bres_line.c

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/*
 * \file bres_line.c
 *
 * \brief GIS Library - Bresenham line routines.
 *
 * (C) 2001-2008 by the GRASS Development Team
 *
 * This program is free software under the GNU General Public License
 * (>=v2). Read the file COPYING that comes with GRASS for details.
 *
 * \author GRASS GIS Development Team
 *
 * \date 1999-2008
 */

#include <grass/gis.h>


int G_bresenham_line(int x0, int y0, int x1, int y1, int (*point) (int, int))
{
    int dx, dy;
    int xinc, yinc;

    register int res1;
    int res2;

    xinc = 1;
    yinc = 1;
    if ((dx = x1 - x0) < 0) {
        xinc = -1;
        dx = -dx;
    }

    if ((dy = y1 - y0) < 0) {
        yinc = -1;
        dy = -dy;
    }
    res1 = 0;
    res2 = 0;

    if (dx > dy) {
        while (x0 != x1) {
            point(x0, y0);
            if (res1 > res2) {
                res2 += dx - res1;
                res1 = 0;
                y0 += yinc;
            }
            res1 += dy;
            x0 += xinc;
        }
    }
    else if (dx < dy) {
        while (y0 != y1) {
            point(x0, y0);
            if (res1 > res2) {
                res2 += dy - res1;
                res1 = 0;
                x0 += xinc;
            }
            res1 += dx;
            y0 += yinc;
        }
    }
    else {
        while (x0 != x1) {
            point(x0, y0);
            y0 += yinc;
            x0 += xinc;
        }
    }

    point(x1, y1);

    return 0;
}