LCOV - code coverage report
Current view: directory - gfx/cairo/cairo/src - cairo-slope.c (source / functions) Found Hit Coverage
Test: app.info Lines: 17 0 0.0 %
Date: 2012-06-02 Functions: 1 0 0.0 %

       1                 : /* cairo - a vector graphics library with display and print output
       2                 :  *
       3                 :  * Copyright © 2002 University of Southern California
       4                 :  *
       5                 :  * This library is free software; you can redistribute it and/or
       6                 :  * modify it either under the terms of the GNU Lesser General Public
       7                 :  * License version 2.1 as published by the Free Software Foundation
       8                 :  * (the "LGPL") or, at your option, under the terms of the Mozilla
       9                 :  * Public License Version 1.1 (the "MPL"). If you do not alter this
      10                 :  * notice, a recipient may use your version of this file under either
      11                 :  * the MPL or the LGPL.
      12                 :  *
      13                 :  * You should have received a copy of the LGPL along with this library
      14                 :  * in the file COPYING-LGPL-2.1; if not, write to the Free Software
      15                 :  * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA
      16                 :  * You should have received a copy of the MPL along with this library
      17                 :  * in the file COPYING-MPL-1.1
      18                 :  *
      19                 :  * The contents of this file are subject to the Mozilla Public License
      20                 :  * Version 1.1 (the "License"); you may not use this file except in
      21                 :  * compliance with the License. You may obtain a copy of the License at
      22                 :  * http://www.mozilla.org/MPL/
      23                 :  *
      24                 :  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
      25                 :  * OF ANY KIND, either express or implied. See the LGPL or the MPL for
      26                 :  * the specific language governing rights and limitations.
      27                 :  *
      28                 :  * The Original Code is the cairo graphics library.
      29                 :  *
      30                 :  * The Initial Developer of the Original Code is University of Southern
      31                 :  * California.
      32                 :  *
      33                 :  * Contributor(s):
      34                 :  *      Carl D. Worth <cworth@cworth.org>
      35                 :  */
      36                 : 
      37                 : #include "cairoint.h"
      38                 : 
      39                 : #include "cairo-slope-private.h"
      40                 : 
      41                 : /* Compare two slopes. Slope angles begin at 0 in the direction of the
      42                 :    positive X axis and increase in the direction of the positive Y
      43                 :    axis.
      44                 : 
      45                 :    This function always compares the slope vectors based on the
      46                 :    smaller angular difference between them, (that is based on an
      47                 :    angular difference that is strictly less than pi). To break ties
      48                 :    when comparing slope vectors with an angular difference of exactly
      49                 :    pi, the vector with a positive dx (or positive dy if dx's are zero)
      50                 :    is considered to be more positive than the other.
      51                 : 
      52                 :    Also, all slope vectors with both dx==0 and dy==0 are considered
      53                 :    equal and more positive than any non-zero vector.
      54                 : 
      55                 :    <  0 => a less positive than b
      56                 :    == 0 => a equal to b
      57                 :    >  0 => a more positive than b
      58                 : */
      59                 : int
      60               0 : _cairo_slope_compare (const cairo_slope_t *a, const cairo_slope_t *b)
      61                 : {
      62               0 :     cairo_int64_t ady_bdx = _cairo_int32x32_64_mul (a->dy, b->dx);
      63               0 :     cairo_int64_t bdy_adx = _cairo_int32x32_64_mul (b->dy, a->dx);
      64                 :     int cmp;
      65                 : 
      66               0 :     cmp = _cairo_int64_cmp (ady_bdx, bdy_adx);
      67               0 :     if (cmp)
      68               0 :         return cmp;
      69                 : 
      70                 :     /* special-case zero vectors.  the intended logic here is:
      71                 :      * zero vectors all compare equal, and more positive than any
      72                 :      * non-zero vector.
      73                 :      */
      74               0 :     if (a->dx == 0 && a->dy == 0 && b->dx == 0 && b->dy ==0)
      75               0 :         return 0;
      76               0 :     if (a->dx == 0 && a->dy == 0)
      77               0 :         return 1;
      78               0 :     if (b->dx == 0 && b->dy ==0)
      79               0 :         return -1;
      80                 : 
      81                 :     /* Finally, we're looking at two vectors that are either equal or
      82                 :      * that differ by exactly pi. We can identify the "differ by pi"
      83                 :      * case by looking for a change in sign in either dx or dy between
      84                 :      * a and b.
      85                 :      *
      86                 :      * And in these cases, we eliminate the ambiguity by reducing the angle
      87                 :      * of b by an infinitesimally small amount, (that is, 'a' will
      88                 :      * always be considered less than 'b').
      89                 :      */
      90               0 :     if ((a->dx ^ b->dx) < 0 || (a->dy ^ b->dy) < 0) {
      91               0 :         if (a->dx > 0 || (a->dx == 0 && a->dy > 0))
      92               0 :             return +1;
      93                 :         else
      94               0 :             return -1;
      95                 :     }
      96                 : 
      97                 :     /* Finally, for identical slopes, we obviously return 0. */
      98               0 :     return 0;
      99                 : }

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