# Tutorials/Basics Running Pixie

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Pixie is a renderer. It means Pixie reads a scene description and produces an image of that scene. A scene description contains

- Geometry (Polygons, NURBS, Subdivision Surfaces etc.)
- Surface Description (Color/Opacity, Shaders etc.)
- Camera Description (Resolution, Focal Parameters etc.)
- Transformations (Rotate, Translate etc.)

RenderMan interface defines a set of commands that fall into one of these categories. There are two main ways of specifying commands. The most common approach is to write a text file that contains these commands and give it to Pixie. Alternatively, you can create a C/C++ program that calls these commands directly. Every RenderMan command has two versions; a C function that your program can call, or a text command. For example;

    Rotate 90 1 0 0

and

    RiRotate(90,1,0,0);

are the same command that instruct the renderer to rotate everything that is defined after this command 90 degrees counterclockwise around the x axis. The first version is a text command that Pixie can read from a text file and the second form is a C function that you can call from your code.

To render a scene description from a text file, you should use rndr. The text files that contain the RenderMan scene description are called RIB, for Renderman Interface Bytestream.

To specify the scene description from your program, you should include ri.h (which defines all RenderMan commands) and link against ri.lib/libri.so.

Most users of Pixie do not actually need to bother with RenderMan commands or specifying a scene. Because there are translators that take your Maya/3DS Max/SoftImage/Lightwave/Blender scene and creates the scene description using RenderMan commands for you. A good example is Liquid for Maya. This is a very high quality (and production proven) scene translator that takes your Maya scene, creates the RenderMan commands that Pixie understands to render the image.

Knowing RenderMan is still very useful especially if you would like to create your scene procedurally. Furthermore, to use advanced features of Pixie, you will need some familiarity with RenderMan interface.

Retrieved from "http://www.george-graphics.co.uk/pixiewiki/Tutorials/Basics_Running_Pixie"

Category: Tutorials

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