| /* 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; |
| } |