Legacy render layer concepts

Master layers and layer membership

The Master layer contains all the objects and materials in the scene. There is always a Master layer in your scene; it’s exposed in the Render Layer editor. It is only visible in the Render Layer editor if there is more than one layer (in which case it is non-renderable by default).

When you create new layers, you can make any objects or nodes (including lights) members of only that layer, multiple layers, or all layers. Only objects in a specific layer affect or contribute to that layer; this includes lights, reflections, shadows, and so on.

In addition to segmenting your scene into render layers, you can change the characteristics of each layer or object on a layer by creating layer overrides. (By definition, you can't override the characteristics of the Master layer.) Maya stores each of the layer and attribute overrides as changes between that layer and the Master layer. See the next section.

Changes to a layer or to objects on a layer (overrides)

There are two types of overrides for attributes: per layer and per object.

• Per layer overrides change attributes, characteristics, or material assignments that affect the entire layer. This can include the renderer for the layer, the image size for the rendered image of that layer, whether or not all objects on the layer cast shadows or receive shadows, or a material assigned to all objects in the layer.
• Per object overrides change the value of an attribute or material assignment on an object in a specific layer on which overrides exist. This can include the material assignment for an object on the layer, render stats for that object (such as casting or receiving shadows), or attributes of the object, or on per-object shaders (such as transparency).

There are two ways to create overrides: auto and manual.

• Auto overrides immediately change the value of the attribute to be different than the one specified on the Master layer, without any additional action required on your part.
• Manual overrides require you to explicitly tell Maya that you want that attribute value to be different than the one specified on the Master layer.
  • Per layer auto-overrides include shader assignments (to all objects in a layer); see Work with layer overrides.
  • Per layer manual overrides include changes to per-layer render settings and member overrides (render stats). See Work with layer overrides.
  • Per object auto-overrides include material assignments to objects; see Work with attribute overrides.
  • Per object manual overrides include all other attribute change; see Work with attribute overrides.

Viewing layers and managing layers

Render layers affect the scene view, Hypergraph, Hypershade, and so on. Switching layers means that lights, geometry, or nodes are visible or not depending on whether those objects are in a particular render layer. (Previously, objects always appeared in the scene view and were either present or not present in a render.)

Visibility of Display layers and Render layers interact subtractively. That is, if you have a Display layer that contains objects and turn off visibility on that layer, you will also not see these objects in any of your Render layers.

• There are three different ways to create per-layer changes:
  • overrides that affect the entire layer
  • auto-overrides to render stats or material assignment of an object on a layer
  • manual overrides to any other attribute.

What you can do with render layers: summary

Once you understand the basic concepts of Master layer, layer and object overrides (auto or manual), render settings, and presets, you can do the following on a layer-by-layer basis:

• select the renderer and override Render Settings (formerly known as Render Globals) both in the Common tab and in the renderer-specific tab.
• create layer overrides. You can override settings that affect rendering; for example, you can turn off Cast Shadows and turn on Visible in Refractions and Visible in Reflections for a layer.
• override material assignments:
  • per component (for example, assign certain faces a different material for any layer).
  • per object (for example, assign certain surfaces a different material for any layer)
• override any renderable attribute (for example, set a different value for transparency on a object on a particular layer)
• assign the blending modes for layers directly in the Render layer editor, and preview the layer composite in the Render View.

Advantages of rendering in layers and passes

Rendering separate objects in layers and passes takes more time and effort to plan, but it offers the following advantages:

• More creative freedom.

  For example, you can render different layers with different render options. You can then color correct or add special effects to each rendered layer in a compositing application.

• Flexibility to accommodate unanticipated requests for changes.

  For example, you can change a ceramic vase to a glass vase without re-rendering the entire scene.

• Increased speed to meet production schedules.

  For example, you can quickly render the foreground layer where most changes occur, instead of the whole scene or background, where objects tend to be static. You can also render smaller portions of large scenes, reducing the load on computer memory.

General tips for rendering for compositing

• Plan to separate a scene into elements early in the production process.
• If you plan on compositing rendered images, make sure the scene’s background is black. To change the color of the background, see the Lights and camera’s chapter.
• Understand the type of image that compositors require: premultiplied or not.