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/*****************************************************************************
** This is part of the CTSim program
** Copyright (c) 1983-2001 Kevin Rosenberg
**
** $Id: bresenham.cpp 7061 2003-09-07 06:34:45Z kevin $
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License (version 2) as
** published by the Free Software Foundation.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
******************************************************************************/
// REFERENCES FOR BRESENHAM'S ALGORITHM
// Newman & Sproll, "Principals of Interactive Computer Graphics", page 25.
// Foley & van Dam, "Fundementals of Interactive Computer Graphics", page 433
void
bresenham (int x1, int y1, int x2, int y2)
{
int delta_x = x2 - x1;
int dx_abs = (delta_x >= 0 ? delta_x : -delta_x);
int delta_y = y2 - y1;
int dy_abs = (delta_y >= 0 ? delta_y : -delta_y);
// draws a line when abs(dx) >= abs(dy)
if (dx_abs > dy_abs) {
int count = dx_abs + 1;
int major_inc = (x1 <= x2 ? 1 : -1);
int min_inc = (delta_y >= 0 ? 1 : -1); // determine direction of minor axis
int d = dy_abs * 2 - dx_abs; // Put decision variable in d
int dinc1 = (dy_abs - dx_abs) * 2;
int dinc2 = 2 * dy_abs;
bresx (x1, y1, major_inc, d, d1, d2);
} else { //For plotting lines with abs(dy) > abs(sx)
int count = dy_abs + 1;
int major_inc = (y1 <= y2 ? 1 : -1);
int min_inc = (delta_x >= 0 ? 1 : -1); // check direction of minor axis
int d = dx_abs * 2 - dy_abs;
dinc1 = (dx_abs - dy_abs) * 2;
dinc2 = 2 * dx_abs;
bresy (x1, y1, major_inc, min_inc, count, d, d1, d2);
}
}
static void
bresx (int x, int y, int majorinc, int minorinc, int count, int d, int d1, int d2)
{
do {
setpixel();
x += majorinc;
if (d < 0)
d += dinc2;
else {
d += dinc1;
y += min_inc;
}
} while (--count > 0);
}
static void
bresy (int x, int y, int majorinc, int minorinc, int count, int d, int d1, int d2)
{
do {
setpixel();
y += majorinc;
if (d < 0)
d += dinc2;
else {
d += dinc1;
x += min_inc;
}
} while (--count > 0);
}
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