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/* cairo - a vector graphics library with display and print output
*
* Copyright © 2002 University of Southern California
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library 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
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* Author: Carl D. Worth <cworth@isi.edu>
*/
#include "cairoint.h"
void
_cairo_slope_init (cairo_slope_t *slope, cairo_point_t *a, cairo_point_t *b)
{
slope->dx = b->x - a->x;
slope->dy = b->y - a->y;
}
/* Compare two slopes. Slope angles begin at 0 in the direction of the
positive X axis and increase in the direction of the positive Y
axis.
WARNING: This function only gives correct results if the angular
difference between a and b is less than PI.
< 0 => a less positive than b
== 0 => a equal to be
> 0 => a more positive than b
*/
int
_cairo_slope_compare (cairo_slope_t *a, cairo_slope_t *b)
{
cairo_fixed_48_16_t diff;
diff = ((cairo_fixed_48_16_t) a->dy * (cairo_fixed_48_16_t) b->dx
- (cairo_fixed_48_16_t) b->dy * (cairo_fixed_48_16_t) a->dx);
if (diff > 0)
return 1;
if (diff < 0)
return -1;
if (a->dx == 0 && a->dy == 0)
return 1;
if (b->dx == 0 && b->dy ==0)
return -1;
return 0;
}
/* XXX: It might be cleaner to move away from usage of
_cairo_slope_clockwise/_cairo_slope_counter_clockwise in favor of
directly using _cairo_slope_compare.
*/
/* Is a clockwise of b?
*
* NOTE: The strict equality here is not significant in and of itself,
* but there are functions up above that are sensitive to it,
* (cf. _cairo_pen_find_active_cw_vertex_index).
*/
int
_cairo_slope_clockwise (cairo_slope_t *a, cairo_slope_t *b)
{
return _cairo_slope_compare (a, b) < 0;
}
int
_cairo_slope_counter_clockwise (cairo_slope_t *a, cairo_slope_t *b)
{
return ! _cairo_slope_clockwise (a, b);
}
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