Multi-render passes reduce the need to use render layers, thus reducing compute times for scene translation and rendering. If you work with complex multi-layered compositions, rendering may also be several times faster.
Using multi-render passes, you can render an unlimited number of render passes and group them into render pass sets.
For advanced users, you can also select a subset of the objects or lights in your scene to contribute to each render pass. This subset is called a render pass contribution map. Render pass contribution maps allow you to perform scene segmentation at render time.
Currently, the multi-render pass workflow is supported for the following shaders:
Refer to mi_metallic_paint_x_passes, mia_material_x_passes, misss_fast_shader_x_passes, mi_car_paint_phen_x_passes shaders for a list of passes supported by each of the mi_metallic_paint_x_passes, mia_material_x_passes, misss_fast_shader_x_passes and mi_car_paint_phen_x_passes shaders.
The mental ray mi_metallic_paint_x_passes, mia_material_x_passes, misss_fast_shader_x_passes, and mi_car_paint_phen_x_passes shaders only support object pass contribution map capabilities but not light pass contribution map capabilities. All lights in your scene contribute to a render pass for a pass contribution map that includes these shaders.
Standard surface materials support all render passes mentioned in Available render passes; however, there are some non-standard shaders which contribute only to a subset of applicable passes, such as volume shaders, hair, and fur shaders, and so forth.
Setting up your scene to use multi-render passes
To set up multi-render passes, do the following:
button in the Passes tab to open the Create Render Passes window, and select the render passes that you want to create.
See Create Render Passes window for more information.
See Passes tab for more information.
See Render pass Attribute Editor for more information.
See Passes tab for more information.
See Relationship Editor for more information.
A render pass contribution map associates a subset of lights and renderable objects in your scene with one or more render passes.
For example, if your render layer consists of 5 objects and 2 lights, you can create a diffuse pass, an ambient pass, and a specular pass for only 3 of the objects and 1 of the lights.
Alternatively, you can click the New pass contribution map button 
in the Passes tab in the Render Settings window.
See Render Layer Editor for more information.
See Create Render Passes window for more information.
See Passes tab for more information.
You can create multiple pass contribution maps for each render layer, or, share a pass contribution map between two or more layers.
When rendering a given render layer, only the pass contribution maps linked to the layer are applied. Render passes that are not connected to any objects through pass contribution maps are implicitly associated to all objects.
For each render layer, if there are many passes associated with your render layer, you can group your render passes into logical groups called render pass sets. For example, you can group your Reflection, Shadow and Specular passes into an Illumination render pass set.
You can create a render pass set by clicking the Create new render pass set 
button in the Render Settings: Passes tab. Alternatively, you can create your render pass set at the same time as you create your render passes. Click the Create
new render pass button to open the Create Render Passes window and enable the Create Pass Set option. For more information, see Passes tab and Create Render Passes window.
Using render pass sets in your scene provides a sample workflow of how to incorporate render pass sets in your render layer.
Render pass sets should not be confused with <RenderPassFileGroup>, which is a token for constructing a file name for your render output. The Render Pass Attribute Editor contains an attribute called Pass Group Name. The text in this field is fed into the <RenderPassFileGroup> token when constructing file names for the render output. This allows you to control how different passes are grouped into a file. For example, if the File name prefix is: <RenderLayer>_<Camera>_<RenderPassFileGroup>.exr, then all images with the same layer, camera, and render pass file group are grouped into the same .exr file. See Render pass Attribute Editor for more information.
Choose from the following render passes:
| Render Pass | Description |
|---|---|
| 2D Motion Vector | Relative motion (in raster coordinates) of objects in your scene; in other words, how far each pixel is moving between two frames. Vector is expressed in normalized pixels. |
| 3D Motion Vector | 3D motion vector in world space. In mental ray for Maya, the 3D motion vector is expressed in internal space. |
| Ambient | Ambient contribution of the surface. In Maya, this is the material color multiplied by the ambient light color. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Ambient Irradiance | Amount of ambient light received by the surface. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Ambient Occlusion | Ambient occlusion contribution from both self ambient occlusion as well as primary ambient occlusion, which is derived from surrounding objects. You must enable Ambient Occlusion in the Render Settings: Features tab in order to use this render pass. |
| Ambient Material Color | Reflectivity of the material with respect to ambient light. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Beauty | Final color computed by mental ray for Maya. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Beauty Without Reflections or Refractions | Beauty pass without reflections or refractions. See Render pass Attribute Editor for more information on the attributes for this pass. You may want to create this pass and a separate reflection or refraction pass, then composite the results. This allows you to tune the tint and intensity of the reflection/refraction separately from the rest of your passes. |
| Camera Depth / Camera Depth Remapped | Extracts the distance between the camera and the intersection point. Choose between normalized distance and real scene distance. See Camera Depth render pass attributes for more information on the attributes for this pass. |
| Coverage | mental ray Coverage frame buffer. This frame buffer offers only silhouette coverage. Self-coverage is currently not supported. |
| Custom Color / Custom Depth / Custom Label / Custom Vector | Use in conjunction with the writeToColorBuffer, writeToDepthBuffer, writeToVectorBuffer, and writeToLabelBuffer shaders to write data to the framebuffer. Or, create your own custom pass if you are using custom shaders. See mental ray render pass utility shaders for more information. |
| Diffuse | Diffuse shading of material. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Diffuse Without Shadows | Diffuse pass without shadowing information. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Diffuse Material Color | Provides constant diffuse color or textured diffuse color, excluding light contribution. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Direct Irradiance | Direct light arriving at each sample location. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Direct Irradiance Without Shadows | Direct irradiance without shadowing information. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Glow Source | outGlow output of surface shaders; affected by pass contribution maps. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Incandescence | Additive color. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Incidence (Light/Normal) | Measures the difference between the direction of the light ray and the surface normal. If the surface normal is facing the light, this value is 1. If the normal is facing away from the light, the value is 0. Create a pass contribution map to isolate the light ray of your choice. If there is no pass contribution map in your scene, Maya performs its calculations based on the sum of all lights in your scene. |
| Indirect | Indirect lighting from final gather, global illumination, and caustics. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Light Volume | Extracts all light-centric volume effects, for example, a light cone volume effect. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Material Incidence (Camera/Normal) | Measures the difference between the direction of the camera ray and the surface normal. If the surface normal is pointing to the camera, this value is 0. If the normal is facing away from the camera, the value is 1. Any angle greater than 90 degrees is also translated to 1. If bump mapping is applied to the shading network, it will appear in this pass. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Material Normal (Camera Space / Object Space / World Space) | Interpolated surface normal. Choose from one of Camera space,Object space and World space. If bump mapping is applied to the shading network, it will appear in this pass. |
| Matte | The object's matte, excluding transparency/opacity. This pass serves as the render layer compositing mask. Should be solid white in areas where objects are intersected. Independent of transparency/translucency. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Normalized 2D Motion Vector | Relative motion (in raster coordinates) of objects in your scene; in other words, how far each pixel is moving between two frames. Pixel displacement is normalized to (0—1). Static objects are expressed with 0.5,0.5 values. See Normalized 2D Motion Vector render pass attributes for more information on the attributes for this pass. |
| Object Incidence (Camera/Normal) | Similar to the Material Incidence (Camera/Normal) pass but does not support bump mapping. |
| Object Normal (Camera Space / Object Space / World Space) | Similar to the Material Normal (Camera Space / Object Space / World Space) pass does not support bump mapping. |
| Object Volume | Extracts all object-centric volume effects, for example, smoke that is contained in a glass object. Also includes volume particles, volume fur, and fluids. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Opacity | The object's opacity, which is derived from transparency/refraction. In compositing, the object's opacity can be controlled independently from the render layer matte. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Raw Shadow | Similar to the Shadow pass but calculated only with respect to the irradiance in the scene. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Reflection | Reflection results. Includes self-reflection, primary reflections, secondary reflections and environment reflections. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Reflected Material Color | The reflected color parameter of the material. Pure constant reflection color or textured reflection. Used as a reflection matte to determine where reflection would be revealed (colored and noncolored). See Render pass Attribute Editor for more information on the attributes for this pass. |
| Refraction | Refraction results. Includes self-refraction, primary refraction, and environment refraction. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Refraction Material Color | The transparency color parameter of the material. Pure constant refraction color or textured reflection. Used as a refraction/transparency matte to determine where refraction is revealed (colored and non-colored). See Render pass Attribute Editor for more information on the attributes for this pass. |
| Scatter | Scattering effects that result from the material’s scattering attributes (for example, Scatter Radius, Scatter Color). See Render pass Attribute Editor for more information on the attributes for this pass. |
| Scene Volume | Extracts all scene-centric volume effects such as fog, layered fog, haze, and so forth. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Shadow | Pure shadow contribution for both self-shadowing as well as direct shadows. The shadow pass can be luminance or colored shadows. Takes into account material contributions. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Specular | Specular shading. The specular component is modulated differently depending on the type of material associated with the object. For example, Phong, PhongE, Blinn, and Anisotropic materials produce specular contributions differently. On a Phong material, the specular pass can be modulated using cosine power and specular color. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Specular Without Shadows | Similar to Specular but without shadow occlusions. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Translucence | Back shading contribution revealed on the front surface. See Render pass Attribute Editor for more information on the attributes for this pass. |
| Translucence Without Shadows | Similar to Translucence but without shadows. See Render pass Attribute Editor for more information on the attributes for this pass. |
| UVPass |  A UV pass converts UV values to R/G values and creates a rasterized version of UV space. Using a UV pass, you can replace textures in 3d renderings as a post-process, without having to track new textures in place. |
| World Position | A world position pass converts position (x,y,z) values to R, G, B values. Use this pass for relighting workflows in compositing. |
