Each new scene, by default, has a single 'Base Shader' item. Shaders read the information from the Shader Tree and compute the effect of the illumination in a scene. They also control the rate that pixels are evaluated before being sent to the Render item. Additionally, they control visibility of surfaces in a scene and what rays are allowed to see the surfaces. In most cases, user won't ever touch the settings in the Base Shader, however, in cases where specific surfaces need additional control, such as limiting Monte Carlo shading to a Fur surface, or hiding lights from illuminating a surface, or even hiding an entire object from the Camera, additional Shader items will need to be added with appropriate settings applied. Due to the layered approach of the shader tree, the additional shaders will need to be placed above the Base Shader in the tree within their own material group mask (otherwise the settings of the base shader will simply override them).
For information regarding adding and working with Shader Tree Items Layers, please reference the Shader Tree page of the documentation.
Layer--
Enable: Toggles the effect of the layer on and off, duplicating the functionality of toggling visibility in the Shader Tree. When un-checked (disabled), the layer has no effect on the shading of the scene. However, disabled layers are saved with the scene and are persistent across modo sessions.
Invert: Inverts the illumination of the scene/layer producing a negative effect.
Blend Mode: Affects blending between different layers of the same effect type, allowing user the ability to stack several layers for different effects. For more on blending, please reference the 'Blend Modes' page of the documentation.
Opacity: Changes the transparency of the current layer. Reducing this values will increasingly reveal lower layers in the shader tree if present, or dim the effect of the layer itself on the surface.
Shader--
Shading Rate:The Shading Rate (also known as the "Coarse Shading Rate") determines how finely to shade each pixel in the materials feeding the selected Shader Item during initial shading. The default value of 1 indicates that the pixel will be evaluated once before being evaluated for further refinement (see Refinement Threshold). Decreasing the Shading Rate results in a more finely evaluated pixel which generally yields longer render times. For instance, if you change the value to .5 the pixel is effectively cut in half horizontally and vertically and each "sub pixel" is evaluated. In this case you have reduced the rate by half but increased the amount of evaluation by 4 times. Keep this in mind as small changes to the shading rate can yield large changes to performance.
Generally the Shading Rate can be left at one and further refinement can be achieved via the Antialiasing level or the Refinement Shading settings. However, in the cases of aliasing seen in reflections or refractions or on procedural textures it is possible to rectify them via the Shading Rate setting. Since this will effect all pixels evaluated it is a fairly 'brute force' solution. Therefore, you should manually restrict the pixels that are effected by the Shading rate by creating Shaders for specific problem areas via Masks and only decrease the Shading Rates where absolutely necessary.
Direct Illumination Multiplier: Direct Illumination is light coming from traditional 3D light sources such as Directional, Spot, Area, Distant, Cylinder, Dome, and Point. At the Shader item level it is possible to globally affect the direct light intensity via the Direct Illumination Multiplier. By default the value is set to 100%. If we imagine a project with three lights of varying intensity such as 100%, 70% and 30%, setting the 'Direct Illumination Multiplier' to 50% would drive these values down to 50%. 35% and 15% respectively. This is often a handy method for tweaking overall light effects as well as balancing Direct and Indirect light contributions.
Indirect Illumination Multiplier: Indirect Light comes from global illumination sources such as luminous geometry, image based lighting via environments and simple bounced light from diffuse surfaces. The Indirect Illumination Multiplier provides a global method for controlling the Indirect light contribution to the final render. This is very useful when Indirect Light sources are too subtle/pronounced or for simply balancing Direct and Indirect Light contributions.
Indirect Illumination Saturation: One of the many benefits of indirect illumination is the color bleeding between surfaces. As rays take into account not only the color of the lights, and the environment, but the surfaces color as well. The 'Indirect Illumination Saturation' setting allows the user to control the strength of the colors generated by indirect illumination independent of the illumination itself. Increasing the value above 100% will make the colors stronger and more saturated, and values below 100 will decrease the effect.
Indirect illumination Type: Generally, indirect illumination is controlled globally through the Render Properties Global Illumination tab. In some instances, the user may want to control the type of global illumination per surface by using a shader with an associated mask. This gives the user the option of using Irradiance Caching for say an exterior scene, but on complex surfaces such as the trees and bushes, the monte carlo method would provide better results. The user could create a selection set for just the trees and bushes (Select > Assign Selection Set), and in the shader tree, add an additional material 'Group' item above the base shader. In the group properties panel set Tag Type to 'Selection Set' and highlight the named set under 'Polygon Tag'. In this group add its own 'Shader' and set the properties 'Indirect Illumination Type' to 'Monte Carlo'. Now most of the scene will use irradiance caching while only the trees and bushes would use Monte Carlo. The Indirect Illumination type will draw its values from the Render Properties Global illumination tab. The number of rays used for the Monte Carlo method is indicated by the 'Indirect Rays' value of the aforementioned properties tab of the Render item.
Visibility--
There are several toggle options to control visibility of various attributes of the elements feeding the shader. For instance, with these controls you could create a bright luminous polygon that is visible to Indirect Illumination but invisible to reflections, ray traced shadows, reflection and the camera. This would create a nice virtual light element that can be placed anywhere in the scene for illumination purposes without worrying about it effecting any other visual aspect of the project. The options include:
Cast Shadows: Disabling this toggle will cause all elements controlled by the shader to be ignored by shadow rays so they do not create any shadows in the scene. Light will simply pass through the elements. This will not disable shadow effects from indirect illumination as this only affects direct light sources.
Receive Shadows: Disabling this toggle causes the elements to stop receiving ray traced shadows from other geometry in the project.
Visible to Camera: Disabling this toggle will simply hide any item or element controlled by the shader from the camera. These elements may still appear in shadows, reflections and refractions even when hidden to camera.
Visible to Indirect Rays: Indirect Light is any light calculated during Global Illumination such as luminous geometry, Images used as light sources and other light bounced from geometry. Toggling this option off will remove the elements controlled by the shader from Indirect Light calculations.
Visible to Reflection Rays: Disabling this value will remove the elements controlled by the shader from reflecting in mirror surfaces.
Visible to Refraction Rays: Disabling this value will cause the elements controlled by the shader to be invisible when looking at them through refractive surfaces.
Visible to Occlusion Rays: Disabling this value will cause the elements controlled by the shader to be invisible to Occlusion Ray calculations.
Alpha Type: The 'Alpha Type' selector allows the user to choose how surfaces contribute to a rendered alpha channel. When set to 'Opacity' the transparency of each individual surface determines the alpha value. 'Constant' allows the user to specify a fixed alpha value for all associated surfaces. 'Shadow Catcher' is a slightly different function, as it makes all associated surface attributes invisible, exclusively rendering shadows cast by direct and indirect illumination. This is a great tool for composing rendered images with background photos right in modo. A ground plane can 'catch' the shadows cast by other object, without contributing any shadows of its own. When a photo is specified as a background, the objects and shadows all render together in one pass.
Alpha Value: When 'Constant' is selected as the alpha type, the 'Alpha Value' overrides surface opacity settings and determines to what degree surfaces contribute to a rendered alpha channel.
Light Group: Light linking allows users to control, on a shader level, what lights in a scene effect what surfaces. The 'Light Group' selector allows the user to specify which group of lights to control. Light groups can be easily made in the 'Groups' palette. Click 'new group' to create a base group, rename it if you wish, and add items by selecting the lights in the 3D viewport, hold down shift to select multiple items. Now right click on the group title and select 'Add Items' from the drop down menu. Users can also drag and drop items directly from the 3D viewport onto any group item to add them.
Mode: The 'Mode' selector allows the user to specify how the lights affect surfaces, If set to 'Include', the lights will affect the shaded surfaces and set to 'Exclude, the lights will not.
The Fog options found on the Shader Item allow a simulated fog effect by applying the fog color to relevant materials with increased intensity as the geometry is further from the camera. This is also a great option to fade objects into a background increasing the apparent depth of an image.
Fog Type: The Fog Type popup allows you to choose the fog types options.
None- Disables Fog from rendering.
Linear- When selected, Fog will render in the scene based on the Start and End distances, where there is no fog up to the starting distance, then surfaces will attenuate toward the 'Fog Color' and maximum 'Fog Density' at the end distance.
Exponential- When selected, Fog will render starting at the cameras position, increasing in strength the further a surface is from the camera. Based on exponential values, the strength will increase non-linearly and is directly influenced by the 'Fog Density' setting.
Underwater-
The 'Underwater' fog option is basically the same as the Exponential function, except that the fog will have a tendency to absorb Red colors more readily, producing a bluish cast and reduces color saturation with distance overall as well.
Use Environment Color: This option is only available when Backdrop Fog has been enabled. With backdrop fog modo adds the fog color to all materials with increasing intensity as the distance to the camera increases. With Use Environment Color active the Environment Material or textures will be used to color the fog. This option will give the illusion that the mesh is fading into the background.
Fog Color: This color component determines the color value that is applied to materials receiving fog.
Fog Start/End Distance: When the Fog type is set to linear, users can specify specific starting and ending distances for the fog effect.
Fog Density: This percentage value determines how thick the fog is just in front of the camera. The default value of 10% indicates that geometry just in front of the camera will have a 10% blend of the fog color. The density of the fog will increase as it recedes further from the camera.
