Controlling depth of render-time subdivision

[jrockstad]

Hi guys, so, I'm almost positive this has come up on the forums before, but searching around a bit has failed me. The issue is that I generally prefer to use the Render Polygons As Subdivision option for my renders and just use the Subdivide node to preview, which is normally just fine, but I'm finding the mesh just a tad chunky on this close-up shot I'm working on. I assume the default subdivision depth is 2, and that there must be a parameter hidden away somewhere allowing this to be modified, but I haven't found anything after digging around a bit in the render parameters. Is there a geometry attribute to control this, or a parameter that I'm missing...?

Thanks!

[edward]

You mean doing this in the viewport? Try hitting the + hotkey in the viewport.

[jrockstad]

Ah, I probably confused things by mentioning the Subdivide SOP, but no, this isn't a viewport but rather a render issue. I want to know if, using the Render Polygons As Subdivision parameter on an object, it is possible to control the depth of the rendered subdivision surface.

[Guest tar]

Not that I've heard of, from the documentation, these options are available:

 

Polygons as subdivision (Mantra)

Houdini

vm_rendersubd

IFD

object:rendersubd

Render polygons as a subdivision surface. The creaseweight attribute is used to perform linear creasing. This attribute may appear on points, vertices or primitives.

Subdivision Style

Houdini

vm_subdstyle

IFD

object:subdstyle

The algorithm used to render subdivision surfaces. Currently, this can be either mantra_catclark orosd_catclark.

[jrockstad]

Yeah, those are the only ones I found as well. It seems strange to me that this wouldn't be an option, unless the subdivision depth is absolutely hard-coded into Houdini. I've been using Modo a lot lately and this an area where I think Houdini could take some cues from that package - in Modo, you press the tab key, get a sub-d mesh preview in the viewport and in your render, nice and simple, and you've got separate parameters for viewport and render subdivision depth as well. Yes, I realize Maya's smooth-mesh preview does pretty much the same thing, but I like Modo more. 

[Guest tar]

Cool - there are many things that are needed to improve the sub-d workflow in Houdini. Please send it into SideFx so they can log it as a feature request.

 

Thanks!

[Andy58]

2 hours ago, jrockstad said:

Yeah, those are the only ones I found as well. It seems strange to me that this wouldn't be an option, unless the subdivision depth is absolutely hard-coded into Houdini. I've been using Modo a lot lately and this an area where I think Houdini could take some cues from that package - in Modo, you press the tab key, get a sub-d mesh preview in the viewport and in your render, nice and simple, and you've got separate parameters for viewport and render subdivision depth as well. Yes, I realize Maya's smooth-mesh preview does pretty much the same thing, but I like Modo more. 

There are no similar controls you might know from other programs/rendering engines. Which handle subd levels for viewport and rendering in levels of 0,1,2,...
In Houdini/Mantra this is controlled by the shading quality. Have a look at the docs:

Quote

Shading quality

Houdini

vm_shadingquality

IFD

object:shadingquality

This parameter controls the geometric subdivision resolution for all rendering engines and additionally controls the shading resolution for micropolygon rendering. With all other parameters at their defaults, a value of 1 means that approximately 1 micropolygon will be created per pixel. A higher value will generate smaller micropolygons meaning that more shading will occur - but the quality will be higher.

In ray tracing engines, shading quality only affects the geometric subdivision quality for smooth surfaces (NURBS, render as subdivision) and for displacements - without changing the amount of surface shading. When using ray tracing, pixel samples and ray sampling parameters must be used to improve surface shading quality.

The effect of changing the shading quality is to increase or decrease the amount of shading by a factor ofvm_shadingquality squared - so a shading quality of 2 will perform 4 times as much shading and a shading quality of 0.5 will perform 1/4 times as much shading.

So with a shading quality of 1 Mantra will always subdivide for a smooth surface down to the pixel. If you lower the shading quality at some point you will see polygonal edges in your shading/silhouette. There are cases I wish it would be controllable with a similiar option of a subd level as with other rendering engines.

I hope this helps,

Andy

 

[jrockstad]

Thank you Andy, yes indeed that is very helpful. I thought the shading quality setting was only used for the micropoly engine and didn't realize that it also affected subdivision mesh quality. In the meantime I will log that request with Side Effects as you suggest as well Marty. Thanks!