A question about technique...

Hi all,


I'm looking for someone to help explain the simulated 3D effect that is used for fire and other things like flowers etc.

Here is a link to a screen grab for creating a flower that illustrates what I am curious about.

http://www.freepgs.com/wizzie/SecondLife/TutorialQuestion/tq1.jpg

This example has three elements, I've seen similar constructions with four panels.

My question is how is this done? Is it the same picture copied exactly the same on each side of the panels, or snap shots from various angles inside a 3D program like Maya?

Thanks for the help.

Kindest regards,
wizzie

It depends a bit, but most of them use the same design on each of the prims, with the prims crossing at the trunk/stem if relevant.

Alpha sorting and the general rendering then do the rest, in combination with brains that interpret things in a 3D fashion.

Also, don't forget, when you're doing this, to use a Transparent texture (one with a totally black Alpha channel) on the top and sides of each of those prims, to help maintain the illusion. (You don't want to be able to see the sides and top at all.)

Hope this helps!

Yes it's normally the same image on all sides.

This technique is used to simulate "Billboarding", where a 2D face is always rotated and presented to the viewer from the front. Particles in SL are "billboards". By placing 3 planes centred and rotated by 60 degrees from each other you can simulate billboards because you can be pretty sure at least one of those faces will be nearly straight on to the viewer.

Hi all,
Thanks for the replys.

It is simpler than I thougt.

I had tried an experiment where I rendered group of flowers in 3D with Maya, but the result in world was less than spectacular.



wizzie

It'll depend a lot on how you go about doing that. rendering multiple views of such flowers by rotating the camera aimed at them around (a poor man's "bullet time" render) and then using these views on flat slices arranged like on your screenshot.. it can give more realistic results than the same image used for all the slices, as long as you can prevent the usual problems with sorting transparent surfaces.

Could you please explain "usual problems with sorting transparent surfaces" ... the problems part? How does one 'fix' the problem?

thanks,
wizzie

The problem: usual way to sort prims which use transparency-mapped textures is to check the centre point of such prim, then sort all these prims based on distance from viewer.

This generally work well enough, but if you have multiple prims wih their centre points right next to each other, the sorting becomes unpredictable. One frame one of these prims can be determined to be in front, then a next frame it's another of such prims. The effect is very noticeable, it's like the prims are swapping places with any slightest move you make, or sometimes even on their own.

This is exactly what happens with these texture mapped flowers and such -- because illusion is done through copying the same primitive and rotating it, all these slices share the same centre. And the oogly prim flipping starts :<

A sort-of solution for it is to ensure your prims have their centre points in different spots in world. In this particular case, it'd involve split each of texture mapped slices in two halves (each of them becoming a separate prim) along the line where they all cross every other. Then, when the player moves around, it's easier for the game client to correctly determine order in which they all should be rendered.

Hope this helps, it's admittedly quite confusing and hard to explain better ^^;;

OK, yes you are correct that's as clear a strong coffee with cream and sugar

Let me see if I have an understanding lol
http://www.freepgs.com/wizzie/SecondLife/TutorialQuestion/SecondLifeTextureQuestion.htm

regards,
wizzie

If you look in your library in your inventory, you'll see that there are many linden-made plants in there, potted flowers and such. Rez them and examine how they're made. You'll see that it's just a simple criss-cross setup, just as described in Eloise's first reply. If you want to make your own, just do it the same way.

As for Joannah's suggestion of making sure the center points are in different locations, with respect, I'd recommend against that. That will hurt the illusion, as the object will appear to move around in space, depending on the camera angle. The way it will work if they all share the same center point is that the plane most facing the camera will always be visible, and the others will sort "behind" it, creating the illusion that your plant (or flame, or whatever it is) looks correct from all sides.