Falloff

[gdogg2k]

is there a way to emulate 3dsmax4's falloff map?

[richard-sher]

You could plug a texture map (or a gradient, or anything else) into the lights intensity. Or maybe into the start/stop or the spread.

I guess it all depends on what aspect of the fall off you want to control with a map. I can't remember specifically what was controlled by the fall off map in 3dsmax.

[anmtek]

In Max you can use a Falloff map based on the location of just about anything in the scene.

I use Falloff(in Maya and Max) for a veriety of lighting effects. It also works great for refections based on angle. I would love to be able to use it in conjunction with information on where the lights are(light direction).
I can't find a way to do that in XSI. There is no info.sampler node that would provide that information. It seams I am limited to Camera and up vector of the object. Being able to use scene data(not to mention the data from other shaders) would go a long way to solving some of my problems with lighting effects and subsurface scattering.
So far I like XSI, but when it comes to creating shader trees, I feel like I'm working blind. I can't pass info from scene nodes and between nodes of shaders on different objects.
If anyone understands what I'm talking about and I'm just missing some concept in XSI, please let me know!

[devdoka]

I understand where you're coming from, and you're right, you cannot do that in XSI at the moment because the required nodes just aren't there......yet.

In order to do a truly accurate falloff in the material shader, you need a material shader that understands what you're trying to achieve. Such a shader is not difficult to write, but somebody needs to take the time to write it. Same goes for lights and cameras.

In your case, you can use the incidence shader to extract the ray angle between the light and/or camera with whatever target it hits. This can be used to modulate the intensity of the surface. If you need more information about start and end points of rays, or normal info, you can use the scalar_state and vector_state nodes to get that. You won't be able to modulate the reflection depth because that requires casting a secondary ray from the material along the required path. There aren't any nodes to do that yet. But you can modulate the intensity of the returned reflected color using passes or the compositor to put humpty dumpty together again.

In the meantime, you'll have to approximate. Be careful when using data from the scene in the rendertree because mental ray does all it's math in it's own "internal" coordinate system that does not necessarily match XSI's global coordinate space. mental leaves internal space undefined, therefore it changes depending on which context you're using information. In most cases, internal space is the same as world space, but not always.

Matt

---

Matt Lind
Animator / Technical Director
Softimage certified instructor:
Softimage|3D
Softimage|XSI
speye_21@hotmail.com

[devdoka]

I understand where you're coming from, and you're right, you cannot do that in XSI at the moment because the required nodes just aren't there......yet.

In order to do a truly accurate falloff in the material shader, you need a material shader that understands what you're trying to achieve. Such a shader is not difficult to write, but somebody needs to take the time to write it. Same goes for lights and cameras.

In your case, you can use the incidence shader to extract the ray angle between the light and/or camera with whatever target it hits. This can be used to modulate the intensity of the surface. If you need more information about start and end points of rays, or normal info, you can use the scalar_state and vector_state nodes to get that. You won't be able to modulate the reflection depth because that requires casting a secondary ray from the material along the required path. There aren't any nodes to do that yet. But you can modulate the intensity of the returned reflected color using passes or the compositor to put humpty dumpty together again.

In the meantime, you'll have to approximate. Be careful when using data from the scene in the rendertree because mental ray does all it's math in it's own "internal" coordinate system that does not necessarily match XSI's global coordinate space. mental leaves internal space undefined, therefore it changes depending on which context you're using information. In most cases, internal space is the same as world space, but not always.

Matt

---

Matt Lind
Animator / Technical Director
Softimage certified instructor:
Softimage|3D
Softimage|XSI
speye_21@hotmail.com

[pen-pen]

You say that you use the falloff map in max and maya,
i use both max and maya and am currently trying to create fresnal falloff using maya, you seem to know what your talking about, just wondering if you could help clarify it for me, in regards to maya

sorry this isnt an xsi related post, i mean no disrespect posting a maya related question in the xsi forum : ]

[fishon]

INCIDENCE is basically what you are looking for or there is a falloff node that you can hook up to anything.

when you uderstand the tree it is very similar to the way max works only a different graphic display.