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
¢er)
virtual SoDetail * createLineSegmentDetail (SoRayPickAction *action,
const SoPrimitiveVertex *v1, const SoPrimitiveVertex *v2,
SoPickedPoint *pp)
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.
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.
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.
Author
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