0,0 → 1,99 |
/* 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 either under the terms of the GNU Lesser General Public |
* License version 2.1 as published by the Free Software Foundation |
* (the "LGPL") or, at your option, under the terms of the Mozilla |
* Public License Version 1.1 (the "MPL"). If you do not alter this |
* notice, a recipient may use your version of this file under either |
* the MPL or the LGPL. |
* |
* You should have received a copy of the LGPL along with this library |
* in the file COPYING-LGPL-2.1; if not, write to the Free Software |
* Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA |
* You should have received a copy of the MPL along with this library |
* in the file COPYING-MPL-1.1 |
* |
* The contents of this file are subject to the Mozilla Public License |
* Version 1.1 (the "License"); you may not use this file except in |
* compliance with the License. You may obtain a copy of the License at |
* http://www.mozilla.org/MPL/ |
* |
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY |
* OF ANY KIND, either express or implied. See the LGPL or the MPL for |
* the specific language governing rights and limitations. |
* |
* The Original Code is the cairo graphics library. |
* |
* The Initial Developer of the Original Code is University of Southern |
* California. |
* |
* Contributor(s): |
* Carl D. Worth <cworth@cworth.org> |
*/ |
|
#include "cairoint.h" |
|
#include "cairo-slope-private.h" |
|
/* 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. |
|
This function always compares the slope vectors based on the |
smaller angular difference between them, (that is based on an |
angular difference that is strictly less than pi). To break ties |
when comparing slope vectors with an angular difference of exactly |
pi, the vector with a positive dx (or positive dy if dx's are zero) |
is considered to be more positive than the other. |
|
Also, all slope vectors with both dx==0 and dy==0 are considered |
equal and more positive than any non-zero vector. |
|
< 0 => a less positive than b |
== 0 => a equal to b |
> 0 => a more positive than b |
*/ |
int |
_cairo_slope_compare (const cairo_slope_t *a, const cairo_slope_t *b) |
{ |
cairo_int64_t ady_bdx = _cairo_int32x32_64_mul (a->dy, b->dx); |
cairo_int64_t bdy_adx = _cairo_int32x32_64_mul (b->dy, a->dx); |
int cmp; |
|
cmp = _cairo_int64_cmp (ady_bdx, bdy_adx); |
if (cmp) |
return cmp; |
|
/* special-case zero vectors. the intended logic here is: |
* zero vectors all compare equal, and more positive than any |
* non-zero vector. |
*/ |
if (a->dx == 0 && a->dy == 0 && b->dx == 0 && b->dy ==0) |
return 0; |
if (a->dx == 0 && a->dy == 0) |
return 1; |
if (b->dx == 0 && b->dy ==0) |
return -1; |
|
/* Finally, we're looking at two vectors that are either equal or |
* that differ by exactly pi. We can identify the "differ by pi" |
* case by looking for a change in sign in either dx or dy between |
* a and b. |
* |
* And in these cases, we eliminate the ambiguity by reducing the angle |
* of b by an infinitesimally small amount, (that is, 'a' will |
* always be considered less than 'b'). |
*/ |
if ((a->dx ^ b->dx) < 0 || (a->dy ^ b->dy) < 0) { |
if (a->dx > 0 || (a->dx == 0 && a->dy > 0)) |
return -1; |
else |
return +1; |
} |
|
/* Finally, for identical slopes, we obviously return 0. */ |
return 0; |
} |