SoNurbsCurve(3) The SoNurbsCurve class is a node for representing smooth curves.


#include <Inventor/nodes/SoNurbsCurve.h>

Inherits SoShape.

Public Member Functions

virtual SoType getTypeId (void) const

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 SoType getClassTypeId (void)

static void initClass (void)

Public Attributes

SoSFInt32 numControlPoints

SoMFFloat knotVector

Protected Member Functions

virtual const SoFieldData * getFieldData (void) const

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)

Static Protected Member Functions

static const SoFieldData ** getFieldDataPtr (void)

Additional Inherited Members

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.)

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 }


    NurbsCurve {
        numControlPoints 0
        knotVector 0


Constructor & Destructor Documentation

SoNurbsCurve::SoNurbsCurve (void)


SoNurbsCurve::~SoNurbsCurve () [protected], [virtual]


Member Function Documentation

SoType SoNurbsCurve::getClassTypeId (void) [static]

This static method returns the SoType object associated with objects of this class.

Reimplemented from SoShape.

SoType SoNurbsCurve::getTypeId (void) const [virtual]

Returns the type identification of an object derived from a class inheriting SoBase. This is used for run-time type checking and 'downward' casting.

Usage example:

  void foo(SoNode * node)
    if (node->getTypeId() == SoFile::getClassTypeId()) {
      SoFile * filenode = (SoFile *)node;  // safe downward cast, knows the type

For application programmers wanting to extend the library with new nodes, engines, nodekits, draggers or others: this method needs to be overridden in all subclasses. This is typically done as part of setting up the full type system for extension classes, which is usually accomplished by using the pre-defined macros available through for instance Inventor/nodes/SoSubNode.h (SO_NODE_INIT_CLASS and SO_NODE_CONSTRUCTOR for node classes), Inventor/engines/SoSubEngine.h (for engine classes) and so on.

For more information on writing Coin extensions, see the class documentation of the toplevel superclasses for the various class groups.

Reimplemented from SoShape.

const SoFieldData ** SoNurbsCurve::getFieldDataPtr (void) [static], [protected]

This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.

Reimplemented from SoShape.

const SoFieldData * SoNurbsCurve::getFieldData (void) const [protected], [virtual]

Returns a pointer to the class-wide field data storage object for this instance. If no fields are present, returns NULL.

Reimplemented from SoShape.

void SoNurbsCurve::initClass (void) [static]

Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.

Reimplemented from SoShape.

void SoNurbsCurve::GLRender (SoGLRenderAction *action) [virtual]

Action method for the SoGLRenderAction.

This is called during rendering traversals. Nodes influencing the rendering state in any way or who wants to throw geometry primitives at OpenGL overrides this method.

Reimplemented from SoShape.

void SoNurbsCurve::rayPick (SoRayPickAction *action) [virtual]

Calculates picked point based on primitives generated by subclasses.

Reimplemented from SoShape.

void SoNurbsCurve::getPrimitiveCount (SoGetPrimitiveCountAction *action) [virtual]

Action method for the SoGetPrimitiveCountAction.

Calculates the number of triangle, line segment and point primitives for the node and adds these to the counters of the action.

Nodes influencing how geometry nodes calculates their primitive count also overrides this method to change the relevant state variables.

Reimplemented from SoShape.

void SoNurbsCurve::getBoundingBox (SoGetBoundingBoxAction *action) [virtual]

Redefined to notify open caches that this shape contains lines.

Reimplemented from SoShape.

void SoNurbsCurve::sendPrimitive (SoAction *a, SoPrimitiveVertex *p)

This method is part of the original SGI Inventor API, but not implemented in Coin, as it looks like a method that should probably have been private in Open Inventor.

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.

SoDetail * SoNurbsCurve::createLineSegmentDetail (SoRayPickAction *action, const SoPrimitiveVertex *v1, const SoPrimitiveVertex *v2, SoPickedPoint *pp) [protected], [virtual]

Will create line detail for a SoPickedPoint. This method will only be called internally, when generatePrimitives() is used for picking (SoShape::rayPick() is not overridden).

This method returns NULL in Open Inventor, and subclasses will need to override this method to create details for a SoPickedPoint.

This is not necessary with Coin. Of course, if you choose to override it, it will work in the same way as Open Inventor.

For this to work, you must supply a face or line detail when generating primitives. If you supply NULL for the detail argument in SoShape::beginShape(), you'll have to override this method.

Reimplemented from SoShape.

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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