forked from KolibriOS/kolibrios
100 lines
3.5 KiB
C
100 lines
3.5 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 either 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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* (the "LGPL") or, at your option, under the terms of the Mozilla
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* Public License Version 1.1 (the "MPL"). If you do not alter this
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* notice, a recipient may use your version of this file under either
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* the MPL or the LGPL.
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*
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* You should have received a copy of the LGPL along with this library
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* in the file COPYING-LGPL-2.1; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA
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* You should have received a copy of the MPL along with this library
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* in the file COPYING-MPL-1.1
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*
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* The contents of this file are subject to the Mozilla Public License
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* Version 1.1 (the "License"); you may not use this file except in
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* compliance with the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
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* OF ANY KIND, either express or implied. See the LGPL or the MPL for
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* the specific language governing rights and limitations.
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*
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* The Original Code is the cairo graphics library.
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*
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* The Initial Developer of the Original Code is University of Southern
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* California.
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*
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* Contributor(s):
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* Carl D. Worth <cworth@cworth.org>
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*/
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#include "cairoint.h"
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#include "cairo-slope-private.h"
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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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This function always compares the slope vectors based on the
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smaller angular difference between them, (that is based on an
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angular difference that is strictly less than pi). To break ties
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when comparing slope vectors with an angular difference of exactly
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pi, the vector with a positive dx (or positive dy if dx's are zero)
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is considered to be more positive than the other.
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Also, all slope vectors with both dx==0 and dy==0 are considered
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equal and more positive than any non-zero vector.
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< 0 => a less positive than b
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== 0 => a equal to b
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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 (const cairo_slope_t *a, const cairo_slope_t *b)
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{
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cairo_int64_t ady_bdx = _cairo_int32x32_64_mul (a->dy, b->dx);
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cairo_int64_t bdy_adx = _cairo_int32x32_64_mul (b->dy, a->dx);
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int cmp;
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cmp = _cairo_int64_cmp (ady_bdx, bdy_adx);
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if (cmp)
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return cmp;
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/* special-case zero vectors. the intended logic here is:
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* zero vectors all compare equal, and more positive than any
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* non-zero vector.
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*/
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if (a->dx == 0 && a->dy == 0 && b->dx == 0 && b->dy ==0)
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return 0;
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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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/* Finally, we're looking at two vectors that are either equal or
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* that differ by exactly pi. We can identify the "differ by pi"
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* case by looking for a change in sign in either dx or dy between
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* a and b.
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*
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* And in these cases, we eliminate the ambiguity by reducing the angle
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* of b by an infinitesimally small amount, (that is, 'a' will
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* always be considered less than 'b').
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*/
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if ((a->dx ^ b->dx) < 0 || (a->dy ^ b->dy) < 0) {
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if (a->dx > 0 || (a->dx == 0 && a->dy > 0))
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return -1;
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else
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return +1;
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}
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/* Finally, for identical slopes, we obviously return 0. */
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return 0;
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}
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