直线段裁剪算法

直线段裁剪算法一：Cohen-Sutherland算法

//编译环境：Visual C++ 6.0，EasyX_20190219(beta)
#include 
#include 
#include 
#define left 1
#define right 2
#define bottom 4
#define top 8
using namespace std;
//设置裁剪框的大小和位置
double xl=120,xr=320,yt=240,yb=150;

//编码
void encode(double x,double y,int &code)
{
   int c=0;
   if(xxr)  {c=c+right;}
   if(yyt)  {c=c+top;}
   code=c;
}

//Cohen-Sutherland裁剪算法
int CS_LineClip(double x1,double y1,double x2,double y2)
{
   int code1,code2,code;
   int x,y;
   encode(x1,y1,code1);
   encode(x2,y2,code2);
   while(code1!=0||code2!=0)//都在里面时，直接画线，否则进行判断
   {
     if((code1&code2)!=0)  return 0;//都在外面舍弃
	 code=code1;
	 if(code1==0)  code=code2;
	 if((left&code)!=0)
	 {x=xl;y=y1+(y2-y1)*(xl-x1)/(x2-x1);}
	 else if((right&code)!=0)
	 {x=xr;y=y1+(y2-y1)*(xr-x1)/(x2-x1);}
     else if ((bottom&code) != 0)       
	 {y=yb;x=x1+(x2-x1)*(yb-y1)/(y2-y1);}     
     else if ((top&code) != 0)      
	 {y=yt;x=x1+(x2-x1)*(yt-y1)/(y2-y1);}
     if(code==code1)
	 {x1=x;y1=y;encode(x,y,code1);}
	 else
	 {x2=x;y2=y;encode(x,y,code2);}
   }
   line(x1,y1,x2,y2);
   return 0;
}


int main()
{   
	double x1,y1,x2,y2;
    initgraph(640, 480);  
    POINT points[]={ {xl,yt}, {xr,yt}, {xr,yb}, {xl,yb}};
	polygon(points,4);
    //用鼠标来获取两个点的坐标
	MOUSEMSG m;        // 定义结构体保存鼠标消息
    while (true)
    {flag:
        m = GetMouseMsg();// 获取一次鼠标消息
        switch (m.uMsg)//判断鼠标信息类型
        {
            case WM_LBUTTONDOWN:
			x1 = m.x; y1 = m.y;    //鼠标第一次按下时，获取鼠标当前坐标
            while (true)
            {
                m = GetMouseMsg();// 再次获取一条鼠标消息
                switch (m.uMsg)
                {
                case WM_LBUTTONDOWN:
					x2 = m.x; y2 = m.y;//鼠标第二次按下时,得到坐标
					setcolor(RED);
					line(x1, y1, x2, y2);
					setcolor(YELLOW);
					CS_LineClip(x1, y1, x2, y2);
					goto flag;
                }
            }
		}
	} 
	_getch();
	closegraph();
return 0;
}

演示如下所示：

直线段裁剪算法二：梁友栋-Barsky线段裁剪算法

//编译环境：Visual C++ 6.0，EasyX_20190219(beta)
#include
#include
#include
using namespace std;

//设置裁剪框的大小和位置,全局变量
double xl=120,xr=250,yt=270,yb=160;

bool ClipT(double q,double d,double &t0,double &t1)
{//当线段完全不可见时，返回false，否则，返回true
	double r;
	if(q<0)
	{
		r=(double)d/(double)q;
     	if(r>t1)
		  return false;
	    else if(r>t0)
		{t0=r;return true;}
	}
	else if(q>0)
	{
		r=(double)d/(double)q;
		if(r

直线时裁剪框以内的线段，演示如下：