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RixProjectionFactory is a subclass of RixShadingPlugin, and therefore shares the same initialization, synchronization, and parameter table logic as other shading plugins; please refer to that page for more details. Projections do not support lightweight instances, and therefore CreateInstanceData() need not and should  should not be overridden as any created instance data will not be returned to the pluginfactory.

The renderer uses the RixProjectionFactory object by invoking RixBxdfFactory::CreateProjection()  to obtain a  RixProjection. A description of various options associated with the current render are provided to the factory via the RixProjectionEnvironment &env. This class includes information about the current format (the width and height of the image in pixels and the pixel aspect ratio), the screen window, the shutter time values, the near and far clipping planes, and the world to camera transform. Developers are expected to use this information, along with the arguments supplied to the plugin via the RixParameterList pList, to create an instance of RixProjection that encapsulates the information necessary to model the desired camera and lens behavior.

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