C Program for COHEN-SUTHERLAND 2D LINE CLIPPING ALGORITHM

 

To identify the portion of line that is inside or outside a specified region

The region against which a line is to be clipped is called clipping window. The portion of lines inside the clipping window are retain for display.

ALGORITHM:

1.      Start

2.      Read two end points of a line P1,P2 (x1,y1) and (x2,y2)

3.      Read two  corners of window(wx1,wy1) and (wx2,wy2)

4.      Assign the region codes for two end points using following steps

a.       Set bit 1 if x < wx1

b.      Set bit 2 if x>wx2

c.       Set bit 3 if y<wy2

d.      Set bit 4 if y> wy1

5.      Check for the visibility of the line

a.       If region codes for both end points are 0 then the line is completely visible. Draw the line. Go to 10

b.      If the region codes are not zero and the logical AND ing of them is also non zero then the line is completely invisible. Go to 10

c.       If the region codes for two end points do not satisfy the conditions in 5 a and 5 b the line is partially visible

       6.      Determine the intersecting edge of the clipping window by inspecting the region codes of two end points

a.       If the region codes foe both end points are non zero find the intersection point P1’ and P2’ with boundary edges of clipping window with respect to P1 and P2  respectively

b.      If the region code for any one end point is non zero then find intersection point P1’ or P2’ with the boundary edge of the clipping window with respect to it.

7.      Divide the line segments considering the intersection points

8.      Reject the line segment if any one end point of it appears outside the clipping window

9.      Draw the remaining line segments

10.  Stop.

PROGRAM:

#include<stdio.h>

#include<conio.h>

#include<dos.h>

#include<graphics.h>

#include<stdlib.h>

typedef struct coord

{

int x,y;

char code[4];

}PT;

void drawwindow();

void drawline(PT p1,PT p2,int c1);

PT setcode(PT p);

int visibility(PT p1,PT p2);

PT resetendpt(PT p1,PT p2);

void main()

{

int gd=DETECT,gm,v;

PT p1,p2,ptemp;

initgraph(&gd,&gm,"");

cleardevice();

printf("\t\tCOHEN-SUTHERLAND LINE CLIPPING ALGORITHM");

printf("\nEnter the two end points p1(x,y)");

scanf("%d%d",&p1.x,&p1.y);

printf("Enter the two end points p2(x,y):");

scanf("%d%d",&p2.x,&p2.y);

cleardevice();

printf("\t\tCLIPPING WINDOW");

drawwindow();

getch();

printf("\tCOHEN-SUTHERLAND LINE CLIPPING ALGORITHM");

printf("\n\t\tBEFORE CLIPPING");

drawline(p1,p2,4);

getch();

p1=setcode(p1);

p2=setcode(p2);

v=visibility(p1,p2);

switch(v)

{

  case 0:

   cleardevice();

   //printf("\t\tCLIPPING WINDOW");

   drawwindow();

   drawline(p1,p2,15);

  break;

 case 1:

   cleardevice();

   drawwindow();

  break;

  case 2:

   cleardevice();

   p1=resetendpt(p1,p2);

   p2=resetendpt(p2,p1);

   drawwindow();

   printf("\tCOHEN-SUTHERLAND LINE CLIPPING ALGORITHM");

   printf("\n\t\tAFTER CLIPPING");

   drawline(p1,p2,15);

  break;

 }

 getch();

 closegraph();

//return(0);

}

void drawwindow()

{

 setcolor(RED);

 setlinestyle(DOTTED_LINE, 1, 1);

 line(150,100,100,100);

 line(150,100,150,50);

 line(450,100,500,100);

 line(450,100,450,50);

 line(450,350,500,350);

 line(450,350,450,400);

 line(150,350,150,400);

 line(150,350,100,350) ;

 line(150,100,100,100);

 line(150,100,150,50);

 setlinestyle(SOLID_LINE, 1, 1);

 line(150,100,450,100);

 line(450,100,450,350);

 line(450,350,150,350);

 line(150,350,150,100);

 outtextxy(450,30,"1001");

 outtextxy(470,200,"1000");

 outtextxy(470,370,"1010");

 outtextxy(300,370,"0010");

 outtextxy(120,370,"0110");

 outtextxy(120,200,"0100");

 outtextxy(120,30,"0101");

 outtextxy(300,30,"0001");

 outtextxy(300,200,"0000");

}

void drawline(PT p1,PT p2,int c1)

{

 setcolor(c1);

 line(p1.x,p1.y,p2.x,p2.y);

}

PT setcode(PT p)

{

 PT ptemp;

 if(p.y<100)

  ptemp.code[0]='1';

 else

  ptemp.code[0]='0';

 if(p.y>350)

  ptemp.code[1]='1';

 else

  ptemp.code[1]='0';

 if(p.x>200)

  ptemp.code[2]='1';

 else

  ptemp.code[2]='0';

 if(p.x<150)

  ptemp.code[3]='1';

 else

  ptemp.code[3]='0';

  ptemp.x=p.x;

  ptemp.y=p.y;

 return(ptemp);

}

int visibility(PT p1,PT p2)

{

 int i,flag=0;

 for(i=0;i<4;i++)

 {

  if((p1.code[i]!='0')||(p2.code[i]!='0'))

  flag=1;

 }

 if(flag==0)

 return(0);

 for(i=0;i<4;i++)

 {

  if((p1.code[i]==p2.code[i])&&(p1.code[i]=='1'))

  flag=0;

 }

 if(flag==0)

 return(1);

 return(2);

}

PT resetendpt(PT p1,PT p2)

{

 PT temp;

 int x,y,i;

 float m,k;

 if(p1.code[3]=='1')

 x=150;

 if(p1.code[2]=='1')

 x=450;

 if((p1.code[3]=='1')||(p1.code[2]=='1'))

 {

  m=(float)(p2.y-p1.y)/(p2.x-p1.x);

  k=(p1.y+(m*(x-p1.x)));

  temp.y=k;

  temp.x=x;

  for(i=0;i<4;i++)

  {

   temp.code[i]=p1.code[i];

   if(temp.y<=350 && temp.y>=100)

    return(temp);

  }

  if(p1.code[0]=='1')

  y=100;

  if(p1.code[1]=='1')

  y=350;

  if((p1.code[0]=='1')||(p1.code[1]=='1'))

  {

   m=(float)(p2.y-p1.y)/(p2.x-p1.x);

   k=(float)p1.x+(float)(y-p1.y)/m;

   temp.y=y;

   temp.x=k;

   for(i=0;i<4;i++)

   temp.code[i]=p1.code[i];

   return(temp);

  }

 }

 else

 return(p1);

 return(p2);

}

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