/* 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; | |

} |