Render: Polygons as SDS

[LEO-oo-]

I try to render a model with displacement - all works. When I switch in Model/Render the option "Geometry" to "Polygons as Subdivision Surfaces" to avoid the cracks - Houdini wont render the scene. MPlay is open and I see a grey field

Anybody have an idea whats wrong?

[thekenny]

When you are referring to cracks, do you mean from displacement bounds, or from different uv coordinates on the poly surface?

If you are seeing cracks in your displacement you have to increase the Displacement bounds option under the render tab.

If you are seeing separation of the surface when you render it as a subD then that's something else.

Have you tired to render your geometry without the displacement as a subD?

Is this renderman or mantra?

-k

I try to render a model with displacement - all works. When I switch in Model/Render the option "Geometry" to "Polygons as Subdivision Surfaces" to avoid the cracks - Houdini wont render the scene. MPlay is open and I see a grey field

Anybody have an idea whats wrong?

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[stu]

Without seeing a file I'm making a bunch of wild guesses but here goes...

Based on the two problems that you're describing I'd guess that your geometry has exclussively unique points (hard edges). The displacement is pulling the faces apart at rendertime (causing the cracks), and because mantra doesn't have crease support, there is no way to lock down unshared points while rendering with sub'ds (Mark, are you listening? ) all of the faces with non-shared points will be reduced to nothing.

Again, without a .hip file I'm just guessing.

Solutions:

1. Can you use a bump instead?

or

2. Make all the points shared and using the polybevel SOP, and give each edge a very small bevel, giving the impression that all of the edges are hard.

or

3. This is the most cumbersome - there are ways to shade a surface using the unique point normals but displace using shared point normals, but this will require a bit of setup in both the SOP network and the shader.

Hope this helps,

stu

[LEO-oo-]

Thank you for the response and the suggestions. I think my problem is the export of the displacement in ZBrush.

I have try the ZBrush-Displacement-Sample and it works.

Thanks again! Leo

[eloop]

This may be a bug with mantra barfing on displaced SDS's. I reported something similar a while back and to my knowledge it hasn't been fixed yet. You should probably report it to SideFX.

-Drew

[DaJuice]

Are you sure? Pretty much everything I've been rendering lately has been SDS with displacement, and I don't think I've encountered any outright bugs. I'm curious what the problem was.

[LEO-oo-]

@DaJuice:

1. Thanks for your post at ZBrushCentral - I have use your setup.

2. I cant render this head with the SDS-option. I found out about this morning! I use version 7.0.231.

3. And there is one more problem: In your displacement-shader you use "UV Transform" to flip the image. I have try this in v7.0.231 and it wont work. The image is complete white. I have to flip the image in Photoshop to get the correct result. Any idea?

[Moose]

I've tried it on the zb head and also the sword, and I too get problems (artifacts and renders stopping midway through - or not starting at all). I narrowed it down to one of the lights casting a shadow - when I render without shadows everything seems to work alright - and looks very nice too. So I don't know if the problem's with Houdini, ZB or perhaps even my slowly ageing computer. Rendering a default box with sds, shadows and a Fractal Dent disp shader works as expected for me (if that means anything).

[eloop]

Yep, it was verified and logged by support .

-Drew

Are you sure? Pretty much everything I've been rendering lately has been SDS with displacement, and I don't think I've encountered any outright bugs. I'm curious what the problem was.

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[DaJuice]

Ah, I see.

Hey Leo, glad to see it was of some use. That's weird about the UV Transform. What happens when you try to render as SDS, won't start?

Moose, by artifacts do you mean these irregularly shaped, dark splotches all over the model? If that's it maybe try using a rayshadow SHOP for your light and tinker with the Bias parameter. That might not be it, but I can't think of anything else right now. Also if the displace bound is too high it can really screw with your render times when using displacement in conjunction with GI (though I don't know if you're using GI) and make it seem like your render won't start at all.

[LEO-oo-]

@DaJuice

What happens when you try to render as SDS, won't start?

This is up to the camera-position/zoom. With a closeup of the head, it starts to render and stops after a while. When I zoom out - it won't start to render

[Jason]

@DaJuice

What happens when you try to render as SDS, won't start?

This is up to the camera-position/zoom. With a closeup of the head, it starts to render and stops after a while. When I zoom out - it won't start to render 

15989[/snapback]

What version are you attempting to render with?

Without reading the rest of this thread - there might be degenerate polys / zero area polys in a part of the model. Try to clean the model (Clean SOP and such) and view primitive numbers and inspect the model for strange or bad geometry.

[edward]

I finally got curious and tried this out myself. The problem with the UVTransform is that the default pivot is set to (0,0,0). You need to change it to (0,0.5,0) so that it is correctly flipped. In my own file, I flipped the uv's in SOP space using a UVTransform and so I could tell if it was doing it the way I want in the UV viewport.

[LEO-oo-]

Thanks Edward - you are right with the pivot-option!