Scene Blackout

[altbighead]

hello all.

I am in SOP level with a couple of objects model in houdin and a few importing as a *.odj format.

As soon as I try to merge the two group together , all of the models disappered except for the OBJ group .nope.. It has nothing to do with normal since all the normals are facing to right direction.

before

after

[Jason]

Hmm, that IS curious. So you're certain that all the inputs into the Merge have either NO point normals or all have correct point nornals?

If you follow the merge with a AttributeSOP and delete point "N", does it look better?

[altbighead]

Hmm, that IS curious. So you're certain that all the inputs into the Merge have either NO point normals or all have correct point nornals?

If you follow the merge with a AttributeSOP and delete point "N", does it look better?

21476[/snapback]

I tried plugging facet SOP on both group before merging and it works.Just the I got a yellow warning saying that " A mis match of attributes on the inputs was detected".

I also tried your AttributeSOP and it works perfectly.

AM i missing something?

[Jason]

I tried plugging facet SOP on both group before merging and it works.Just the I got a yellow warning saying that " A mis match of attributes on the inputs was detected".

I also tried your AttributeSOP and it works perfectly.

AM i missing something?

21477[/snapback]

Yeah - when merging geometry together where only some of the inputs have point normals defined then it initializes the point normals on the undefined portion of geometry to be {0,0,0}, regardless of the primitive normals. While this seems counter-intuitive (like, "why doesn't it just compute point normals from the face normals for the undefined part?"), it has a couple of reasons behind it.

Firstly, Houdini wants you to be very conscious of the work you ask it to do. Computing normals can be take some time on large geometry - so Houdini'd rather you computed it explicitly instead of not realizing the work you're asking the MergeSop to do.

Secondly, internally in Houdini, attributes have simple defaults for missing attributes - there is no way to define a function for Houdini to invoke to compute missing attributes, AFAIK.

Unfortunatey this will continue to trip you up for years to come But you begin to recognize the sign instantly.

[altbighead]

ok .. I got this render problem.. not sure if it is a geometry problem or render setting but it must be some basic setting that I couldn't figure out..

pretty.. help me

[Jason]

Ah, if this is happening with a really recent version of Houdini then it's a bug that Side Effects know about and may even fix it this coming Monday (so, Tuesday's build). I got the same thing on a scene of my own where I am using GI in conjuction with a shader which invokes the diffuse() call twice. I'll write here if I hear if the bug gets fixed on Mon.

Just so you know, what causes things like this is called NANs (Not A Number) - which you can produce pretty easily if you, for example, accidently divide by zero in a shader. However because I've seen (and reported) some recent NAN occurences I highly doubt this particular incidence of NANs is your fault. The white pixels are where the shading sample returns this invalid result and affects the pixel covering the sample and all the other pixels around it, depending on the Pixel Filter width - which is be default a "gaussian 2x2" filter. This explains why its not a tiny point only but appears as a little square.

- and a little comment on your scene if I may: it looks like several of your objects - the knife blad ande the wooden rack - need to be cusped properly. Either simply Facet(Unique Points) or EdgeCusp or PolyBevel a simple bevel in there. They're not shading faceted like they should.