Hi.

I am running into a minor, but frustrating problem. When I began modeling the creature, it was shading great. Then , as model got more complex, and I merged it with some legacy mesh, its shading went south. I am modeling it as a sub-division model. To check shading I append Sub-Divide tile to finished mesh. However I only send the cage, without Sub-Divide tile, to OBJECTS and set its Render/Geometry as Polygons As Sub-Division Surfaces. I use Sub-Divide tile to check shading in OpenGL, and sub-division Mantra rendering to check render quality. In both cases I am having shading anamolies in same places.
So to check myself, I exported the cage mesh as OBJ, and imported it into Lightwave. There I converted it into Lightwave's sub-division surfaces. As the cage mesh has only quads and triangles, without vertex weights, the sub-division in Lightwave and Houdini yields same smooth surface. The sub-divided surface in Lightwave shades as it should.
Since I know that Lightwave's OBJ importer ignores vertex normals, and resets face normals, and becouse the model shades great in Lightwave, my conclusion is that somehow, vertex normals in my Houdini model got screwed up. I need to reset them to a consistent smoothing angle of 25 degrees across the whole mesh. However I cannot find the SOP tile that does the trick.

Please take a look at the OpenGL caps I posted;
http://sv2.3dbuzz.com/vbforum/imgView.php?imgID=5463 [sv2.3dbuzz.com]

The Lightwave shading is being done with smoothing angle of 25. Notice that Houdini OpenGL shading , of sub-divided mesh, is alot smoother, with subtle details being lost, and serious darkening where there shoudn't be any.
I tried using COMB sop but it just shifts darkening from one side of the effected vertex to another. Other SOPs don't do it. Perhaps I haven't used the right one, or haven't used them as they should be.
I need to reset the smoothing angle of the whole mesh. Which SOP or SOPs should I use?

Thank you in advance
David Rindner

Hi David,

You can use the Facet SOP with Compute Normals & Orient Polygons turned On.

Please let me know if that helps.

Cheers!
steven

HI David,
In addition to what Steven suggests (which should clear it up) you can turn on Primitive Normals, hide most of your model, then check out the areas that are causing problems. If worst comes to worst, you can use a Reverse operation (or many on the offending polygons.
I am an old Lightwave guy, and as you've noticed, Lightwave double-sides everything (but restricts you to quads or triangles for SubD stuff) and gets around the problem… I find that in Houdini I have to lay down a few Reverses to fix up troublesome polys, but it all comes out fine in the end… Your model is looking cooler and cooler, btw )

Cheers,
Peter “Voice on the Video” B

Thanks guys. But I am sorry, your suggestions did not work. I had previously tried Facet SOP. Though I did it again with new suggestions, but it did not change anything. I did check normals, one of the 1st things that I did. They are all facing in the right direction, both vertex and face, but some vertex normals are skewed. Especcially on areas where the angle between segments is extreme, more then 90 degrees. Using Comb SOP shifts the normal like it should, but instead of getting rid of the dark area it merely shifts it about the vertex normal. Its very frustrating. What I want is actually very simple. Like LW, Maya, and MAX, I am looking for Smoothing Angle control. In Lightwave it is done through Surface Manager. That is smoothing is defined by material, in MAX and Maya, smoothing is assigned to vertex or face selections. MAX, for example, has smoothing groups. Maya has command, under Model->Polygons->Smoothing Angle. What SOP is used to alter smoothing angle in Houdini?

Dave Rindner

Hi David,

I think I know what your problem is. Append an Attribute SOP after the last Merge SOP of your network. Next, type “N” (without the quotes) in the Delete Attribute parameter.

If the above solves your problem, then it is due to the merging of geometry with the Normal attribute “N” & geometry without the attribute.

To prevent this, please ensure all merging geometry has the same Attribute, namely the Normal attribute “N”, in your case.

Please remember to remove the Attribute SOP after everything's done.

I hope the above helps!

Cheers!
steven

Thanks. I am sorry if I am being dense, but I just cannot make your suggestion work. Right now my cage is a single mesh. The last merging was done generations of files ago. I have sence deleted history dozens of times and edited, split, re-edited, the mesh countless times.
I appended AttributeCreate but there is not Delete Attribute option in it. In any case this SOP doesn't fix my problem. The only Attribute SOP that has it is AttributeUV and if I put N in either Point, Vertex, Primitive,or Detail tabs Delete Attribute options, the SOP generates an error (red play button). Likewise the Delete Attribute SOP has no Delete Attribute line in it. So I am not sure how to implement your advice. I would appreciate more advice on this.

Dave Rindner

Hi David,

Please Middle Mouse click & hold on the last node to get something similiar to the following:
_____________________________________________
80 Points
12 Primitives
96 Vertices
12 Polygons
____________________________________
Size: 1.02, 1.02, 1.02
Center: 0.00999999, 0.00999999, 0.00999999
Bounds: 0.52, 0.52, 0.52
-0.5, -0.5, -0.5
____________________________________
1 Point Attributes: N

____________________________________
Approximate Memory Usage: 7 Kb
____________________________________
Notice the "1 Point Attributes: N“ line?

If it exists when you middle mouse click, append an Attribute SOP & type ”N“ in the Delete Attribute under the Point tab. If it says ”1 Primitive Attributes: N", then it's the Primitive tab.

Please let me know how it goes.

Cheers!
steven

Sorry. It just doesn't work for me. Like you showed, my geometry does have 1 Point Attribute N. I appended Attribute SOP (the icon with UV letters in it) to the end of network. Placed N in Point tab. While there is no error, there is no change shading either.
Thank you for your time and effort though. The odd thing is that I can't seem to get rid of shading anamolies at all. I tried exporting it as OBJ then bring it back in. Same with BGEO format. The OBJ imports into MAX and Lightwave perfectly and shades great in those apps, both as a cage and as sub-division surface. Only in Houdini I have problem with it. I even tried re-exporting the OBJ out of MAX and LW and bring it into Houdini, hoping that vertex normals would be filtered. I exported w/o normals and smoothing option. But when it comes back into Houdini its like it never left the app at all. Definatly a head scratcher.

Dave Rindner

Hi David,

Please try the Cusp Polygon option of the Facet SOP. Set it to a value above 90 & see whether does it help you at all.

Cheers!
steven

Tried that, no go. While it gets rid of shading anamolies, the cusped vertices do not subdivide. The cage sub-divides, in both Sub-Divide tile and Mantra, as if there are cracks in it where vertices are cusped.
I attempted to compensate with Overid Crease Weight in Sub-Divide tile and Stitching Cracks Close in Sub-Divide tile, but to no effect.
Then attempted to follow Facet tile with Fuse tile, and it returns the model to its weird shading state. If you want I can send you the BGEO, OBJ or HIP file for you to look at. My email is daverindner@yahoo.com

http://sv2.3dbuzz.com/vbforum/imgView.php?imgID=5489 [sv2.3dbuzz.com]

This is how it should shade. This is the latest development of the creature. I imported the cage into Lightwave to do screen caps.

Dave Rindner

Did you get the shading problem solved? I'd love to know what the problem was and the fix. Just for future reference, as I too am working heavily with the sub-Ds in Houdini.

Yes. With help from Steve and Pete from SideFX.
Its done with Attribute SOP.
First step is acertain of there are attributed normals. This is done by middle clicking on the last SOP. In message box there should be a line with 'Point #'. In place of point there can be Vertex, Primitive or Detail.
So the topological level of normal attribute is important.
Second step is to append Attribute SOP. In Point tab (or appropriate tab) place N in the Delete Attribute.
While the sub-d cage may STILL exibit some shading anamolies, those shading anamolies, are not passed down to the sub-division mesh in Subdivision SOP, or into the sud-d render-mesh, of cage is used w/o Subdivision SOP but with ‘Polygons as Subdivision Surfaces’ in Render attributes tab in OBJECTS.

I only encounter this problem when I merge (Merge SOP) polygonal geometry that was made in Houdini with imported OBJ geometry (from Maya, Lightwave, MAX, Rhino, or formZ).
Often what happens immidiatly at Merge SOP is that one of the merged areas looses all shading attributes. That is, its shaded flat black. This problem is solved by appending Fuse SOP immidiatly after Merge. If shading anamolies remain, and are passed down to sub-d geometry, then I have to append Attribute SOP as described above.

Dave Rindner

i might be jumping in here without really reading the thread ah the luxury of just seeing and typing.

but if your geoA and geoB before the MergeSOP do not have the same attributes pt or prim, often the MergeSOP will make one of the geos black. my solution has always been to make sure that geometry which is going to be merged should have the same attributes. so get them shading correct before the merge, facet/fuse/compute normals, delete attributes then merge.

that should fix that one.

i believe it has to do with some internals of the mergeSOP, and how it handles the data.

but like i said before i'm just jumping in here.

-k

you're right, in the same SOP you cannot have some geometry with attributes and others without. so when you merge two pieces of geometry, houdini will add the attributes to the one without and try to choose sensible defaults when it can. this doesn't always work out as planned so rather be safe than sorry and create the correct attributes on ALL pieces of geometry before the merge… (or process them after the merge)

Just to chime in here, I was having a very similar issue, and simply could not get any solution (across C4D, Houdini, Maya, Zbrush) to solve my faceted geo problem. What worked for me just now was consolidating points (or normals, seemingly) in the facet SOP. Don't know if this will help anyone, but I found this thread and it would have helped me.

The original issue (from 18 years ago, damn…) can now be sorted with a Normal SOP that provides the smoothing angle control the OP was after.