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Golara
Account closed
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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Mixer
Registered: Apr 2008
Posts: 452 |
Answer to all of your current and future VIC questions :) VIC Article [english] |
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TWW
Registered: Jul 2009
Posts: 545 |
I used this to generate the horizontal sine-values:
.var sinus = 0
SinusXLo:
.for (var i = 0 ; i < 256 ; i++) {
.eval sinus = RadiusX - 7 + RadiusX*sin(toRadians(i*360/256))
.if (sinus < 0) .eval sinus = sinus - 9
.byte sinus
}
SinusXHi:
.for (var i = 0 ; i < 256 ; i++) {
.eval sinus = RadiusX - 7 + RadiusX*sin(toRadians(i*360/256))
.if (sinus < 0) .eval sinus = 256
.byte >sinus
}
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JackAsser
Registered: Jun 2002
Posts: 2014 |
This is all there is to it. When you really understand this chart it will explain almost everything: https://www.linusakesson.net/programming/vic-timing/victiming.p.. |
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Oswald
Registered: Apr 2002
Posts: 5094 |
sprite stretching is very easy, just turn on/off y stretch bit on each line. horizontal timing is doesnt matter except the 1 cycle where it results in another trick called sprite crunch. |
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Golara
Account closed
Registered: Jan 2018
Posts: 212 |
Aha, that's really great. I must have missunderstand the article on sprite stretching, I thought it was cycle accurate and sprite crunching is the same trick but in a different cycle. I made a simple loop of various lenghts like this:
ldx .xPosCounter
lda sprite_stretch, x
adc #10
tay
lda #$ff
l1:
inc $d021
sta $d017
eor #$ff
sta $d017
dec $d021
dey
bne l1
And it seems like I do a sprite crunch at some frames, can you confirt that it is in fact sprite crunch ? My sprites appear twice.
I also decided to do a logo instead of DYSP for now, it's made out of 6 sprites. I swing it from 0 to 255 and set the 9th bit at the correct position, or so I think... It blinks sometimes, do you see anything I do wrong ?
lda #$00
sta $d020
sta $d021
sta $d010 ; 9th X bit
ldx .xPosCounter
lda sprite_border_sin_1, x
cmp #230
bcc skip5
tay
lda #%01111100
sta $d010
tya
skip5:
cmp #230-24
bcc skip4
tay
lda #%00111100
sta $d010
tya
jmp skip1
skip4:
cmp #230-24-24
bcc skip3
tay
lda #%00011100
sta $d010
tya
jmp skip1
skip3:
cmp #230-24-24-24
bcc skip2
tay
lda #%00001100
sta $d010
tya
jmp skip1
skip2:
cmp #230-24-24-24
bcc skip1
tay
lda #%00000100
sta $d010
tya
skip1:
clc
sta $d00e
adc #24
sta $d00c
adc #24
sta $d00a
adc #24
sta $d008
adc #24
sta $d006
adc #24
sta $d004
I'll try to make it the last question. |
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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 |
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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 ? |
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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. |
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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.
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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) |
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