KiCad PCB EDA Suite
geometry_utils.cpp
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1 /*
2  * This program source code file is part of KiCad, a free EDA CAD application.
3  *
4  * Copyright (C) 2018 Jean-Pierre Charras, jp.charras at wanadoo.fr
5  * Copyright (C) 1992-2019 KiCad Developers, see AUTHORS.txt for contributors.
6  *
7  * This program is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU General Public License
9  * as published by the Free Software Foundation; either version 2
10  * of the License, or (at your option) any later version.
11  *
12  * This program is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License
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20  * or you may search the http://www.gnu.org website for the version 2 license,
21  * or you may write to the Free Software Foundation, Inc.,
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23  */
24 
30 #include <stdint.h> // for int64_t
31 #include <algorithm> // for max, min
32 
33 #include <eda_rect.h>
35 #include <math/util.h> // for KiROUND
36 
37 // To approximate a circle by segments, a minimal seg count is mandatory
38 #define MIN_SEGCOUNT_FOR_CIRCLE 6
39 
40 int GetArcToSegmentCount( int aRadius, int aErrorMax, double aArcAngleDegree )
41 {
42  // calculate the number of segments to approximate a circle by segments
43  // given the max distance between the middle of a segment and the circle
44 
45  // avoid divide-by-zero
46  aRadius = std::max( 1, aRadius );
47 
48  // error relative to the radius value:
49  double rel_error = (double)aErrorMax / aRadius;
50  // minimal arc increment in degrees:
51  double arc_increment = 180 / M_PI * acos( 1.0 - rel_error ) * 2;
52 
53  // Ensure a minimal arc increment reasonable value for a circle
54  // (360.0 degrees). For very small radius values, this is mandatory.
55  arc_increment = std::min( 360.0/MIN_SEGCOUNT_FOR_CIRCLE, arc_increment );
56 
57  int segCount = KiROUND( fabs( aArcAngleDegree ) / arc_increment );
58 
59  // Ensure at least one segment is used (can happen for small arcs)
60  return std::max( segCount, 1 );
61 }
62 
63 
64 double GetCircletoPolyCorrectionFactor( int aSegCountforCircle )
65 {
66  /* calculates the coeff to compensate radius reduction of circle
67  * due to the segment approx.
68  * For a circle the min radius is radius * cos( 2PI / aSegCountforCircle / 2)
69  * this is the distance between the center and the middle of the segment.
70  * therefore, to move the middle of the segment to the circle (distance = radius)
71  * the correctionFactor is 1 /cos( PI/aSegCountforCircle )
72  */
73  aSegCountforCircle = std::max( MIN_SEGCOUNT_FOR_CIRCLE, aSegCountforCircle );
74 
75  return 1.0 / cos( M_PI / aSegCountforCircle );
76 }
77 
78 
79 /***
80  * Utility for the line clipping code, returns the boundary code of
81  * a point. Bit allocation is arbitrary
82  */
83 inline int clipOutCode( const EDA_RECT *aClipBox, int x, int y )
84 {
85  int code;
86 
87  if( y < aClipBox->GetY() )
88  code = 2;
89  else if( y > aClipBox->GetBottom() )
90  code = 1;
91  else
92  code = 0;
93 
94  if( x < aClipBox->GetX() )
95  code |= 4;
96  else if( x > aClipBox->GetRight() )
97  code |= 8;
98 
99  return code;
100 }
101 
102 
103 bool ClipLine( const EDA_RECT *aClipBox, int &x1, int &y1, int &x2, int &y2 )
104 {
105  // Stock Cohen-Sutherland algorithm; check *any* CG book for details
106  int outcode1 = clipOutCode( aClipBox, x1, y1 );
107  int outcode2 = clipOutCode( aClipBox, x2, y2 );
108 
109  while( outcode1 || outcode2 )
110  {
111  // Fast reject
112  if( outcode1 & outcode2 )
113  return true;
114 
115  // Choose a side to clip
116  int thisoutcode, x, y;
117 
118  if( outcode1 )
119  thisoutcode = outcode1;
120  else
121  thisoutcode = outcode2;
122 
123  /* One clip round
124  * Since we use the full range of 32 bit ints, the proportion
125  * computation has to be done in 64 bits to avoid horrible
126  * results */
127  if( thisoutcode & 1 ) // Clip the bottom
128  {
129  y = aClipBox->GetBottom();
130  x = x1 + (x2 - x1) * int64_t(y - y1) / (y2 - y1);
131  }
132  else if( thisoutcode & 2 ) // Clip the top
133  {
134  y = aClipBox->GetY();
135  x = x1 + (x2 - x1) * int64_t(y - y1) / (y2 - y1);
136  }
137  else if( thisoutcode & 8 ) // Clip the right
138  {
139  x = aClipBox->GetRight();
140  y = y1 + (y2 - y1) * int64_t(x - x1) / (x2 - x1);
141  }
142  else // if( thisoutcode & 4), obviously, clip the left
143  {
144  x = aClipBox->GetX();
145  y = y1 + (y2 - y1) * int64_t(x - x1) / (x2 - x1);
146  }
147 
148  // Put the result back and update the boundary code
149  // No ambiguity, otherwise it would have been a fast reject
150  if( thisoutcode == outcode1 )
151  {
152  x1 = x;
153  y1 = y;
154  outcode1 = clipOutCode( aClipBox, x1, y1 );
155  }
156  else
157  {
158  x2 = x;
159  y2 = y;
160  outcode2 = clipOutCode( aClipBox, x2, y2 );
161  }
162  }
163  return false;
164 }
165 
int GetArcToSegmentCount(int aRadius, int aErrorMax, double aArcAngleDegree)
int clipOutCode(const EDA_RECT *aClipBox, int x, int y)
int GetX() const
Definition: eda_rect.h:111
int GetBottom() const
Definition: eda_rect.h:124
int GetRight() const
Definition: eda_rect.h:121
#define MIN_SEGCOUNT_FOR_CIRCLE
a few functions useful in geometry calculations.
bool ClipLine(const EDA_RECT *aClipBox, int &x1, int &y1, int &x2, int &y2)
Test if any part of a line falls within the bounds of a rectangle.
EDA_RECT handles the component boundary box.
Definition: eda_rect.h:44
int GetY() const
Definition: eda_rect.h:112
constexpr ret_type KiROUND(fp_type v)
Round a floating point number to an integer using "round halfway cases away from zero".
Definition: util.h:61
double GetCircletoPolyCorrectionFactor(int aSegCountforCircle)