SUTHERLAND – HODGEMANN POLYGON CLIPPING ALGORITHM

SUTHERLAND – HODGEMANN POLYGON CLIPPING ALGORITHM

Aim :

To write a C program to implement SUTHERLAND – HODGEMANN polygon

clipping algorithm.

Algorithm:

Step 1: Start the program.

Step 2: Input Coordinates of all vertices of the polygon

Step 3: Input coordinates of the clipping window

Step 4: Consider the left edge of the window

Step 5: Compare the vertices of each edge of the polygon , individually with the clipping plane

Step 6: Save the resulting intersections and vertices in the new list of vertices according to four

possible relationships between the edge and the clipping boundary discussed

earlier

Step 7: Repeat the steps 4 and 5 for remaining edges of the clipping window. Each time the

resultant list of vertices is successively passed to process the next edge of the

clipping window

Step 8: Stop the Program.

PROGRAM:

#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 xwmin,xwmax,ywmin,ywmax;

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)*(ywmax-y0)/(y1-y0);

 y = ywmax;

 }

 else

 if(outcodeOut & BOTTOM)

 {

 x = x0+(x1-x0)*(ywmin-y0)/(y1-y0);

 y = ywmin;

 }

 else

 if(outcodeOut & RIGHT)

 {

 y = y0+(y1-y0)*(xwmax-x0)/(x1-x0);

 x = xwmax;

 }

 else

 {

 y = y0+(y1-y0)*(xwmin-x0)/(x1-x0);

 x = xwmin;

 }

 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(xwmin,ywmin,xwmax,ywmax);

}

outcode CompOutCode(float x,float y)

{

 outcode code = 0;

 if(y>ywmax)

 code|=TOP;

 else

 if(y<ywmin)

 code|=BOTTOM;

 if(x>xwmax)

 code|=RIGHT;

 else

 if(x<xwmin)

 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",&xwmin,&ywmin,&xwmax,&ywmax);

/* initialize graphics and local variables */

initgraph(&gdriver, &gmode, "c:\\tc\\bgi");

outtextxy(150,20,"POLYGON BEFORE CLIPPING");

drawpoly(n+1,poly);

rectangle(xwmin,ywmin,xwmax,ywmax);

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