Turn off self-shadows but still receive shadows?

# 1 11-10-2016 , 03:09 PM

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Turn off self-shadows but still receive shadows?

I just spend ages carefully modelling a plane to match actual real-world terrain, for the sole purpose of having a shadow look natural as it moves over the eneven surface. Now I can't seem to figure out ho to render ONLY the shadow cast from the moving object. I was planning on using a surface shader, but I just realised they don't receive shadows from anywhere unless I'm mistaken. Turning off "casts shadows" on the surface, doesn't stop self-shadows. Isn't there a shadow linking editor like the light linking one, that determines which objects may cast shadows onto which?
I'll be comping into live footage, so I can't have the self shadow there. I'm almost tempted to just render with all the self-shadow, and just animate a mask around the shadow in AE. It's fairly diffuse so, with a feathered mask, it might be the quickest way. I just assumed Maya would have a one-click solution for things like this. Or are people comping shadows cast onto perfectly flat planes into live footage?

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# 2 11-10-2016 , 03:27 PM

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Ohhhh...I guess I can use the uneven geometry to create a bump map to apply to a flat plane....IF I remember how. Think I have a tutorial somewhere. In fact, I think I got it from here. user added image

EDit. No, that's just silly. Then I'd have troublesome fake self-shadow that I don't want, instead of troublesome real self-shadow that I don't want. D'oh!

Edit. I think what I'll try first is rendering a pass with just my surface, then one with the surface and the shadow I want, then try a difference blend mode in AE. I've never used one before, but if it does what it sounds like it does, I should be in business

Edit. Hmmm...doesn't seem to work. I made a new comp and added first the geometry without the shadow, then the same scene but with the shadow. I added it using the difference blending mode and it looked like it worked, since I could only see the shadow, but when I added that comp to the main comp, I just got a big black hole in the shape of the surface geometry. I'll play around with other blending modes maybe. I already tried keying out the shadow, but it's too similar to the surface to get a good key. There's gotta be a way to do this in Maya.
Anyone?

EDit: I tried a Use background shader, but it still casts self-shadow for some reason. So far, only surface shaders do not, but I can't find a way to make them RECEIVE shadow

Edit: tried a lambert with the amient colour the same as the colour. That got rid of the self shadow, but, for some reason, it also eliminates the shadow cast onto the surface

This is driving me nuts. All I wanna do is have a shadow follow an uneven surface - as I know Maya can do - without that surface casting self-shadow - which I also know Maya can do - and render out JUST the shadow - which I ALSO know Maya can do. I don't see why it can't do all three at once. Where is that damn smilie with the guy hitting himself in the head with a mallet?

Last edited by xgabrielx; 11-10-2016 at 06:23 PM.

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# 3 12-10-2016 , 03:02 PM

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Join Date: May 2011

Location: Riyadh, Saudi Arabia

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Hi xgabrielx, which render engine are you using? Shadow passes/catchers are implemented slightly different by the different render engines.

Earth: The crazy asylum of the universe.

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# 4 12-10-2016 , 03:30 PM

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Mental ray. But it doesn't need to be. I've already rendered everything but the shadows.
I only have the renderers that come with Maya, but I can probably get access to others if
needs be. There's no huge time issue here

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# 5 12-10-2016 , 06:46 PM

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Join Date: May 2011

Location: Riyadh, Saudi Arabia

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You have a couple of options. You can go with the use background shader or you can use the mental ray production shaders.

Jay has a tutorial on the usebackground shader https://vimeo.com/18536683 (Is this supposed to be available on Vimeo?)

Zap's mental ray tips has an explanation and sample scenes for using the production shaders. Just before the comments section he describes how to modify the setup so you can use the output for compositing. https://mentalraytips.blogspot.com/20...-examples.html

In both scenarios the alpha channel contains the shadow information. (Watch out for shadows on shadows during compositing)

Earth: The crazy asylum of the universe.

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# 6 12-10-2016 , 07:33 PM

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ahh, thanks. I looked into the use background shader before, but it seems to cast shadows on itself. I never looked too deeply though. I'll check those links out. I can't believe they don't make it much easier to do

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Turn off self-shadows but still receive shadows?

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