Shadow casting without object rendering?

[cookey]

Does anyone know if you can make a model cast a shadow without the model itself rendering in the scene.

I have some trees that have foliage made out of hairs. Takes forever to render with the shadow option on.

I was going to fake the shadow of the tree by decaling a single patch with an image of the tree as a cookie cut,

then placing it correctly in the scene so that it casts an approximate shadow of the real tree.

The trouble is the cookie cut patch renders in the scene as well and I can't see anyway of making it none renderable

whilst still casting a shadow. If I place the cookie cut out of the view of the camera then I can't get the

shadow position correct.

 

I've tried using Z-Buffered lights to create my shadows which are much faster, but they produce inaccurate

shadows on other objects in my scene. A set of iron gates for instance gets a shadow that looks completely wrong.

If anybody has any ideas on this or how to speed up rendering when using raytraced lights and hair with shadows

then I would be grateful

[Luuk Steitner]

You could render with the shadow buffer on (render options), and place the shadow layer in your final composite. Then you can render your scene without those cookie cut images.

But maybe someone knows a better trick...

[robcat2075]

Rendering to EXR format enables separate buffers for shadows and lights and almost anything you'd want to separate.

 

It is possible to manipulate the mix of these buffers in an A:M EXR "composition" (I can't explain it all here, I'm just sayin' it's out there)

 

A more convenient way to use these buffers is in a compositing app such as After Effects that can read EXR files and their various buffers.

 

This is advanced VFX stuff. It's great that A:M supports it, it just needs some more documentation to make it accessible to more A:M users.

[robcat2075]

I've tried using Z-Buffered lights to create my shadows which are much faster, but they produce inaccurate

shadows on other objects in my scene. A set of iron gates for instance gets a shadow that looks completely wrong.

If anybody has any ideas on this or how to speed up rendering when using raytraced lights and hair with shadows

then I would be grateful

 

"Light Lists" limit the light from a light to particular objects in a scene. You might use that to selectively light things. This is very situation specific and may or may not help in your case.

[Rodney]

I think... think... think... I know the answer to this.

I cannot test and confirm at the moment.

 

Can you not toggle off the Render Mode in the Chor for the object and still have it cast a shadow?

Thats the wireframe looking thing to the right of your Chor object.

 

That use to work.

[cookey]

Switching the object render mode to "hidden" hides the object in the choreography window display, but it

still appears when you render the scene.

 

Messing around with surface properties of a model I noticed that if you set the transparency to 100% and the density

to 1% or less (not 0 tho) the model doesn't appear but still casts its shadow. Unfortunately this only works with Z-Buffered Shadows.

Might be a useful trick for other people out there tho.

 

I've managed to hide my cookie cut shadow casting patches inside the foliage of the trees for the time been.

They are hardly visible but still cast an approximate shadow in my scene.

 

My project is a graveyard with a landscape, trees, grass and gravestones etc.

I want to render my scene out as an animation and the render time was impractically long. Each frame would have taken about 30mins

and a 1000 frame animation would take 20 days to render.

 

Thanks for the help. I will have to perhaps have a re-think on how I light the scene maybe to get that hair particle system (foliage)

to render faster with shadows.