In this third post in a series on mental ray for Maya 2016 Render Settings, we assume you are familiar with the concepts presented in the introductory post and the second post on adjusting quality.

Modern Materials and Lights

We recommend physically-based materials and lights to fit a modern workflow. In this post, we focus mostly on the materials, and we will follow-up with more posts on lights. These materials are designed to work more compatibly with unified sampling, and the simpler UI quality controls. They provide the flexibility of balance in adjusting global vs. local sampling quality controls.

Materials

The Layering (MILA) material not only provides better compatibility with unified sampling and quality controls, but it also provides simple passes which can help you to adjust the quality settings.

For example, this interior scene using mila materials clearly demonstrates the difference between direct and indirect lighting. The left picture has no indirect diffuse lighting as it is turned off in the Render Setting Quality tab, and the right picture has Indirect Diffuse (GI) Mode turned On with a depth of 4. Note that the 2 pictures below are organized in a gallery, so that if you click on them, you can see a larger version. Click on x upper left to get back to this page.

The direct lighting quality is controlled with Lighting Quality, while the indirect quality is controlled with Indirect Diffuse Quality when Indirect Diffuse (GI) Mode is On.

If using mila_materials, we can easily turn on the direct_diffuse and the indirect_diffuse passes in the Scene tab under Camera>Passes.

Then, we can see the relationship between the pass results with respect to their quality. Note again that the 4 pictures below are organized in a gallery, so that if you click on them, you can see a larger version, and step through each with a right, left arrow.

Below we increase the Indirect Diffuse (GI) Quality to reduce noise in that pass.

Adjusting (MILA) Material Quality

Use the (MILA) Material Quality to address noise caused by the material sampling.  For the layering library (MILA) materials with either glossy reflection/transmission or scatter components, the Material Quality controls the number of samples, ie the outgoing rays split out from the interaction of the material with an incoming ray. In a sense, this is the indirect quality aside from the indirect diffuse, i.e., the indirect glossy and scatter components.

When Advanced Settings are on, we provide separate Glossy Quality and Scatter Quality controls in case the noise differs significantly between these components. Note that the material quality settings are relative, so controlling Material Quality will continue to control both glossy and scatter quality.  The material quality is multiplied by glossy or scatter quality to determine a quality for each respective component, with all defaults at 1.0.

Note that the passes for indirect glossy/specular and scatter directly correlate in quality to these settings.

Increasing Glossy Quality

Increasing Scatter Quality

 

Scene Settings Shared across Materials

Note that for the MILA shaders, we provide quality settings by scene. In other words, all the materials in the scene share the settings. This makes it easier to control in a typical scene with many materials, rather than per-shader. It also allows the renderer implementation to optimize better.

Besides quality, we have several other useful render settings that are shared by the mila materials. They are in the Scene tab in the Materials section.

Layering (MILA)

Reducing very high dynamic range results

MILA Clamp Output

Clamps the output of mila_material. This is an enable, for using the clamp level. If off, light transports through the scene in the most physically-accurate way, though with high dynamic range lighting, more quality may be required. The default is off.

MILA Clamp Level

The level used for clamping, typically between 1 and 10, based on desired output.

Understanding internal reflection

When making a material to model colored glass, not only do transmission paths inside the glass need to be colored, but also, if one of those paths reflect inside the glass again (internal reflection), it should be colored. Depending on your scene, this may be more or less subtle of an effect visually.

A material with a reflection component could be on the outside or the inside, so the max distance parameter for a reflection component needs information as to whether it is modeling physically-correct internal reflection, or modeling the legacy max distance render trick for the external reflections. We recommend using colored max distance primarily for internal reflection, when combined with a transmission component, and therefore, make this the default.

MILA Use Max Distance Inside

Use the max distance for reflection internally for colored glass. On is the default. If off, the max distance is used for external reflections, those bouncing off the outside of an object, instead of internal reflections.

Scatter look adjustment

Modern rendering uses more quantities that depend on scene units, such as the distance to scatter with mila_scatter. In the Materials section of the Scene tab, we provide a global scaling factor for scatter distances.

MILA Scatter Scale

The MILA Scatter Scale is very convenient for re-using materials across different size scenes. It multiplies by the local scale control, if exposed, in the (MILA) scatter component. Below we show how increasing the scale makes the scatter pass look more like the diffuse pass, with less and less scattering.

For practically good results the scatter pass should look barely noticeable when mixed in with all the other passes.

Layering complexity not a significant performance factor

At SIGGRAPH 2015, I noticed how many users were still concerned that the number of layers in a material may affect performance. For modern materials, such as MILA and MDL, this should not be of concern. The elemental component structure provides the renderer with this ability. The material can either be selectively sampled or flattenend for a single minimal BSDF representation, and as the depth of a ray increases, more optimizations can occur.

Lights

Use physically-based mental ray lights such as the Physical  Area or Environment lights. See Create>Lights>mental ray section

All lights in this section default to quadratic falloff for physically-based lighting, and compatibility with the modern techniques including Light Importance Sampling (LIS). With LIS, the Lighting Quality can be used for direct lighting quality.

In our next post, we will introduce the Physical Area Light, and in another post we will provide more detail for the Object Light, which is a special case of the Physical Area Light assigned to an object for emission. We will also provide a post on how to use the newly packaged Environment Lights.

The vMaterials are a collection of MDL materials designed for physically based rendering, representing real world materials. You can register for a free download here. vMaterials can be rendered with mental ray 3.13 as well as with any Iray plugin, such as NVIDIA® Iray® for Maya.

 

To use the vMaterials for rendering with mental ray for Maya 2016, you have to add the following definition to your Maya.env file (on Windows):

MI_MDL_PATH=C:\ProgramData\NVIDIA Corporation\mdl;C:\Users\<YourUsername>\Documents\mdl;

To find out how to apply the MDL materials in your scene, check our post on Using MDL with mental ray for Maya 2016.

Some materials are dependent on the scene unit and assume meter by default. You can either change the scene scale to meter or you can convert the scene unit dependent parameters. For example, the clarity parameter in the gem materials should be multiplied by 100 if the linear working unit is centimeter.

Note: mental ray 3.13 supports MDL v1.1 and the vMaterials are based on MDL v1.2.  Nevertheless, most materials are compatible and can be rendered with mental ray 3.13 out of the box.

Deep OpenEXR files allow to store a variable number of samples per pixel at different depth locations to aid advanced depth compositing workflows.

To render a Deep OpenEXR file with mental ray, open the Render Settings dialog and make sure that the image output format is set to “exr” in the Common tab:

In the Scene tab, enable the “Use Deep Image format” checkbox:

The  Deep OpenEXR file is written in multi-part, which means that files can contain a number of separate but related images. Each render pass gets its own part (i. e. direct_diffuse, indirect_diffuse).

In order to save memory during rendering, mental ray creates tiled Deep OpenEXR files. These files need to be converted to scanline for use in compositing applications like Nuke. This conversion can be performed using imf_copy, a command line tool that is part of your mental ray for Maya installation. It can be found in the bin directory. Call

imf_copy -s tiled-exr-file.exr scanline-exr-file.exr

to perform the conversion. Click on the image below to see a screenshot of the tool executed on a Windows system:

Please note that currently only z front is supported. This means that rendering deep volumes is not possible yet. Deep and flat data cannot be mixed in the same OpenEXR file.

 

 

In Maya 2016 we are introducing basic support for loading and rendering MDL materials with mental ray. In this post we want to take a closer look at how these materials can be used in Maya. For a general introduction to MDL in mental ray, check out this post.

The MDL Node

In Maya, MDL materials are represented by a new surface shader node called mdl_material, which is located in the mental ray surface material section of the “Create Material” window or “Hypershade”.

When you assign an mdl_material to an object, you will see that it contains two drop down lists: One for choosing an MDL module and another one for choosing an MDL material:

An MDL module is a file which can contain one or more MDL materials and has a “.mdl” extension. By default, mental ray for Maya 2016 ships only one module, that contains the default_material, a light grey diffuse. Because of that, both drop down lists contain just one entry.

To populate the lists you will need more materials. In the next section, we will see how to get some.

Adding MDL materials

As already announced in the MDL introduction post, example materials can be downloaded here.

1) Unzip the archive to a temporary directory.

By default, mental ray for Maya uses one root directory for placing MDL modules, the directory shaders/mdl within your mentalrayForMaya2016 installation.

2) Copy the folder mdl_examples_for_maya_3dsmax into the MDL root directory as shown below:

If you do not have write permissions in the Program Files directory or would generally prefer another location, you can define additional MDL root directories by specifying the MI_MDL_PATH. To do so, open the Maya.env file, which can be found in the Maya 2016 user directory:

Add the line

MI_MDL_PATH=<Path to MDL files>

If you, for example, make an MDL root directory called “mdl” in your Maya/2016 user directory, as shown in the screenshot above, your MI_MDL_PATH path needs to look like

MI_MDL_PATH=C:\users\<USERNAME>\Documents\Maya\2016\mdl

More than one path can be specified, separated by a “;”.

A note on packages

In most cases, MDL modules are organized into packages, just like our example package. On disk, a package corresponds to a directory. The name of the package is the name of the directory. Packages can be nested to organize complex libraries. Within a package, modules can reference each other and contained resources (like textures) relative to each other or the package root directory. Because of this, it is important to always retain the package structure. Never just copy single mdl files or subdirectories out of a package into your MDL root directory, always use the full package, including the root folder.

Rendering MDL materials with mental ray for Maya

Now that our example package has been put into place, start Maya. Create an object and assign a mdl_material to it. The MDL Module drop down list should look like this:

When you choose a module, the material drop down list will be populated with the materials contained in the selected module, and the first material will automatically be selected. The “MDL Material Parameters” section shows the parameters of that material, which you can modify to your liking.

Other MDL materials, focused on requirements from the automotive industry are available for download in the Advanced Rendering Forum.

Limitations

MDL materials are closed entities. They cannot be used in a shading network. Even though Maya allows connections to traditional shader and utility nodes, mental ray will ignore these  connections. However, MDL materials can be used alongside with traditional materials and shaders.

In its initial state, the mdl_material node does not come with a swatch render, has no viewport representation and is also not supposed to work with IPR. These limitations will be removed in future releases.

This is the first in a series of posts on mental ray for Maya 2016 Render Settings

Introduction

We significantly changed the mental ray for Maya 2016 Render Settings User Interface (UI) in order to reduce time spent adjusting renders. The defaults aim for no-fuss rendering of the most frequently used and up-to-date features. Of specific note, our newest Global Illumination (GI) mode significantly increases ease-of-use and productivity.

We provide almost everything a user needs here within this UI. For example, a user should not have to type in string options anymore.

Goals

Members of both NVIDIA ARC and Autodesk, including UI designers and developers, collaborated to make this change significant. As stated in the Maya 2016 documentation for mental ray Render Settings, we aim to:

• Enable complete rendering without requirement to adjust or enable most settings. The defaults should enable the most frequently used features.
• Increase ease-of-use when adjusting settings to control for optimization and quality.
• Provide single global controls to reduce repetitive and potentially error-inducing settings across scene elements.

We also want to retain the flexibility of mental ray for production users. So we provide an Advanced Settings option on each of the new tabs. We hide less frequently used features in favor of a cleaner, more productive and simpler control for basic workflow. This leads users of all levels to what is fundamentally important to control.

Render Settings Tabs

We re-organized the mental ray Render Settings into four main tabs:

The Quality tab contains quality settings for controlling sampling. By using quality settings, instead of sample counts, we take advantage of better optimization schemes internally. We also believe it will be conceptually easier, once the community gets familiar with this style of control.

The Scene tab contains shared settings across scene elements, such as camera settings that should be applied to all renderable cameras. This is where we provide the new simplified mental ray Passes.

The Configuration tab contains settings that are more likely to be used across Maya sessions, and how a user likes to work with the scene. For example, the interactive rendering control for progressive rendering depends on a machine’s resources.

The Diagnostics tab contains settings that help a user with problem solving, or identification of areas for optimization.

Quality Settings

Here, we provide an overview of how to adjust your scenes with the new UI, suggesting our recommended practice.

For new scenes, use the Overall Quality setting in the Sampling section as the primary control for speed vs. quality. It is located at the top of the Quality tab.This controls samples across a scene. Samples are not fixed per pixel. Rather, they vary in density per pixel region. More samples are taken in each region until the quality is matched.

In the next section, we provide detail to better understand how to adjust quality beyond the Overall Quality setting. With better understanding, we hope you can more quickly achieve your desired results. 

Understanding more about quality adjustment

Here, we introduce the concept of global vs. local sampling. This concept is key to adjusting quality now and in the future, as rendering technology evolves.

The Overall Quality setting is a global setting that controls samples across a scene. Each sample starts a ray traced from the camera out into the scene. In essence, we sample the scene from the eye (E). Below, we show an eye ray (in green) over a work by Albrecht Dürer.

When an eye ray intersects an object, the eye ray may split into several samples. We will call those the local samples, in contrast to the global samples, because they are local to each eye ray. Below, we show a diffuse distribution of local samples split out for diffuse reflection.

We separate the local samples into two categories at an intersection point: the samples used for lights and the samples used for materials.

For materials, the sample directions depend on the type of surface at the intersection point. For example, above a diffuse surface creates samples in the hemisphere above the intersection point. Because these samples tend to hit objects, it represents indirect light.

For lighting, the samples are taken from all visible lights in the scene. Below, we see a single light sample for the same intersection point. There could be more light samples depending on number and size of lights. Light samples represent direct light.

Traditionally, lights were only those elements specified explicitly as lights in the scene, and they had no size. However, as rendering implementations evolved, so did lights, from point to area lights, and now, emissive objects. Also, consider the light from an environment. Environments convert automatically into light sources by enabling environment light emission. When enabled, we provide a separate quality control for the environment lighting.Note that it is grayed out when not enabled. Furthermore, now one can create such a light more directly. See for example Create > Lights > Environment Image (IBL).

Similarly, we provide a separate control for indirect diffuse (GI) quality in materials, even though it is conceptually a part of material quality.As global illumination techniques have evolved considerably, so have the ways to control these techniques. Yet, the Indirect Diffuse Quality applies to any Indirect Diffuse (GI) Mode selected, and to any material used.

In our next mental ray for Maya 2016 Render Settings post, we provide more details and examples for Adjusting Quality.