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Luca
Registered: Apr 2002
Posts: 178 |
Twister's primer
How to obtain simple/cool/elaborate primer graphics (bitmap) for a general vertical twister effect (let's say simply 3 colours+background colour)? Should I draw'em on PC first, with a 3DMax or similars, then convert'em? Which height in pixels would be enough to smoothly describe and include the whole 360° rotation?
For a very basic one, I could simply draw a slice of column in two colours by drawing them with a sin(x) function, what with more complex stuff? |
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Luca
Registered: Apr 2002
Posts: 178 |
OMG I've just seen I got zero answers after almost a year, it's a world record, great! :D |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: How to obtain simple/cool/elaborate primer graphics (bitmap) for a general vertical twister effect (let's say simply 3 colours+background colour)? Should I draw'em on PC first, with a 3DMax or similars, then convert'em? Which height in pixels would be enough to smoothly describe and include the whole 360° rotation?
For a very basic one, I could simply draw a slice of column in two colours by drawing them with a sin(x) function, what with more complex stuff?
Depending on the shape of your twister you need different amount of angles to smoothly rotate it. F.e. a cube based needs to rotate 90 degrees before being symmetrical again. Typically u want as many angles as possible, so it's always a trade off between that and loading time / memory usage. One VIC bank can easily contain 256 angles, in three different twister shapes, which should be enough for most applications.
To render a twister, simply use your favorite raytracer or code one on your own.
/JackAsser
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Twoflower
Registered: Jan 2002
Posts: 434 |
Or pixel it. :-) |
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HCL
Registered: Feb 2003
Posts: 728 |
Quoting JackasserOne VIC bank can easily contain 256 angles, in three different twister shapes
Hmm, sounds like a magic formula :), how's that obtained? Of course it depends on how much data each animation needs, easiest case (?) would be 8 stretched sprites, and then you have space for 2 * 256 angles. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: Quoting JackasserOne VIC bank can easily contain 256 angles, in three different twister shapes
Hmm, sounds like a magic formula :), how's that obtained? Of course it depends on how much data each animation needs, easiest case (?) would be 8 stretched sprites, and then you have space for 2 * 256 angles.
In that magic lies the limitation that you only show one of the three shapes at any given frame and that you're only using 7 sprites in width (21 bytes).
Sprite offsets 0-20 for the first shape, 21-41 for the second shape and finally offsets 42-62 for the third shape.
But yes, using 8 sprites limits you to only two shapes per sprite. |
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Luca
Registered: Apr 2002
Posts: 178 |
Thanks guys, I'll try that.
I would admit I afforded the problem from the wrong side (my difficulties in rendering/converting a primer), instead of facing the code first.
I'm very interest in all the different approaches to twisters: one seems to be a sort of "special plasma", with sintables and all the rest; another one seems to be playing with DMA delay. A good example is the double-twister in Zenith of Puberty on Plus/4, which probably shows both. |
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Scout
Registered: Dec 2002
Posts: 1570 |
If you want to know how it is done on a DTV, check the sources of Twistro
There's also an exomized twister bitmap (256x256) which I made in Photoshop.
You can decompress it and load it back as RAW image in Photoshop/GIMP/Paintshop. |
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WVL
Registered: Mar 2002
Posts: 902 |
Quote: In that magic lies the limitation that you only show one of the three shapes at any given frame and that you're only using 7 sprites in width (21 bytes).
Sprite offsets 0-20 for the first shape, 21-41 for the second shape and finally offsets 42-62 for the third shape.
But yes, using 8 sprites limits you to only two shapes per sprite.
The all-border sprite zoomer in Pearls for Pigs uses this technique :)
There's 7 sprites on screen, the picture is 64 pixels high and there's 12 different x-sprite sizes for every sprite. These 12 different sizes are made using 256/64 = 4 and I can fit 3 sizes in each sprite (by offsetting in y with 0,7 or 14). 4*3 = 12.
Maybe to explain it better :
If I want to show the full width, i put my sprites at y-offsets of 0,1,2,3,4,5 and 6, and i use sprite-images 0-63 (changing each line) to show the picture. I can also chose 64-127, 128-191 or 192-255, to make all sprites 1,2 or 3 pixels smaller.
If i want to make them 4 pixels smaller, i use offsets 7,8,9,10,11,12 and 13 and sprite images 0-63 again.
Ofcourse the code allows for any combination of y-offsets :)
The fact that you can only have max 7 sprites with sprite-fpp and open border suddenly becomes an advantage, because you can use the memory 3x more efficiently :) |
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Mace
Registered: May 2002
Posts: 1799 |
@ WVL: please explain this to me again, on paper, at X-2010 (before we drink beer) ;-) |
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Luca
Registered: Apr 2002
Posts: 178 |
Quote: If you want to know how it is done on a DTV, check the sources of Twistro
There's also an exomized twister bitmap (256x256) which I made in Photoshop.
You can decompress it and load it back as RAW image in Photoshop/GIMP/Paintshop.
Thanks Scout, that would be a very good starting point, though I am still not able to understand how to use it (if color infos are not needed, if I have to read it as hires then assign some colours...). |
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Oswald
Registered: Apr 2002
Posts: 5094 |
sprite fpp is a wonderful thing indeed :) who invented it btw? |
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WVL
Registered: Mar 2002
Posts: 902 |
I honestly don't know :( I didnt know about it until Royal Arte, but I'm sure it has been used plenty of times before that.. |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
There is no twister, its just to print some chars that animate so they look like twisting, using a pretyped char index table, sorry to break your dreams :D |
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Skate
Registered: Jul 2003
Posts: 494 |
FPP is a very old effect.
http://www.codebase64.org/doku.php?id=base:demo_world_records_a..
Codebase64 says it's from 1989, I think it might even be older. |
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Radiant
Registered: Sep 2004
Posts: 639 |
FPP != sprite FPP.
Coding your own raytracer for generating the twister graphics isn't a bad idea. You can always touch the result up manually afterwards if you want to. The graphics for the "twister" in Patterns was generated by simply texturemapping a cylinder with different texture offsets. |
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Oswald
Registered: Apr 2002
Posts: 5094 |
"Coding your own raytracer for generating the twister graphics isn't a bad idea."
its like coding your own ext editor for the twister's code... |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: "Coding your own raytracer for generating the twister graphics isn't a bad idea."
its like coding your own ext editor for the twister's code...
I see your point, however, it's not valid to me. For me, learning some 3d program to generate the gfx takes longer than doing a simple raytracer. However, as complexity of the objects increases, using a real tool becomes more and more sane. F.e. the wireframe cube in Andropolis was generated using povray. (And now that I know povray I don't think I'd make my own raytracer again for a twister. :) )
The horizontal twisters in The Wild Bunch and Amplifire both used a custom raytracer that only could render such an object (i.e. some cylinders and planes). |
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Oswald
Registered: Apr 2002
Posts: 5094 |
okay, in some cases it is a good idea indeed :) but I'd guess most coder's cant just slap together a raytracer even this simple in 5-10 minutes, it needs some perequisites like in the case of using a tool. :) |
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Pantaloon
Registered: Aug 2003
Posts: 124 |
a simple twist tracer in kickasm script, stores which side is visible for each line.
.for (var side = 0; side < 4; side++)
{
.var y0 = round(coords.get(side*2+0))
.var y1 = round(coords.get(side*2+1))
.var ydiff = y1 - y0
.if (ydiff > 0)
{
.for (var y = y0; y < y1; y++)
.eval points.put(y,side)
}
}
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Mace
Registered: May 2002
Posts: 1799 |
@ Pantaloon: don't you forget declaring 'coords' as a List()? Or something... |
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Pantaloon
Registered: Aug 2003
Posts: 124 |
was just a little snippet. you need to rotate the coords first, and store them in a list. |
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MagerValp
Registered: Dec 2001
Posts: 1078 |
POV-Ray is perfect for these kinds of tasks. It's trivial to get it to render a series of 21x1 pixel (or whatever you need) cubes, and as a programmer you gotta love its scene description language. Slapping out a POV-Ray'd twister is faster than coding your own raytracer too, even if you've never used POV before. |
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Krill
Registered: Apr 2002
Posts: 2980 |
Depending on the type of twister, you can also simply generate the graphics on the c64 itself, like i did here in 4k: Bar4Kode - doesn't look as cool as raytraced, but still nice enough. :) |
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Mace
Registered: May 2002
Posts: 1799 |
Hey, this was the kind of stuff I was looking for :-)
Thanks Krill. |
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Krill
Registered: Apr 2002
Posts: 2980 |
Mace: I can send you the source if need be.. But it's uncommented and generally not up to my current standards :D |
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Luca
Registered: Apr 2002
Posts: 178 |
Plenty of available choices, I see.
I tried POV-ray but as a complete prophan, I ran away in pain. Probably a bit more patience would be needed. The Krill's solution looks tasty too.
Scout: I still dunno how to use the .raw image, because I didn't understand if that twister's primer is deliberately drawn in 3 colors, or there's something I missed around it (probably my ignorance in DTV...). |
