Before rendering the main image, the render pass will render all needed shadow maps. This panel controls whether to render shadow maps or not and list details about what shaders to use in a shadow render.
Figure 3.50: The Shadow Maps panel
‘Render Shadow Maps’
This attribute controls wether the shadow maps will be rendered or not. Its default value is on.
‘Use Displacement Shaders in Shadows’
This attribute controls if the displacement shaders are used in the shadow maps ren- dering. By default this toggle is on. Note that turning this toggle off might speed up shadow map rendering but produce incorrect shadows depending on how much the geometry is displaced.
‘Use Surface Shaders in Shadows’
This attribute controls if the surface shaders are used in the shadow maps rendering. By default this toggle is off. It is recommended to turn on this attribute only if some surface shaders are displacing the geometry or modifying the opacity.
‘Use Atmosphere Shaders In Shadows’
This attribute controls if the atmosphere shaders are used in the shadow maps ren- dering, and it is off by default. It is recommended to turn this option on only if deep shadow maps are rendered.
‘Use Interior Shaders In Shadows’
This attribute controls if the atmosphere shaders are used in the shadow maps ren- dering, and it is off by default. It is recommended to turn this option on only if deep shadow maps are rendered.
‘Z Threshold’
Only objects with opacities greater than or equal to the ‘Z Threshold’ will appear in shadow maps. The default value is [1.0, 1.0, 1.0] which means that only completely opaque objects are rendered into shadow maps. If this value is set to [0.0, 0.0, 0.0] all
Chapter 3: The User Interface 63
objects will be included in the shadow map, even completely transparent ones. Note that this parameter is only useful for depth shadow maps as deep shadow maps correctly handle semi-opaque surfaces. For users familiar with the RenderMan standard, this is the equivalent of the following RiOption:
Option "limits" "zthreshold" [r g b] ‘Depth Filter’
This attribute offers the same control as the light attributes node’s "depth filter" attribute. Note that setting the render pass’ depth filter attribute will have no effect on any shadow maps except when a shadow map is produced by one of the render pass’ display. In other words, if a render pass has no primary nor secondary display that use the ‘shadowmap’ display driver, no shadow maps will be affected by this attribute. The available values are:
‘min’ This is the default value.
‘max’
‘average’
‘midpoint’ This value is a little slower to compute but is usually very good at getting rid of the self-shadowing problems.
‘Volume Interpretation’
This attribute will affect only deep shadow maps rendered in one of the displays of the render pass node. Deep shadow maps defined in light attributes nodes will not be affected by this parameter. The available values are:
‘Discrete’ This value should be used to compute shadows cast by solid objects.
‘Continuous’
This value should be preferred for computing shadows cast by participat- ing media (fog, clouds, smoke, etc.)
‘Distance Inside’
‘Shadow Linking’
This attribute controls what type of light linking will be used to determine the list of objects shadowed by a given light. The available values are:
‘Use Light Links’
Objects will cast shadows from the lights that are considered illuminating the objects by the light linker. This is the default.
‘Use Shadow Links’
Objects will cast shadows from the lights that are considered shadowing the objects by the light linker, allowing object-light relations for illumia- tion distinct from those for shadowing.
‘Ignore Light & Shadow Links’
All visible objects will cast shadows from all lights.
This attribute will affect both ray-traced shadows and mapped shadows. It is possible to override its value on a per-light basis by using the "Shaodw Objects" attribute of an assigned light attributes node (although sets must then be used to specify which objects are shadowed by the light; see Section 3.8.3 [Light Attribute Node Shadow Objects], page 41).