lt88.c

programs in <C program design>

# include "stdio.h"
 # include "graphics.h"
 # define X0 500
 # define X1 100
 # define Y0 100
 # define Y1 300
 void main( )
 {
 	int g_driver,g_mode,g_error;
 	g_driver=VGA;
 	g_mode=VGAHI;
 	initgraph(&g_driver,&g_mode,"");
 	g_error=graphresult();
 	if (g_error<0)
 	   {printf("initgraph error: %s\n",grapherrormsg(g_error));
 	   exit(1);
 	   };
 midpointline(X0,Y0,X1,Y1,YELLOW);
 }
 midpointline(x0,y0,x1,y1,color)
 int x0,y0,x1,y1,color;
 {
 int i,a,b,delta1,j,k,s1,s2,delta2,d,x,y;
 	cleardevice();
        for (j=1;j<=5;j++)
        {
        x=x0;
        y=y0;
   delta1=abs(x1-x0);
   delta2=abs(y1-y0);
       if (x1-x0>=0)
       s1=1;
 	 else
 	   s1=-1;
       if (y1-y0>=0)
       s2=+1;
 	  else
 	    s2=-1;
    if (delta2>delta1)
 	 {
 	 a=delta1;
 	 delta1=delta2;
 	 delta2=a;
 	 b=1;
 	 }
      else
 	b=0;
      d=2*delta2-delta1;
 	  for (i=1;i<=delta1;i++)
       {
 	if (j<=2)
 	    putpixel(x,y,GREEN);
 	  else if (j<=3)
 	    putpixel(x,y,WHITE);
 	else
 	    putpixel(x,y,color);
 	if (d>=0)
 	   if (b=1)
 	   x=x+s1;
 	     else
 	       {
 	       y=y+s2;
 	       d=d-2*delta1;
 	       }
 	   if (b=1)
 	     y=y+s2;
 		else
 		{
 		x=x+s1;
 		d=d+2*delta2;
 		}
        }
   if (j<=2)
    {
      x0=100;
      x1=500;
      y0=100;
      y1=300;
      }
       else if(j<=3)
 	{
 	x0=300;
 	x1=0;
 	y0=100;
 	y1=150;
 	}
  }
 getchar();
 textmode(180);
  }