View Full Version : skip_inside_refl and brdf/fresnel

01 January 2009, 01:31 AM
if you have an object that has a lot of flipped normals in some places, in this case i'm working with a model that is translated from CAD data and has flipped normals all over the place but is otherwise a good model, i've noticed a strange effect with the "skip_inside_refl" of the mia/mia_x.

the render has a lot of glossy surfaces, and because of all the flipped normals, i obviously am going to want to uncheck skip_inside_refl so that i get refl everywhere and not just on the normals facing outward.

what i've noticed is that if you use fresnel and IOR to define the reflection properties, by setting "brdf_fresnel = 1", faces which have their normals facing the wrong way lose their refl glossiness, and render like a mirror.

if "brdf_fresnel = 0", and you use the BRDF parameters 0,90, and curve to define the reflection properties, faces with normals facing the wrong way render properly, with glossy as whatever you set it to.

what this means is that any time you have objects with flipped normals, you can't use fresnel to define any material that has glossy reflections, you have to use the BRDF curve. also for anyone using shaders_p, which doesn't have the BRDF curve controls, only fresnel, the problem is more serious.

i've linked a picture to show what i'm talking about. just wondering if anyone has run into this problem before, knows of a solution. or if i'm just making a stupid mistake and missing something simple.

any help greatly appreciated. big up to the community.

01 January 2009, 12:41 AM
poor old fresnel. relegated to front faces only. when mr is so capable of rendering faces both front and back.

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01 January 2009, 12:41 AM
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