Shadow on inside of curtain

[halfstone]

I have a light outside a window, with a sheer curtain on the inside.  The shadow of the window frame does not show up on the sheer curtain.  I know that I've done this before and it has worked fine but nothing I do works. 

I've set up a test scene with just a window frame, a spotlight for the shadows and a couple of low-intensity directional lights just for balance. There is no glass in the window for this test. 

Maya 2016

mental ray render

mia material on window frame, 100% diffuse

mia material on sheer curtain, no reflectivity, 50% transparent

trace depth set to 4 on light, 6 in render settings. 

See images - shadow appears on the back of the curtain (outside) but not the front (inside) where I want it to be.  

I have also tried this with the Maya renderer and lambert surfaces, with the same result. 

[damaggio · Accepted solution]

In this case for fabric you should use a double sided shader either with the mia or the mila....kinda the same principle for leaves.

Use the cutout opacity just a touch, and set transparency to fully transparent at 1.0

https://www.youtube.com/watch?v=gNUeRMDpyro

[damaggio]

Also note that the twosided node with front and back is plugged into Translucency and there's a weight slider there to control transparency as well.

[damaggio]

sample...

[halfstone]

Thanks for this answer.  Works great up to a point - I used the Mia material; haven't gotten around to the Mila yet but everything works as it should. However, take a look at the attached - neither the colormap I used for the curtain nor the shadow that is cast on it is reflected in the shadow that is cast on the floor - the curtain just appears as an untextured plane without a secondary shadow. 

Any advice on this?  I increased the trace depth and the ray depth limit but they don't seem to help.  I also tried Daryl's bug solution of changing the Shadow Method to "Simple" instead of "Segmented", which I didn't think would work  - and it didn't. 

Thanks, though, for the help you provided.  Definitely works for the shadows on the curtain. 

[damaggio]

I' m a little confused halfstone ..this line doesn't seem to be written right.... "neither the colormap I used for the curtain nor the shadow that is cast on it is reflected in the shadow that is cast on the floor"

Looking at the picture seems correct to me, I see the shadow on the curtain, I see the shadow of the curtain and the window frame cast on the floor.

[halfstone]

Maybe "reflected" is the wrong word.  Inasmuch as the curtain has some texture on it, I would expect to see that texture in the shadow as well.  I did figure this out, though. - The transparency of the curtain is what the shadow is based on; in this instance the texture is applied to the translucency which is not used in the calculation of the shadow. 

I took the file texture and piped it through another multiply/divide node, then through a luminance node and connected it to the transparency attribute of the mia material.  There's some adjustment that still needs to be done to get the right balance, but the concept is there.  

Take a look at the attached image and you'll see what I mean - there's a very subtle texture in the shadow of the curtain, which is what was missing in the first image.  

Thanks again for your help.  I've used the two-sided shaders before in a lot of situations, but none like this.  To me it is counter-intuitive that it would be needed for shadows on transparencies.  

[damaggio]

Cool, I see what you meant now, you figured out the rest...nice.

Best.