In Maya 2016, the mental ray Render Settings tabs have been redesigned to use the most up-to-date rendering approaches with the latest mental ray features. Everything that a user needs to adjust in order to render with mental ray is available in this Render Settings user interface.
The goals of the redesign:
Enable complete rendering without the requirement to adjust or enable most settings. The defaults should enable the most frequently used features.
Ease-of-use when adjusting settings to control optimization and quality.
Provide single global controls to reduce repetitive and potentially error-inducing settings across scene elements.
In particular, material optimizations such as sampling settings have been moved out of material shaders and their Attribute Editor nodes and into the Render Settings as quality controls. Some per-element settings have been removed to take advantage of automatic rendering core optimizations.
The mental ray tabs now consists of four main tabs:
Focuses on optimization for quality settings using the latest mental ray features for controlling sampling. Most sampling settings for the render are now derived from a user-oriented quality control.
Contains shared settings across scene elements, such as camera settings that should be applied to all renderable cameras. For example, a new mental ray Passes control section that is shared by all renderable cameras is available in the Camera section of the Scene tab.
Contains settings that are more likely to be used across Maya sessions, related to machine resources capability, and how a user likes to work with the scene. For example, the interactive rendering control for progressive rendering is available in this tab, as well as any other settings that take advantage of the GPU.
Contains settings that help a user with problem solving, or identification of areas for optimization.
To allow for a faster workflow, the mental ray tabs contain a toggle to show or hide advanced settings. This ability to hide less frequently used features offers a cleaner, more productive and simpler control for a basic workflow. This also allows you to understand what are the most important attributes to adjust.
To support legacy scenes, the original Passes tab can also be shown. To see this tab, select Window > Settings/Preferences > Preferences to open the Preferences window. In the Rendering section, enable Show Maya Legacy Passes to display the Passes tab in the Render Settings window.
For backwards compatibility, you can also revert back to the Maya 2015 mental ray Render Settings. Enable Use Legacy Render Settings and Show Maya Legacy Passes in the Rendering category of the Preferences window and restart Maya.
For new scenes, the defaults have been set so that you can use the Overall Quality attribute in the Sampling section as the primary control for speed versus quality. This control is located at the top of the Quality tab.
This controls samples across a scene, which are not fixed per pixel, but rather follow the quality setting to determine, in a given area of the scene, per pixel region, the number of samples that are required.
The Overall Quality setting is a global setting for sampling quality across a scene. Each sample starts with a ray traced from the camera out into the scene. In essence, the scene is sampled from the eye (E); or, in other words, the rendered camera. When this ray intersects with a scene element such as an object, it is possible, in traditional ray tracing methodology, that several samples are spawned. These are referred to as local samples, in contrast to the global samples setting, because they are local to each eye ray.
Local samples can be divided into two categories at an intersection point: the samples used for lighting and the samples used for materials. For lighting, the samples are taken from known lights in the scene. For materials, the samples are taken based on the type of surface at the intersection point. That determines where the sample continues into the scene from the intersection point.
The image on the left shows one light sample, and on the right, one material sample.
You may be familiar with a further separation of local sampling control, such as lighting from lights in the scene as compared to lighting from the environment created as a light. See, for example, Create > Lights > Environment Image (IBL) which creates an environment as a light.
And for material samples, you may be familiar with a separation, at least for indirect diffuse (GI) interactions in the material. As settings for global illumination techniques have varied considerably historically, so have the ways to control these techniques. Therefore, the user interface currently maintains separate indirect diffuse and material quality controls. However, the indirect diffuse quality presents itself in a greatly simplified form compared to GI control presentations in the past.
In general, use the global Overall Quality control. Use the local quality controls when there is an unbalanced amount of noise from lighting or from materials. For example, if the direct lighting appears to create more noise than other aspects of the scene, the lighting quality can be increased for possible optimum speed versus quality tradeoff.