View Full Version : Mental ray SSS shader stucks my rendering

07 July 2011, 01:31 AM
Hey guys,
I have a problem with rendeing my scene, when there are SSS shaders in it. I was rendering it using IPR when tweeking settings and it rendered fine, but when I render it normally, it just shows the blue render viewport and render doesnt do anything, but it wont show that it is done (as it happens when its out of physical memory), it just pretends that it is rendering but it wont render anything (I let it run for few hours). I have rendered many projects with SSS shaders in them and I never had this problem so far, so I dont know what is causing it.

My scene contains:

spot lights
area light
SSS shaders
transparent/translucent blin shader

rendered by mental ray 3200 x 2400px (300 dpi) with only raytracing enabled
all usual settings

pls help. Xquick

07 July 2011, 11:07 AM
use higher verbosity and tell us what the output windows is churning out. Do you by any chance have FG in SSS activated ? It used to be a real memory killer for me.

07 July 2011, 10:24 AM
Output window
PHEN 0.8 progr: 16.0% sss lightmap generation
PHEN 0.10 progr: 100.0% sss lightmap generation
RCLM 0.10 progr: lightmap mesh run 0:0 done, 44032 triangles
PHEN 0.6 progr: 54.0% sss lightmap generation
(this goes on and on)
it seems to spend all the time on generating lightmaps. I lunched rendering 10 minutes ago and it still generates lightmap, that I use only 1 in my scene. How come it takes so long to calculate ? I dont know whole much about lightmaps, all I set are samples which I have on 256 (this number doesnt really effect render time I think).

07 July 2011, 11:18 AM
Assuming a recent version of maya, the light map resolution will be set via an expression to be twice the horizontal width of your render resolution, so you are waiting for a 6400x 2400 lightmap to render. This may be way higher than you need to make your render look nice. I would delete the expression and manually enter something like 1024x512 and see what kind of speed you get and what it looks like. Increase in small amounts if required. Sometimes you'll notice artifacts depending on how much detail in your geometry, and the strength of the SSS, but often I have found it looks just fine and renders are a whole lot faster.


07 July 2011, 11:46 AM
I tried resizing it down as you said, but it didnt speed it up so much. I was browsing through my settings and I found out that as I was copy_pasting my lights in the scene, I had my 5 lights all set to raytrace shadows with some pretty high numbers and that is really sick to render :) so that was the problem.

I am just wondering how is possible, that IPR rendered it with no problems. What is really the difference in IPR rendering ?

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07 July 2011, 11:46 AM
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