View Full Version : mia material issue with maya lights

10-02-2007, 08:39 PM
i've attached a preview render of a building i'm working on - rendered in MRfM on 8.5, all mia/mi shaders. lighting setup is a physicalSun on the angle shown, and some point lights but they shouldn't affect the objects in this shot as they're on the floors underneath casting raytraced shadows.

problem is you can see the walls inside (right of center) are lit up brightly and the floor isn't (the floor is correct). i've just traced the problem to the pointLights, if i hide them it all renders correctly, but i don't get it... how can the lights be affecting the interior when they're nowhere near those walls, they have decay and are casting shadows....? lol confused. the inside floors/cieling and walls are all the same mia material, a white non-reflective matte.

i thought maybe it could be related to backface cull on the glazing's mia shader, but all combinations of backface cull and/or double sided on the object seems to have an issue with rendering what's behind the glazing.

any tips much apprec :)

10-03-2007, 12:36 PM
It's not the lovable huggable Maya shadow trace depth (http://mentalraytips.blogspot.com/2007/10/mayas-default-shadow-settings.html)?

10-04-2007, 03:07 AM
It's not the lovable huggable Maya shadow trace depth (http://mentalraytips.blogspot.com/2007/10/mayas-default-shadow-settings.html)?

no, trace depth would only come into the equation if the pointLights were shining into the room through transparent surfaces but they're not, they're beneath solid floors so only 1 shadow ray is needed. AFAIK trace depth can't be set on the MR physicalSun, so that also shouldn't be an issue...

10-04-2007, 04:59 AM
no, trace depth would only come into the equation if the pointLights were shining into the room through transparent surfaces but they're not

No no no, that's not how the maya "shadow trace depth" works! It's not the trace depth of how many surfaces the light penetrates (which - I admit - would make sense).

It's if you see an area through trace depth X, the shadows for that light is disabled if it has a lower trace depth than X.

In Maya I think the default shadow trace depth is 1. This means that if you see through glass (which you do) the shadows of that light will be disabled.

Shadow trace depth 1:


Notice how the light gladly penetrates 3 blue glass blocks (6 surfaces) and still makes a shadow... yet when viewing it through the red glass block (2 surfaces) we see no shadows at all on the ground!

Shadow trace depth 3:


A depth of only 3, gets os through the 2 surfaces of the red glass block, and we now see shadows.

So as you see, the "ray depth limit" on shadows apply to the trace depth (counted from the eye) of the shading point for which to calculate shadows or not, and NOT the number of surfaces light has to go through from the light!

Note you must turn this up both in the light (Ray Depth Limit) AND in the mental ray render globals "Shadows" under "Ray Tracing".


10-04-2007, 10:17 AM
Thanks Zap for clearing up another mental mystery!

Here's another demonstration of this:


10-04-2007, 09:55 PM
thanks for that info - after all that turns out there was a another group of pointLights i hadn't tested this out on (and their ray depth limit was left at 1). they should make it 3 by default lol.

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10-04-2007, 09:55 PM
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