Sem 4‎ > ‎CG LAB‎ > ‎

Z: Line Clipping

posted Apr 7, 2012, 5:00 AM by Neil Mathew   [ updated Apr 7, 2012, 5:02 AM ]

The Program I've done on this is rather complex and time consuming. 
Not ideal for an exam with one hour to complete. 

So, made this simple one:

PROUD OF THIS CODE REALLY.
Although it is limited to one line (can be changed if needed), it is short and rather direct.
Also, overcame two problems I faced with Line Clipping.

1.
By making the coordinates DOUBLE, accurate clippings seen.

2.
 By putting slope in equation rather than a separate variable, overcame the crashing 
whenever slope matched one of the axis and caused a division by zero error.

3.
Made use of Call by reference, being default for arrays and enforced it for PINSIDE()


CODE


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#include<iostream.h>
#include<graphics.h>
#include<conio.h>
 
/* In Line Clipping:
 
INPUT()
Enter 1st pt, 2nd pt. (Keep window fixed.)
 
CHECK()
check each point and MAP 4 3 2 1 CODE
 
AND()
return if inside or outside
 
CLIP() & PINSIDE()
Y=MX+C
 
DRAW()
just the lines and window
 
*/
 
double x1,y1,x2,y2;
double Xmin,Ymin,Xmax,Ymax;
int CODE1[4];
int CODE2[4];
 
void INPUT()
{
cout<<"\n Enter First Point: ";
cin>>x1>>y1;
 
cout<<"\n Enter Second Point: ";
cin>>x2>>y2;
 
Xmin=100;
Ymin=100;
Xmax=300;
Ymax=300;
}
 
void DRAW()
{
 
setcolor(CYAN);
rectangle(Xmin,Ymin,Xmax,Ymax);
 
setcolor(WHITE);
line(x1,y1,x2,y2);
 
}
 
 
void CHECK(int x,int y, int CODE[4])
{                       //arrays call by reference
 
if(y > Ymax)
CODE[3]=1;
else
CODE[3]=0;
 
if(y < Ymin)
CODE[2]=1;
else
CODE[2]=0;
 
if(x > Xmax)
CODE[1]=1;
else
CODE[1]=0;
 
if(x < Xmin)
CODE[0]=1;
else
CODE[0]=0;
}
 
int AND(int code1[4], int code2[4])
{
 
for(int i=0; i<4; i++)
{
if( code1[i] == 1 && code2[i] == 1 )
return 1;
}
 
return 0;
}
 
 
 
void PINSIDE(double &x, double &y)
{
 
 
if( x < Xmin )
{
y=y + (  ((y2-y1)/(x2-x1)) * (Xmin-x) );
x=Xmin;
}
 
if( x > Xmax )
{
y=y + (  ((y2-y1)/(x2-x1)) * (Xmax-x) );
x=Xmax;
}
 
if( y > Ymax )
{
x=x + ( (x2-x1)/(y2-y1) * (Ymax-y) );
y=Ymax;
}
 
 
if( y < Ymin )
{
x=x + ( (x2-x1)/(y2-y1) * (Ymin-y) );
y=Ymin;
}
 
 
}
 
 
 
void CLIP()
{
 
CHECK(x1,y1,CODE1);
CHECK(x2,y2,CODE2);
 
int flag=AND(CODE1,CODE2);
 
if( flag==1 )
{
cout<<" COMPLETELY OUTSIDE ";
x1=0;
x2=0;
y1=0;
y2=0;
 
DRAW();
}
else if( flag==0 )
{
 
if( CODE1[0]==1 || CODE1[1]==1 || CODE1[2]==1 || CODE1[3]==1 )
{
cout<<" PARTIALLY INSIDE ";
PINSIDE(x1,y1);
}
 
if( CODE2[0]==1 || CODE2[1]==1 || CODE2[2]==1 || CODE2[3]==1 )
{
cout<<" PARTIALLY INSIDE ";
PINSIDE(x2,y2);
}
 
if( CODE1[0]==0 && CODE1[1]==0 && CODE1[2]==0 && CODE1[3]==0
    &&  CODE2[0]==0 && CODE2[1]==0 && CODE2[2]==0 && CODE2[3]==0 )
{
cout<<" COMPLETELY INSIDE";
}
 
DRAW();
}
 
}
 
 
 
void main()
{
INPUT();
 
int gdriver=DETECT, gmode;
initgraph(&gdriver,&gmode,"C:/TC/BGI");
 
DRAW();
getch();
 
cleardevice();
CLIP();
 
DRAW();
getch();
 
closegraph();
}
 
 
 





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