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bresh.c

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/*
##########################################
# bresh.c -
#   Algorithm for drawing a line in an image.
#
# RCS: $Id: bresh.c,v 2.1 1999/01/14 15:37:32 conner Exp $ 
# 
# Digital Image Analysis Lab
# Dept. of Electrical and Computer Engineering
# University of Arizona
##########################################
*/

/*
    Breshenham line drawing algorithm

Modified so that the points to be drawn 
      are in one function.  
      plot_point(x,y)  is only function that uses the 
      external variables.

Also:  All of the lines are draw
       from ymax values to ymin values.
       X ordering doesn't matter.

*/

#include <stdio.h>
/*#include <sys/param.h>*/
#include <sys/types.h>

/* RCS Indentification information */
static char rcsid[] = "$Id: bresh.c,v 2.1 1999/01/14 15:37:32 conner Exp $";

extern int **x_array_buffer;    /* Window Size */
extern int count_point;
extern int point;

brshnm (x1, y1, x2, y2)
     int x1, y1, x2, y2;
{

  int x, y;
  int tempx, tempy;
  int dely, delx;
  int ebar;
  int i;

#ifdef  DEBUG
  printf ("x1 = %d , y1 = %d\n", x1, y1);
  printf ("x2 = %d , y2 = %d\n", x2, y2);
#endif

  if ((x1 > x2) && (y1 > y2))
    {

      /* ------------------------------------------------------
       *  Case 1
       *  Neg. Slope
       *  X1, Y1 is greater than X2, Y2
       *  ie. Line starts at low end of screen and goes up
       */

#ifdef  DEBUG
      printf ("First point is greater than second point\n");
      printf ("x1 = %d , y1 = %d\n", x1, y1);
      printf ("x2 = %d , y2 = %d\n", x2, y2);
#endif

      pos_hor_slope (x1, y1, x2, y2);

    }
  else if ((x1 > x2) && (y1 == y2))
    {

      /* ------------------------------------------------------
       *  Case 2.
       *  Horizontal Line where 
       *  X1 > X2
       *  ie. Line starts at right and goes left
       */

      pos_hor_slope (x1, y1, x2, y2);

    }
  else if ((x1 < x2) && (y1 > y2))
    {

#ifdef  DEBUG
      printf (" Neg slope points \n");
#endif

      neg_slope (x1, y1, x2, y2);

    }
  else if ((x1 > x2) && (y1 < y2))
    {

#ifdef  DEBUG
      printf ("Neg slope points w/ \n");
      printf ("Start at Upper right  to Lower Left \n");
#endif

      neg_slope (x1, y1, x2, y2);

    }
  else if ((x1 == x2) && (y1 != y2))
    {

      /* ------------------------------------------------------
       *  Case 3. 
       *  VERTICAL line 
       */

#ifdef  DEBUG
      printf ("Vertical Slope\n");
#endif

      vertical_slope (x1, y1, x2, y2);

    }
  else
    {

      pos_hor_slope (x1, y1, x2, y2);

    }

}

/* ------------------------------------------------------ */
/* This routine plots point by point vertical lines.
 * 
 */
vertical_slope (x1, y1, x2, y2)
     int x1, y1, x2, y2;
{
  int x, y, tempy;
  x = x1;

  if (y1 < y2)
    {
      for (y = y1; y <= y2; y++)
        {
          plot_points (x, y);
        }
    }
  else
    {
      for (y = y1; y >= y2; y--)
        {
          plot_points (x, y);
        }
    }
}

/* ------------------------------------------------------ */
/* This routine plots point by point  lines with
 * Neg slope .
 */
neg_slope (x1, y1, x2, y2)
     int x1, y1, x2, y2;
{
  int x, y;
  int delx, dely;
  int ebar;
  int i;

  delx = abs (x2 - x1);
  dely = abs (y2 - y1);

  /* Initialization
     of loop
   */
  x = x1;
  y = y1;

  if (dely < delx)
    {
      /*
       * Slope is less than 1
       */
      ebar = 2 * dely - delx;
      for (i = 0; i < delx; i++)
        {
          plot_points (x, y);

          if ((x1 < x2) && (y1 > y2))
            {

              while (ebar > 0)
                {
                  y = y - 1;
                  ebar = ebar - 2 * delx;
                }

              x = x + 1;
              ebar = ebar + 2 * dely;

            }
          else
            {

              while (ebar > 0)
                {
                  y = y + 1;
                  ebar = ebar - 2 * delx;
                }

              x = x - 1;
              ebar = ebar + 2 * dely;

            }
        }
    }

  else
    {
      /*
       * Slope Greater than 1
       */
#ifdef  DEBUG
      printf ("Slope greater than 1\n");
#endif

      ebar = 2 * delx - dely;
      for (i = 0; i < dely; i++)
        {
          plot_points (x, y);

          if ((x1 < x2) && (y1 > y2))
            {

              while (ebar > 0)
                {
                  x = x + 1;
                  ebar = ebar - 2 * dely;
                }

              y = y - 1;
              ebar = ebar + 2 * delx;

            }
          else
            {

              while (ebar > 0)
                {
                  x = x - 1;
                  ebar = ebar - 2 * dely;
                }

              y = y + 1;
              ebar = ebar + 2 * delx;

            }
        }
    }
}

/* ------------------------------------------------------ */
/* This routine plots point by point  lines with
 * Pos slope and horizontal lines.
 */
pos_hor_slope (x1, y1, x2, y2)
     int x1, y1, x2, y2;
{
  int x, y;
  int delx, dely;
  int ebar;
  int i;

  /* Initialization
     of loop
   */
  x = x1;
  y = y1;

  delx = abs (x2 - x1);
  dely = abs (y2 - y1);

  if (dely < delx)
    {
      /*
       * Slope is less than 1
       */
      ebar = 2 * dely - delx;
      for (i = 0; i < delx; i++)
        {
          plot_points (x, y);

          while (ebar > 0)
            {
              if (y1 < y2)
                {
                  y = y + 1;
                }
              else
                {
                  y = y - 1;
                }
              ebar = ebar - 2 * delx;
            }

          if (x1 < x2)
            {
              x = x + 1;
            }
          else
            {
              x = x - 1;
            }
          ebar = ebar + 2 * dely;

        }

    }
  else
    {
      /*
       * Slope Greater than 1
       */

#ifdef  DEBUG
      printf ("Slope greater than 1\n");
      printf ("than 1\n");
#endif

      ebar = 2 * delx - dely;
      for (i = 0; i < dely; i++)
        {
          plot_points (x, y);

          while (ebar > 0)
            {
              if (x1 < x2)
                {
                  x = x + 1;
                }
              else
                {
                  x = x - 1;
                }
              ebar = ebar - 2 * dely;
            }

          if (y1 < y2)
            {
              y = y + 1;
            }
          else
            {
              y = y - 1;
            }
          ebar = ebar + 2 * delx;
        }
    }

}

/* 
   Uses global variables to either count or fill the 
   passed array.
*/
plot_points (x, y)
     int x, y;
{

#ifdef  DEBUG
  printf ("x = %d, y= %d \n", x, y);
#endif

  if (count_point)
    {

      point++;
#ifdef  DEBUG
      printf ("Points allocated %d\n", point);
#endif

    }
  else
    {

      if (x < 0)
        {
          printf ("Bad X value %d\n", x);
        }
      else
        {

          x_array_buffer[point][0] = x;
          x_array_buffer[point++][1] = y;

        }

    }

}

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