SoNurbsCurve Class Reference
[Node Classes]

The SoNurbsCurve class is a node for representing smooth curves.A general explanation of NURBS is beyond the scope of the Coin documentation. For detailed information, refer to the specialized literature on the topic (for example "An Introduction to NURBS: With Historical Perspective" by David F. Rogers). A basic overview of curve and surface rendering using NURBS can be found in chapter 8 of "The Inventor Mentor". More...

#include <Inventor/nodes/SoNurbsCurve.h>

Inheritance diagram for SoNurbsCurve:

List of all members.

Public Member Functions
	SoNurbsCurve (void)
virtual void	GLRender (SoGLRenderAction *action)
virtual void	rayPick (SoRayPickAction *action)
virtual void	getPrimitiveCount (SoGetPrimitiveCountAction *action)
virtual void	getBoundingBox (SoGetBoundingBoxAction *action)
void	sendPrimitive (SoAction *, SoPrimitiveVertex *)
Static Public Member Functions
static void	initClass (void)
	Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.
Public Attributes
SoSFInt32	numControlPoints
SoMFFloat	knotVector
Protected Member Functions
virtual	~SoNurbsCurve ()
virtual void	generatePrimitives (SoAction *action)
virtual void	computeBBox (SoAction *action, SbBox3f &box, SbVec3f &center)
virtual SoDetail *	createLineSegmentDetail (SoRayPickAction *action, const SoPrimitiveVertex *v1, const SoPrimitiveVertex *v2, SoPickedPoint *pp)

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Detailed Description

The SoNurbsCurve class is a node for representing smooth curves.

A general explanation of NURBS is beyond the scope of the Coin documentation. For detailed information, refer to the specialized literature on the topic (for example "An Introduction to NURBS: With Historical Perspective" by David F. Rogers). A basic overview of curve and surface rendering using NURBS can be found in chapter 8 of "The Inventor Mentor".

Note that knot values should be specified as [0, 1, 2,..., a] rather than [0, 1/a, 2/a,..., 1] to avoid tesselation errors due to floating point precision problems. (Even if the rendered curve looks correct, such issues might surface when e.g. doing picking, since the tesselated representation used internally is not the same as the one you see rendered by OpenGL on-screen.)

Each control point has a weight that changes the shape of its basis function. Weight is analogous to having magnets pulling on the curve. Coordinate3 sets control points to have an equal weight of 1.0 (nonrational). Use Coordinate4 to specify x, y, z and weight values (rational).

A small usage example (drawing a circle using a rational curve):

  #Inventor V2.1 ascii

  Coordinate4 {
     point [
       0.0 -5.0     0.0 1.0,
       2.5 -2.5     0.0 0.5,
       2.5 -0.66987 0.0 1.0,
       0.0  1.94013 0.0 0.5,
      -2.5 -0.66987 0.0 1.0,
      -2.5 -2.5     0.0 0.5,
       0.0 -5.0     0.0 1.0
     ]
  }

  NurbsCurve {
     numControlPoints 7
     knotVector [ 0, 0, 0, 1, 1, 2, 2, 3, 3, 3 ]
  }

  # debug: show all the control points
  BaseColor { rgb 1 1 0 }
  DrawStyle { pointSize 3 }
  PointSet { numPoints 7 }

FILE FORMAT/DEFAULTS:

    NurbsCurve {
        numControlPoints 0
        knotVector 0
    }

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Constructor & Destructor Documentation

SoNurbsCurve::SoNurbsCurve

(

void

)

Constructor.

SoNurbsCurve::~SoNurbsCurve

(

)

[protected, virtual]

Destructor.

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Member Function Documentation

void SoNurbsCurve::rayPick

(

SoRayPickAction *

action

)

[virtual]

Calculates picked point based on primitives generated by subclasses.

Reimplemented from SoShape.

void SoNurbsCurve::getBoundingBox

(

SoGetBoundingBoxAction *

action

)

[virtual]

Redefined to notify open caches that this shape contains lines.

Reimplemented from SoShape.

void SoNurbsCurve::generatePrimitives

(

SoAction *

action

)

[protected, virtual]

The method implements action behavior for shape nodes for SoCallbackAction. It is invoked from SoShape::callback(). (Subclasses should not override SoNode::callback().)

The subclass implementations uses the convenience methods SoShape::beginShape(), SoShape::shapeVertex(), and SoShape::endShape(), with SoDetail instances, to pass the primitives making up the shape back to the caller.

Implements SoShape.

void SoNurbsCurve::computeBBox	(	SoAction *	action,
		SbBox3f &	box,
		SbVec3f &	center
	)			[protected, virtual]

Calculates the bounding box of all control points, and sets the center to the average of these points.

Implements SoShape.

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Member Data Documentation

SoSFInt32 SoNurbsCurve::numControlPoints

Number of control points to use in this NURBS curve.

SoMFFloat SoNurbsCurve::knotVector

The knot vector.

Values should be specified as [0, 1, 2,..., a] rather than [0, 1/a, 2/a,..., 1] to avoid tesselation errors due to floating point precision problems.

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The documentation for this class was generated from the following files:

• SoNurbsCurve.h
• SoNurbsCurve.cpp