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多边形扫描转换算法

关键词:多边形扫描转换算法  阅读(713) 赞(13)

[摘要]本文是对多边形扫描转换算法的讲解,希望对您学习C++有所帮助!

最近学习计算机图形学,写了个多边形扫描转换算法,贴出来分享一下;
 

MFC还不是太明白,主要还是运用OnDraw函数...
大家多指教...

void CPolyFillView::OnDraw(CDC* pDC)
{
    CPolyFillDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    // TODO: add draw code for native data here

    const int POINTNUM=6;      //多边形点数.

/******定义结构体用于活性边表AET和新边表NET***********************************/
    typedef struct XET
    {
        float x;
        float dx,ymax;
        XET* next;
    }AET,NET;
/******定义点结构体point******************************************************/
    struct point
    {
        float x;
        float y;
    }polypoint[POINTNUM]={250,50,550,150,550,400,250,250,100,350,100,100};//多边形顶点
    //mypoint[POINTNUM]={100,100,200,100,200,200,100,200};//正方形
    
/******计算最高点的y坐标(扫描到此终了)****************************************/
    int MaxY=0;
    int i;
    for(i=0;i<POINTNUM;i++)
        if(polypoint[i].y>MaxY)
            MaxY=polypoint[i].y;
        
/*******初始化AET表***********************************************************/
        AET *pAET=new AET;
        pAET->next=NULL;
        
/******初始化NET表************************************************************/
        NET *pNET[1024];
        for(i=0;i<=MaxY;i++)
        {
            pNET[i]=new NET;
            pNET[i]->next=NULL;
        }
/******扫描并树立NET表*********************************************************/
        for(i=0;i<=MaxY;i++)
        {
            for(int j=0;j<POINTNUM;j++)
                if(polypoint[j].y==i)
                {                    
                    if(polypoint[(j-1+POINTNUM)%POINTNUM].y>polypoint[j].y)
                    {
                        NET *p=new NET;
                        p->x=polypoint[j].x;
                        p->ymax=polypoint[(j-1+POINTNUM)%POINTNUM].y;
                        p->dx=(polypoint[(j-1+POINTNUM)%POINTNUM].x-polypoint[j].x)/(polypoint[(j-1+POINTNUM)%POINTNUM].y-polypoint[j].y);
                        p->next=pNET[i]->next;
                        pNET[i]->next=p;
                        
                    }
                    if(polypoint[(j+1+POINTNUM)%POINTNUM].y>polypoint[j].y)
                    {
                        NET *p=new NET;                        
                        p->x=polypoint[j].x;
                        p->ymax=polypoint[(j+1+POINTNUM)%POINTNUM].y;
                        p->dx=(polypoint[(j+1+POINTNUM)%POINTNUM].x-polypoint[j].x)/(polypoint[(j+1+POINTNUM)%POINTNUM].y-polypoint[j].y);
                        p->next=pNET[i]->next;
                        pNET[i]->next=p;
                    }
                }
        }
/******树立并更新活性边表AET*****************************************************/
        for(i=0;i<=MaxY;i++)
        {
    //计算新的交点x,更新AET********************************************************/
            NET *p=pAET->next;
            while(p)
            {
                p->x=p->x + p->dx;
                p=p->next;
            }
    //更新后新AET先排序*************************************************************/
                //断表排序,不再开辟空间
            AET *tq=pAET;
            p=pAET->next;
            tq->next=NULL;
            while(p)
            {
                while(tq->next && p->x >= tq->next->x)
                    tq=tq->next;
                NET *s=p->next;
                p->next=tq->next;
                tq->next=p;
                p=s;
                tq=pAET;
            }
    //(改进算法)先从AET表中删除ymax==i的结点****************************************/
            AET *q=pAET;
            p=q->next;
            while(p)
            {
                if(p->ymax==i)
                {
                    q->next=p->next;
                    delete p;
                    p=q->next;
                }
                else
                {
                    q=q->next;
                    p=q->next;
                }
            }
    //将NET中的新点参与AET,并用拔出法按X值递增排序**********************************/
            p=pNET[i]->next;
            q=pAET;
            while(p)
            {
                while(q->next && p->x >= q->next->x)
                    q=q->next;
                NET *s=p->next;
                p->next=q->next;
                q->next=p;
                p=s;
                q=pAET;
            }
/******配对填充颜色***************************************************************/
            p=pAET->next;
            while(p && p->next)
            {
                for(float j=p->x;j<=p->next->x;j++)
                    pDC->SetPixel(static_cast<int>(j),i,RGB(255,0,0));
                p=p->next->next;//思索端点情况
            }    
        }
}

PolyFill.rar



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