为什么Sutherland-Hodgeman Line Clipping算法的代码没有给出错误的输出？

Question

这里，蓝线是要修剪的多边形边。黄色，线是剪切多边形的边缘。

//Sutherland-Holdgman Line Clipping
#include "Line2d.h"
#include "Rectangle2d.h"
#include "Coordinates2d.h"
#include "Bits.h"
#include "Polygon2d.h"
#include <list>

typedef enum PointPosition 
{
    Left, Right
} PointPosition;

typedef enum LinePosition 
{
    CompletelyOut, CompletelyIn, ClippingCandidate, ClippingCandidateExtended
} LinePosition;

void EnumToString(LinePosition lnPos)
{
    switch(lnPos)
    {
    case CompletelyOut: 
        std::cout<<lnPos<<". CompletelyOut"; 
        break;
    case CompletelyIn: 
        std::cout<<lnPos<<". CompletelyIn"; 
        break;
    case ClippingCandidate: 
        std::cout<<lnPos<<". ClippingCandidate"; 
        break;
    case ClippingCandidateExtended: 
        std::cout<<lnPos<<". ClippingCandidateExtended"; 
        break;
    }
}

class ClippingPolygon2d
{
private:
    Rectangle2d rectangle;
    Polygon2d polygon;
    PointPosition CheckPointAgainstALine(Line2d line, Point2d pt)
    {
        double c = (((line.GetEnd().x - line.GetStart().x)
                    *(pt.y - line.GetStart().y)) 
                    -((line.GetEnd().y - line.GetStart().y)
                    *(pt.x - line.GetStart().x)));

        if(c>=0) return Left;
        else return Right;
    }
public:
    LinePosition CheckLineAgainstEdge(Line2d polygonEdge, Line2d line)
    {
        LinePosition linePosition;
        PointPosition startPoint = CheckPointAgainstALine(polygonEdge, line.GetStart());
        PointPosition endPoint = CheckPointAgainstALine(polygonEdge, line.GetEnd());

        if(startPoint==Left && endPoint==Left)
        {
            linePosition = CompletelyOut;
        }
        else if(startPoint==Right && endPoint==Right)
        {
            linePosition = CompletelyIn;
        }       
        else if(startPoint==Left && endPoint==Right)
        {
            linePosition = ClippingCandidateExtended;
        }
        else if(startPoint==Right && endPoint==Left)
        {
            linePosition = ClippingCandidate;
        }
        return linePosition;
    }
};



int main()
{
    Coordinates2d::ShowWindow("Sutherland-Hodgeman Line Clipping");

    ClippingPolygon2d clip;

    Line2d edge(Point2d(20,20), Point2d(160,140));
    Line2d ln(Point2d(100,120), Point2d(100,140));

    LinePosition lnPos = clip.CheckLineAgainstEdge(edge, ln);

    EnumToString(lnPos);

    Coordinates2d::Draw(edge, Blue);
    Coordinates2d::Draw(ln, Yellow);

    Coordinates2d::Wait();

    return 0;
}

<< img src =“ https://image.soinside.com/eyJ1cmwiOiAiaHR0cHM6Ly9pLnN0YWNrLmltZ3VyLmNvbS9UVjhXSi5wbmcifQ==” alt =“在此处输入图像说明”>

Answer 1

您可以使用std::vector而不初始化其大小，并且它支持随机访问。要添加为空的std::vector，请使用push_back

std::vector<MyType> vec;
vec.push_back(MyType(10, 'a', "Hi"));
vec.push_back(MyType(20, 'b', "Hello"));
vec.push_back(MyType(30, 'c', "Bye"));

MyType t = vec[1];//20,'b', "Hello"...

Edit：此答案是最初提出的问题。