Transparent shadow problem

[pdwyer]

It's probably just me since I'm a noob but I can't figure out how to get this right.

In the two pics below, the first is a Progressive "04. Metropolis Light Transport (BPT)", it's almost what I want but the clock hands show no shadows. This is a real clock on my dining room wall so I know that they do in fact cast shadows in spite of being behind tinted glass. perhaps my materials are wrong.



The second is a high quality photon map, it has the shadows on the hands but not the glass (other than a minute tint on the wall)



Any lower quality on progressive and the glass shadow is opaque, "interior +" will work like "04. Metropolis Light Transport (BPT)" and normal interior will make the shadow opaque again.

I can have the material not render shadows on the glass and I get similar to what I see in the photon map.

Is there perhaps a custom render I can set up with more depth in the number of ray bounces or something? or is that barking up the wrong tree and have just stuffed the materials or lights? The glass is common glass with an alpha of 4 and an IOR reduced to 1.15

Thanks


(great product by the way , coming from blender/yafaray I'm really enjoying sketchup+twilight )

[Fletch]

pdwyer,

sure, it's odd if it doesn't work on Easy 10. can you share the scene?

Caustics through the glass on Easy 09 only work with light emitting materials, not with point lights or sun.

[pdwyer]

Thanks for the offer to look at it, it's not a big industry secret!

http://www.dwyer-family.net/download/Clock1.skp

It's about 3mb.

The progressive render tool about 9hrs on my quad core (left it overnight while I went to bed) but even with my limited experience with twilight I can tell that the shadows in this case probably should have been starting to become visible in the first few passes

[Gaieus]

Not as if I could add anything more than Fletch when he looks into the scene so just want to mention that it's a cool model/render this way! Hope you guys figure out the missing shadows!

[pdwyer]

Cheers!

Actually I think the shadows are there just not very visible. You can see a bit near the "9" on the clock but in places where the clock face is obscured by both the tinted glass and the glass shadow the hand shadows are not visible any more. This makes me wonder if it's a material issue but the alpha is already very low

I'll keep playing I guess, I really want those shadows (hands and glass)

[pdwyer]

I've been doing some more tests on this which have raised a few more questions

I tried architechual glass which is good for all the shadows but there is no IOR. I seem to rememeber reading that these are "fake" and so to be expected

I tried the libraries since the manual suggest times like this is a good time to use them, "car glass" is pretty close but there is also no IOR. I opened the xml file and it says that car glass is 1.52 IOR but it's icon and in usage shows as 1 which doesn't look realisitic. Is it possible that the car glass is an architectual based material? There are others that work well but the wrong colour, you don't seem to be able to edit lib colours so I'll see if I can download on or learn how to make one I guess.

Now I'm just trying other materials at random with the alpha turned right down to see if I get lucky

any thoughts re the libs?

Cheers

(this is all a learning experience for me )

[Fletch]

ok... great test scene for learning! Nice and simple.
The problem is mainly the lighting.

Clock2.skp

(2.8 MiB) Downloaded 401 times

easy09-Closeup-Fnumber2.8-11passes-3m50s.jpg (101.01 KiB) Viewed 10138 times

easy09-commonglass-clear-white-7passes2m7s.jpg (102.05 KiB) Viewed 10137 times

if rendering in unbiased mode, it's best/fastest/most realistic to use a light emitting material on a face.
see attached scene.
rendered only 3 passes on corei7 with Easy 09 Interior setting in less than 1 minute.

1. common glass material template (same as yours) color white alpha 0
2. set sky to medium grey so that too much "ambient" (global) light is not "hiding" your shadows.
3. Camera Tab: exposure 1.2, gamma at .85
4. light emitting material power: 1600 (w/m2 at 2% efficiency)

IMPORTANT!:
group any geometry that is curving and must be smooth... or it will not be smooth.
reversed faces of glass - set view to monochrome in the scene you shared, and you can see all faces of glass are blue - this means they are backwards. This may not be critical, but can't hurt to fix it, as refraction depends on the face normals being correctly oriented. See topic: Materials on Back / Reversed Faces and UV Tools Fix

ps - segmented clock face - could use more arc segments so that closeup renders would look better. When you click the circle or arc tool in SketchUp, before you click anywhere else, type in 48 and hit enter, then draw your circle... should render better.

[pdwyer]

Thanks for this,

I usually always check that my face normals are correct (not blue) I don't how how that slipped by me, thanks for that.

I'm going to play with your settings a bit more to understand them better.

One thing I am noticing though, changing the alpha level by 10-20% seems to have no effect on the shade of the shadow cast even in unbiased renders, that seems wrong. (won't go as far as to say the "bug" word as I'm not that sure of myself yet.

Will get back to you after some playing over the next few days

[Fletch]

Well, with this template, the "alpha" is actually only changing the weight of the refraction, and it is not a 1:1 relationship. That is to say that 50% alpha in the realistic glass common template is about equal to a refraction weight of .849. It's not a bug, just a 'limitation' of this style of setting up glass. You can of course set up any glass you like in Kerkythea's advanced material editor studio, and then use the library you make here with Twilight.

you can get a glass library here
How to install Kerkythea Material Libraries to use with Twilight Render.
List of Kerkythea Material Libraries (4 pages!).

[pdwyer]

Thanks!

I'm still working with the files you uploaded trying to understand this better though. I'll definately look into the other materials