outline_decomposer.cpp

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/*
 * This program source code file is part of KICAD, a free EDA CAD application.
 *
 * Copyright (C) 2021 Ola Rinta-Koski <[email protected]>
 * Copyright (C) 2021 Kicad Developers, see AUTHORS.txt for contributors.
 *
 * Outline font class
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, you may find one here:
 * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 * or you may search the http://www.gnu.org website for the version 2 license,
 * or you may write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
#include <font/outline_decomposer.h>
#include <bezier_curves.h>
 
using namespace KIFONT;
 
OUTLINE_DECOMPOSER::OUTLINE_DECOMPOSER( FT_Outline& aOutline ) :
 m_outline( aOutline ),
 m_contours( nullptr )
{
}
 
 
static VECTOR2D toVector2D( const FT_Vector* aFreeTypeVector )
{
 return VECTOR2D( aFreeTypeVector->x * GLYPH_SIZE_SCALER,
 aFreeTypeVector->y * GLYPH_SIZE_SCALER );
}
 
 
void OUTLINE_DECOMPOSER::newContour()
{
 CONTOUR contour;
 contour.m_Orientation = FT_Outline_Get_Orientation( &m_outline );
 m_contours->push_back( contour );
}
 
 
void OUTLINE_DECOMPOSER::addContourPoint( const VECTOR2D& p )
{
 // don't add repeated points
 if( m_contours->back().m_Points.empty() || m_contours->back().m_Points.back() != p )
 m_contours->back().m_Points.push_back( p );
}
 
 
int OUTLINE_DECOMPOSER::moveTo( const FT_Vector* aEndPoint, void* aCallbackData )
{
 OUTLINE_DECOMPOSER* decomposer = static_cast<OUTLINE_DECOMPOSER*>( aCallbackData );
 
 decomposer->m_lastEndPoint = toVector2D( aEndPoint );
 
 decomposer->newContour();
 decomposer->addContourPoint( decomposer->m_lastEndPoint );
 
 return 0;
}
 
 
int OUTLINE_DECOMPOSER::lineTo( const FT_Vector* aEndPoint, void* aCallbackData )
{
 OUTLINE_DECOMPOSER* decomposer = static_cast<OUTLINE_DECOMPOSER*>( aCallbackData );
 
 decomposer->m_lastEndPoint = toVector2D( aEndPoint );
 
 decomposer->addContourPoint( decomposer->m_lastEndPoint );
 
 return 0;
}
 
 
int OUTLINE_DECOMPOSER::quadraticTo( const FT_Vector* aControlPoint, const FT_Vector* aEndPoint,
 void* aCallbackData )
{
 return cubicTo( aControlPoint, nullptr, aEndPoint, aCallbackData );
}
 
 
int OUTLINE_DECOMPOSER::cubicTo( const FT_Vector* aFirstControlPoint,
 const FT_Vector* aSecondControlPoint, const FT_Vector* aEndPoint,
 void* aCallbackData )
{
 OUTLINE_DECOMPOSER* decomposer = static_cast<OUTLINE_DECOMPOSER*>( aCallbackData );
 
 GLYPH_POINTS bezier;
 bezier.push_back( decomposer->m_lastEndPoint );
 bezier.push_back( toVector2D( aFirstControlPoint ) );
 
 if( aSecondControlPoint )
 {
 // aSecondControlPoint == nullptr for quadratic Beziers
 bezier.push_back( toVector2D( aSecondControlPoint ) );
 }
 
 bezier.push_back( toVector2D( aEndPoint ) );
 
 GLYPH_POINTS result;
 decomposer->approximateBezierCurve( result, bezier );
 for( const VECTOR2D& p : result )
 decomposer->addContourPoint( p );
 
 decomposer->m_lastEndPoint = toVector2D( aEndPoint );
 
 return 0;
}
 
 
void OUTLINE_DECOMPOSER::OutlineToSegments( CONTOURS* aContours )
{
 m_contours = aContours;
 
 FT_Outline_Funcs callbacks;
 
 callbacks.move_to = moveTo;
 callbacks.line_to = lineTo;
 callbacks.conic_to = quadraticTo;
 callbacks.cubic_to = cubicTo;
 callbacks.shift = 0;
 callbacks.delta = 0;
 
 FT_Error e = FT_Outline_Decompose( &m_outline, &callbacks, this );
 
 if( e )
 {
 // TODO: handle error != 0
 }
 
 for( CONTOUR& c : *m_contours )
 c.m_Winding = winding( c.m_Points );
}
 
 
// use converter in kimath
bool OUTLINE_DECOMPOSER::approximateQuadraticBezierCurve( GLYPH_POINTS& aResult,
 const GLYPH_POINTS& aBezier ) const
{
 wxASSERT( aBezier.size() == 3 );
 
 // BEZIER_POLY only handles cubic Bezier curves, even though the
 // comments say otherwise...
 //
 // Quadratic to cubic Bezier conversion:
 // cpn = Cubic Bezier control points (n = 0..3, 4 in total)
 // qpn = Quadratic Bezier control points (n = 0..2, 3 in total)
 // cp0 = qp0, cp1 = qp0 + 2/3 * (qp1 - qp0), cp2 = qp2 + 2/3 * (qp1 - qp2), cp3 = qp2
 
 GLYPH_POINTS cubic;
 cubic.reserve( 4 );
 
 cubic.push_back( aBezier[0] ); // cp0
 cubic.push_back( aBezier[0] + ( ( aBezier[1] - aBezier[0] ) * 2 / 3 ) ); // cp1
 cubic.push_back( aBezier[2] + ( ( aBezier[1] - aBezier[2] ) * 2 / 3 ) ); // cp2
 cubic.push_back( aBezier[2] ); // cp3
 
 return approximateCubicBezierCurve( aResult, cubic );
}
 
 
bool OUTLINE_DECOMPOSER::approximateCubicBezierCurve( GLYPH_POINTS& aResult,
 const GLYPH_POINTS& aCubicBezier ) const
{
 wxASSERT( aCubicBezier.size() == 4 );
 
 // minimumSegmentLength defines the "smoothness" of the
 // curve-to-straight-segments conversion: the larger, the coarser
 // TODO: find out what the minimum segment length should really be!
 constexpr int minimumSegmentLength = 10;
 BEZIER_POLY converter( aCubicBezier );
 converter.GetPoly( aResult, minimumSegmentLength );
 
 return true;
}
 
 
bool OUTLINE_DECOMPOSER::approximateBezierCurve( GLYPH_POINTS& aResult,
 const GLYPH_POINTS& aBezier ) const
{
 switch( aBezier.size() )
 {
 case 4: // cubic
 return approximateCubicBezierCurve( aResult, aBezier );
 break;
 case 3: // quadratic
 return approximateQuadraticBezierCurve( aResult, aBezier );
 break;
 default:
 // error, only 3 and 4 are acceptable values
 return false;
 }
}
 
 
int OUTLINE_DECOMPOSER::winding( const GLYPH_POINTS& aContour ) const
{
 // -1 == counterclockwise, 1 == clockwise
 
 const int cw = 1;
 const int ccw = -1;
 
 if( aContour.size() < 2 )
 {
 // zero or one points, so not a clockwise contour - in fact not a contour at all
 //
 // It could also be argued that a contour needs 3 extremum points at a minimum to be
 // considered a proper contour (ie. a glyph (subpart) outline, or a hole)
 return 0;
 }
 
 double sum = 0.0;
 size_t len = aContour.size();
 
 for( size_t i = 0; i < len - 1; i++ )
 {
 VECTOR2D p1 = aContour[ i ];
 VECTOR2D p2 = aContour[ i + 1 ];
 
 sum += ( ( p2.x - p1.x ) * ( p2.y + p1.y ) );
 }
 
 sum += ( ( aContour[0].x - aContour[len - 1].x ) * ( aContour[0].y + aContour[len - 1].y ) );
 
 if( sum > 0.0 )
 return cw;
 if( sum < 0.0 )
 return ccw;
 
 return 0;
}