1.使用的工具

libDxf-负责解析dxf文件，提取图形元素

open_Nurbs-负责spline曲线的计算

2.效果如下

左图是CAD绘制的spline曲线，右图是程序中显示的曲线，红色点是在CAD中作图时鼠标点击的拟合点。

3.main.cpp代码

#include"zmDXF.h"

#include"myCanvus.h"

#include"opennurbs_public.h"

#include<iostream>


#include<QApplication>

int  main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    //封装了libDxf，解析dxf文件
    zmDXF dxf;
    dxf.read("F:/Temp/QtTest/1.dxf");

    //自定义一个画布，简单显示一下曲线
    myCanvus canvus;
    canvus.show();

    //处理每一条曲线
    for(int i = 0; i < dxf.getSplines().size(); i++)
    {
        zmSpline spline = dxf.getSplines()[i];
        ON_NurbsCurve curve;

        //创建一条NURBS曲线
        //3维   x,y,z
        //有理
        //阶数=多项式次数+1
        //控制点数量
        curve.Create(3, true, spline.m_info.degree + 1, spline.m_ctrlPts.size());

        //对每个控制点赋值
        for(int j = 0; j < spline.m_ctrlPts.size(); j++)
        {
            ON_3dPoint  point;
            point.x = spline.m_ctrlPts[j].x;
            point.y = spline.m_ctrlPts[j].y;
            point.z = spline.m_ctrlPts[j].z;
            curve.SetCV(j, point);
        }

        //节点和dxf读取的不一致，假如读取的节点是0，0，0，1，2，2，2
        //要设置的节点实际是0，0，1，2，2
        //图形学中：节点数量=控制点数量+阶数，与dxf文件一致
        //ON_NurbsCurve中节点数量比上面少2个
        for(int j = 0; j < spline.m_knots.size() - 2; j++)  {
            curve.SetKnot(j, spline.m_knots[j + 1].k);
        }

        //获取节点向量取值范围
        double range[2] = {0, 0};
        curve.GetDomain(range, range + 1);
        double domain = range[1] - range[0];

        //每条线计算100个点进行显示
        QVector<QPointF>pointfs;
        int resolution = 100;
        for(int j = 0; j < resolution; j++)
        {
            ON_3dPoint pt = curve.PointAt(range[0] + domain * j / (resolution - 1));
            pointfs.append(QPointF(pt.x, pt.y));
        }

        //提取拟合点，用红色显示
        QVector<QPointF>fitPoints;
        for(int j = 0; j < spline.m_fitPts.size(); j++)
        {
            QPointF point;
            point.setX(spline.m_fitPts[j].x);
            point.setY(spline.m_fitPts[j].y);
            fitPoints.append(point);
        }
        canvus.addPath(pointfs);
        canvus.addPoints(fitPoints);

    }


    return a.exec();
}

4.对libDXF的简单封装

#ifndef ZMDXF_H
#define ZMDXF_H

#include<QPointF>
#include"zmSpline.h"
#include"zmPoint.h"
#include"zmLine.h"
#include"zmArc.h"
#include"zmPolyLine.h"

class zmDXF : public DL_CreationAdapter
{
public:
    zmDXF();

    void read(const char *file);

    const std::vector<zmSpline> &getSplines()const;

private:
    void addPoint(const DL_PointData &) override; //解析单个点
    void addLine(const DL_LineData &) override; //解析直线

    void addPolyline(const DL_PolylineData &) override; //解析多段线
    void addVertex(const DL_VertexData &) override; //解析顶点

    void addArc(const DL_ArcData &) override; //解析圆弧
    void addCircle(const DL_CircleData &) override; //解析圆

    void addSpline(const DL_SplineData &) override;//样条曲线
    void addControlPoint(const DL_ControlPointData &) override; //样条控制点
    void addFitPoint(const DL_FitPointData &) override; //样条拟合点
    void addKnot(const DL_KnotData &) override; //样条节点

    void addBlock(const DL_BlockData &) override;//块数据
    void addText(const DL_TextData &) override;
    void addMText(const DL_MTextData &) override;

private:
    std::vector<zmArc>m_arcs;
    std::vector<zmLine>m_lines;
    std::vector<zmPoint>m_points;
    std::vector<zmPolyLine>m_polyLines;

    std::vector<zmSpline>m_splines;
};

#endif // ZMDXF_H

 5.下一步看看能不能自己写一个spline的解析，非均匀有理样条公式有点复杂