Why use detailed shadow maps instead of raytrace for hair/fur?

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Old 04 April 2013   #1
Why use detailed shadow maps instead of raytrace for hair/fur?

This is a fairly well known post:

http://kiryha.blogspot.com.au/2010/...mental-ray.html

Although it is a little old, I have seen it referenced by a good number of other people's blogs. Some even simply copied and pasted it into their blog. And their posts are time stamped 2013.

Where it says "never raytrace with fur" I figured "sure! that makes sense! Raytracing is expensive." So I never even gave it a second thought.

I've been using detailed shadow maps for some time now since maya 2010 and just for the hell of curiosity I chose Use Raytraced Shadows over detailed shadow maps and I was expecting 5 times the render time. But instead I got (virtually) the same render times for a character with 1,000,000 hairs. AND the results were more accurate, more beautiful, more detailed, better shadow and self-shadow casting and more predictable. (By accurate and predictable I mean the where the light terminates from light into shadow on the skin mesh was in the same location where the fur lighting began to terminate. Before with detailed maps there were discrepancies and it resulted in odd looking transitions.)

So my question is: Currently I'm using 2013sp1. Has there been huge optimizations in raytracing since then. Perhaps when mental ray became a true plug-in?

Maybe raytracing is worth experimenting with for those needing fur in the future.

Last edited by egglybagelface : 04 April 2013 at 07:11 AM.
 
Old 04 April 2013   #2
I always thought hair rendered in scan line/software was to prevent massive rendering times, so if it renders for you quickly in mental ray, then more power to you

I dunno if you're using a farm or not. Granted 1 million simulated hairs seems like plenty for a single station to handle. Is your hardware super beefy?

Last edited by jgibz : 04 April 2013 at 09:39 PM.
 
Old 04 April 2013   #3
No it's not really beefy. And not a farm. A single machine.

AMD Phenom II x6 1090T 3.2 Black edition.
16gb ram.

The CPU I think is ruffly the equivalent of an Intel i6, if there were such a thing.

The Maya software composite trick was good in it's day. But you don't get to take advantage of most modern things like indirect lighting and ambient occlusion and fine control with the puppet shaders which only work with mentalray.
 
Old 04 April 2013   #4
16 gigs seems beefy enough, I'm still running on 6 on my personal rig. The last project I worked on with hair we were rendering scanline because mental ray was killing render time, and yes, it looked out of place because of final gather on the character pass.

maybe we should have faked final gather on the hair with a spherical light array, or perhaps secondary fill lights with similar color to the background?
 
Old 05 May 2013   #5
Shadow maps not the only time saver. Hairs requires high AA settings and rasterizer is grate solution for this.
If you have enough render power you should not have any doubts about raytracing fur and using indirect lighting.
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Old 05 May 2013   #6
What kills in render time is raytracing tranparency on hair.
You can turn off transparency for shadows with puppet hair shadow shader
 
Old 05 May 2013   #7
transparent hair and raytracing is fine. Transparent shadows is the killer. But it's a bit excessive imo.
 
Old 05 May 2013   #8
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