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Friday, 15 April 2011

Renderman and Subdivision!

Just got reminded today that polygonal geometry in Renderman needs to be subdivided to appear smoothed during rendering. 

There was this problem about certain faces of an object in rendered appearing much brighter than their neighbouring faces. Those bright faces stood out like sore thumbs in the render. 

For Mengdi and myself, this was our first time doing look-development with Renderman. We did a lot of tests, trying lots of ways to solve it. 

Being quite new at Renderman and look-development, we tried lots of stuff:
- turned on/off the lights one by one
- tweaked shaders
- removed shaders
- disabled reflection lights
- switched between point-based occlusion and real-time rendered occlusion
- switched between baked and on-the-fly reflection occlusion 
- and all of that. 

None of it worked.

During the trial and error stage, it occurred to us that the geometry may not be smoothed. I had meant do tests to find out if the geometry was smoothed/subdivided in our Maya viewport, if it would be similarly subdivided in Renderman. 

We could not tell if our geometry was indeed subdivided because our object was rather large and we kept rendering it in a wide shot, so we had no way to tell if the object was subdivided.

Finally after more than a day of trying to fix the render artifacts (and refining the textures at the same time), I got down to testing the subdivision behaviour of Maya and Renderman. I finally found out for myself that the smoothing in Maya's viewport does not affect the smoothing in Renderman. 

I found out we needed to "tag" the geometry for smoothing, then it would be subdivided at render time.

A lot of frustration and wasted time of trial and error could have been avoided if we knew that in the first place.

However I believe no experience is wasted, and it was a good problem solving experience for us. We ended up more familiar with the Maya-Renderman pipeline and workflow.

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