Program of Nicol Lee Nicol Algorithm for Line Clipping

# include <stdio.h>
# include <conio.h>
# include <graphics.h>
# include <math.h>

int xmin,ymin,xmax,ymax;
void main()
{
    int x1,y1,x2,y2;
    int gdriver = DETECT, gmode, errorcode;
    int findRegionP1(int,int);
    void clipline1(int,int,int,int);
    void clipline2(int,int,int,int);
    void clipline3(int,int,int,int);
    int ch;
    float m;
    clrscr();
    printf(\"\\nEnter the xmin:->\");
    scanf(\"%d\",&xmin);
    printf(\"\\nEnter the ymin:->\");
    scanf(\"%d\",&ymin);
    printf(\"\\nEnter the xmax:->\");
    scanf(\"%d\",&xmax);
    printf(\"\\nEnter the ymax:->\");
    scanf(\"%d\",&ymax);

    initgraph(&gdriver, &gmode, \"C:\\\\TC\\\\BGI\");
    setcolor(15);
    rectangle(xmin,ymin,xmax,ymax);
    printf(\"Enter the x1:->\");
    scanf(\"%d\",&x1);
    printf(\"Enter the y1:->\");
    scanf(\"%d\",&y1);
    printf(\"Enter the x2:->\");
    scanf(\"%d\",&x2);
    printf(\"Enter the y2:->\");
    scanf(\"%d\",&y2);
    setcolor(12);
    line(x1,y1,xmin,ymin);
    line(x1,y1,xmax,ymin);
    line(x1,y1,xmax,ymax);
    line(x1,y1,xmin,ymax);
    getch();
    setcolor(3);
    line(x1,y1,x2,y2);
    getch();
    ch=first_end_point_region(x1,y1);
    switch(ch)
    {
        case 1:
            clipline1(x1,y1,x2,y2);
            break;
        case 2:
            clipline2(x1,y1,x2,y2);
            break;
        case 3:
            clipline3(x1,y1,x2,y2);
            break;
        default:
            printf(\"\\nInvalid select of the option: \");
    }
    getch();
}

int first_end_point_region(int x,int y)
{
    /*    u have two equations:-
        xmin <= x <= xmax;
        ymin <= y <= ymax; */

    if(x>=xmin && x<=xmax && y>=ymin && y<=ymax)
        return 1;
    else if(x<xmin && y>=ymin && y<=ymax)
        return 2;
    else if(x<=xmin && y<=ymin)
        return 3;
    else
        return 0;
}

/* point p1 is inside the clip window */
void clipline1(int x1,int y1,int x2,int y2)
{
    int draw=1;
    float m,m1,m2,m3,m4;
    int nx1,ny1,nx2,ny2;

    /* calculate slopes for all the lines passing thru vertices
        and including the input line :- */

    m=((float)(y2-y1))/(x2-x1);
    m1=((float)(ymin-y1))/(xmin-x1);
    m2=((float)(ymin-y1))/(xmax-x1);
    m3=((float)(ymax-y1))/(xmax-x1);
    m4=((float)(ymax-y1))/(xmin-x1);
    nx1=x1;
    ny1=y1;

    // point p2 is on top
    if(((abs(m)>=m1 && x2<x1) || (abs(m)>abs(m2) && x2>x1)) && y1>y2)
    {
          // point p2 is also inside clip window
          if(y2>ymin)
          {
              nx2=x2;
              ny2=y2;
          }
          // point p2 is outside clip window
          else
          {
              ny2=ymin;
              nx2=x1+(ymin-y1)/m;
          }
    }
    // point p2 is on right side of clip window
    else if(m>m2 && m<m3 && x2>=xmax)
    {
        // point p2 is inside clip window
        if(x2<xmax)
        {
            nx2=x2;
            ny2=y2;
        }
        // point p2 is outside clip window
        else
        {
            nx2=xmax;
            ny2=y1+(xmax-x1)*m;
        }
    }
    // point p2 is on bottom side of clip window
    else if((abs(m)>=m3 && x2>x1) || (abs(m)>abs(m4) && x2<x1))
    {
        // point p2 is inside clip window
          if(y2<ymax)
          {
            nx2=x2;
            ny2=y2;
          }
        // point p2 is outside clip window
          else
          {
            ny2=ymax;
            nx2=x1+(ymax-y1)/m;
          }
    }
    // point p2 is on left side of clip window
    else if(m>m4 && m<m1)
    {
        // point p2 is inside the clip window
        if(x2>xmin)
        {
            nx2=x2;
            ny2=y2;
        }
        // point p2 is outside the clip window
        else
        {
            nx2=xmin;
            ny2=y1+(xmin-x1)*m;
        }
    }
    else
        draw=0;
    getch();
    cleardevice();
    setcolor(18);
    rectangle(xmin,ymin,xmax,ymax);
    if(draw)
    {
        setcolor(12);
        line(x1,y1,xmin,ymin);
        line(x1,y1,xmax,ymin);
        line(x1,y1,xmax,ymax);
        line(x1,y1,xmin,ymax);
        setcolor(5);
        line(nx1,ny1,nx2,ny2);
    }
}

/* Point p1 is in the edge region */
void clipline2(int x1,int y1,int x2,int y2)
{
    int draw=1;
    float m,m1,m2,m3,m4;
    int nx1,ny1,nx2,ny2;

    m=((float)(y2-y1))/(x2-x1);
    m1=((float)(ymin-y1))/(xmin-x1);
    m2=((float)(ymin-y1))/(xmax-x1);
    m3=((float)(ymax-y1))/(xmax-x1);
    m4=((float)(ymax-y1))/(xmin-x1);

    // Point p2 is in Left-Top region
    if(m>m1 && m<m2)
    {
        // Point p2 is inside the clip window
        if(y2>ymin)
        {
            nx1=xmin;
            ny1=y1+m*(xmin-x1);
            nx2=x2;
            ny2=y2;
        }
        // Point p2 is outside the clip window
        else
        {
            nx1=xmin;
            ny1=y1+m*(xmin-x1);
            ny2=ymin;
            nx2=x1+(ymin-y1)/m;
        }
    }
    // Point p2 is in Left-Right region
    else if(m>m2 && m<m3)
    {
        // Point p2 is inside the clip window
        if(x2<xmax)
        {
            nx1=xmin;
            ny1=y1+m*(xmin-x1);
            nx2=x2;
            ny2=y2;
        }
        // Point p2 is outside the clip window
        else
        {
            nx1=xmin;
            ny1=y1+m*(xmin-x1);
            nx2=xmax;
            ny2=y1+(xmax-x1)*m;
        }
    }
    // Point p2 is in Left-Bottom region
    else if(m>m3 && m<m4)
    {
        // Point p2 is inside the clip window
        if(y2<ymax)
        {
            nx1=xmin;
            ny1=y1+m*(xmin-x1);
            nx2=x2;
            ny2=y2;
        }
        // Point p2 is outside the clip window
        else
        {
            nx1=xmin;
            ny1=y1+m*(xmin-x1);
            ny2=ymax;
            nx2=x1+(ymax-y1)/m;
        }
    }
    else
        draw=0;
    getch();
    cleardevice();
    setcolor(18);
    rectangle(xmin,ymin,xmax,ymax);
    if(draw)
    {
        setcolor(12);
        line(x1,y1,xmin,ymin);
        line(x1,y1,xmax,ymin);
        line(x1,y1,xmax,ymax);
        line(x1,y1,xmin,ymax);
        setcolor(5);
        line(nx1,ny1,nx2,ny2);
    }
}

/* Point p1 is in the Corner Region */
void clipline3(int x1,int y1,int x2,int y2)
{
    int draw=1;
    float m,m1,m2,m3,m4,tm1,tm2;
    int nx1,ny1,nx2,ny2;
    int flag,t;
    tm1=((float)(ymin-y1))/(xmin-x1);
    tm2=((float)(ymax-ymin))/(xmax-xmin); //diagonal slope

    m=((float)(y2-y1))/(x2-x1);
    m1=((float)(ymin-y1))/(xmax-x1);
    m2=((float)(ymax-y1))/(xmax-x1);
    m3=((float)(ymin-y1))/(xmin-x1);
    m4=((float)(ymax-y1))/(xmin-x1);

    // Point p1 is towards the left side of the clip window (case2)
    if(tm1<tm2)
    {
        flag=2;
        t=m2;
        m2=m3;
        m3=t;
    }
    // Point p1 is towards the top side of the clip window (case1)
    else
        flag=1;

    // Point p2 is in the Top-Right region
    if(m>m1 && m<m2)
    {
        // Point p2 is outside the clip window
        if(x2>xmax && y2>ymin)
        {
            ny1=ymin;
            nx1=x1+(ymin-y1)/m;
            nx2=xmax;
            ny2=y1+m*(xmax-x1);
        }
        // Point p2 is inside the clip window
        else if(y2>ymin && x2<xmax)
        {
            ny1=ymin;
            nx1=x1+(ymin-y1)/m;
            ny2=y2;
            nx2=x2;
        }
    }
    // Point p2 is Left-Right or Top-Bottom region
    else if(m>m2 && m<m3)
    {
        // Point p2 is in Top-Bottom region (case1)
        if(flag==1)
        {
            // Point p2 is outside the clip window
               if(y2>=ymax)
               {
                   ny1=ymin;
                   nx1=x1+(ymin-y1)/m;
                   nx2=x1+(ymax-y1)/m;
                   ny2=ymax;
               }
               // Point p2 is inside the clip window
               else if(y2>=ymin)
               {
                   ny1=ymin;
                   nx1=x1+(ymin-y1)/m;
                   nx2=x2;
                   ny2=y2;
               }
        }
        // Point p2 is in Left-Right region (case2)
        else
        {
            // Point p2 is outside the clip window
               if(x2>=xmax)
               {
                   nx1=xmin;
                   ny1=y1+m*(xmin-x1);
                   nx2=xmax;
                   ny2=y1+m*(xmax-x1);
               }
               // Point p2 is inside the clip window
               else if(x2>=xmin)
               {
                   nx1=xmin;
                   ny1=y1+m*(xmin-x1);
                   nx2=x2;
                   ny2=y2;
               }
        }
    }
    // Point p2 is in Left-Bottom region
    else if(m>m3 && m<m4)
    {
        // Point p2 is outside the clip window
        if(y2>=ymax)
        {
            nx1=xmin;
            ny1=y1+m*(xmin-x1);
            nx2=x1+(ymax-y1)/m;
            ny2=ymax;
        }
        // Point p2 is inside the clip window
        else if(y2>=ymin)
        {
            nx1=xmin;
            ny1=y1+m*(xmin-x1);
            ny2=y2;
            nx2=x2;
        }
    }
    else
        draw=0;
    getch();
    cleardevice();
    setcolor(18);
    rectangle(xmin,ymin,xmax,ymax);
    if(draw)
    {
        setcolor(12);
        line(x1,y1,xmin,ymin);
        line(x1,y1,xmax,ymin);
        line(x1,y1,xmax,ymax);
        line(x1,y1,xmin,ymax);
        setcolor(5);
        line(nx1,ny1,nx2,ny2);
    }
}