Layering in Maya2015

The Layering shader library (MILA) in mental ray 3.12 provides a flexible, component-based set of shaders designed to work with each other to accommodate most look development needs. It is more optimized for modern rendering usage of unified sampling, and quality control. It is more efficient with light sampling, and built to take advantage of light importance sampling. It also provides a lightmap-less subsurface scattering component.

In this post, we show how to use the Layering (MILA) shaders in the UI for Maya 2015. This is a first step, but the main concepts will be carried through further steps and across DCC applications. We are looking into providing a similar workflow for 3ds max.

Components – base and layers

The first concept is that of a base component with layer components placed over the top of the base. We provide elemental components for layers, and base combination components for the base layer. You may hear us use the term Phenomenon for a pre-combined network of shader nodes. The base components, except for pure Diffuse are these combination components called Phenomena.

A newly created mila_material always starts with a Diffuse base component by default. Here is what you would see in the Attribute Editior (AE) for the mila_material if you wish to select a different base component.

base_component

On the left below, we show a head (courtesy of 3D Scan Store, http://www.3dscanstore.com ), using only Diffuse, and on the right, the Diffuse (Scatter) base component.

head_diff        head_diff_scatter

 

As mentioned, we have a set of elemental components for layering over the base. These provide for elemental material characteristics such as diffuse, glossy, specular reflection and transmission. We have a diagram below left that we typically show so you can see the light path representation of these elemental components. On the right, we render each of these components isolated on each sphere to correlate with that diagram.

dgs mila_dgs

 

On the left below, we show the Diffuse (Scatter) to compare with the right, where we have layered two glossy reflection components on top of that base.

head_diff_scatter  head_glossy_diff_scatter

elemental_componentsOn the right, we show the elemental components you may select in the UI currently, categorized by Reflection, Transmission, Subsurface Scattering and Emission. All of these can be layered on top of the base or other layers.

To add a new layer on top of the current layers, a user clicks on the +layer tab/button on top of the UI in the AE for the mila_material, before being presented this elemental component selection menu.

layer_add

There are three different types of layers, for which we need to explain weight.

What is weight?

For a given layer, the weight represents a percentage of the incoming energy.  A layer can be weighted simply, or can have some directional dependency. For example, a Fresnel weighted curve derived from an Index of Refraction can be used to multiply by the weight, so that the layer has higher weight at grazing angles.

layer_type

 

 

A Weighted layer is simple, as the weight represents the incoming light energy used.

A Fresnel layer uses an index of refraction input for directional dependency.

A Custom layer uses a Schlick approximation for directional dependency. Those familiar with the mia_material may recognize the controls for weight at facing and grazing angles and a curve exponent.

 

The mila_material AE UI presents layers in a top-down fashion, so one could imagine how the energy comes in at 100% from the top, while each layer takes away a percentage of that energy. It gives you a notion of the material as if looking at a cross-section. The base on the bottom is always considered as 100% of whatever is leftover, and therefore we don’t expose the weight for the base layer in the UI.

layer_diagram1

Above, the top layer receives 20% of the incoming light energy. The middle layer receives 25% of the 80% leftover energy from the top layer. One quarter of 80% makes another 20% of the overall incoming energy, and the base receives the leftover energy from the middle layer, which is now 60% of the initial incoming energy.

Mixing components

The UI also provides for mixing components in a given layer. One can think of a mix like a blend of two paints. This diagram depicts three layers, with the middle layer containing a mix of two components. The mix is built as the layer components are placed on top of each other.

layer_diagram2

In the Maya AE UI for mila_material, when there is a layer on top of the base component, a user can  click on the +mix tab/button to mix a component into the top layer. The weight of the mix will take energy away within that layer. There will still be an overall layer weight for the mixed components. In the example below, this is actually a Fresnel layer mixing two different roughness variations of glossy reflection in a 50-50 mix.

mix_add  mix_glossy

Masked layers

The weight may also be considered conceptually like a masking function, for a material placed on top of another material, as can be shown with the following image on top of the head we’ve already shown above. Now he’s ready for paintball.

head_paint_glossy_diff_scatter  head_layers

 

Look Development

So what does this mean for look development in terms of how to approach layering for something you want to match?

In our GTC presentation, David Hackett from The Mill used the following example, from a Norfolk Southern commercial (assets used for demonstration here are courtesy of Norfolk Southern Copr., “City of Possiblities”).

Here we see the final layered material rendered with a background plate and reference mirror and gray balls.

NorfolkSouthern1

To start, we can now think about the look of the original object based on its material properties, rather than which shader node attributes to tweak. We examine a variety of references. This one obviously has bright light hitting it.

NorfolkSouthern2

How shiny is it? How shiny are the various layers? Is it a blend of shiny characteristics?

Where do other properties like rust or dust show up as potential layers?

Note the rust is not as shiny, and has more noisy color variation.NorfolkSouthern3

NorfolkSouthern4

This translates into various component layers for the mila_material, including masks for weighting. These masks can be generated in Mudbox or Mari using UV tiles.

NorfolkSouthern5 NorfolkSouthern6 NorfolkSouthern7 NorfolkSouthern8 NorfolkSouthern9

We think about the individual parts starting with the base paint layer which is primarily diffuse below left. Then, add a glossy reflection layer using the Fresnel layer. The roughness has a texture mapped to it below right.

NS_layer1  NS_layer3

Now we use a mask to weight a Grime layer. On the left below, we show it more obviously with a red color, and on the right we use the diffuse reflection component we intend.

NS_layer3_red NS_layer4

At this point we have three layers in the UI. A base diffuse with a glossy layer, and then on top of that, the masked diffuse layer for the rust. That is what we see on the left below. For further detail, we add a more subtle dust component and mix it in with the rust. On the right below, we see the resulting mila_material AE UI, noting slight gray color shift for each level down in the shader network heirarchy. Note also that we’ve collapsed the original rust diffuse reflection component displayed underneath the new dust diffuse reflection.

NS_UI2  NS_UI3

With more subtle additions, we again make the dust component red, in order to spot it, on the left below. Then the final look development image with extra tweaks, we see on the right.

NS_layer4_red  NS_layer4_final

This workflow will continue to be developed, as there are already plans for enabling more complex components, while making the selection of those components easier. For a simple example, we could have created the dust layer first on a separate material; then later, choose that material from a menu of existing mila_materials, as a component to be layered.

The layering shaders provide a glimpse into NVIDIA’s Material Definition Language (MDL), which is designed to provide material sharing across rendering platforms. For better compatiblity with MDL, many of the optimizing shader controls of the past have been moved out of the MILA shaders and into string option controls. This also allows better ability to optimize more automatically in the renderer, and the ability to provide sweeping quality control changes over a large scene full of many materials.

More to come

This post provides a brief glimpse into what the layering shaders provide, and there will be more posts to discuss the global string options available for quality control, the base Phenomena in more detail, and the render passes provided as emulation of Light Path Expressions (LPE), another forward looking technology coupled with MDL.

mental ray for Maya 2015

In this post, we give a short intro to the newest features of the mental ray for Maya 2015 plugin that is delivered with Autodesk Maya 2015. This is an overview: we will dig deeper into some of the topics on later posts.

Rendering ptex made as simple as possible

We have streamlined the workflow significantly for rendering ptex in Maya 2015.  You can simply specify your ptex file in the file node and render.  The ptex filter parameters are exposed in the file node.  You can render color, as well as scalar and vector displacement, and normal maps.

dino

Support for UV-tiles

UV-tiled images are output from Mudbox, Z-brush and Mari. It’s a gigantic texture that is decomposed into a grid of small textures. The positioning of the tiles is specified by a naming scheme.
Some of you might have used the scripts that are available to render uv-tiles with mental ray for Maya and that create a shader chain to do the placement of all tiles of a uv-tile image.  However, now you can render as if it was a simple texture in the regular file node.  The user only has to specify the first tile and the naming scheme.

AO GPU exposed

The AO GPU plugin has been a part of mental ray since version 3.11. It allows one to render the AO pass at a very high quality in parallel to the beauty pass. With a recent GPU, the user gets the AO pass for free.  AO GPU is now enabled in mentalray for Maya2015 as parameter of the AO render pass.
The new ‘useGPU’ checkbox enables it. You might want to start setting the number of rays to 8 or 16. This usually results in sufficient quality.  Please, let us know on our forum http://forum.nvidia-arc.com if you have other experiences.

hunter

 

 

 

 

 

 

 

 

 

 

 

 

Native IBL exposed

mental ray’s native environment lighting delivers higher quality at better performance compared to the classical shader based solution.  It can now be enabled for image based lighting when you select the ’emitLight’ checkbox in the IBL shape node.  The only control that is exposed at the basic level is Quality. Advanced controls expose ‘Resolution’ and ‘Resolution Samples’ to control the building of the acceleration structure, as well as a ‘Color Gain’ control.

 NorfolkTrainNativeIBLWithCredits

Xgen Hair

Autodesk Maya 2015 provides Xgen for generation of hair, fur and other primitives.  The Xgen shader for mental ray allows to render Xgen created content with mental ray.
SvenHair2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

mila shaders coming with a UI now!

The layering shaders will be discussed in depth in a later post.

Happy Rendering!

Julia

Welcome

https://vimeo.com/76482820

Hi mental ray users, friends, rendering beginners and pro’s:

We are very pleased to announce this blog as a new, direct source of information about mental ray, one of the most used 3D rendering technologies in the world.  We like to use this channel to reach out to you and tell you about the exciting new features we are currently working on, but also about efficient workflows and best practices inside the various applications that have mental ray integrated or as plugins, like Autodesk Maya, 3ds Max, Softimage and Cinema4D or mental ray Standalone.

These are exciting times for rendering!  Traditional and well established lighting and shading techniques meet with physically based rendering approaches in order to compute highly realistic imagery with the push of a button while taking advantage of all available hardware.  We believe mental ray is flexible enough and continuously progressing to be used successfully in both of those domains, and anything in between.

We aim to accompany and support you in your daily work with mental ray, show the best and easiest ways to use it, or achieve a certain look or visual effect, and spread the word about the latest and greatest additions and changes.

We are looking forward to your feedback and comments, and invite you to follow us.

Happy rendering,

The mental ray development team.
Steffen Roemer, Product Manager Rendering Software, mental ray