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86 lines
2.3 KiB
C
86 lines
2.3 KiB
C
/* cairo - a vector graphics library with display and print output
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*
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* Copyright © 2002 University of Southern California
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License version 2.1 as published by the Free Software Foundation.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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* Author: Carl D. Worth <cworth@isi.edu>
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*/
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#include "cairoint.h"
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void
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_cairo_slope_init (cairo_slope_t *slope, cairo_point_t *a, cairo_point_t *b)
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{
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slope->dx = b->x - a->x;
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slope->dy = b->y - a->y;
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}
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/* Compare two slopes. Slope angles begin at 0 in the direction of the
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positive X axis and increase in the direction of the positive Y
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axis.
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WARNING: This function only gives correct results if the angular
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difference between a and b is less than PI.
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< 0 => a less positive than b
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== 0 => a equal to be
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> 0 => a more positive than b
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*/
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int
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_cairo_slope_compare (cairo_slope_t *a, cairo_slope_t *b)
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{
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cairo_fixed_48_16_t diff;
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diff = ((cairo_fixed_48_16_t) a->dy * (cairo_fixed_48_16_t) b->dx
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- (cairo_fixed_48_16_t) b->dy * (cairo_fixed_48_16_t) a->dx);
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if (diff > 0)
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return 1;
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if (diff < 0)
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return -1;
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if (a->dx == 0 && a->dy == 0)
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return 1;
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if (b->dx == 0 && b->dy ==0)
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return -1;
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return 0;
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}
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/* XXX: It might be cleaner to move away from usage of
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_cairo_slope_clockwise/_cairo_slope_counter_clockwise in favor of
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directly using _cairo_slope_compare.
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*/
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/* Is a clockwise of b?
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*
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* NOTE: The strict equality here is not significant in and of itself,
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* but there are functions up above that are sensitive to it,
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* (cf. _cairo_pen_find_active_cw_vertex_index).
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*/
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int
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_cairo_slope_clockwise (cairo_slope_t *a, cairo_slope_t *b)
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{
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return _cairo_slope_compare (a, b) < 0;
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}
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int
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_cairo_slope_counter_clockwise (cairo_slope_t *a, cairo_slope_t *b)
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{
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return ! _cairo_slope_clockwise (a, b);
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}
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