# Render OpenCascade Geometry Curves in OpenSceneGraph

## Render OpenCascade Geometry Curves in OpenSceneGraph

eryar@163.com

### 一、引言 Introduction

1．直线 Line

2．圆 Circle

3．椭圆 Ellipse

4．抛物线 Parabola

5．双曲线 Hyperbola

6．Bezier曲线 Bezier Curve

7．B-Spline曲线 B-Spline Curve

8．裁剪曲线 Trimmed Curve

9．偏移曲线 Offset Curve

Figure 1.1 Geometry curve class diagram

Figure 1.2 Geom_Curve Inherited class diagram

### 二、程序示例 Code Example

1．FirstParameter();

2．LastParameter();

3．Value(u);

```/*
*
*        File    : Main.cpp
*        Author  : eryar@163.com
*        Date    : 2013-08-09 18:09
*        Version : 1.0v
*
*    Description : Draw OpenCascade Geometry Curves in OpenSceneGraph.
*
*/

// OpenSceneGraph library.
#include <osgViewer/Viewer>
#include <osgViewer/ViewerEventHandlers>
#include <osgGA/StateSetManipulator>

#pragma comment(lib, \"osgd.lib\")
#pragma comment(lib, \"osgDbd.lib\")
#pragma comment(lib, \"osgViewerd.lib\")

#include <TColgp_Array1OfPnt.hxx>
#include <TColStd_Array1OfReal.hxx>
#include <TColStd_Array1OfInteger.hxx>

#include <Geom_Circle.hxx>
#include <Geom_Ellipse.hxx>
#include <Geom_Hyperbola.hxx>
#include <Geom_Parabola.hxx>
#include <Geom_BezierCurve.hxx>
#include <Geom_BSplineCurve.hxx>

#pragma comment(lib, \"TKernel.lib\")
#pragma comment(lib, \"TKMath.lib\")
#pragma comment(lib, \"TKG3d.lib\")

// Curve Segment Delta.
const double CURVE_SEGMENT_DELTA = 0.01;

/*
* @brief Build geometry curve of OpenCascade.
*/
osg::Node* buildCurve(const Geom_Curve& curve)
{
osg::ref_ptr<osg::Geode> geode = new osg::Geode();
osg::ref_ptr<osg::Geometry> linesGeom = new osg::Geometry();
osg::ref_ptr<osg::Vec3Array> pointsVec = new osg::Vec3Array();

gp_Pnt point;
double dFirst = curve.FirstParameter();
double dLast = curve.LastParameter();

Precision::IsNegativeInfinite(dFirst) ? dFirst = -1.0 : dFirst;
Precision::IsInfinite(dLast) ? dLast = 1.0 : dLast;

for (double u = dFirst; u <= dLast; u += CURVE_SEGMENT_DELTA)
{
point = curve.Value(u);

pointsVec->push_back(osg::Vec3(point.X(), point.Y(), point.Z()));
}

// Set the colors.
osg::ref_ptr<osg::Vec4Array> colors = new osg::Vec4Array;
colors->push_back(osg::Vec4(1.0f, 1.0f, 0.0f, 0.0f));
linesGeom->setColorArray(colors.get());
linesGeom->setColorBinding(osg::Geometry::BIND_OVERALL);

// Set the normal in the same way of color.
osg::ref_ptr<osg::Vec3Array> normals = new osg::Vec3Array;
normals->push_back(osg::Vec3(0.0f, -1.0f, 0.0f));
linesGeom->setNormalArray(normals.get());
linesGeom->setNormalBinding(osg::Geometry::BIND_OVERALL);

// Set vertex array.
linesGeom->setVertexArray(pointsVec);

return geode.release();
}

/**
* @breif Build geometry curve of OpenCascade.
*/
osg::Node* buildScene()
{
osg::ref_ptr<osg::Group> root = new osg::Group();

// 1. Build circle curve.
Geom_Circle circle(gp::YOZ(), 1.0);

// 2. Build ellipse curve.
Geom_Ellipse ellipse(gp::ZOX(), 1.0, 0.3);

// 3. Build Hyperbola curve.
Geom_Hyperbola hyperbola(gp::XOY(), 1.0, 0.6);

// 4. Build parabola curve.
Geom_Parabola parabola(gp::ZOX(), 1.0);

// 5. Build Bezier curve.
TColgp_Array1OfPnt poles(1, 4);
poles.SetValue(1, gp_Pnt(-1, -1, 0));
poles.SetValue(2, gp_Pnt(1, 2, 0));
poles.SetValue(3, gp_Pnt(3, 0, 0));
poles.SetValue(4, gp_Pnt(4, 1, 0));
Geom_BezierCurve bezierCurve(poles);

// 6. Build BSpline curve.
TColgp_Array1OfPnt ctrlPnts(1, 3);
TColStd_Array1OfReal knots(1, 5);
TColStd_Array1OfInteger mults(1, 5);

ctrlPnts.SetValue(1, gp_Pnt(0, 1, 0));
ctrlPnts.SetValue(2, gp_Pnt(1, -2, 0));
ctrlPnts.SetValue(3, gp_Pnt(2, 3, 0));

knots.SetValue(1, 0.0);
knots.SetValue(2, 0.25);
knots.SetValue(3, 0.5);
knots.SetValue(4, 0.75);
knots.SetValue(5, 1.0);

mults.Init(1);

Geom_BSplineCurve bsplineCurve(ctrlPnts, knots, mults, 1);

return root.release();
}

int main(int argc, char* argv[])
{
osgViewer::Viewer myViewer;

myViewer.setSceneData(buildScene());

return myViewer.run();
}```

Figure 2.1 OpenCascade Geometry Curves in OpenSceneGraph

### 三、结论 Conclusion

Figure 3.1 B-Spline in OpenSceneGraph

Figure 3.2 B-Spline in OpenCascade Draw