Studierstube scripting mentor

Creating your first applications

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After the basic syntax of the file format has been explained, we can now start to introduce the most important and useful nodes and create simple scenes with them.

Defining geometry

Open Inventor offers a wide range of shape nodes that can be used to create an application's geometry. Besides the usual 3-dimensional graphics primitives and text, it is possible to create arbitrary polygon or NURBS geometry, possibly exported from a 3D modelling package.

The geometry of primitive objects and text is determined by fields provided by the shape node. For arbitrary shaped surfaces like polygon and NURBS surfaces, it is necessary to specify the coordinates of all vertices, as well as additional information like surface normals, material or texture coordinates for each vertex, explicitly. This information is stored in seperate nodes, to allow sharing of this information between multiple nodes. Vertex coordinates are set by adding a Coordinate3 node to the scene graph, which contains a single field, point, of type MFVec3f to specify the current set of vertices. This node adds the specified coordinates to the traversal state, from which they can be used by shape nodes to render their geometry. For example:

Coordinate3 {                        # defines the set of coordinates to operate on
    point [ 0 0 0 , 0 1 0, 0 0 1, 0 1 1 ]
}
IndexedFaceSet {                     # render an IndexedFaceSet
    coordinateIndex [ 0, 1, 2, -1,   # vertex indices of polygons to render, 
                      1, 2, 3, -1 ]  # -1 starts a new polygon
}

The following table lists the most important geometry nodes provided by Open Inventor. For the beginning, you will be working mostly with basic primitives and text nodes to create simple content. Generic surfaces allow users to create arbitrarily shaped surfaces.

Transformations

For positioning geometry in space, transformation nodes are used. A transformation nodes can be used to translate, rotate or scale geometry. All transformations are accumulated in the traversal state, therefore transformations are cumulative and affect all nodes that are traversed afterwards.

Simple animation can be realized by using animated transformation nodes. These nodes will change their transformation values at a predefined speed.

The following table lists the available transformation nodes:

The following example shows how geometry nodes and transformations are combined:

#Inventor V2.0 ascii


# This is a simple coordinate system, built from geometry primitives
 
DEF AXIS Group {               # this is our Y-axis
    Transform {
        translation 0 0.1 0    # go to center of axis
    }
    DEF LINE Cylinder {        # cylinder stretches in both directions
        radius 0.0025
        height 0.2
    }
    Transform {
        translation 0 0.1 0    # go to tip of axis
    }
    DEF ARROW Cone {           # use cone as arrow
        bottomRadius 0.005
        height 0.02
    }
    Transform {
        translation 0 0 -0.2   # un-do translations
    }
}
Transform {
    rotation 0 0 1 1.5708      # rotate 90 degrees around z-axis
}
USE AXIS                       # X-axis
Transform {
    rotation 0 1 0 1.5708      # rotate 90 degrees around y-axis
}
USE AXIS                       # Z-axis

Material & Appearance

Open Inventor provides several nodes that influence the appearance of geometry. All nodes that are traversed before the geometry node influence the appearance of that node. For example:

Material {               # set the color to red
    diffuseColor 1 0 0
}
DrawStyle {              # set style to wireframe
    style LINES          
}
Sphere {                 # will render a red sphere in wireframe
    radius 0.1
}

The following table lists some useful appearance nodes provided by Open Inventor:

Group Nodes

Group nodes are not only useful for strucutring your files to keep an overview, but can also be referenced as a single object and control how appearance and other properties are applied to their children. The basic group node is SoGroup - it has no side effect besides grouping its children into a single referenceable entity. Another important group node is SoSeparator. A separator stores the traversal state - including material, transformations, textures, cameras, lights... - and will restore the whole traversal state after traversing its children. Therefore, any state change (like material, transformation etc.) defined inside a Separator will not affect nodes that are outside this Separator. For example:

Material { diffuseColor 0 0 1 }      # sets color to blue
DEF SPHERE Sphere {}                 # renders a blue sphere
Transform { translation 1 0 0 }      # move 1 meter in x-direction
Separator {                          # push state to the stack
    Material { diffuseColor 1 0 0 }  # sets color to red
    USE SPHERE                       # renders a red sphere
}                                    # state is reset again
Transform { translation 1 0 0 }      # move 1 meter in x-direction
USE SPHERE                           # renders BLUE sphere

Note that transformations are also influenced by a separator - if the first transform in the above example would have been defined inside the separator, it would have been reset after the separator, resulting in the 2nd and 3rd sphere being drawn at the same location. Because the transformation is defined at the top level, the transformations accumulate, resulting in the three spheres being positioned next to each other.

Another fundamental group node is the Switch node, which will select one of its children for traversal, as set by the whichChild field.

The following table gives an overview of the most useful group nodes:

example1.iv contains an elaborate example that uses some of the features introduced in this section.

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