster irq
lda #<irq ;set up interrupt vector
sta $fffe
lda #>irq
sta $ffff
lda #$35
sta $01
cli
jmp *
irq
sta tempa+1
stx tempx+1
sty tempy+1
;do your stuff
lsr $d019 ;acknowledge irq (if you dont do this your irq routine will be reentered right after the rti again and again.., resulting in a mess)
tempa lda #$00
tempx ldx #$00
tempy ldy #$00
rti
even if you wont use this I think this helps in understanding whats going on more, than the messy tricky double irq example.
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Trifox
Account closed
Registered: Mar 2006
Posts: 108 |
har har, but this way i have full screen bars .... but i can not do anything else then displaying those bars... |
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Oswald
Registered: Apr 2002
Posts: 5031 |
both methods allows you to have fullscreen bars. |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Quote: har har, but this way i have full screen bars .... but i can not do anything else then displaying those bars...
You want to do an IRQ every rasterline so you can use some "remaining time"? Forget about this, even if you do almost nothing there are not enough clock cycles to have an IRQ each rasterline. |
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Oswald
Registered: Apr 2002
Posts: 5031 |
graham, if ninja can do every 2nd line fli with separated irqs, how much impossible is this ? :) |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Yes, every 2nd line FLI is ofcourse the perfect beginner example :P
Anyway, you might be able to do every line IRQ, but it wont help you. Your rasterbars will be buggy because you change colors in the middle of the screen, and you wont have much cycles free. |
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