The SoVRMLExtrusion node specifies geometric shapes based on a two-dimensional cross section extruded along a three-dimensional spine. The cross section can be scaled and rotated at each spine point to produce a wide variety of shapes.

<font color="#0000FF">NOTE:</font> This class does not exist in Open Inventor 10.0 and later.

VRML97 SPECIFICATION

This section describes the expected behavior of the node in a conforming VRML97 browser application. In some cases, the application is responsible for implementing portions of the expected behavior. Open Inventor viewer classes and IVF classes implement some of the application behaviors.

This section may reference portions of the VRML97 specification that are not present in this help file. The complete VRML97 spec is available at http://www.web3d.org.

The SoVRMLExtrusion node specifies geometric shapes based on a two-dimensional cross section extruded along a three-dimensional spine. The cross section can be scaled and rotated at each spine point to produce a wide variety of shapes.

An SoVRMLExtrusion is defined by a 2D crossSection piecewise linear curve (described as a series of connected vertices), a 3D spine piecewise linear curve (also described as a series of connected vertices), a list of 2D scale parameters, and a list of 3D orientation parameters. Shapes are constructed as follows: The cross-section curve, which starts as a curve in the XZ plane, is first scaled about the origin by the first scale parameter (first value scales in X, second value scales in Z). It is then rotated about the origin by the first orientation parameter, and translated by the vector given as the first vertex of the spine curve. It is then extruded through space along the first segment of the spine curve. Next, it is scaled and rotated by the second scale and orientation parameters and extruded by the second segment of the spine, and so on. The number of scale and orientation values must equal the number of spine points, or contain one value that is applied to all points. The scale values must be > 0.

A transformed cross section is found for each joint (that is, at each vertex of the spine curve, where segments of the extrusion connect), and the joints and segments are connected to form the surface. No check is made for self-penetration. Each transformed cross section is determined as follows:

Start with the cross section as specified, in the XZ plane.

Scale it about (0, 0, 0) by the value for scale given for the current joint.

Apply a rotation so that when the cross section is placed at its proper location on the spine it will be oriented properly. Essentially, this means that the cross section's Y axis ( up vector coming out of the cross section) is rotated to align with an approximate tangent to the spine curve.

For all points other than the first or last: The tangent for spine[ i ] is found by normalizing the vector defined by (spine[ i +1] - spine[ i -1]).

If the spine curve is closed: The first and last points need to have the same tangent. This tangent is found as above, but using the points spine[0] for spine[ i ], spine[1] for spine[ i +1] and spine[ n -2] for spine[ i -1], where spine[ n -2] is the next to last point on the curve. The last point in the curve, spine[ n -1], is the same as the first, spine[0].

If the spine curve is not closed: The tangent used for the first point is just the direction from spine[0] to spine[1], and the tangent used for the last is the direction from spine[ n -2] to spine[ n -1].

In the simple case where the spine curve is flat in the XY plane, these rotations are all just rotations about the Z axis. In the more general case where the spine curve is any 3D curve, you need to find the destinations for all 3 of the local X, Y, and Z axes so you can completely specify the rotation. The Z axis is found by taking the cross product of:

(spine[ i -1] - spine[ i ]) and (spine[ i +1] - spine[ i ]).

If the three points are collinear then this value is zero, so take the value from the previous point. Once you have the Z axis (from the cross product) and the Y axis (from the approximate tangent), calculate the X axis as the cross product of the Y and Z axes.

Given the plane computed in step 3, apply the orientation to the cross-section relative to this new plane. Rotate it counterclockwise about the axis and by the angle specified in the orientation field at that joint.

Finally, the cross section is translated to the location of the spine point.

Surfaces of revolution: If the cross section is an approximation of a circle and the spine is straight, then the SoVRMLExtrusion is equivalent to a surface of revolution, where the scale parameters define the size of the cross section along the spine.

Cookie-cutter extrusions: If the scale is 1, 1 and the spine is straight, then the cross section acts like a cookie cutter, with the thickness of the cookie equal to the length of the spine.

Bend/twist/taper objects: These shapes are the result of using all fields. The spine curve bends the extruded shape defined by the cross section, the orientation parameters twist it around the spine, and the scale parameters taper it (by scaling about the spine).

SoVRMLExtrusion has three parts: the sides , the beginCap (the surface at the initial end of the spine) and the endCap (the surface at the final end of the spine). The caps have an associated SFBool field that indicates whether it exists (true) or doesn't exist (false).

When the beginCap or endCap fields are specified as true, planar cap surfaces will be generated regardless of whether the crossSection is a closed curve. (If crossSection isn't a closed curve, the caps are generated as if it were equivalent to adding a final point to crossSection that's equal to the initial point. Note that an open surface can still have a cap, resulting (for a simple case) in a shape something like a soda can sliced in half vertically.) These surfaces are generated even if spine is also a closed curve. If a field value is false, the corresponding cap is not generated.

SoVRMLExtrusion automatically generates its own normals. Orientation of the normals is determined by the vertex ordering of the triangles generated by SoVRMLExtrusion. The vertex ordering is in turn determined by the crossSection curve. If the crossSection is counterclockwise when viewed from the +Y axis, then the polygons will have counterclockwise ordering when viewed from 'outside' of the shape (and vice versa for clockwise ordered crossSection curves).

Texture coordinates are automatically generated by extrusions. Textures are mapped so that the coordinates range in the U direction from 0 to 1 along the crossSection curve (with 0 corresponding to the first point in crossSection and 1 to the last) and in the V direction from 0 to 1 along the spine curve (again with 0 corresponding to the first listed spine point and 1 to the last). When crossSection is closed, the texture has a seam that follows the line traced by the crossSection's start/end point as it travels along the spine. If the endCap and/or beginCap exist, the crossSection curve is uniformly scaled and translated so that the largest dimension of the cross-section (X or Z) produces texture coordinates that range from 0.0 to 1.0. The beginCap and endCap textures' S and T directions correspond to the X and Z directions in which the crossSection coordinates are defined.

See "Concepts - Geometry Nodes" for a description of the ccw, solid, convex, and creaseAngle fields.

NOTE: If your extrusion appears to twist unexpectedly, try setting environment variable OIV_EXTRUSION_EPSILON to a value slightly smaller number than the default, which is .998.

FILE FORMAT/DEFAULT

VRMLExtrusion {

beginCap	true
ccw	true
convex	true
creaseAngle	0
crossSection	[ 1 1, 1 -1, -1 -1, -1 1, 1 1 ]
endCap	true
orientation	0 0 1 0
scale	1 1
solid	true
spine	[ 0 0 0, 0 1 0 ]
metadata	NULL

}

EVENTS

eventIn

SoMFVec2f	set_crossSection
SoMFRotation	set_orientation
SoMFVec2f	set_scale
SoMFVec3f	set_spine
SoSFNode	set_metadata

eventOut

SoSFNode

metadata_changed

Obsoletesince Open Inventor 9500 The VRML API is no longer supported. See section http://oivdoc95.vsg3d.com/content/compatibility-notes-4#Deprecation of the Reference Manual.

Reference