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SoNurbsCurve.3coin2

NAME

SoNurbsCurve -

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'.  

SYNOPSIS

#include <Inventor/nodes/SoNurbsCurve.h>

Inherits SoShape.

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)

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)

Friends

class SoNurbsCurveP

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 }
 

FILE FORMAT/DEFAULTS:

     NurbsCurve {
         numControlPoints 0
         knotVector 0
     }
 
 

 

Constructor & Destructor Documentation

SoNurbsCurve::SoNurbsCurve (void)Constructor.

References knotVector, and numControlPoints.

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

Member Function Documentation

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.

References SoAction::getState(), SoState::pop(), SoState::push(), SoFieldContainer::set(), and SoShape::shouldGLRender().

void SoNurbsCurve::rayPick (SoRayPickAction * action) [virtual]Calculates picked point based on primitives generated by subclasses.

Reimplemented from SoShape.

References SoAction::getState(), SoState::pop(), SoDebugError::postWarning(), SoState::push(), SoFieldContainer::set(), and SoShape::shouldRayPick().

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.

References SoShape::getBoundingBox(), and SoAction::getState().

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.

References SbBox3f::extendBy(), SoAction::getState(), SbBox3f::makeEmpty(), and numControlPoints.

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::numControlPointsNumber of control points to use in this NURBS curve.

Referenced by computeBBox(), and SoNurbsCurve().

SoMFFloat SoNurbsCurve::knotVectorThe 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.

Referenced by SoNurbsCurve().

Author

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