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Shaders often need to perform calculations in non-standard coordinate systems. The coordinate systems with predefined names are: "raster," "screen," "camera," "world," and "object." At any time, the current coordinate system can be marked for future reference.
RiCoordinateSystem ( RtToken space )
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The table below shows which commands may be specified inside a RiMotionBegin-RiMotionEnd block. If the Motion Blur capability is not supported by a particular implementation, only the transformations, geometry, and shading parameters from t0 are used to render each moving object.
Moving Commands
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Resources
Resources generally encapsulate some part of the graphics state, or other information specific to the renderer such as a in-memory RIB archive. Resources are always named and have a type associated with them. Resources are unique in that they can exist outside the rest of the graphics state, and are thus not subject to standard scoping rules; instead, they have their own scoping block mechanism. An example of a resource is the ability to save the entirety of the current attribute state, and restore it at a future point, independent of the current attribute stack.
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The following table describes which parts of the graphics state are manipulated by "string subset". In addition, PRMan allows for multiple subsets to be combined using comma separated lists. Hence, restoring the "shading,geometry" subset will be the same as restoring both the "shading" and "geometry" subsets.
| Subset Name | Attributes Restored by Subset |
|---|---|
| shading |
|
| |
| transform | Transformation calls (RiConcatTransform, RiTranslate, etc.) |
| geometrymodification | |
| geometrydefinition |
| hiding | Attribute "hide" |
Note
PRMan currently has limitations related to user attributes and scoped coordinate systems: user attributes or coordinate systems whose values are overridden while in anAttributeBegin-AttributeEnd scope may not save the correct value (the last value set in the current scope will be restored). In other words:
AttributeBegin Attribute "user" "string mytex" ["grass.tex"] Resource "grass" "attributes" "string operation" "save" Attribute "user" "string mytex" ["flowers.tex"] AttributeEnd Resource "flowers" "attributes" "string operation" "save" Resource "grass" "attributes" "string operation" "restore" "string subset" "shading"
When the named attribute state "grass" is restored, the attribute user:mytex will contain flowers.tex, not grass.tex. This limitation may be addressed in a future release.
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