SUTHERLAND HODGEMAN POLYGON CLIPPING

The algorithm begins with an input list of all vertices in the subject polygon. Next, one side of the clip polygon is extended infinitely in both directions, and the path of the subject polygon is traversed. Vertices from the input list are inserted into an output list if they lie on the visible side of the extended clip polygon line, and new vertices are added to the output list where the subject polygon path crosses the extended clip polygon line.

#include <stdio.h>
#include <graphics.h>
#include <conio.h>
#include <math.h>
#include <process.h>
#define TRUE 1
#define FALSE 0
typedef unsigned int outcode;
outcode CompOutCode(float x,float y);
enum  {  TOP = 0x1,
BOTTOM = 0x2,
RIGHT = 0x4,
LEFT = 0x8
};
float xmin,xmax,ymin,ymax;
void clip(float x0,float y0,float x1,float y1)
{
outcode outcode0,outcode1,outcodeOut;
int accept = FALSE,done = FALSE;
outcode0 = CompOutCode(x0,y0);
outcode1 = CompOutCode(x1,y1);
do
{
if(!(outcode0|outcode1))
{
accept = TRUE;
done = TRUE;
}
else
if(outcode0 & outcode1)
done = TRUE;
else
{
float x,y;
 
outcodeOut = outcode0?outcode0:outcode1;
if(outcodeOut & TOP)
{
x = x0+(x1-x0)*(ymax-y0)/(y1-y0);
y = ymax;
}
else
if(outcodeOut & BOTTOM)
{
x = x0+(x1-x0)*(ymin-y0)/(y1-y0);
y = ymin;
}
else
if(outcodeOut & RIGHT)
{
y = y0+(y1-y0)*(xmax-x0)/(x1-x0);
x = xmax;
}
else
{
y = y0+(y1-y0)*(xmin-x0)/(x1-x0);
x = xmin;
}
if(outcodeOut==outcode0)
{
x0 = x;
y0 = y;
outcode0 = CompOutCode(x0,y0);
}
else
{
x1 = x;
y1 = y;
outcode1 = CompOutCode(x1,y1);
}
}
}while(done==FALSE);
if(accept)
line(x0,y0,x1,y1);
outtextxy(150,20,"POLYGON AFTER CLIPPING");
 
rectangle(xmin,ymin,xmax,ymax);
}
outcode CompOutCode(float x,float y)
{
outcode code = 0;
if(y>ymax)
code|=TOP;
else
if(y<ymin)
code|=BOTTOM;
if(x>xmax)
code|=RIGHT;
else
if(x<xmin)
code|=LEFT;
return code;
}
void main( )
{
float x1,y1,x2,y2;
/* request auto detection */
int gdriver = DETECT, gmode, n,poly[14],i;
clrscr( );
printf("Enter the no of sides of polygon:");
scanf("%d",&n);
printf("\nEnter the coordinates of polygon\n");
for(i=0;i<2*n;i++)
{
scanf("%d",&poly[i]);
}
poly[2*n]=poly[0];
poly[2*n+1]=poly[1];
printf("Enter the rectangular coordinates of clipping window\n");
scanf("%f%f%f%f",&xmin,&ymin,&xmax,&ymax);
/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "c:\\tc\\bgi");
 
outtextxy(150,20,"POLYGON BEFORE CLIPPING");
drawpoly(n+1,poly);
rectangle(xmin,ymin,xmax,ymax);
getch( );
cleardevice( );
for(i=0;i<n;i++)
clip(poly[2*i],poly[(2*i)+1],poly[(2*i)+2],poly[(2*i)+3]);
getch( );
restorecrtmode( );
}

/*
OUTPUT:
Enter the no of sides of polygon:5
Enter the coordinates of polygon
50
50
200
100
350
350
80
200
40
80
Enter the rectangular coordinates of clipping window
150
150
300
300*/


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