Holographic Materials

[Hageta]

There are some stickers, cloths and possibly other things, that have an holographic effect.
One such example would be the invisibility cloak from Harry Potter. How are these cases handled currently?

[Orion Pobursky]

The best practice would be like what we did for the temperature changing sticker and do multiple states with a "-fN" suffix.

[Hageta]

The best practice would be like what we did for the temperature changing sticker and do multiple states with a "-fN" suffix.

What is the sticker you mentioned?

[Chris Böhnke]

The thermo sticker is here:
https://library.ldraw.org/parts/sticker-sheets/13648

Other existing holo-foil stickers are for example:
https://library.ldraw.org/parts/1075 (Simple Glitter effect, but plain silver used instead)
https://library.ldraw.org/parts/43561 (Same Glitter effect, with texmap)
https://library.ldraw.org/parts/1141 (Triangles, colored individually)
https://library.ldraw.org/parts/49954 (Complex hologram image, with texmap)

As you can see, there's no definitive standard at the moment.

[Hageta]

The thermo sticker is here:
https://library.ldraw.org/parts/sticker-sheets/13648

Other existing holo-foil stickers are for example:
https://library.ldraw.org/parts/1075 (Simple Glitter effect, but plain silver used instead)
https://library.ldraw.org/parts/43561 (Same Glitter effect, with texmap)
https://library.ldraw.org/parts/1141 (Triangles, colored individually)
https://library.ldraw.org/parts/49954 (Complex hologram image, with texmap)

As you can see, there's no definitive standard at the moment.

I think something like the triangle example would at least work with most programs.

[N. W. Perry]

It just occurred to me, for holographic effects, could you simulate something similar to lenticular printing using tiny prism shapes with patterned sides, so you get a different image depending on the view angle?

A labor-intensive process, no doubt, but also probably automatable if someone took the time to do it. Could make an interesting proof of concept. :-)

[Chris Böhnke]

It just occurred to me, for holographic effects, could you simulate something similar to lenticular printing using tiny prism shapes with patterned sides, so you get a different image depending on the view angle?

A labor-intensive process, no doubt, but also probably automatable if someone took the time to do it. Could make an interesting proof of concept. :-)

Are you thinking of the Game Boy screen cards? I think there's an older example too, from Belville or HP...

Possible? Maybe yes.
But the amount of tiny triangles is likely not worth it. Might also make the model very hard to handle for renderers.

IMO this would be the best example for a technique like the heat sensitive UFO sticker - just make one simple file for each individual "frame".