Hello
I would like to know if it’s normal that the 3D Image Object [Animated] does not spin the “back” of a photo/image in “Plane” mode (all other modes work)
A simple example:
X, Y, Z start at zero, and finish is X,Z at zero and Y at 360 (for a vertical spin)
But the result is I have plenty empty layers, all the layers between 90 degrees and 270 are empty
Other shapes are working fine, though as you can see, it’s only the “plane” mode:
The various lighting models offered are simple to compute, but from such simplicity arises cases where the lighting model does not work. In this case, surface normals (Normal (geometry) - Wikipedia ) that point away from the camera do not render.
Among most pre-made geometric objects offered by the filter, this is not a problem, as their facets enclose volumes; this non-rendering case arises only with interior-facing surfaces. The plane is just a single facet, however. It is not visible in orientations where its single normal points away from the camera. One could probably fix the issue by offering a two-facet plane — two facets pasted back-to-back — so that one or the other facet always offers a forward facing normal.
I haven’t looked at this issue at any depth; this is just an initial estimate. Perhaps not a hard fix, but not an easy, straightforward one either.
It does look like, maybe, a ray-tracing glitch. I recall first PC - DOS 3.3 and rendering a sphere with POV - forgot to add light source - 40 minutes rendering - for blank image.
For gimp_gimp-qt and the “plane” option if you keep to specific quadrants Front 0-90 / Back 270-360 / F 10-90 / B 270-360 (-ish)
You can get a complete rotation.
One snag with gmic is transparency, or lack of it for the render. Easily fixed if you know gimp and have a few old scripts.
Hi
I’m very sorry for that very late answer, 
Thanks @grosgood for your explanations, 
Thanks @rich2005 for your example and pointing me in the right direction, that’s very clever.
I do have a glitch, though, like a “jump” (especially the boat) when it shows the “back/inverted image”, any suggestion? Am I missing something?
(I did exactly and in the order you did say >> Front 0-90 / Back 270-360 / F 10-90 / B 270-360 (-ish)
here the xcf if needed (a bit big), I did remove the empty layers.
IMG-9.xcf.7z (17.7 MB)
Yes, a bit of a jump there. A bit of a miss-match between front and back.
I thought I had a spinning plugin somewhere, and eventually got back to the spinning coin plugin which uses the Gimp Map Object plugin not gmic.
About the only thing I can offer is some python “plugins” Not really plugins, more macro scripts, Three of them for the various stages, using front and back face images.
Looks like this: https://i.imgur.com/wIxhCYY.mp4
…and you are more than welcome to make something from them. The scripts here: https://filedn.com/lkb9dw6mEfXSsOu9uKLaM14/spinning.zip
Wonderful! It works nicely.
thank you very much @rich2005
