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Forums > C64 Coding > Sine sprites in the sideborder. VSP garbage and more

2018-01-22 11:35

Golara
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Registered: Jan 2018
Posts: 212

Sine sprites in the sideborder. VSP garbage and more

Hello everyone. I'm working on my first C64 demo / intro. I managed to open the sideborder at the top and obviously I immediately put some X-sinus sprites there (I'm still trying to figure out how a DYSP works, right know i have opened lines with 0 and 8 sprites). I noticed that the positioning of the sprites on the X axis is a bit weird. Position 0 is slighty on the left border, but if you want to go all the way to the left you have to use X 500 or there about. My question is, is there some sinus maker or converter that would take care of this ? (so it goes from 0 to ~500 looking like smooth movement to the left). Another question, what is the good way of handling the 9th bit of X position ? What I do is generate a 256 words sinus with values 0 to 500 and use c++ program to split that into 2 256 bytes tables like

sin_1:
1,2,3,4,5,6,7,55,33,....
sin_2:
1,0,0,0,0,1,0,0,1.... where 1 means to set the bit and 0 to not do that.
My sprite 0 is bugging out in the right most border while other sprites display just fine. Why is that ? I've read somewhere that sprite 0 is evil, but could not find any details on why.

I also do VSP by turning on the screen at the right moment together with XSCROLL for smooth scrolling. I see few pixel lines of garbage just above the image, I cover that with the illegal screen mode, disable it at line 56. Is that a good idea ? Another thing about VSP is that it seems to move the whole screen down by one char on the scrolled side (makes sence I guess, as the part of the chars that are outside of the image are displayed on the next text line). So should I copy the 25 lines of graphics in each column when scrolling for seamless scroll or do people not do that ?

Here's a picture of what it looks right know. A big mess !
(PETSCII picture by Archmage as a placeholder. I can't find any pics in binary and that was the easiest to take out of a compiled prg) Hope you have the patience to help a lamer out.
https://i.imgur.com/byWFRsH.jpg[/url]

HughJass from Poland

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2018-01-24 14:20

Oswald

Registered: Apr 2002
Posts: 5094

just keep asking :)

1. for proper sprite stretch u have to make sure on/off exactly per line, thats why it doesnt always stretch

2. might be not proper d010 setting and sprite teleporting under border or writing X in a magical cycle when sprite is being displayed iirc then sprite disappears. you should handle 9th bit per sprite and ora into d010, something is probably bugged in there

2018-01-24 15:14

Golara
Account closed

Registered: Jan 2018
Posts: 212

I'm setting the X and $d01d registers at line 251 and set sprites Y at 255, so there's no way I'm writing X register while displaying the sprite. I've made this ff->d017 00->d017 loop just to see if the stretching works, I assumed it would just randomly spaz out (which it did) but I also get sprites drawn twice which is the effect of sprite crunching from what I've read. (because the internal byte counter gets incremented by 1 instead of 3 once and so the counter doesn't reach 63 and the sprite gets drawn again).

Btw, does sprite stretching steal more cycles ? That is, on each line where a sprite is drawn, even when using the stretching bug, it still takes away the cycles ? Does that mean I have to trigger the stretching bug before the sprite DMA or after ? or it doesn't matter ?

2018-01-24 16:26

Oswald

Registered: Apr 2002
Posts: 5094

ah, yes you are right. then I guess it must be buggy d010 usage.

yep, if you do stretching sprites steals same amount of cycles as if displayed normally.

2018-01-25 14:35

Golara
Account closed

Registered: Jan 2018
Posts: 212

Damn, I didn't realise you can change the X register while displaying a sprite, I thought it was locked like Y. Makes it very easy to do a sprite TECH-TECH, dude nice.

6 sprites on the line, I change the first 4 sprites's X on one line and the other two on the other while opening the borders. It was rather easy, but I can't figure out how to make it go all the way to the right border, damn, this 9th bit makes it tricky and the fact that 0 position is not the top most left position makes it even harder.

2018-01-25 16:13

Golara
Account closed

Registered: Jan 2018
Posts: 212

Stretching side border tech tech, am I pro or what ? :v

That reminds me a bit of the super stretching in the DEMODE, is it the same thing, just, you know, much better ? (d017 stretches and changing X for tech-tech)

2018-01-25 17:48

ChristopherJam

Registered: Aug 2004
Posts: 1409

Huh. So I know the gap in X position comes from there being 63 cycles per line, hence 63*8=504 possible sprite start locations, but this thread got me wondering about NTSC.

I was worried that our friends across the pond might not be able to smoothly scroll an x-expanded sprite off the screen, as there are 8 positions for which no register value exists (65*8=520 locations, and you only get 512 from MSB+xpositionregister).

Going by a quick test in VICE however, it seems that position 511 is one pixel to the left of position 0, and position 0x1e9 covers all but the rightmost pixel of an x-expanded sprite. All is good, and those slackers across the ocean can just use 16 bit positions without any fuss.

I'm assuming vic artikel covers where the gap is, I'm just amused that it's not where I was concerned it might have been.

2018-01-25 17:50

ChristopherJam

Registered: Aug 2004
Posts: 1409

Gnarly tech tech, HughJass!

2018-01-25 18:01

Golara
Account closed

Registered: Jan 2018
Posts: 212

Quote: Gnarly tech tech, HughJass!

If you're talking about gaps in my sprites it's in the sprite definition, I drew them for multicolor but didn't switch to multicolor and I thought they looked kinda neat. I only spend about an hour each week day (when tired of coding enterprise(tm) c++ code), but I'll spend some more time on the weekend. I decided to start from scratch, because first I started with vsp and then multiplexer and opening borders, interrupts all over and no usefully code between them. Now I do a stable raster at line 250, disable bottom border and open the sides for bottom and top. Filling the nops with what I can (like this stretcher) and then I'll do smooth vsp again at line $30 and something cool in the middle again.... I like these old-school demos like raster blast or the demos from Upfront with lots of sprites and nice rasters etc. The part in Insomnia with tech tech image and dysp over it is super cool. I've been following the c64 and Amiga demoscene since 2013 or so, I never owned either computer (born in the 90s) but now I own both and finally started coding some shit on c64 last week.

2018-01-25 18:55

ChristopherJam

Registered: Aug 2004
Posts: 1409

Haha sorry, talking Australian. Gnarly = so good that it attracts the viewers attention and earns their respect.

Yes, the gaps are cool!

2018-01-25 19:01

Golara
Account closed

Registered: Jan 2018
Posts: 212

Quote: Haha sorry, talking Australian. Gnarly = so good that it attracts the viewers attention and earns their respect.

Yes, the gaps are cool!

This was my first go at drawing sprites (by typing bytes myself before finding a sprite editor, doh) I'll try to make a better logo, but I'm so inept in any form of arts haha. I'd like to make it as wide as the screen, but I don't think I'll have enough raster time to toy with 9th bit. Although definitely there's a way because people did full screen stretching scrollers with lots of colors so... I'm just missing out on something

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