/*Program to implement Ploygon Clipping */
#include<graphics.h>
#include<stdio.h>
#include<conio.h>
#include<dos.h>

union REGS i,o;
struct pt
{
	int x,y;
};

float xl,xr,yt,yb,m,slope[20];
int bc=0,xc,yc,n=0,k,dy,dx,x,y,temp,a[20][2],xi[20];

struct point
{
	float x,y;
};

enum bound {left,right,bottom,top};

int inside(struct point p, enum bound b)
{
	int c=1;
	switch(b)
	{
	case left  :  if(p.x<xl)
				  c=0;
				  break;
	case right  : if(p.x>xr)
				  c=0;
				  break;
	case bottom : if(p.y>yb)
				  c=0;
				  break;
	case top    : if(p.y<yt)
				  c=0;
				  break;
	}
  return(c);
}

struct point intersect (struct point p1,struct point p2,enum bound b)
{
	struct point t;
	float m=0;
	if(p2.x!=p1.x) 	m=(p2.y - p1.y)/(p2.x-p1.x);

	switch(b)
	{
		case left :  t.x =xl;
					 t.y = p2.y+(xl-p2.x)*m;
					 break;
		case right:  t.x=xr;
					 t.y = p2.y + (xr-p2.x)*m;
					 break;
		case bottom: t.y = yb;
					 if(p1.x==p2.x) t.x=p2.x;
					 else t.x = p2.x +(yb-p2.y)/m;
					 break;
		case top   : t.y = yt;
					 if(p1.x==p2.x) t.x=p2.x;
					 else t.x = p2.x +(yt-p2.y)/m;
					 break;
	}
	return t;
}

initmouse()
{
	i.x.ax=0;
	int86(0x33,&i,&o);
	return(o.x.ax);
}

showmouseptr()
{
	i.x.ax=1;
	int86(0x33,&i,&o);
	return(0);
}

hidemouseptr()
{
	i.x.ax=2;
	int86(0x33,&i,&o);
	return(0);
}

getmousepos(int *button,int *x,int *y)
{
	i.x.ax=3;
	int86(0x33,&i,&o);
	*button=o.x.bx;
	*x=o.x.cx;
	*y=o.x.dx;
}

void main()
{
	enum bound b;
	int cou,i,gd=DETECT,gm,flag;
	struct point p[30],pout[30],z;
	initgraph(&gd,&gm,"");
	cleardevice();
	showmouseptr();
	while(bc!=2)    //poly
	{
		getmousepos(&bc,&xc,&yc);
		if(bc==1)
		{
			p[n].x=xc;
			p[n].y=yc;
			n++;
			hidemouseptr();
			if(n>1)
			line(p[n-2].x,p[n-2].y,xc,yc);
			showmouseptr();
			delay(200);
		}
	}
	p[n]=p[0];
	hidemouseptr();
	line(p[n-1].x,p[n-1].y,p[n].x,p[n].y);
	showmouseptr();
	getmousepos(&bc,&xc,&yc);
	flag=1;
	bc=0;
	while(bc!=2)      //window
	{
		if((bc==1) && (flag==1))
		{
			xl=xc;
			yt=yc;
			flag=2;
			delay(200);
		}
		else
		{
			xr=xc;
			yb=yc;
			delay(200);
		}
		getmousepos(&bc,&xc,&yc);
	}
	hidemouseptr();
	rectangle(xl,yt,xr,yb);
	getch();
	for(b=left;b<=top;b++)
	{
		cou =-1;
		for(i=0;i<n;i++)
		if((inside(p[i],b)==0) && (inside(p[i+1],b)==1))
		{
			z=intersect(p[i],p[i+1],b);
			pout[++cou] =z;
			pout[++cou]=p[i+1];
		}
		else
		if((inside(p[i],b)==1)&&(inside(p[i+1],b)==1)) pout[++cou]=p[i+1];
		else
		if((inside(p[i],b)==1)&&(inside(p[i+1],b)==0))
		{
			z = intersect(p[i],p[i+1],b);
			pout[++cou]=z;
		}
		pout[++cou]=pout[0];
		n=cou;
		for(i=0;i<=n;i++) p[i]=pout[i];
	}
	getch();
	cleardevice();
	rectangle(xl,yt,xr,yb);
	for(i=0;i<n;i++) line(p[i].x,p[i].y,p[i+1].x,p[i+1].y);
	getch();
	for(i=0;i<=n;i++)
	{
		a[i][0]=p[i].x;
		a[i][1]=p[i].y;
	}
	getch();
}