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2006-03-26 16:10

Trifox
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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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2006-03-28 16:25

Trifox
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Registered: Mar 2006
Posts: 108

hmm, but i do not get it exactly, to repeat what i know :

Q: How to Make C64 Raster Bars ( Changing Color of subsequent Raster lines without jitter ( like on the good old amiga with help of copper ))

A: 1. Catch a certain rasterline
- via Double Interrupt, so it is stable
- via single interrupt, but it jitters
- via loop and check for $d012
2. Delay exactly 63 clock cycles between colors
- problems: Bad Lines
- how to handle bad lines ?
- use a delay table so that each 8th line waits less
- query for bad line status
- switch off display

what you say, what is the best method now ??! i managed rasterbars only with a stable interrupt and switching of the display .. :/

2006-03-28 17:50

Oswald

Registered: Apr 2002
Posts: 5094

trifox, its really not that complicated, just invest some time into it.

I suggest to you to try my irq setup with the color change routine from the other topic.

then debug debug debug.

a non double irq will jitter, but there's enough wide invisible area on the sides to hide that with correct timing.

#1 make sure the 1st line that set by the routine is a bad line, and the first color change is on the left, invisible, side of the screen.

#2 check the routine with 1 color change, 2, 3, 4, 5,6.. 8, and adjust the timing / delay, its not that hard to see whats going on, and wether the delay is too short or not.

#3 you may count every cycle and design a loop on paper so it does 63 cycles 7 times and 23 cycle one time. (more likely the (63*7)+(23*1) time for one char height will be constant, than cycle times for each raster line)

#4
keep in mind that the delay routine adds 5 cycles at each loop, except the last which is 4. I'm not sure but maybe the outside loop needs an extra nop. when I posted that routine my calculations told me its incorrect, but I clearly remember it worked this way.

(I have done my part of (flickerfree) rasterbars, and I never needed a stable irq..., secondly there was noone there to tell me how, I had to work out everything, even setting up the damn raster irq, I've copyed some code from a booklet, and used it for years without having the slightest idea what it really does... so be happy with all the help here;)

2006-03-28 17:56

Trifox
Account closed

Registered: Mar 2006
Posts: 108

yes, iam and it is really funny that there are so many people who still know what is going on in the c64

2006-05-21 10:10

moz
Account closed

Registered: May 2006
Posts: 7

I'm messing around with raster bars at the moment too. That ASM was a nice example, although I don't understand it all yet (I need to spend more time reading).

I was also trying to set sprite multi-colour 2 for each line but found that it really slowed everything down, should this be expected? I thought it would simply be a case of changing a memory address, but the more sprites I have on the specified line the greater the delay seems to be.

I'd love to be able to change border+screen+MC2 per line. Am I asking for too much?

2006-05-21 11:01

Honesty

Registered: Jan 2003
Posts: 121

Read the posts...

Problem is that vic needs more time to fetch sprite data and put it to the screen...

So u have less time each line for lda/sta stuff.
So far i know also the sprites have different values for how long the data fetch take.

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