chamfer.cpp

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/*
 * This program source code file is part of KiCad, a free EDA CAD application.
 *
 * Copyright (C) 2023 KiCad Developers, see AUTHORS.txt for contributors.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
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 * of the License, or (at your option) any later version.
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#include <geometry/chamfer.h>
 
std::optional<CHAMFER_RESULT> ComputeChamferPoints( const SEG& aSegA, const SEG& aSegB,
 const CHAMFER_PARAMS& aChamferParams )
{
 const int line_a_setback = aChamferParams.m_chamfer_setback_a;
 const int line_b_setback = aChamferParams.m_chamfer_setback_b;
 
 if( line_a_setback == 0 && line_b_setback == 0 )
 {
 // No chamfer to do
 // In theory a chamfer of 0 on one side is kind-of valid (adds a collinear point)
 // so allow it (using an and above, not an or)
 return std::nullopt;
 }
 
 if( aSegA.Length() < line_a_setback || aSegB.Length() < line_b_setback )
 {
 // Chamfer is too big for the line segments
 return std::nullopt;
 }
 
 // We only support the case where the lines intersect at the end points
 // otherwise we would need to decide which inside corner to chamfer
 
 // Figure out which end points are the ones at the intersection
 const VECTOR2I* a_pt = nullptr;
 const VECTOR2I* b_pt = nullptr;
 
 if( aSegA.A == aSegB.A )
 {
 a_pt = &aSegA.A;
 b_pt = &aSegB.A;
 }
 else if( aSegA.A == aSegB.B )
 {
 a_pt = &aSegA.A;
 b_pt = &aSegB.B;
 }
 else if( aSegA.B == aSegB.A )
 {
 a_pt = &aSegA.B;
 b_pt = &aSegB.A;
 }
 else if( aSegA.B == aSegB.B )
 {
 a_pt = &aSegA.B;
 b_pt = &aSegB.B;
 }
 
 if( !a_pt || !b_pt )
 {
 // No intersection found, so no chamfer to do
 return std::nullopt;
 }
 
 // These are the other existing line points (the ones that are not the intersection)
 const VECTOR2I& a_end_pt = ( &aSegA.A == a_pt ) ? aSegA.B : aSegA.A;
 const VECTOR2I& b_end_pt = ( &aSegB.A == b_pt ) ? aSegB.B : aSegB.A;
 
 // Now, construct segment of the set-back lengths, that begins
 // at the intersection point and is parallel to each line segments
 SEG setback_a( *a_pt, *b_pt + VECTOR2I( a_end_pt - *a_pt ).Resize( line_a_setback ) );
 SEG setback_b( *b_pt, *b_pt + VECTOR2I( b_end_pt - *b_pt ).Resize( line_b_setback ) );
 
 // The chamfer segment then goes between the end points of the set-back segments
 SEG chamfer( setback_a.B, setback_b.B );
 
 // The adjusted segments go from the old end points to the chamfer ends
 
 std::optional<SEG> new_a;
 
 if( a_end_pt != chamfer.A )
 new_a = SEG{ a_end_pt, chamfer.A };
 
 std::optional<SEG> new_b;
 
 if( b_end_pt != chamfer.B )
 new_b = SEG{ b_end_pt, chamfer.B };
 
 return CHAMFER_RESULT{ chamfer, new_a, new_b };
}