Light Blocker in Mantra

[notintricate]

Hi! I wonder if it's possible to reproduce the same effect in Mantra as Arnold renderer has, I'm speaking of Light Blocker filter described here: https://support.solidangle.com/display/AFHUG/Light+Blocker

So what I actually want is to have some kind of hidden geometry that could block all the lightsources in the scene including environment light. I need this Light Blocker to have some kind of ramp control to adjust falloff to have soft edges.

Thnx for any clues!

Edited April 25, 2016 by notintricate

[davpe]

why don't you simply create any geometry you want and hide it from camera rays? gradient light blocking can be achieved by putting a ramp SHOP in material's opacity.

[mestela]

Blockers would be handy. From what I understand (based on long chats with the render architect guys at work) its more efficient to do this as a light modifier than as a piece of geometry; it then doesn't have to do tests against it for visibility or sampling or shadowing etc, and if done right can help steer samples ala geometry lights (but less heavy than geometry lights).

The built in shapes for round/square and ramps would also be nice to have. Ooh, and the ability to define it as a 2d blocker or 3d volume blocker.

RFE!

 

[davpe]

well you can assign a shader to the light and make a ramp or whatever pattern you want to define light intensity/color. not sure if the math behind this is the same like Arnold's blockers though.

[notintricate]

12 hours ago, davpe said:

why don't you simply create any geometry you want and hide it from camera rays? gradient light blocking can be achieved by putting a ramp SHOP in material's opacity.

Can you elaborate a bit more on the gradient part? I can't figure out how to make opacity act like density gradient in case of sphere object for example.

[Atom]

Here is my attempt at trying to implement the gradient controls SHOP opacity. I don't know how to hide an object from the camera, in C4D there is a check box, I guess there is a checkbox somewhere in Houdini as well.

 

I just plugged a Ramp parameter into Of.

ap_light_blocker.hipnc

Edited April 25, 2016 by Atom

[notintricate]

Hey Atom, unfortunately that isn't the desired result, However I almost achieved what I wanted. I converted sphere to a fog volume and applied matte shader to it. I'm sure it's not the best way, but at least in some degree It works.

shadow density 1 

shadow density 5

ap_light_blocker.hipnc

[davpe]

see attached file. shows both light blocking by shader and by geometry. geometry blocking is slower but is useful sometimes.

cheers, D.

textured lights.hiplc

[Atom]

Thanks for the example files, they both work. Now we have an additional Arnold feature implementable in Mantra.

[notintricate]

One more thing to mention, using my method it's a good idea to set light-blocker's render visibility to "invisible to primary rays (phantom)", otherwise this light-blocker object could appear in Op_Id render pass if you have one.

[Atom]

So where do I make that setting? Is that done in the object or in the Mantra node?

[notintricate]

1 hour ago, Atom said:

So where do I make that setting? Is that done in the object or in the Mantra node?

It's in object's render settings tab: