Program of scanfill algorithm

# include <dos.h>
# include <stdio.h>
# include <graphics.h>
# include <iostream.h>
# include <conio.h>
# include <math.h>

struct Polygon
{
    int x;
    int y;
};

struct edRecord
{
    int YUpper;
    float XIntersect;
    float dxperscan;
    struct edRecord *Next;
};

typedef struct edRecord Edge;
typedef struct Polygon Nodes;
Edge  *Active;
Edge **Edges;
int Cntr=6;
Nodes NodesObj[6]={{100,100},{150,150},{150,200},{100,250},{50,200},{50,150}};

void Scanfill();
void InsertEdge(Edge*,Edge*);
void BuildEdgeList(int,Nodes*);
int YNext(int);
void MakeEdgeRec(Nodes,Nodes,int,Edge*);
void BulidActiveList(int);
void UpdateActiveList(int);
void DeleteAfter(Edge*);
void ResortActiveList(void);
void ResortActiveList(int);

//**************************************************************************
void main()
{
    int gDriver = DETECT, gMode;
    int n,xArray[12];
    int iCntr,jCntr;

    initgraph(&gDriver,&gMode,\"c:\\\\tc\\\\bgi\");

    for(iCntr=0,jCntr=0;iCntr<12;iCntr+=2,jCntr++)
        xArray[iCntr] = NodesObj[jCntr].x;
    for(iCntr=1,jCntr=0;iCntr<12;iCntr+=2,jCntr++)
        xArray[iCntr] = NodesObj[jCntr].y;

    drawpoly(6,xArray);

    line(NodesObj[5].x,NodesObj[5].y,NodesObj[0].x,NodesObj[0].y);   //TO CLOSE POLYGON
    getch();

    Scanfill();
    getch();
    closegraph();
    restorecrtmode();
    return;
}

//**************************************************************************

void Scanfill()
{
    int iCntr,Scan;
    //initialize edgelists with dummy nodes
    Edges=new Edge*[getmaxy()];
    for(iCntr=0;iCntr<getmaxy();iCntr++)
    {
        Edges[iCntr] = new Edge;
        Edges[iCntr]->Next = NULL;
    }
    //initialize Active edgeList with dummy nodes
    Active = new Edge;
    Active->Next = NULL;
    BuildEdgeList(Cntr,NodesObj);
    for(Scan=0;Scan<getmaxy();Scan++)
    {
        BulidActiveList(Scan);
        if (Active->Next != NULL)
        {
            ResortActiveList(Scan);
            UpdateActiveList(Scan);
            ResortActiveList();
        }
    }
}

//**************************************************************************

void InsertEdge(Edge* edgeList,Edge* InitialEdge)
{
    Edge *PEdge,*QEdges;

    QEdges=edgeList;
    PEdge=QEdges->Next;
    while(PEdge!=NULL)
    if(InitialEdge->XIntersect < PEdge->XIntersect)
    PEdge=NULL;
    else
    {
        QEdges=PEdge;
        PEdge=PEdge->Next;
    }
    InitialEdge->Next = QEdges->Next;
    QEdges->Next = InitialEdge;
}

//**************************************************************************

void BuildEdgeList(int Cntr,Nodes* Vertices)
{
    Edge* NewEdge;
    Nodes Vertex1,Vertex2;
    int YPrev,iCntr;
    Vertex1.x=Vertices[Cntr-1].x;
    Vertex1.y=Vertices[Cntr-1].y;
    YPrev = Vertices[Cntr-2].y;
    for(iCntr=0;iCntr<Cntr;iCntr++)
    {
        Vertex2.x = Vertices[iCntr].x;
        Vertex2.y = Vertices[iCntr].y;
        if(Vertex1.y != Vertex2.y)
        {
            NewEdge = new Edge;
            if(Vertex1.y < Vertex2.y)
                MakeEdgeRec(Vertex1,Vertex2,YNext(iCntr),NewEdge);
            else
                MakeEdgeRec(Vertex2,Vertex1,YPrev,NewEdge);
        }
        YPrev = Vertex1.y;
        Vertex1.x = Vertex2.x;
        Vertex1.y = Vertex2.y;
    }
}

//**************************************************************************

void BulidActiveList(int Scan)
{
    Edge *PEdge,*QEdges;
    PEdge=Edges[Scan]->Next;
    while(PEdge!=NULL)
    {
        QEdges=PEdge->Next;
        InsertEdge(Active,PEdge);
        PEdge=QEdges;
    }
}

//***************************************************************************

void ResortActiveList(int Scan)
{
    Edge *iEdge,*jEdge;
    int iCntr;
    iEdge = Active->Next;
    while(iEdge!=NULL)
    {
        jEdge = iEdge->Next;
        for(iCntr=iEdge->XIntersect;iCntr<=jEdge->XIntersect-1;iCntr++)
            putpixel(iCntr,Scan,RED);
        iEdge=jEdge->Next;
    }
}
//***************************************************************************

void UpdateActiveList(int Scan)
{
    Edge *PEdge,*QEdges;
    QEdges=Active;
    PEdge=Active->Next;
    while(PEdge!=NULL)
    {
        if(Scan>=PEdge->YUpper)
        {
            PEdge=PEdge->Next;
            DeleteAfter(QEdges);
        }
        else
        {
            PEdge->XIntersect+=PEdge->dxperscan;
            QEdges=PEdge;
            PEdge=PEdge->Next;
        }
    }
}
//***************************************************************************
void ResortActiveList()
{
    Edge *PEdge,*QEdges;
    PEdge=Active->Next;
    Active->Next=NULL;
    while(PEdge!=NULL)
    {
        QEdges=PEdge->Next;
        InsertEdge(Active,PEdge);
        PEdge=QEdges;
    }
}

//***************************************************************************

int YNext(int YCurr)
{
    int jCntr;
    if(YCurr+1>Cntr)
        jCntr=1;
    else
        jCntr=YCurr+1;
    while(NodesObj[YCurr].y == NodesObj[jCntr].y)
    {
        if(jCntr+1>Cntr)
            jCntr=1;
        else
            jCntr++;
    }
    return(NodesObj[jCntr].y);
}

//***************************************************************************

void DeleteAfter(Edge* QEdges)
{
    Edge* PEdge;

    PEdge = QEdges->Next;
    QEdges->Next = PEdge->Next;
    delete PEdge;
}

//***************************************************************************

void MakeEdgeRec(Nodes Lower,Nodes Upper,int YComp,Edge* CurrEdge)
{
    CurrEdge->dxperscan = (Upper.x - Lower.x) / (Upper.y - Lower.y);
    CurrEdge->XIntersect = Lower.x;
    if(Upper.y < YComp)
        CurrEdge->YUpper = Upper.y - 1;
    else
        CurrEdge->YUpper = Upper.y;
    InsertEdge(Edges[Lower.y],CurrEdge);
}