8. Liang Barsky Line Clipping Algorithm

/*************************************************************************
TITLE:  Program to implement Liang Barsky Line Clipping Algorithm.
*************************************************************************/

#include<iostream.h>
#include<conio.h>
#include<graphics.h>
int main()
{
	int gd=DETECT,gm; //Detects the graphics drivers automatically
	initgraph(&gd,&gm," "); //Initialize to graphics mode

	int x1,y1,x2,y2,xmax,xmin,ymax,ymin,xx1,yy1,xx2,yy2,dx,dy,i;
	int p[4],q[4];
	float t1,t2,t[4];

     //To plot the quadrants
     line(0,240,639,240);
     line(320,0,320,479);
     outtextxy(295,243,"0,0");
     setcolor(WHITE);

     //To plot the window
	cout<<" Enter the lower left co-ordinates of the window : ";
	cin>>xmin>>ymin; //Lower left co-ordinates of the window
	cout<<" Enter the upper right co-ordinates of the window : ";
	cin>>xmax>>ymax; //Upper right co-ordinates of the window
	setcolor(12);
	rectangle(320+xmin,240-ymin,320+xmax,240-ymax); //Plot the window

     //To plot the line to be clipped
	cout<<" Enter x1 : ";
	cin>>x1; //X co-ordinate of the first point of the line
	cout<<" Enter y1 : ";
	cin>>y1; //Y co-ordinate of the first point of the line
	cout<<" Enter x2 : ";
	cin>>x2; //X co-ordinate of the second point of the line
	cout<<" Enter y2 : ";
	cin>>y2; //Y co-ordinate of the second point of the line

	line(320+x1,240-y1,320+x2,240-y2);//Plotting the line

	dx=x2-x1; //Difference between the x-co-ordinates
	dy=y2-y1; //Difference between the y-co-ordinates

	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;

	//To check if the line to be clipped lies inside the window or not
	for(i=0;i < 4;i++)
	{
		if(p[i]!=0)
        {
			t[i]=(float)q[i]/p[i];
		}
		else
			if(p[i]==0 && q[i] < 0)
				cout<<" The line lies completely outside the window.";
			else
				if(p[i]==0 && q[i] >= 0)
					cout<<" The line lies completely inside the window.";
	}
	if (t[0] > t[2])
    {
		t1=t[0];
	}
	else
	{
		t1=t[2];
	}
	if (t[1] < t[3])
	{
		t2=t[1];
	}
	else
	{
		t2=t[3];
	}
	if (t1 < t2) //If t1<t2 then draw a line from (xx1, yy1) to (xx2,yy2)
	{
		xx1=x1+t1*dx;
		xx2=x1+t2*dx;
		yy1=y1+t1*dy;
		yy2=y1+t2*dy;
		cout<<" The line after clipping is displayed.";
		setcolor(WHITE);
		line(320+xx1,240-yy1,320+xx2,240-yy2);
	}
	else //If the line crosses over the window, you will see (xx1, yy1) and (xx2,yy2) are intersection between line and edge
	{
		cout<<" The line lies out of the window.";
	}
    getch(); //Pauses the Output Console until a key is pressed
    closegraph(); //Closes the graphics mode
    return 0;
    }