liang-barsky_C和C ++中的Liang Barsky线裁剪算法

我不是女神ヾ 2022-12-07 14:00 192阅读 0赞

![899526911fc525605c0a6dc906bca67d.png][]

liang-barsky

Here you will learn about liang barsky line clipping algorithm in C and C++.

在这里，您将了解C和C ++中的liang barsky线裁剪算法。

This Algorithm was developed by Liang and Barsky. It is used for line clipping as it is more efficient than Cyrus Beck algorithm and [Cohen Sutherland algorithm][] because it uses more efficient parametric equations to clip the given line.

该算法由Liang和Barsky开发。 它比Cyrus Beck算法和[Cohen Sutherland算法][Cohen Sutherland algorithm]更有效，因为它使用更有效的参数方程式裁剪给定的线，因此它比Cyrus Beck算法和[Cohen Sutherland算法][Cohen Sutherland algorithm]更有效。

These parametric equations are given as:

这些参数方程式为：

x = x1 + tdx

y = y1 + tdy, 0 <= t <= 1

y = y1 + tdy，0 <= t <= 1

Where dx = x2 – x1 & dy = y2 – y1

dx = x2 – x1＆dy = y2 – y1

Liang Barsky line clipping algorithm uses 4 inequalities with 2 parameters p & q which are defined in the algorithm below.

Liang Barsky线裁剪算法使用4个不等式以及2个参数p＆q，这些参数在下面的算法中定义。

### 算法 **(**Algorithm**)** ###

**1.** Read 2 endpoints of line as p1 (x1, y1) & p2 (x2, y2).

**1.**将线的2个端点读取为p1(x1，y1)和p2(x2，y2)。

**2.** Read 2 corners (left-top & right-bottom) of the clipping window as (xwmin, ywmin, xwmax, ywmax).

**2.**将剪切窗口的2个角(左上角和右下角)读取为(xwmin，ywmin，xwmax，ywmax)。

**3.** Calculate values of parameters pi and qi for i = 1, 2, 3, 4 such that

**3.**计算i = 1、2、3、4的参数pi和qi的值，使得

p1 = -dx, q1 = x1 – xwmin

p1 = -dx，q1 = x1 – xwmin

p2 = dx, q2 = xwmax – x1

p2 = dx，q2 = xwmax – x1

p3 = -dy, q3 = y1 – ywmin

p3 = -dy，q3 = y1 – ywmin

p4 = dy, q4 = ywmax – y1

p4 = dy，q4 = ywmax – y1

**4.** if pi = 0 then line is parallel to ith boundary

**4.**如果pi = 0，则线平行于第i个边界

if qi < 0 then line is completely outside boundary so discard line

如果qi <0，则线完全在边界之外，因此丢弃线

else, check whether line is horizontal or vertical and then check the line endpoints with the corresponding boundaries.

否则，检查线是水平还是垂直，然后检查具有相应边界的线端点。

**5.** Initialize t1 & t2 as

**5.**初始化t1和t2为

t1 = 0 & t2 = 1

t1 = 0＆t2 = 1

**6.** Calculate values for qi/pi for i = 1, 2, 3, 4.

**6.**计算i = 1、2、3、4时qi / pi的值。

**7.** Select values of qi/pi where pi < 0 and assign maximum out of them as t1.

**7.**在pi <0的情况下选择qi / pi的值，并将其中的最大值分配为t1。

**8.** Select values of qi/pi where pi > 0 and assign minimum out of them as t2.

**8.**在pi> 0的情况下选择qi / pi的值，并将其中的最小值指定为t2。

**9.** if (t1 < t2) \{ xx1 = x1 + t1dx

**9.**如果(t1 <t2)\{xx1 = x1 + t1dx

xx2 = x1 + t2dx

yy1 = y1 + t1dy

yy2 = y1 + t2dy

line (xx1, yy1, xx2, yy2) \}

行(xx1，yy1，xx2，yy2)\}

**10.** Stop.

**10.**停下来。

### 优点 **(**Advantages**)** ###

1. More efficient than other algorithms as line intersection with boundaries calculations are reduced.

1.与其他算法相比，效率更高，因为与边界计算的线相交减少了。

2. Intersections of line are computed only once.

2.线的交点仅计算一次。

## 用C和C ++编写Liang Barsky剪线算法程序 **(**Program for Liang Barsky Line Clipping Algorithm in C and C++**)** ##

### C程序 **(**C Program**)** ###

#include<stdio.h>
    #include<graphics.h>
    #include<math.h>
    #include<dos.h>
     
    void main()
    {
    	int i,gd=DETECT,gm;
    	int x1,y1,x2,y2,xmin,xmax,ymin,ymax,xx1,xx2,yy1,yy2,dx,dy;
    	float t1,t2,p[4],q[4],temp;
    	
    	x1=120;
    	y1=120;
    	x2=300;
    	y2=300;
    	
    	xmin=100;
    	ymin=100;
    	xmax=250;
    	ymax=250;
    	
    	initgraph(&gd,&gm,"c:\\turboc3\\bgi");
    	rectangle(xmin,ymin,xmax,ymax);
    	dx=x2-x1;
    	dy=y2-y1;
    	
    	p[0]=-dx;
    	p[1]=dx;
    	p[2]=-dy;
    	p[3]=dy;
    	
    	q[0]=x1-xmin;
    	q[1]=xmax-x1;
    	q[2]=y1-ymin;
    	q[3]=ymax-y1;
    	
    	for(i=0;i<4;i++)
    	{
    		if(p[i]==0)
    		{
    			printf("line is parallel to one of the clipping boundary");
    			if(q[i]>=0)
    			{
    				if(i<2)
    				{
    					if(y1<ymin)
    					{
    						y1=ymin;
    					}
    				
    					if(y2>ymax)
    					{
    						y2=ymax;
    					}
    				
    					line(x1,y1,x2,y2);
    				}
    				
    				if(i>1)
    				{
    					if(x1<xmin)
    					{
    						x1=xmin;
    					}
    					
    					if(x2>xmax)
    					{
    						x2=xmax;
    					}
    					
    					line(x1,y1,x2,y2);
    				}
    			}
    		}
    	}
    	
    	t1=0;
    	t2=1;
    	
    	for(i=0;i<4;i++)
    	{
    		temp=q[i]/p[i];
    		
    		if(p[i]<0)
    		{
    			if(t1<=temp)
    				t1=temp;
    		}
    		else
    		{
    			if(t2>temp)
    				t2=temp;
    		}
    	}
    	
    	if(t1<t2)
    	{
    		xx1 = x1 + t1 * p[1];
    		xx2 = x1 + t2 * p[1];
    		yy1 = y1 + t1 * p[3];
    		yy2 = y1 + t2 * p[3];
    		line(xx1,yy1,xx2,yy2);
    	}
    	
    	delay(5000);
    	closegraph();
    }

### C ++程序 **(**C++ Program**)** ###

#include<iostream.h>
    #include<graphics.h>
    #include<math.h>
    #include<dos.h>
     
    void main()
    {
    	int i,gd=DETECT,gm;
    	int x1,y1,x2,y2,xmin,xmax,ymin,ymax,xx1,xx2,yy1,yy2,dx,dy;
    	float t1,t2,p[4],q[4],temp;
    	
    	x1=120;
    	y1=120;
    	x2=300;
    	y2=300;
    	
    	xmin=100;
    	ymin=100;
    	xmax=250;
    	ymax=250;
    	
    	initgraph(&gd,&gm,"c:\\turboc3\\bgi");
    	rectangle(xmin,ymin,xmax,ymax);
    	dx=x2-x1;
    	dy=y2-y1;
    	
    	p[0]=-dx;
    	p[1]=dx;
    	p[2]=-dy;
    	p[3]=dy;
    	
    	q[0]=x1-xmin;
    	q[1]=xmax-x1;
    	q[2]=y1-ymin;
    	q[3]=ymax-y1;
    	
    	for(i=0;i<4;i++)
    	{
    		if(p[i]==0)
    		{
    			cout<<"line is parallel to one of the clipping boundary";
    			if(q[i]>=0)
    			{
    				if(i<2)
    				{
    					if(y1<ymin)
    					{
    						y1=ymin;
    					}
    				
    					if(y2>ymax)
    					{
    						y2=ymax;
    					}
    				
    					line(x1,y1,x2,y2);
    				}
    				
    				if(i>1)
    				{
    					if(x1<xmin)
    					{
    						x1=xmin;
    					}
    					
    					if(x2>xmax)
    					{
    						x2=xmax;
    					}
    					
    					line(x1,y1,x2,y2);
    				}
    			}
    		}
    	}
    	
    	t1=0;
    	t2=1;
    	
    	for(i=0;i<4;i++)
    	{
    		temp=q[i]/p[i];
    		
    		if(p[i]<0)
    		{
    			if(t1<=temp)
    				t1=temp;
    		}
    		else
    		{
    			if(t2>temp)
    				t2=temp;
    		}
    	}
    	
    	if(t1<t2)
    	{
    		xx1 = x1 + t1 * p[1];
    		xx2 = x1 + t2 * p[1];
    		yy1 = y1 + t1 * p[3];
    		yy2 = y1 + t2 * p[3];
    		line(xx1,yy1,xx2,yy2);
    	}
    	
    	delay(5000);
    	closegraph();
    }

**Output**

**输出量**

![Liang-Barsky Line Clipping Algorithm in C and C++][Liang-Barsky Line Clipping Algorithm in C and C]

**Author Bio:**

**作者简介：**

I am Rahul Maheshwari from India currently pursuing engineering degree in Computer Science. I am passionate about programming and loves to code as much as I can and likes to help people to become better in programming.

我是印度的Rahul Maheshwari，目前正在攻读计算机科学的工程学位。 我对编程充满热情，并且热衷于编码，并且喜欢帮助人们在编程方面变得更好。

**Connect with him:** [Facebook][] | [Linkedin][]

**与他联系：** [Facebook][] | [领英][Linkedin]

Comment below if you have doubts or found anything incorrect in above liang barsky line clipping algorithm in C and C++.

如果您对以上使用C和C ++的liang barsky线裁剪算法有疑问或发现任何不正确之处，请在下面评论。

> 翻译自: [https://www.thecrazyprogrammer.com/2017/02/liang-barsky-line-clipping-algorithm.html][https_www.thecrazyprogrammer.com_2017_02_liang-barsky-line-clipping-algorithm.html]

liang-barsky

[899526911fc525605c0a6dc906bca67d.png]: /images/20221123/d805d2f5303047ff83735b78a08edda1.png
[Cohen Sutherland algorithm]: https://www.thecrazyprogrammer.com/2017/02/cohen-sutherland-line-clipping-algorithm.html
[Liang-Barsky Line Clipping Algorithm in C and C]: /images/20221123/21d691e516844629abe2ba2fe14e90ff.png
[Facebook]: https://www.facebook.com/rahul.maheshmaheshwari
[Linkedin]: https://www.linkedin.com/in/rahul-maheshwari-597bb2b6
[https_www.thecrazyprogrammer.com_2017_02_liang-barsky-line-clipping-algorithm.html]: https://www.thecrazyprogrammer.com/2017/02/liang-barsky-line-clipping-algorithm.html