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# Liang-Barsky Line Clipping Graphics Algorithm

## Computer graphics program in C++

Liang-Barsky Line Clipping Algorithm using C++ graphics library

### C++

``````# include <iostream>
# include<graphics.h>
# include<conio.h>
# include<math.h>
using namespace std;

class LineCoordinates
{
public:
float x_1;
float y_1;
float x_2;
float y_2;

LineCoordinates(const float x1,const float y1,
const float x2,const float y2)
{
x_1=x1;
y_1=y1;
x_2=x2;
y_2=y2;
}
};
class WindowCoordinates{

public:
float x_min;
float y_min;
float x_max;
float y_max;

WindowCoordinates(const float x1,const float y1,
const float x2,const float y2)
{
x_min=x1;
y_min=y1;
x_max=x2;
y_max=y2;
}
};

const int clip_line(const WindowCoordinates,LineCoordinates&);
const int check_line(const float,const float,float&,float&);
void Rectangle(const int,const int,const int,const int);
void Line(const int,const int,const int,const int);

int main( )
{
int driver=VGA;
int mode=VGAHI;
initgraph(&driver,&mode,"");
WindowCoordinates WC(200,150,450,350);
setcolor(15);
Rectangle(WC.x_min,WC.y_min,WC.x_max,WC.y_max);
LineCoordinates LC_1(150,160,120,320);
LineCoordinates LC_2(250,100,150,200);
LineCoordinates LC_3(160,200,490,260);
LineCoordinates LC_4(300,300,400,380);
LineCoordinates LC_5(550,300,450,400);
LineCoordinates LC_6(440,110,400,370);
setcolor(6);
Line(LC_1.x_1,LC_1.y_1,LC_1.x_2,LC_1.y_2);
Line(LC_2.x_1,LC_2.y_1,LC_2.x_2,LC_2.y_2);
Line(LC_3.x_1,LC_3.y_1,LC_3.x_2,LC_3.y_2);
Line(LC_4.x_1,LC_4.y_1,LC_4.x_2,LC_4.y_2);
Line(LC_5.x_1,LC_5.y_1,LC_5.x_2,LC_5.y_2);
Line(LC_6.x_1,LC_6.y_1,LC_6.x_2,LC_6.y_2);
char Key=NULL;
do
{
Key=getch( );
}
while(Key!='1');
setcolor(14);
if(clip_line(WC,LC_1))
Line(LC_1.x_1,LC_1.y_1,LC_1.x_2,LC_1.y_2);

if(clip_line(WC,LC_2))
Line(LC_2.x_1,LC_2.y_1,LC_2.x_2,LC_2.y_2);

if(clip_line(WC,LC_3))
Line(LC_3.x_1,LC_3.y_1,LC_3.x_2,LC_3.y_2);

if(clip_line(WC,LC_4))
Line(LC_4.x_1,LC_4.y_1,LC_4.x_2,LC_4.y_2);

if(clip_line(WC,LC_5))
Line(LC_5.x_1,LC_5.y_1,LC_5.x_2,LC_5.y_2);

if(clip_line(WC,LC_6))
Line(LC_6.x_1,LC_6.y_1,LC_6.x_2,LC_6.y_2);

getch( );
return 0;
}

const int clip_line(const WindowCoordinates wc,LineCoordinates &lc)
{
float u_1=0;
float u_2=1;

float dx=(lc.x_2-lc.x_1);
float dy=(lc.y_2-lc.y_1);

float p1=(-dx);
float p2=dx;
float p3=(-dy);
float p4=dy;

float q1=(lc.x_1-wc.x_min);
float q2=(wc.x_max-lc.x_1);
float q3=(lc.y_1-wc.y_min);
float q4=(wc.y_max-lc.y_1);

if(check_line(p1,q1,u_1,u_2) && check_line(p2,q2,u_1,u_2) &&
check_line(p3,q3,u_1,u_2) && check_line(p4,q4,u_1,u_2))
{
if(u_2<1)
{
lc.x_2=(lc.x_1+(u_2*dx));
lc.y_2=(lc.y_1+(u_2*dy));
}

if(u_1>0)
{
lc.x_1+=(u_1*dx);
lc.y_1+=(u_1*dy);
}

lc.x_1=(int)(lc.x_1+0.5);
lc.y_1=(int)(lc.y_1+0.5);
lc.x_2=(int)(lc.x_2+0.5);
lc.y_2=(int)(lc.y_2+0.5);

return 1;
}

return 0;
}

const int check_line(const float p,const float q,float &u_1,float &u_2)
{
int flag=1;

float r=(q/p);

if(p<0)
{
if(r>u_2)
flag=0;

else if(r>u_1)
u_1=r;
}

else if(p>0)
{
if(r<u_1)
flag=0;

else if(r<u_2)
u_2=r;
}

else
{
if(q<0)
flag=0;
}

return flag;
}

void Rectangle(const int x_1,const int y_1,const int x_2,const int y_2)
{
Line(x_1,y_1,x_2,y_1);
Line(x_2,y_1,x_2,y_2);
Line(x_2,y_2,x_1,y_2);
Line(x_1,y_2,x_1,y_1);
}

void Line(const int x_1,const int y_1,const int x_2,const int y_2)
{
int color=getcolor( );

int x1=x_1;
int y1=y_1;

int x2=x_2;
int y2=y_2;

if(x_1>x_2)
{
x1=x_2;
y1=y_2;

x2=x_1;
y2=y_1;
}

int dx=abs(x2-x1);
int dy=abs(y2-y1);
int inc_dec=((y2>=y1)?1:-1);

if(dx>dy)
{
int two_dy=(2*dy);
int two_dy_dx=(2*(dy-dx));
int p=((2*dy)-dx);

int x=x1;
int y=y1;

putpixel(x,y,color);

while(x<x2)
{
x++;

if(p<0)
p+=two_dy;

else
{
y+=inc_dec;
p+=two_dy_dx;
}

putpixel(x,y,color);
}
}

else
{
int two_dx=(2*dx);
int two_dx_dy=(2*(dx-dy));
int p=((2*dx)-dy);

int x=x1;
int y=y1;

putpixel(x,y,color);

while(y!=y2)
{
y+=inc_dec;

if(p<0)
p+=two_dx;

else
{
x++;
p+=two_dx_dy;
}

putpixel(x,y,color);
}
}
}
``````
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