- All Implemented Interfaces:
public class SoExtrusion extends SoBaseExtrusionGeometric shape formed by extruding a 2D cross section along a 3D spine. The
SoExtrusionnode 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.
SoExtrusionis defined by:
The shape that will be extruded, defined by a 2D piecewise linear curve in the XZ plane (described as a series of connected vertices).
The cross-section is extruded along this path, defined by a 3D piecewise linear curve (described as a series of connected vertices). This field is inherited from the parent class
The cross-section curve is scaled by this value on the X and Z axes. If one value is specified it applies to every spine point, else there should be as many values as there are points in the spine. All scale values must be > 0.
orientationvalues, The cross-section curve is rotated by this value relative to a local reference system with origin at the current spine point and X / Z axes in the plane containing the cross-section curve. If one value is specified it applies to every spine point, else there should be as many values as there are points in the spine.
Shapes are constructed as follows - For each point in the spine, the cross-section curve, which is a curve in the XZ plane, is scaled about the origin by the corresponding
scaleparameter (first value scales in X, second value scales in Z), rotated about the origin by the corresponding
orientationparameter and translated by the vector defined by the corresponding vertex of the
spinecurve. Each instance of the cross-section is then connected to the following instance.
scaleModefield is used to select the points that will be scaled by the current transformation (for example
SoTransform), if any. Translation and rotation are applied in all cases. The options are:
- DEFAULT : Every point in the generated geometry is scaled.
- SPINE_ONLY : Only the spine points are scaled. The cross section points are not scaled, so the cross section shape is undistorted even is scaling is non-uniform.
- SECTION_ONLY : Only the cross section points are scaled. Not currently implemented.
- NONE :
SoExtrusionignores the scaling state. Not currently implemented.
A transformed cross section is found for each joint (that is, at each vertex of the
spinecurve, 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
scalegiven 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.
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[ i ],
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,
If the spine curve is not closed: The tangent used for the first point is just the direction from
spine, 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:
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
orientationto the cross-section relative to this new plane. Rotate it counterclockwise about the axis and by the angle specified in the
orientationfield at that joint.
- Finally, the cross section is translated to the location of the
Surfaces of revolution: If the cross section is an approximation of a circle and the spine is straight, then the
SoExtrusionis equivalent to a surface of revolution, where the
scaleparameters 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).
SoExtrusionhas 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).
endCapfields are specified as true, planar cap surfaces will be generated regardless of whether the
crossSectionis a closed curve. (If
crossSectionisn't a closed curve, the caps are generated as if it were
equivalent to adding a final point to
crossSectionthat'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
spineis also a closed curve. If a field value is false, the corresponding cap is not generated.
SoExtrusionautomatically generates its own normals. Orientation of the normals is determined by the vertex ordering of the quads generated by
SoExtrusion. The vertex ordering is in turn determined by the
crossSectioncurve. If the
crossSectionis 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
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
crossSectioncurve (with 0 corresponding to the first point in
crossSectionand 1 to the last) and in the V direction from 0 to 1 along the
spinecurve (again with 0 corresponding to the first listed
spinepoint and 1 to the last). When
crossSectionis 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
crossSectioncurve 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
endCaptextures' S and T directions correspond to the X and Z directions in which the
crossSectioncoordinates are defined.
Also 3D texture coordinates are automatically generated, in a similar way to 2D textures.
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.
beginCap true endCap true spine [ 0 0 0, 0 1 0 ] scaleMode DEFAULT crossSection [ 1 1, 1 -1, -1 -1, -1 1, 1 1 ] orientation 0 0 1 0 scale 1 1
- See Also:
Nested Class Summary
Nested classes/interfaces inherited from class com.openinventor.inventor.nodes.SoBaseExtrusion
Nested classes/interfaces inherited from class com.openinventor.inventor.nodes.SoShape
Nested classes/interfaces inherited from class com.openinventor.inventor.nodes.SoNode
Fields Modifier and Type Field Description
crossSectionThe shape that will be extruded, defined by a 2D piecewise linear curve in the XZ plane (described as a series of connected vertices).
orientationThe cross-section curve is rotated by this value relative to a local reference system with origin at the current spine point and X / Z axes in the plane containing the cross-section curve.
scaleThe cross-section curve is scaled by this value on the X and Z axes.
Fields inherited from class com.openinventor.inventor.nodes.SoBaseExtrusion
beginCap, endCap, extrusionMode, scaleMode, spine
Constructors Constructor Description
Methods inherited from class com.openinventor.inventor.nodes.SoShape
getShapeType, isPrimitiveRestartAvailable, isPrimitiveRestartAvailable
Methods inherited from class com.openinventor.inventor.nodes.SoNode
affectsState, callback, copy, copy, distribute, doAction, getAlternateRep, getBoundingBox, getByName, getMatrix, getPrimitiveCount, getRenderEngineMode, getRenderUnitID, GLRender, GLRenderBelowPath, GLRenderInPath, GLRenderOffPath, grabEventsCleanup, grabEventsSetup, handleEvent, isBoundingBoxIgnoring, isOverride, pick, rayPick, search, setOverride, touch, write
Methods inherited from class com.openinventor.inventor.fields.SoFieldContainer
copyFieldValues, copyFieldValues, enableNotify, fieldsAreEqual, get, getAllFields, getEventIn, getEventOut, getField, getFieldName, hasDefaultValues, isNotifyEnabled, set, setToDefaults
Methods inherited from class com.openinventor.inventor.misc.SoBase
dispose, getName, isDisposable, isSynchronizable, setName, setSynchronizable
public final SoMFVec2f crossSectionThe shape that will be extruded, defined by a 2D piecewise linear curve in the XZ plane (described as a series of connected vertices). Default is a square [ 1 1, 1 -1, -1 -1, -1 1, 1 1 ].
public final SoMFRotation orientationThe cross-section curve is rotated by this value relative to a local reference system with origin at the current spine point and X / Z axes in the plane containing the cross-section curve. If one value is specified it applies to every spine point, else there should be as many values as there are points in the spine. Default is no rotation.
public final SoMFVec2f scaleThe cross-section curve is scaled by this value on the X and Z axes. If one value is specified it applies to every spine point, else there should be as many values as there are points in the spine. All scale values must be > 0. Default is (1,1) meaning no scaling.