The Sprite Gallery

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The Sprite Gallery

Postby tikibear » Fri Dec 26, 2008 6:38 pm

My sprite experiments ended up as a small, spooky age.

This is meant only to add to the Wiki sprite description.

The sprite types are represented by the value (in D'ni) of the least-significant, four bits of the sprite flags.

Sprite 1 keeps its current Y axis aligned to the camera's view of its original Z axis. It is well-behaved near the equator of the original Z axis.

Sprite 2 takes the ray in the original XY plane that is aligned with the camera's view of the original Z axis and aligns that current ray to the camera's view of the original Z axis.
It is well-behaved near the zenith and nadir of the original Z axis.

Sprite 4 aligns the current Y axis with the original Y axis. It is well-behaved near the equator.

Sprite 8 does not impose any alignment. It is well-behaved at all angles. Since arbitrary rotations aren't orthogonal the sprite's orientation is dependent on its rotation history.

The sprite displays in the gallery limit the views to well-behaved geometries. You can see sprite 8 from many angles, but sprite 2 only from angles near the zenith of its original Z axis. The original Z axis points up.

Enjoy the gallery and let me know if any or all of this is nonsense!
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Re: The Sprite Gallery

Postby tikibear » Fri Dec 26, 2008 10:29 pm

I get to be the first to laugh at my own geometry! Let me try that again:

Sprite 1 keeps its current Y axis aligned to the camera's view of its original Z axis. It is well-behaved near the equator of the original Z axis.

Sprite 2 keeps its current Y axis aligned to the camera's view of its original Y axis. It is well-behaved near the equator of the original Y axis.

Sprite 4 aligns the current Y axis with the original Y axis. It is well-behaved near the equator.

Sprite 8 does not impose any alignment. It is well-behaved at all angles.

It seems odd that sprites 1 and 2 are so similar. More experiments may be needed...
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Re: The Sprite Gallery

Postby tikibear » Fri Dec 26, 2008 11:42 pm

I have had several corrupt uploads of The Sprite Gallery. Hopefully this latest will be correct.

I made the display for sprite 1 "sideways". That means I can make all the inital Y vectors point down. I'm not sure that tells us anything.
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Re: The Sprite Gallery

Postby Corvus » Sat Dec 27, 2008 4:25 am

Tried to download, but it says: "No mirrors available". :(
"To regard the imagination as metaphysics is to think of it as part of life, and to think of it as part of life is to realize the extent of artifice. We live in the mind."

-Wallace Stevens-
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Re: The Sprite Gallery

Postby tikibear » Sat Dec 27, 2008 10:57 am

Please try again. I sent another update.
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Re: The Sprite Gallery

Postby J'Kla » Sat Dec 27, 2008 12:51 pm

I managed to get a download by right clicking and choosing version 1 although the ULM informs me this may be an incomplete download it appears to work. ;)
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Re: The Sprite Gallery

Postby Corvus » Sat Dec 27, 2008 1:03 pm

The ULM is sometimes acting confusing. I couldn't download by using the "Download newest" button, but by rightclicking on the age icon and choosing "Download Version1" (I couldn't choose Version 2). Looking at the "Age Properties" says I have Version2, and also that some files were invalid. :?

But good news: I could link to your age and all seems OK! This age is a very good idea.
I'm still dizzy from turning round and round to watch the effects. :lol:
The big lollipops are hiding the sight on sprite 1 a bit.

Btw, I like your sky. How can one make those twinkling stars?

Edit: J'Kla posted while I was writing (and disturbed by family :roll: ).
"To regard the imagination as metaphysics is to think of it as part of life, and to think of it as part of life is to realize the extent of artifice. We live in the mind."

-Wallace Stevens-
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Re: The Sprite Gallery

Postby tikibear » Sat Dec 27, 2008 3:49 pm

I made another update. Hopefully ULM is in sync now.

The idea of the obtrusive disks is to explicitly restrict view of the sprites to the angles where the sprites are well-behaved. So, for sprite 1 we see that if you want to go under the sprite you don't want to be able to go on either side (+/- local Z for the sprite). For sprite 2 or 4 if you want to be able to go all the way around the sprite then don't allow the explorer to go under or over it (+/- local Y for the sprite). Sprite 8 is well-behaved at any angle, but the image isn't aligned to any fixed direction.

Remember that sprites 1 and 2 have the same behavior, but align to different axes. Sprite 1 keeps its Y in the same plane as its initial Z. Sprite 2 keeps its Y in the same plane as its initial Y.

If you look at sprites 1, 2 or 4 along vectors near their geometric singularities they'll appear to spin around as you move.

The stars are on a sphere around the floor, as you'd guess. Inside the starry sphere is a sphere with an alpha stucco texture. So, the inner sphere's transparency varies randomly along its surface. By spinning the inner sphere relative to the starry sphere the stars appear to twinkle. The problem with this is, as with sprites, the axis has singularities. Twinkling slows as you look higher or lower. There is no twinkling at zenith or nadir.
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Re: The Sprite Gallery

Postby ametist » Sun Dec 28, 2008 12:58 am

Downloaded version 3 and it worked allright.
Nice way of explaining the behavior of the Sprite-species :) Thank you! But I have to admit I had to look at your post here and then at the sprites back and forth a couple of times to get the grip of them Sprites :D

Very good looking sky there /me clap
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Re: The Sprite Gallery

Postby tikibear » Sun Dec 28, 2008 2:55 am

It would be better to have some kind of geometric display in the Gallery with explanations. I'll try to come up with something.
Meanwhile, I've added a zenith-crossing display. I tried to come up with a use for zenith crossing, but nothing looked good. I am open to suggestions.
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