Render OpenCascade Geometry Curves in OpenSceneGraph
在OpenSceneGraph中绘制OpenCascade的曲线
Render OpenCascade Geometry Curves in OpenSceneGraph
摘要Abstract:本文简要说明OpenCascade中几何曲线的数据,并将这些几何曲线在OpenSceneGraph中绘制出来。
关键字KeyWords:OpenCascade、Geometry Curve、OpenSceneGraph、B-Spline、NURBS
一、引言 Introduction
结合《BRep Format Description White Paper》对OpenCascade中的几何数据结构有详细的介绍。OpenCascade中BRep格式中的曲线总共分为九种,不过有二维三维之分:
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
曲线的几何数据都有一个抽象基类Geom_Curve,类图如下所示:
Figure 1.1 Geometry curve class diagram
抽象基类Geom_Curve有几个纯虚函数FirstParameter()、LastParameter()、Value(),根据这几个虚函数,就可以计算曲线上对应参数U的值。类图如下图所示:
Figure 1.2 Geom_Curve Inherited class diagram
每种曲线都对那些纯虚函数进行实现,使计算曲线上点的方式统一。
二、程序示例 Code Example
根据抽象基类Geom_Curve的几个纯虚函数:
1.FirstParameter();
2.LastParameter();
3.Value(u);
利用多态可将曲线上点都以统一的方式计算出来,并使用GL_LINE_STRIP绘制出来。示例程序如下所示:
/*
* Copyright (c) 2013 eryar All Rights Reserved.
*
* 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 <osgDB/ReadFile>
#include <osgViewer/Viewer>
#include <osgViewer/ViewerEventHandlers>
#include <osgGA/StateSetManipulator> #pragma comment(lib, "osgd.lib")
#pragma comment(lib, "osgDbd.lib")
#pragma comment(lib, "osgGAd.lib")
#pragma comment(lib, "osgViewerd.lib") // OpenCascade library.
#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);
linesGeom->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::LINE_STRIP, , pointsVec->size())); geode->addDrawable(linesGeom.get()); 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); root->addChild(buildCurve(circle)); // 2. Build ellipse curve.
Geom_Ellipse ellipse(gp::ZOX(), 1.0, 0.3); root->addChild(buildCurve(ellipse)); // 3. Build Hyperbola curve.
Geom_Hyperbola hyperbola(gp::XOY(), 1.0, 0.6); root->addChild(buildCurve(hyperbola)); // 4. Build parabola curve.
Geom_Parabola parabola(gp::ZOX(), 1.0); root->addChild(buildCurve(parabola)); // 5. Build Bezier curve.
TColgp_Array1OfPnt poles(, );
poles.SetValue(, gp_Pnt(-, -, ));
poles.SetValue(, gp_Pnt(, , ));
poles.SetValue(, gp_Pnt(, , ));
poles.SetValue(, gp_Pnt(, , ));
Geom_BezierCurve bezierCurve(poles); root->addChild(buildCurve(bezierCurve)); // 6. Build BSpline curve.
TColgp_Array1OfPnt ctrlPnts(, );
TColStd_Array1OfReal knots(, );
TColStd_Array1OfInteger mults(, ); ctrlPnts.SetValue(, gp_Pnt(, , ));
ctrlPnts.SetValue(, gp_Pnt(, -, ));
ctrlPnts.SetValue(, gp_Pnt(, , )); knots.SetValue(, 0.0);
knots.SetValue(, 0.25);
knots.SetValue(, 0.5);
knots.SetValue(, 0.75);
knots.SetValue(, 1.0); mults.Init(); Geom_BSplineCurve bsplineCurve(ctrlPnts, knots, mults, ); root->addChild(buildCurve(bsplineCurve)); return root.release();
} int main(int argc, char* argv[])
{
osgViewer::Viewer myViewer; myViewer.setSceneData(buildScene()); myViewer.addEventHandler(new osgGA::StateSetManipulator(myViewer.getCamera()->getOrCreateStateSet()));
myViewer.addEventHandler(new osgViewer::StatsHandler);
myViewer.addEventHandler(new osgViewer::WindowSizeHandler); return myViewer.run();
}
因抛物线和双曲线的FirstParameter()和LastParameter()为负无穷和正无穷,所以对其进行处理,只输出了部分曲线。
程序效果如下图所示:
Figure 2.1 OpenCascade Geometry Curves in OpenSceneGraph
三、结论 Conclusion
OpenCascade的几何数据使用还是很方便的,只要将相应的曲线构造出来之后,计算曲线上的点使用函数Value()即可,还可计算相应参数处的微分值等。
通过理解《BRep Format Description White Paper》,可将BRep文件中数据导入OpenCascade中与上面实现的程序进行对比,结果正确。如下图所示:
Figure 3.1 B-Spline in OpenSceneGraph
Figure 3.2 B-Spline in OpenCascade Draw
PDF Version: Draw OpenCascade Geometry Curves in OpenSceneGraph
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