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Flavioweb
Registered: Nov 2011
Posts: 463 |
Sprites over rasterbars: where?
Someone can tell me a demo/intro name where are sprites movin' over rasterbars?
Or, at least, sprites without movement over rasterbars?
Tnx. |
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Skate
Registered: Jul 2003
Posts: 494 |
There are many. I leave others to give you examples. But i will try to give you the main idea about sprites with rasterbars.
First of all, you need to think of just one rasterline (or scanline if you prefer). You need to calculate timings for that line alone. If sprites are moving among Y axis, things gets much harder because of it. Each rasterline will have different timings. But of course there are smart workarounds.
I think most popular trick is using $d017 stretch. All lines will have the same amount of sprites enabled and Y coordinates will be the same and fixed. At each line, all you do is $d017 trick. Instead of stretching all sprite lines, you just stretch the first sprite line which you should leave blank. That way you have 20 pixel high sprites instead of 21 but you will have stable timing. If inner screen is open, you need to take care of DMA lines of course. That's how it is done.
Another way is to use more than one timing routine for a few different Y coordinate changes (think about a DYSP). But after a few different frames, you go back to first timing routine and swap sprite pointers just like smooth scrolling routines (like changing $d016 a few times and sliding characters etc.). This method is harder but you are free to use all 21 lines.
Basicly these two methods have adventages/disadvantages
$d017 stretch method:
+ You are allowed to change sprite Y positions (using $d017 stretch of course) freely with any sinus tables, even variating ones.
+ If you like, you can stretch other than blank sprite lines without any extra effort.
- You are not allowed to use the full sprite area but at least one line shorter.
- $d017 trick steals a few more cycles each line.
different timing tables method:
+ You are allowed to use all 21 sprite lines
+ You have more free cycles each line
- Y changes must be well planned and hard to change once it is done. (if you don't make/use a code generator tool for it)
- You can't stretch the sprites using that method.
I hope you were looking for the techniques. I thought it's better this way than examining the codes. If you just needed the demo names, you can forget about my answer. :) |
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Mixer
Registered: Apr 2008
Posts: 447 |
Just had to post this:
Mixer
+ so many others. |
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DeeKay
Registered: Nov 2002
Posts: 363 |
If you don't mind that in Badlines your rasterbars are 2 pixels high and may jitter a bit on the very left, I found this cheapass Timing-table-less Rasterbar routine quite useful, which is totally independent from any sprites:
LDY #$00
LDA $Rasterbar-Table,Y
TAX
LDA $D012
CMP $D012
BNE -6
STX $d020
STX $d021
INY
BNE start+2
...forgive any errors, i cannot test right now and I haven't coded in quite a while! Also, IANAC! ;-) |
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Skate
Registered: Jul 2003
Posts: 494 |
@Deekay: I didn't try the code but i guess $d012 comparison part is wrong.
lda $d012
cmp $d012
beq *-3
makes more sense to me. |
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chatGPZ
Registered: Dec 2001
Posts: 11360 |
"If you don't mind that in Badlines your rasterbars are 2 pixels high and may jitter a bit on the very left"
few people are coding NTSC intros today.... |
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Peiselulli
Registered: Oct 2006
Posts: 81 |
Maybe look into Jars's Revenge ingame code ... there are no rasterbars, but the border is disabled (which is more time critical) with moving sprites ...
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Wile Coyote
Account closed
Registered: Mar 2004
Posts: 646 |
Pimplesqueezer 3
This was one of the first demos I got to see, and it blew my socks off. There's a great part with swinging (into side-border) sprites over rasters + grey RAWHEAD sprites moving over the same rasters. The part in question still impresses the hell out of me. The whole demo is gold. |
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Flavioweb
Registered: Nov 2011
Posts: 463 |
Quoting SkateThere are many. I leave others to give you examples. But i will try to give you the main idea about sprites with rasterbars.
I hope you were looking for the techniques. I thought it's better this way than examining the codes. If you just needed the demo names, you can forget about my answer. :)
Yes, i want to know "how things works".
I don't start this thread into "coding" section, because i don't know how many people want to share his knowledge, but if someone want to help me into learning how to do sprites moving over rasterbars... any help is welcome...
Maybe some moderator will change thread section =) |
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Codey
Registered: Oct 2005
Posts: 79 |
also if you use fld for your timing, your rasters will be perfect and can have sprites moving over them iirc. the only drawback is no char mode.. |
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Flavioweb
Registered: Nov 2011
Posts: 463 |
Quoting PeiselulliMaybe look into Jars's Revenge ingame code ... there are no rasterbars, but the border is disabled (which is more time critical) with moving sprites ...
At a first look, seems that is used a stable irq (inverted timer) with code for every line unrolled, and jitter is compensated "on the fly" when -cycles- goes on new raster line...
I'm on right path?
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Real DYSP |
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iAN CooG
Registered: May 2002
Posts: 3187 |
Dingy
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Zaz
Account closed
Registered: Mar 2004
Posts: 33 |
This Is What It Is |
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ready.
Registered: Feb 2003
Posts: 441 |
a part of this demo:
20 Minutes in the Future |
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raven
Account closed
Registered: Jan 2002
Posts: 137 |
Continuing what Skate has started, there's a 3rd method which is easiest to implement & also most versatile, as it basically takes care of itself.
Use a timer to count down from 63 and branch according to its value. This code must be done each line.
If you'd like bad-lines active, they'll require different handling.
The line code will look something like this:
lda #cycles
sbc $dd04
sta *+4
bcs *
lda #$a9
lda #$a9
...
bit $ea
...rest of raster code...
+ Sprites can be moved freely without restrictions, no update of the timings is required for non bad-lines
- Doesn't leave much raster-time per line |
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Trash
Registered: Jan 2002
Posts: 122 |
Another simple solution if you dont want graphics behind the sprites is:
outer_loop:
lda #raster_row
ldx #count_rows
cmp $d012
bne * - 3
inner_loop:
lda coltable, x
sta $d020
sta $d021
lda $d011
and #7
ora #16
sta $d011
dex
bne inner_loop
; move sprites around here
jmp outer_loop |
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Oswald
Registered: Apr 2002
Posts: 5086 |
or you can do it as Ninja, set a CIA timer to count down from 63 & set the irq vector over the CIA timer & set the register before to jump instruction $4c, and it will select the routine needed for the desired timing automagically. Beware, this eplanation is very rough, just added to drop in the idea. |
