You can use the wireframe shader to drive the opacity of a standard_surface.
The wireframe shader itself doesn’t support opacity, and neither do the flat, utility, and ambient_occlusion shaders. They are all color shaders (RGB). In Arnold, only shaders that return closures can support opacity.
In the more general case, where the opacity isn’t coming from the same shader, you can use the emission for the color:
You can use use color_correct with alpha_is_luminance enabled, like this:
![](https://arnoldsupport.files.wordpress.com/2019/01/triplanar_bump.jpg")
To jitter color with user data, you need to connect an aiUserDataInt to the data input parameter, like this:
The user data is an mtoa_constant attribute on the shape. For example, if add an extra attribute named mtoa_constant_jitterID to some shapes, then you can use aiUserDataInt to read the jitterID.
If you want to use the shapes as standins, and be able to set the jitterID in the scene, then export the shapes without the mtoa_constant_jitterID attribute. In the scene, you’ll be able to add mtoa_constant_jitterID to the aiStandin node. The aiUserDataInt node in the ASS file will use that jitterID.
If you want to export ASS files from Softimage and use them in Maya, all you have to do is add the SItoA shaders (eg SItoA\Application\Plugins\bin\nt-x86-64) to the Plugin Search Path
ASS files from Softimage use SItoA-specific shaders, so you need to tell Arnold where to find those SItoA shaders. For example, since SItoA 4.0, there’s a new Closure node that connects shaders like Standard Surface to color parameters. MtoA doesn’t have a Closure node, because MtoA took a different approach to dealing with the fact that Standard Surface returns a closure data structure, not a color.
In this case, the question was “why doesn’t layeredTexture work in Arnold 5?”
This is a common question/problem with Arnold 5: shaders plugged into color slots.
In Arnold 5, shaders like Standard Surface (and Lambert too) don’t return colors. So in general, you can’t plug them into color parameters. And Blinns are translated into Standard Shaders by MtoA, so you can’t plug a Blinn into a color either.
Instead of a layeredTexture, you can use a layeredShader. It knows how to handle shaders that don’t return colors. Or you could use the Arnold aiMix shader.
So, if these shaders don’t return colors, what do they return?
Closures. They return closures.
A closure is not a color, it’s a bundle of data that tells Arnold how the surface (or volume) scatters light. Arnold takes care of all the ray tracing and light sampling, and then uses the closure to figure out the surface color.
From Master Zap:
“The addition of “closures” is a complete godsend. This relegates the work of rendering to the renderer, as it should be. No longer are material shaders little dumb raytracers that count lights and shoot reflection rays. A material shader returns mix of BxDF closures, and the renderer itself takes care of doing “the right thing” with them”.
From the Arnold 5 release notes:
Closures: a new closure parameter type has been added, which shaders can output instead of final colors. There are BSDF, BSSRDF, emission, matte, transparency and volume closures. See the API documentation and examples for more details on how to use these. Linking a color to a closure parameter will automatically create an emission closure with that color. A closure parameter however can’t be linked or converted to a color, as the integrator only computes lighting after shader evaluation.
Question: how do you set up the Arnold ambient_occlusion shader so that it ignores self-occlusion?
Let’s start with the default ambient occlusion. here’s a sphere and a plane. Each has it’s own Ambient Occlusion shader. For the sphere, Ambient Occlusion.Black is Red.
Now, let’s disable Receives Shadows on the sphere.
That means no occlusion based on the plane (shadow rays from the sphere ignore the plane); but there’s still self-occlusion.
Next, Cast Shadows disabled. No self-occlusion, but no ambient occlusion on the plane either
And finally, Self Shadows disabled. Now, there’s no self-occlusion. The ambient occlusion on the sphere is coming solely from the plane
In this case, we have a torus as a mesh light.
The mesh light color is facing-ratio ramp, so that in the Beauty AOV, the polygons facing the incoming camera ray are red, and polygons facing away are green.
The plane below the light has a [slightly non-realistic] combination of diffuse, specular, and reflection (Kd=0.7, Ks=0.5, Kr=0.2).
The question here is: why do we see red in the reflection AOV, but green only in the diffuse and specular AOVs? Why does the facing-ratio ramp return red for reflection rays, but green for diffuse and glossy rays?
The answer is that there are no diffuse or glossy rays in this situation. A mesh light gets a meshLightMaterial shader, which MtoA assigns to the mesh light color (and to the torus shape) when MtoA translates the scene to Arnold.
The meshLightMaterial shader doesn’t handle diffuse, glossy, or shadow rays. The first few lines of the meshLightMaterial shader look like this:
if (sg->Rt & (AI_RAY_DIFFUSE | AI_RAY_GLOSSY | AI_RAY_SHADOW))
{
sg->out.RGBA = AI_RGBA_BLACK;
return;
}
Let’s take a look at what’s happening in the different AOVs.
The reflection rays hit the bottom of the torus, go through the facing-ratio ramp, and return red because most of the polygons are facing down towards the plane. In this case, we get the facing ratio of the polygon normals and the reflection ray.
We get the green from the light sampling, where there’s no rays.
Since there’s no rays, we get the dot product of the surface normal and 0 0 0, which is 0. And that returns green from the ramp:
The diffuse rays don’t make a contribution (because the meshLightMaterial doesn’t handle them) so we get green from the light sampling (just like for specular).
This would be black, since the meshLightMaterial doesn’t handle glossy rays, so the mesh light makes no contribution to the glossy reflections.
The Utility shader has a super-fast ndoteye shading mode. This shading mode doesn’t trace any rays: it simply shades based on the angle between camera (eye vector) and the surface normal (ndoteye = dot product of the Normal and Eye vectors).
Here’s an example of the Utility shader. The middle mesh has the ndoteye shade mode (the left mesh has plastic, and right ambocc).
Note that with ndoteye you get just black in the glossy reflection. That’s because in ndoteye shade mode, the Utility shader handles camera rays only. No secondary rays like glossy or refraction.
Any time you see “node … is not installed” and “unresolved reference” warnings when you try to kick an ASS file exported from Maya, the problem is missing MtoA shaders.
00:00:00 18MB WARNING | [ass] line 259: node "MayaFile" is not installed 00:00:00 18MB WARNING | [ass] line 288: node "MayaShadingEngine" is not installed 00:00:03 23MB WARNING | [ass] line 238: pSphereShape1.mtoa_shading_groups: unresolved reference to 'aiStandard2SG' 00:00:03 23MB WARNING | [ass] line 137: aiSkyDomeLightShape1.color: unresolved reference to 'file1' 00:00:03 23MB WARNING | [ass] line 188: pPlaneShape1.shader: unresolved reference to 'aiStandard1SG' 00:00:03 23MB WARNING | [ass] line 197: pPlaneShape1.mtoa_shading_groups: unresolved reference to 'aiStandard1SG' 00:00:03 23MB WARNING | [ass] line 229: pSphereShape1.shader: unresolved reference to 'aiStandard2SG'
When you render with kick, you need to specify the location of the MtoA shaders. You can do this several ways:
export ARNOLD_PLUGIN_PATH=/home/render/solidangle/mtoa/2016/shaders
set ARNOLD_PLUGIN_PATH=C:\solidangle\mtoadeploy\2016\shaders
Arnold doesn’t support .mov files for textures, but with C4DtoA you can use the Bitmap shader to load image sequences like seq_0000.tx, seq_0000.tx, seq_0000.tx, …
Under the covers, C4DtoA doesn’t actually implement the Bitmap Shader. Instead, C4DtoA translates the Bitmap Shader to an Arnold Image shader
Arnold Support Corner 