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Guest mantragora

Render Artifacts

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Guest mantragora

Hi.

Every time I render something I get those ugly artifacts that you can see on attached pictures. At first I thought that this is because of badly modeled geometry, but this is not the reason. This model on picture is made from one piece rotated around, so if it was broken, each piece should get the same artifacts.

They show quite randomly, but only on completely FLAT surfaces on geometry that have added "polygons as subdivision" attribute. I can take simple tube, scale one end, cap it, add bevel to maintain shape and flag it with "polygons as subdivision" and in the render I get completely clean render everywhere beside this caped, flat place.

What's the problem ?

If I add Subdivide node on the end, bump it sometimes even to 2, it helps, but then it makes no sense to use "polygons as subdivision". It happens in all modes in H12 and H11 - Micropoly, Raytracying, PBR. I don't get it only in MicroPoly mode in H10, but in PBR it shows.

BTW. Mantra is the only renderer out there that produces those artifacts with this geometry. MR, Modo, Vray - all renders clean geometry.

Help !

post-7494-133718230507_thumb.jpg

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Can you attach a .bgeo that reproduces this?

If you imported this geo with normals present, it may be helpful to delete them and use a Facet SOP to add them back.

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Yeah it looks like you've got disconnected points or duplicate edges, doubt this would show up in MR/Vray because they don't use rendertime subdivision surfaces. You would see the same thing in Renderman or 3Delight, subdivision smooths the mesh and will pull apart anything that's not connected. Try picking (not box selecting) one of the offending edges and moving it out of the way, I'd bet there's another edge under there sitting in the same spot. Throw down a Clean SOP at the end of your network and toggle everything on, see if that fixes it.

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Guest mantragora

Here it is. I modified ge this geo on one side just to see if adding some geometry there solves problem, but nope. I added there render that was made with exact camera setup that is made in this file.

Desktop.rar

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Guest mantragora

Yeah it looks like you've got disconnected points or duplicate edges, doubt this would show up in MR/Vray because they don't use rendertime subdivision surfaces. You would see the same thing in Renderman or 3Delight, subdivision smooths the mesh and will pull apart anything that's not connected. Try picking (not box selecting) one of the offending edges and moving it out of the way, I'd bet there's another edge under there sitting in the same spot. Throw down a Clean SOP at the end of your network and toggle everything on, see if that fixes it.

Yeah, I know that it look like that, but if it was this, it should be visible on each piece always, not show up randomly.

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Ok so you just need to turn the "Surface as Subdivision" off at /obj level.

Because you have so many n-gons, it just doesn't know what to do with them at rendertime.

Try and keep your meshes to quads. In the mean time, just turn subdivision off.

Christian

post-6175-133718767794_thumb.jpg

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Guest mantragora

Because you have so many n-gons, it just doesn't know what to do with them at rendertime.

But even when I reduce geometry just to those couple polygons Mantra still doesn't know how to Subdivide them correctly ? That sucks. I was hoping that it can handle at least those couple ngons. Especially that those are completely flat surfaces, no bumps.

post-7494-133718832249_thumb.jpg

Anyway, thanks for looking at this.

Edited by mantragora

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But it's standard to never do ngons for a pretty good reason!

Just model with quads only....

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Do you have the very latest build installed?

There was this entry in yesterday's Journal:

Monday, May 14, 2012

Houdini 12.0.626: Fixed a problem that would produce cracks when rendering subdivision surfaces with micropolygon rendering.

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Guest mantragora

But it's standard to never do ngons for a pretty good reason!

Yeah. But I thought that for completely flat surface this rule can be a little bended :).

Thank you.

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Guest mantragora

Do you have the very latest build installed?

There was this entry in yesterday's Journal:

Nope, I'm downloading it like now :).

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