/*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,"c:\\tc\\bgi");
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();
}