cpml/cpml-close.c

   1 /* CPML - Cairo Path Manipulation Library
   2  * Copyright (C) 2008, 2009  Nicola Fontana <ntd at entidi.it>
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this library; if not, write to the
  16  * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  17  * Boston, MA  02110-1301, USA.
  18  */
  19
  20 /**
  21  * SECTION:close
  22  * @title: Closing path lines
  23  * @short_description: APIs to manage closing path virtual primitives
  24  *
  25  * The following functions manipulate %CAIRO_PATH_CLOSE_PATH
  26  * #CpmlPrimitive. No check is made on the primitive struct, so be
  27  * sure the <structname>CpmlPrimitive</structname> is effectively
  28  * a close operation before calling these APIs.
  29  *
  30  * This primitive management is almost identical to straight lines,
  31  * but taking properly start and end points.
  32  **/
  33
  34 #include "cpml-close.h"
  35 #include "cpml-pair.h"
  36
  37 /**
  38  * cpml_close_get_npoints:
  39  *
  40  * Returns the number of points needed to properly specify a close primitive.
  41  *
  42  * Return value: 1
  43  **/
  44 int
  45 cpml_close_get_npoints(void)
  46 {
  47     return 1;
  48 }
  49
  50 /**
  51  * cpml_close_pair_at:
  52  * @close: the #CpmlPrimitive close data
  53  * @pair: the destination pair
  54  * @pos:  the position value
  55  *
  56  * Given the @close path virtual primitive, finds the coordinates
  57  * at position @pos (where 0 is the start and 1 is the end) and
  58  * stores the result in @pair.
  59  *
  60  * @pos can be less than 0 or greater than 1, in which case the
  61  * coordinates are interpolated.
  62  **/
  63 void
  64 cpml_close_pair_at(CpmlPrimitive *close, CpmlPair *pair, double pos)
  65 {
  66     cairo_path_data_t *p1, *p2;
  67
  68     p1 = cpml_primitive_get_point(close, 0);
  69     p2 = cpml_primitive_get_point(close, -1);
  70
  71     pair->x = p1->point.x + (p1->point.x - p1->point.x) * pos;
  72     pair->y = p1->point.y + (p2->point.y - p1->point.y) * pos;
  73 }
  74
  75 /**
  76  * cpml_close_vector_at:
  77  * @close:  the #CpmlPrimitive close data
  78  * @vector: the destination vector
  79  * @pos:    the position value
  80  *
  81  * Gets the slope on @close at the position @pos. Being the
  82  * close a straight line, the vector is always the same, so
  83  * @pos is not used.
  84  **/
  85 void
  86 cpml_close_vector_at(CpmlPrimitive *close, CpmlVector *vector, double pos)
  87 {
  88     cairo_path_data_t *p1, *p2;
  89
  90     p1 = cpml_primitive_get_point(close, 0);
  91     p2 = cpml_primitive_get_point(close, -1);
  92
  93     vector->x = p2->point.x - p1->point.x;
  94     vector->y = p2->point.y - p1->point.y;
  95 }
  96
  97 /**
  98  * cpml_close_offset:
  99  * @close:  the #CpmlPrimitive close data
 100  * @offset: distance for the computed parallel close
 101  *
 102  * Given a close segment specified by the @close primitive data,
 103  * computes the parallel close distant @offset from the original one
 104  * and returns the result by changing @close.
 105  *
 106  * The algorithm is practically the same as the one used for
 107  * cpml_line_offset() but using the proper start and end coordinates.
 108  **/
 109 void
 110 cpml_close_offset(CpmlPrimitive *close, double offset)
 111 {
 112     cairo_path_data_t *p1, *p2;
 113     CpmlVector normal;
 114
 115     p1 = cpml_primitive_get_point(close, 0);
 116     p2 = cpml_primitive_get_point(close, -1);
 117
 118     cpml_close_vector_at(close, &normal, 0.);
 119     cpml_vector_normal(&normal);
 120     cpml_vector_set_length(&normal, offset);
 121
 122     p1->point.x += normal.x;
 123     p1->point.y += normal.y;
 124     p2->point.x += normal.x;
 125     p2->point.y += normal.y;
 126 }