Shadows rendering without a floor?

#1

Question: is it possible to render character sprites with a shadow without rendering a floor?
I’m supposed to animate and render characters for a 2d GNU project. Animations will be stored in .PNGs with some data stored in .XML files (sprite source, centering on the map grid and so on). These files contain no data about a background colour to be ignored, it’s all managed by the .PNG alpha.
I already researched this matter in the past and I’m 90% sure that XSI cannot handle that. The point is I must be sure becouse I’m to establish a pipeline.
My XSI version is Foundation 6.02, and I’m supposed to render thousands of frames: editing by hand is not an option.
Thanks for your time.

#2

http://forums.cgsociety.org/showthread.php?f=24&t=358501&highlight=matte+shadow

That should do it. If you select the background objects (shadow recievers) before creating the new shadow pass it should set up the ray visibility overrides for you.

In the end your going to get an Alpha map (which will look inverted) which will be perfect for compositing.

Now there used to be/still may be a simpler way that wouldn’t require any compositing but I cannot seem to get it to work right atm.

If your scene is really complex you may have to set up multiple shadow passes and combine the alpha’s into one during compositing because the way the “shadow” and “simple shadow” illumination nodes are currently working they don’t actually generate any transparency, which if they did, would allow you to accomplish the compositing effect while you render. I’m not sure if somethings changed, or I just can’t find the node/settings that truly work just like Maya’s Matte Shadow material which make this really easy, but I’ve done it once before in XSI 6 so I know it is, or at least was, possible but the above should get you to the same end result.

#3

Thanks Jettatore, that did it!

I followed that post advice and linked a shadow node to the grid material in the render tree and that did the trick. That saved me to export my animations and render them in another application (Blender, for the record).
Many thanks again!

#4

I’m glad that worked, and should be all you need.

However if your scenes become more complicated later, I’ve found a way that is more powerful and very easy to work with.

In the render tree, go to nodes> illumination> more. Then navigate to the Mental Images folder and grab the mip_Matte_Shadow node.

This node is very similar to the regular shadow node in what it does, however it has multiple outputs and more importantly you can use it almost anywhere in your Render Tree where as the regular shadow node can only be plugged into the Material Surface. This means you can use this nodes “shadows_raw” output as an alpha to drive the transparency on an existing shader, which will let you catch shadows but also allows you to have a background image/object behind the shadow receiver.

#5

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