limit geo visibililty to certain rays?

[carstenkolve]

Hi,

Quick newbie question - I'd like to trace against some geometry A in a shader, but not have it visible from camera. I've looked for an extra rendering attribute to add to A that might exclude it from the traces from the eye but make it visible to the traces from my shader - with no luck. maybe someone could point me in the direction?

Thanks,

Carsten

[symek]

1) Easy one is a phantom property installed by default on all objects: it makes an object visible only for secondary rays.

2) In pair to this one are scopes for shadows, reflections and lights. So after phantom mode is turned on, you can tweak shadows/reflections/refractions for this object also: http://www.sidefx.com/docs/houdini10.0/light/lightandshadowlinking

(An alternative to scopes are categories).

3) Scopes can be overwritten by optional parameters on per shader/call basis:

http://www.sidefx.com/docs/houdini10.0/vex/contexts/shading_contexts#rayopts

Any function involving ray tracing accepts "scope" parameter. It works with usual filtering way of Houdini (*,^,?). With this facility you can precisely specify object for every function separately.

4) You could also make a condition while computing opacity of an "hollow" object, making it transparent for anything but reflections, shadows, occlusion bounces, whatever. Ray Bounce Level VOP for example returns 0 for camera, and anything above for another rays.

5) Ultimate solutions is gather()/rayimport() bundle:

http://www.sidefx.com/docs/houdini10.0/vex/functions/gather

This way you could prepare a specific answer for a caller function from a hit object side: "if a ray is sent by 'this and this' behave such, overwise... "

Hope this helps,

skk.

[carstenkolve]

Thanks - this is great info!