Fur's Bounding Box Shows In Ambient Occlusion

[kafl]

When I use the Volume shader as fur shader and use an Ambient occluision shader on any other object, the furs bounding box shows on the other objects in Ambient occlusion.
Any solutions for that?

[joojaa]

longer ray paths for occlusion. I dont think occlusion is such a smart thing with volume fur, it kindof defeats the purpose of occlusion. And thas NOT to calculate shading info, but for raymarcher obviously that means this. You might aswell use final gather directly in that case.

[kafl]

Hi Joojaa

Im not sure wether I missread you post or you missread mine but I use Ambient occ on other objects where I need it. Theese objects dont have fur on them, but the bounding box (or whatever it is) of the fur object, that is applied to some objects in the scene, is now interfeering with the ambient occlusion.

It really simple to make a test to show what the problem is, and im sure its not supposed to be like that.
Just make any object apply fur, change the fur shader to volume in the fur render settings, make a new object that touches the bounding box of the fur and apply an ambien occ shader to that.
Now the bounding box frame act as its a normal invisible model in the Ambient occ object.

Thanks a lot

[joojaa]

QUOTE(kafl @ 01/03/08, 09:56 PM) [snapback]279111[/snapback]
It really simple to make a test to show what the problem is, and im sure its not supposed to be like that.

It is, see occlusion by cg definition is only going to do a hit test no shading (thats the entire idea otherwise its called gather). Its a trick. No such thing as occlusion truly exsists in reality, gather does.

NOW a volume fur is a cube that has volume information inside it so its then ray marched to see how it look like. NOW this raymarching represents shading and occlusion by design inst supposed to shade. Ergo it will look like a box since thats the shape of the unshaded fur object.

that is what you get when you do what you tell the computer to do. However you can unmark the cube form occlusion calcualtion,and make a simple proxy for the futr, Or you can change the shader a bit to continue rays. (tough i have no idea how) and again it would defeat the idea of occlusion. Because its not supposed to shade, its the reason we use it instead of gather.

Thsi si what things are. Your caught up with on the other hand what you want and what you think something is versus what the 2 definitions really are and they conflict.

But yes you can let mr send longer max rays in the occlusion. This should let it ray march. Will test, no maya unlimited at hand.

But as i said its a bit of a contradiction in terms.

Its like asking for a amputation but withiout loosing a part of your body.

[kafl]

Hi Joojaa

Thanks a lot for the good explanation.

Just to fix this for right now how do i unmark the cube from occlusion? Btw i do not want/need the fur to show up in the occlusion.

thanks a lot

[james-cunningham]

I've got a workaround for you, as I just had the exact same problem.
My solution is to make it do my furShape nodes are not seen by the AmbOcc calulations.
In the mib_amb_occlusion node change Id Inclexcl to -1
Now anything in your scene labeled with "miLabel" set to value 1 will now not be 'seen' by the AmbOcc
To do that select the furShape node. Go Attributes, add Attributes, type in miLabel and hit add.
In the channel box set that value to 1.

That works for me.