Getting Custom Attributes Info With Rays

[lisux]

Hi all.

I want to throw rays to get attribute information from hitted surfaces.

The existing functions like trace or rayhittest only returns some predefined attributes like color, alpha, P or N, but what about to retrive custom information attrahed to the hittedt surface?

Is possible?

Thanks

[grasshopper]

Does this do what you want?

rayToGetAttribute.hip

[sibarrick]

I'm guessing he means inside a shader which I don't think is possible at the moment. There are some possible hacks but what exactly are you trying to achieve?

[grasshopper]

I'm guessing he means inside a shader which I don't think is possible at the moment. There are some possible hacks but what exactly are you trying to achieve?

I believe you could adapt this technique for modifying shader attributes as well as long as you create an attribute that is named the same as the shader attribute. The shader will then update. I'll have to try it.

I agree it would be helpful to see a hip file demonstrating the problem.

[grasshopper]

Simon, I'm not sure if this is what you were getting at but here's a version with a shader attribute being modified according to the ray hit. You could do this for a renderman shader attribute by using the mapping parameters in the RenderMan tab of an Attribute SOP.

Pablo, is this any use?

rayToGetAttribute2.hip

[sibarrick]

Simon, I'm not sure if this is what you were getting at but here's a version with a shader attribute being modified according to the ray hit. You could do this for a renderman shader attribute by using the mapping parameters in the RenderMan tab of an Attribute SOP.

Pablo, is this any use?

I was thinking more of situations where you are firing rays inside the shader at render time and trying to pick up an attribute from the hit surface. Say when you don't know what the geometry is that's going to be hit and can't pre-ray onto it, or when it simply isn't efficient to do so, or when the real geometry points are too sparse for attribute transfer to work, that sort of thing. That's why I was wondering the precise details of what lisux was hoping to achieve.

I think it would be handy to have a vex function that could ray trace and query an attribute on any hit surface, even have it eval a shader to get the value perhaps.

[lisux]

I was thinking more of situations where you are firing rays inside the shader at render time and trying to pick up an attribute from the hit surface. Say when you don't know what the geometry is that's going to be hit and can't pre-ray onto it, or when it simply isn't efficient to do so, or when the real geometry points are too sparse for attribute transfer to work, that sort of thing. That's why I was wondering the precise details of what lisux was hoping to achieve.

I think it would be handy to have a vex function that could ray trace and query an attribute on any hit surface, even have it eval a shader to get the value perhaps.

Hi Simon and Grasshopper.

Yes I am in the situatuation described by Simon.

I want to do the same as in RSL, throwing rays to fetch geo data.

I was trying to do this in a volumetric shader I was developing, with different ray marching algorithm that requires raytracing.

At the end, I have leave this option because i have to made many workarounds in the shader to solve the problem of fetcheing data from geometry, and finally the shader is to expensive.

So finally again a I return to my dear sprites

Thanks for your example grasshopper, this is one of the solution I thought but at the end the owrkflow is so dirty, I don't like it, maybe for other effects is good, ie procedural moedeling, but to susbstitue the RSL feature is not so good.

Thanks for your answers.

And please SESI, add this feature to VEX.