teardrop_utils.cpp

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/*
 * This program source code file is part of KiCad, a free EDA CAD application.
 *
 * Copyright (C) 2021 Jean-Pierre Charras, jp.charras at wanadoo.fr
 * Copyright (C) 2023-2024 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
 * 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
 */
 
/*
 * Some calculations (mainly computeCurvedForRoundShape) are derived from
 * https://github.com/NilujePerchut/kicad_scripts/tree/master/teardrops
 */
 
#include <board_design_settings.h>
#include <pcb_track.h>
#include <pad.h>
#include <zone_filler.h>
#include <board_commit.h>
#include <drc/drc_rtree.h>
 
#include "teardrop.h"
#include <geometry/convex_hull.h>
#include <geometry/shape_line_chain.h>
#include <convert_basic_shapes_to_polygon.h>
#include <bezier_curves.h>
 
#include <wx/log.h>
 
 
void TRACK_BUFFER::AddTrack( PCB_TRACK* aTrack, int aLayer, int aNetcode )
{
    auto item = m_map_tracks.find( idxFromLayNet( aLayer, aNetcode ) );
    std::vector<PCB_TRACK*>* buffer;
 
    if( item == m_map_tracks.end() )
    {
        buffer = new std::vector<PCB_TRACK*>;
        m_map_tracks[idxFromLayNet( aLayer, aNetcode )] = buffer;
    }
    else
    {
        buffer = (*item).second;
    }
 
    buffer->push_back( aTrack );
}
 
 
int TEARDROP_MANAGER::GetWidth( BOARD_ITEM* aItem, PCB_LAYER_ID aLayer )
{
    if( aItem->Type() == PCB_VIA_T )
    {
        PCB_VIA* via = static_cast<PCB_VIA*>( aItem );
        return via->GetWidth( aLayer );
    }
    else if( aItem->Type() == PCB_PAD_T )
    {
        PAD* pad = static_cast<PAD*>( aItem );
        return std::min( pad->GetSize( aLayer ).x, pad->GetSize( aLayer ).y );
    }
    else if( aItem->Type() == PCB_TRACE_T || aItem->Type() == PCB_ARC_T )
    {
        PCB_TRACK* track = static_cast<PCB_TRACK*>( aItem );
        return track->GetWidth();
    }
 
    return 0;
}
 
 
bool TEARDROP_MANAGER::IsRound( BOARD_ITEM* aItem, PCB_LAYER_ID aLayer )
{
    if( aItem->Type() == PCB_PAD_T )
    {
        PAD* pad = static_cast<PAD*>( aItem );
 
        return pad->GetShape( aLayer ) == PAD_SHAPE::CIRCLE
               || ( pad->GetShape( aLayer ) == PAD_SHAPE::OVAL
                    && pad->GetSize( aLayer ).x
                               == pad->GetSize( aLayer ).y );
    }
 
    return true;
}
 
 
void TEARDROP_MANAGER::buildTrackCaches()
{
    for( PCB_TRACK* track : m_board->Tracks() )
    {
        if( track->Type() == PCB_TRACE_T || track->Type() == PCB_ARC_T )
        {
            m_tracksRTree.Insert( track, track->GetLayer() );
            m_trackLookupList.AddTrack( track, track->GetLayer(), track->GetNetCode() );
        }
    }
}
 
 
bool TEARDROP_MANAGER::areItemsInSameZone( BOARD_ITEM* aPadOrVia, PCB_TRACK* aTrack ) const
{
    for( ZONE* zone: m_board->Zones() )
    {
        // Skip teardrops
        if( zone->IsTeardropArea() )
            continue;
 
        // Only consider zones on the same layer
        if( !zone->IsOnLayer( aTrack->GetLayer() ) )
            continue;
 
        if( zone->GetNetCode() == aTrack->GetNetCode() )
        {
            if( zone->Outline()->Contains( VECTOR2I( aPadOrVia->GetPosition() ) ) )
            {
                // If the first item is a pad, ensure it can be connected to the zone
                if( aPadOrVia->Type() == PCB_PAD_T )
                {
                    PAD *pad = static_cast<PAD*>( aPadOrVia );
 
                    if( zone->GetPadConnection() == ZONE_CONNECTION::NONE
                        || pad->GetZoneConnectionOverrides( nullptr ) == ZONE_CONNECTION::NONE )
                    {
                        return false;
                    }
                }
 
                return true;
            }
        }
    }
 
    return false;
}
 
 
PCB_TRACK* TEARDROP_MANAGER::findTouchingTrack( EDA_ITEM_FLAGS& aMatchType, PCB_TRACK* aTrackRef,
                                                const VECTOR2I& aEndPoint ) const
{
    int matches = 0;                    // Count of candidates: only 1 is acceptable
    PCB_TRACK* candidate = nullptr;     // a reference to the track connected
 
    m_tracksRTree.QueryColliding( aTrackRef, aTrackRef->GetLayer(), aTrackRef->GetLayer(),
            // Filter:
            [&]( BOARD_ITEM* trackItem ) -> bool
            {
                return trackItem != aTrackRef;
            },
            // Visitor
            [&]( BOARD_ITEM* trackItem ) -> bool
            {
                PCB_TRACK* curr_track = static_cast<PCB_TRACK*>( trackItem );
 
                // IsPointOnEnds() returns 0, EDA_ITEM_FLAGS::STARTPOINT or EDA_ITEM_FLAGS::ENDPOINT
                if( EDA_ITEM_FLAGS match = curr_track->IsPointOnEnds( aEndPoint, m_tolerance ) )
                {
                    // if faced with a Y junction, choose the track longest segment as candidate
                    matches++;
 
                    if( matches > 1 )
                    {
                        double previous_len = candidate->GetLength();
                        double curr_len = curr_track->GetLength();
 
                        if( previous_len >= curr_len )
                            return true;
                    }
 
                    aMatchType = match;
                    candidate = curr_track;
                }
 
                return true;
            },
            0 );
 
    return candidate;
}
 
 
static VECTOR2D NormalizeVector( const VECTOR2I& aVector )
{
    VECTOR2D vect( aVector );
    double norm = vect.EuclideanNorm();
    return vect / norm;
}
 
 
/*
 * Compute the curve part points for teardrops connected to a round shape
 * The Bezier curve control points are optimized for a round pad/via shape,
 * and do not give a good curve shape for other pad shapes
 */
void TEARDROP_MANAGER::computeCurvedForRoundShape( const TEARDROP_PARAMETERS& aParams,
                                                   std::vector<VECTOR2I>& aPoly,
                                                   PCB_LAYER_ID aLayer,
                                                   int aTrackHalfWidth, const VECTOR2D& aTrackDir,
                                                   BOARD_ITEM* aOther, const VECTOR2I& aOtherPos,
                                                   std::vector<VECTOR2I>& pts ) const
{
    // in pts:
    // A and B are points on the track ( pts[0] and  pts[1] )
    // C and E are points on the aViaPad ( pts[2] and  pts[4] )
    // D is the aViaPad centre ( pts[3] )
    double Vpercent = aParams.m_BestWidthRatio;
    int td_height = KiROUND( GetWidth( aOther, aLayer ) * Vpercent );
 
    // First, calculate a aVpercent equivalent to the td_height clamped by aTdMaxHeight
    // We cannot use the initial aVpercent because it gives bad shape with points
    // on aViaPad calculated for a clamped aViaPad size
    if( aParams.m_TdMaxWidth > 0 && aParams.m_TdMaxWidth < td_height )
         Vpercent *= (double) aParams.m_TdMaxWidth / td_height;
 
    int radius = GetWidth( aOther, aLayer ) / 2;
 
    // Don't divide by zero.  No good can come of that.
    wxCHECK2( radius != 0, radius = 1 );
 
    double minVpercent = double( aTrackHalfWidth ) / radius;
    double weaken = (Vpercent - minVpercent) / ( 1 - minVpercent ) / radius;
 
    double biasBC = 0.5 * SEG( pts[1], pts[2] ).Length();
    double biasAE = 0.5 * SEG( pts[4], pts[0] ).Length();
 
    VECTOR2I vecC = (VECTOR2I)pts[2] - aOtherPos;
    VECTOR2I tangentC = VECTOR2I( pts[2].x - vecC.y * biasBC * weaken,
                                pts[2].y + vecC.x * biasBC * weaken );
    VECTOR2I vecE = (VECTOR2I)pts[4] - aOtherPos;
    VECTOR2I tangentE = VECTOR2I( pts[4].x + vecE.y * biasAE * weaken,
                                pts[4].y - vecE.x * biasAE * weaken );
 
    VECTOR2I tangentB = VECTOR2I( pts[1].x - aTrackDir.x * biasBC, pts[1].y - aTrackDir.y * biasBC );
    VECTOR2I tangentA = VECTOR2I( pts[0].x - aTrackDir.x * biasAE, pts[0].y - aTrackDir.y * biasAE );
 
    std::vector<VECTOR2I> curve_pts;
    BEZIER_POLY( pts[1], tangentB, tangentC, pts[2] ).GetPoly( curve_pts, ARC_HIGH_DEF );
 
    for( VECTOR2I& corner: curve_pts )
        aPoly.push_back( corner );
 
    aPoly.push_back( pts[3] );
 
    curve_pts.clear();
    BEZIER_POLY( pts[4], tangentE, tangentA, pts[0] ).GetPoly( curve_pts, ARC_HIGH_DEF );
 
    for( VECTOR2I& corner: curve_pts )
        aPoly.push_back( corner );
}
 
 
/*
 * Compute the curve part points for teardrops connected to a rectangular/polygonal shape
 * The Bezier curve control points are not optimized for a special shape
 */
void TEARDROP_MANAGER::computeCurvedForRectShape( const TEARDROP_PARAMETERS& aParams,
                                                  std::vector<VECTOR2I>& aPoly, int aTdWidth,
                                                  int aTrackHalfWidth,
                                                  std::vector<VECTOR2I>& aPts,
                                                  const VECTOR2I& aIntersection) const
{
    // in aPts:
    // A and B are points on the track ( pts[0] and pts[1] )
    // C and E are points on the pad/via ( pts[2] and pts[4] )
    // D is the aViaPad centre ( pts[3] )
 
    // side1 is( aPts[1], aPts[2] );  from track to via
    VECTOR2I side1( aPts[2] - aPts[1] );  // vector from track to via
    // side2 is ( aPts[4], aPts[0] ); from via to track
    VECTOR2I side2( aPts[4] - aPts[0] );  // vector from track to via
 
    VECTOR2I trackDir( aIntersection - ( aPts[0] + aPts[1] ) / 2 );
 
    std::vector<VECTOR2I> curve_pts;
 
    // Note: This side is from track to pad/via
    VECTOR2I ctrl1 = aPts[1] + trackDir.Resize( side1.EuclideanNorm() / 4 );
    VECTOR2I ctrl2 = ( aPts[2] + aIntersection ) / 2;
 
    BEZIER_POLY( aPts[1], ctrl1, ctrl2, aPts[2] ).GetPoly( curve_pts, ARC_HIGH_DEF );
 
    for( VECTOR2I& corner: curve_pts )
        aPoly.push_back( corner );
 
    aPoly.push_back( aPts[3] );
 
    // Note: This side is from pad/via to track
    curve_pts.clear();
 
    ctrl1 = ( aPts[4] + aIntersection ) / 2;
    ctrl2 = aPts[0] + trackDir.Resize( side2.EuclideanNorm() / 4 );
 
    BEZIER_POLY( aPts[4], ctrl1, ctrl2, aPts[0] ).GetPoly( curve_pts, ARC_HIGH_DEF );
 
    for( VECTOR2I& corner: curve_pts )
        aPoly.push_back( corner );
}
 
 
bool TEARDROP_MANAGER::computeAnchorPoints( const TEARDROP_PARAMETERS& aParams, PCB_LAYER_ID aLayer,
                                            BOARD_ITEM* aItem, const VECTOR2I& aPos,
                                            std::vector<VECTOR2I>& aPts ) const
{
    // Compute the 2 anchor points on pad/via/track of the teardrop shape
 
    SHAPE_POLY_SET c_buffer;
 
    // m_BestWidthRatio is the factor to calculate the teardrop preferred width.
    // teardrop width = pad, via or track size * m_BestWidthRatio (m_BestWidthRatio <= 1.0)
    // For rectangular (and similar) shapes, the preferred_width is calculated from the min
    // dim of the rectangle
 
    int preferred_width = KiROUND( GetWidth( aItem, aLayer ) * aParams.m_BestWidthRatio );
 
    // force_clip = true to force the pad/via/track polygon to be clipped to follow
    // constraints
    // Clipping is also needed for rectangular shapes, because the teardrop shape is restricted
    // to a polygonal area smaller than the pad area (the teardrop height use the smaller value
    // of X and Y sizes).
    bool force_clip = aParams.m_BestWidthRatio < 1.0;
 
    // To find the anchor points on the pad/via/track shape, we build the polygonal shape, and
    // clip the polygon to the max size (preferred_width or m_TdMaxWidth) by a rectangle
    // centered on the axis of the expected teardrop shape.
    // (only reduce the size of polygonal shape does not give good anchor points)
    if( IsRound( aItem, aLayer ) )
    {
        TransformCircleToPolygon( c_buffer, aPos, GetWidth( aItem, aLayer ) / 2, ARC_LOW_DEF,
                                  ERROR_INSIDE, 16 );
    }
    else    // Only PADS can have a not round shape
    {
        wxCHECK_MSG( aItem->Type() == PCB_PAD_T, false, wxT( "Expected non-round item to be PAD" ) );
        PAD* pad = static_cast<PAD*>( aItem );
 
        force_clip = true;
 
        preferred_width = KiROUND( GetWidth( pad, aLayer ) * aParams.m_BestWidthRatio );
        pad->TransformShapeToPolygon( c_buffer, aLayer, 0, ARC_LOW_DEF, ERROR_INSIDE );
    }
 
    // Clip the pad/via/track shape to match the m_TdMaxWidth constraint, and for non-round pads,
    // clip the shape to the smallest of size.x and size.y values.
    if( force_clip || ( aParams.m_TdMaxWidth > 0 && aParams.m_TdMaxWidth < preferred_width ) )
    {
        int halfsize = std::min( aParams.m_TdMaxWidth, preferred_width )/2;
 
        // teardrop_axis is the line from anchor point on the track and the end point
        // of the teardrop in the pad/via
        // this is the teardrop_axis of the teardrop shape to build
        VECTOR2I ref_on_track = ( aPts[0] + aPts[1] ) / 2;
        VECTOR2I teardrop_axis( aPts[3] - ref_on_track );
 
        EDA_ANGLE orient( teardrop_axis );
        int len = teardrop_axis.EuclideanNorm();
 
        // Build the constraint polygon: a rectangle with
        // length = dist between the point on track and the pad/via pos
        // height = m_TdMaxWidth or aViaPad.m_Width
        SHAPE_POLY_SET clipping_rect;
        clipping_rect.NewOutline();
 
        // Build a horizontal rect: it will be rotated later
        clipping_rect.Append( 0, - halfsize );
        clipping_rect.Append( 0, halfsize );
        clipping_rect.Append( len, halfsize );
        clipping_rect.Append( len, - halfsize );
 
        clipping_rect.Rotate( -orient );
        clipping_rect.Move( ref_on_track );
 
        // Clip the shape to the max allowed teadrop area
        c_buffer.BooleanIntersection( clipping_rect );
    }
 
    /* in aPts:
     * A and B are points on the track ( aPts[0] and  aPts[1] )
     * C and E are points on the aViaPad ( aPts[2] and  aPts[4] )
     * D is midpoint behind the aViaPad centre ( aPts[3] )
     */
 
    SHAPE_LINE_CHAIN& padpoly = c_buffer.Outline(0);
    std::vector<VECTOR2I> points = padpoly.CPoints();
 
    std::vector<VECTOR2I> initialPoints;
    initialPoints.push_back( aPts[0] );
    initialPoints.push_back( aPts[1] );
 
    for( const VECTOR2I& pt: points )
        initialPoints.emplace_back( pt.x, pt.y );
 
    std::vector<VECTOR2I> hull;
    BuildConvexHull( hull, initialPoints );
 
    // Search for end points of segments starting at aPts[0] or aPts[1]
    // In some cases, in convex hull, only one point (aPts[0] or aPts[1]) is still in list
    VECTOR2I PointC;
    VECTOR2I PointE;
    int found_start = -1;      // 2 points (one start and one end) should be found
    int found_end   = -1;
 
    VECTOR2I start = aPts[0];
    VECTOR2I pend  = aPts[1];
 
    for( unsigned ii = 0, jj = 0; jj < hull.size(); ii++, jj++ )
    {
        unsigned next = ii+ 1;
 
        if( next >= hull.size() )
            next = 0;
 
        int prev = ii -1;
 
        if( prev < 0 )
            prev = hull.size()-1;
 
        if( hull[ii] == start )
        {
            // the previous or the next point is candidate:
            if( hull[next] != pend )
                PointE = hull[next];
            else
                PointE = hull[prev];
 
            found_start = ii;
        }
 
        if( hull[ii] == pend )
        {
            if( hull[next] != start )
                PointC = hull[next];
            else
                PointC = hull[prev];
 
            found_end = ii;
        }
    }
 
    if( found_start < 0 )   // PointE was not initialized, because start point does not exit
    {
        int ii = found_end-1;
 
        if( ii < 0 )
            ii = hull.size()-1;
 
        PointE = hull[ii];
    }
 
    if( found_end < 0 )   // PointC was not initialized, because end point does not exit
    {
        int ii = found_start-1;
 
        if( ii < 0 )
            ii = hull.size()-1;
 
        PointC = hull[ii];
    }
 
    aPts[2] = PointC;
    aPts[4] = PointE;
 
    // Now we have to know if the choice aPts[2] = PointC is the best, or if
    // aPts[2] = PointE is better.
    // A criteria is to calculate the polygon area in these 2 cases, and choose the case
    // that gives the bigger area, because the segments starting at PointC and PointE
    // maximize their distance.
    SHAPE_LINE_CHAIN dummy1( aPts, true );
    double area1 = dummy1.Area();
 
    std::swap( aPts[2], aPts[4] );
    SHAPE_LINE_CHAIN dummy2( aPts, true );
    double area2 = dummy2.Area();
 
    if( area1 > area2 )     // The first choice (without swapping) is the better.
        std::swap( aPts[2], aPts[4] );
 
    return true;
}
 
 
bool TEARDROP_MANAGER::findAnchorPointsOnTrack( const TEARDROP_PARAMETERS& aParams,
                                                VECTOR2I& aStartPoint, VECTOR2I& aEndPoint,
                                                VECTOR2I& aIntersection, PCB_TRACK*& aTrack,
                                                BOARD_ITEM* aOther, const VECTOR2I& aOtherPos,
                                                int* aEffectiveTeardropLen ) const
{
    bool found = true;
    VECTOR2I start = aTrack->GetStart();    // one reference point on the track, inside teardrop
    VECTOR2I end = aTrack->GetEnd();        // the second reference point on the track, outside teardrop
    PCB_LAYER_ID layer = aTrack->GetLayer();
    int radius = GetWidth( aOther, layer ) / 2;
 
    // Requested length of the teardrop:
    int targetLength = KiROUND( GetWidth( aOther, layer ) * aParams.m_BestLengthRatio );
 
    if( aParams.m_TdMaxLen > 0 )
        targetLength = std::min( aParams.m_TdMaxLen, targetLength );
 
    // actualTdLen is the distance between start and the teardrop point on the segment from start to end
    int actualTdLen;
    bool need_swap = false;     // true if the start and end points of the current track are swapped
 
    // aTrack is expected to have one end inside the via/pad and the other end outside
    // so ensure the start point is inside the via/pad
    if( !aOther->HitTest( start, 0 ) )
    {
        std::swap( start, end );
        need_swap = true;
    }
 
    SHAPE_POLY_SET shapebuffer;
 
    if( IsRound( aOther, layer ) )
    {
        TransformCircleToPolygon( shapebuffer, aOtherPos, radius, ARC_LOW_DEF, ERROR_INSIDE, 16 );
    }
    else
    {
        wxCHECK_MSG( aOther->Type() == PCB_PAD_T, false, wxT( "Expected non-round item to be PAD" ) );
        static_cast<PAD*>( aOther )->TransformShapeToPolygon( shapebuffer, aTrack->GetLayer(), 0,
                                                              ARC_LOW_DEF, ERROR_INSIDE );
    }
 
    SHAPE_LINE_CHAIN& outline = shapebuffer.Outline(0);
    outline.SetClosed( true );
 
    // Search the intersection point between the pad/via shape and the current track
    // This this the starting point to define the teardrop length
    SHAPE_LINE_CHAIN::INTERSECTIONS pts;
    int pt_count;
 
    if( aTrack->Type() == PCB_ARC_T )
    {
        // To find the starting point we convert the arc to a polyline
        // and compute the intersection point with the pad/via shape
        SHAPE_ARC arc( aTrack->GetStart(), static_cast<PCB_ARC*>( aTrack )->GetMid(),
                       aTrack->GetEnd(), aTrack->GetWidth() );
 
        SHAPE_LINE_CHAIN poly = arc.ConvertToPolyline();
        pt_count = outline.Intersect( poly, pts );
    }
    else
    {
        pt_count = outline.Intersect( SEG( start, end ), pts );
    }
 
    // Ensure a intersection point was found, otherwise we cannot built the teardrop
    // using this track (it is fully outside or inside the pad/via shape)
    if( pt_count < 1 )
        return false;
 
    aIntersection = pts[0].p;
    start = aIntersection;      // This is currently the reference point of the teardrop length
 
    // actualTdLen for now the distance between start and the teardrop point on the (start end)segment
    // It cannot be bigger than the lenght of this segment
    actualTdLen = std::min( targetLength, SEG( start, end ).Length() );
    VECTOR2I ref_lenght_point = start;    // the reference point of actualTdLen
 
    // If the first track is too short to allow a teardrop having the requested length
    // explore the connected track(s), and try to find a anchor point at targetLength from initial start
    if( actualTdLen < targetLength && aParams.m_AllowUseTwoTracks )
    {
        int consumed = 0;
 
        while( actualTdLen + consumed < targetLength )
        {
            EDA_ITEM_FLAGS matchType;
 
            PCB_TRACK* connected_track = findTouchingTrack( matchType, aTrack, end );
 
            if( connected_track == nullptr )
                break;
 
            // TODO: stop if angle between old and new segment is > 45 deg to avoid bad shape
            consumed += actualTdLen;
            // actualTdLen is the new distance from new start point and the teardrop anchor point
            actualTdLen = std::min( targetLength-consumed, int( connected_track->GetLength() ) );
            aTrack = connected_track;
            end = connected_track->GetEnd();
            start = connected_track->GetStart();
            need_swap = false;
 
            if( matchType != STARTPOINT )
            {
                std::swap( start, end );
                need_swap = true;
            }
 
            // If we do not want to explore more than one connected track, stop search here
            break;
        }
    }
 
    // if aTrack is an arc, find the best teardrop end point on the arc
    // It is currently on the segment from arc start point to arc end point,
    // therefore not really on the arc, because we have used only the track end points.
    if( aTrack->Type() == PCB_ARC_T )
    {
        // To find the best start and end points to build the teardrop shape, we convert
        // the arc to segments, and search for the segment having its start point at a dist
        // < actualTdLen, and its end point at adist > actualTdLen:
        SHAPE_ARC arc( aTrack->GetStart(), static_cast<PCB_ARC*>( aTrack )->GetMid(),
                       aTrack->GetEnd(), aTrack->GetWidth() );
 
        if( need_swap )
            arc.Reverse();
 
        SHAPE_LINE_CHAIN poly = arc.ConvertToPolyline();
 
        // Now, find the segment of the arc at a distance < actualTdLen from ref_lenght_point.
        // We just search for the first segment (starting from the farest segment) with its
        // start point at a distance < actualTdLen dist
        // This is basic, but it is probably enough.
        if( poly.PointCount() > 2 )
        {
            // Note: the first point is inside or near the pad/via shape
            // The last point is outside and the farest from the ref_lenght_point
            // So we explore segments from the last to the first
            for( int ii = poly.PointCount()-1; ii >= 0 ; ii-- )
            {
                int dist_from_start = ( poly.CPoint( ii ) - start ).EuclideanNorm();
 
                // The first segment at a distance of the reference point < actualTdLen is OK
                // and is suitable to define the reference segment of the teardrop anchor.
                if( dist_from_start < actualTdLen || ii == 0 )
                {
                    start = poly.CPoint( ii );
 
                    if( ii < poly.PointCount()-1 )
                        end = poly.CPoint( ii+1 );
 
                    // actualTdLen is the distance between start (the reference segment start point)
                    // and the point on track of the teardrop.
                    // This is the difference between the initial actualTdLen value and the
                    // distance between start and ref_lenght_point.
                    actualTdLen -= (start - ref_lenght_point).EuclideanNorm();
 
                    // Ensure validity of actualTdLen: >= 0, and <= segment lenght
                    if( actualTdLen < 0 )   // should not happen, but...
                        actualTdLen = 0;
 
                    actualTdLen = std::min( actualTdLen, (end - start).EuclideanNorm() );
 
                    break;
                }
            }
        }
    }
 
    // aStartPoint and aEndPoint will define later a segment to build the 2 anchors points
    // of the teardrop on the aTrack shape.
    // they are two points (both outside the pad/via shape) of aTrack if aTrack is a segment,
    // or a small segment on aTrack if aTrack is an ARC
    aStartPoint = start;
    aEndPoint = end;
 
    *aEffectiveTeardropLen = actualTdLen;
    return found;
}
 
 
bool TEARDROP_MANAGER::computeTeardropPolygon( const TEARDROP_PARAMETERS& aParams,
                                               std::vector<VECTOR2I>& aCorners, PCB_TRACK* aTrack,
                                               BOARD_ITEM* aOther, const VECTOR2I& aOtherPos ) const
{
    VECTOR2I start, end;    // Start and end points of the track anchor of the teardrop
                            // the start point is inside the teardrop shape
                            // the end point is outside.
    VECTOR2I intersection;  // Where the track centerline intersects the pad/via edge
    int track_stub_len;     // the dist between the start point and the anchor point
                            // on the track
 
    // Note: aTrack can be modified if the initial track is too short
    if( !findAnchorPointsOnTrack( aParams, start, end, intersection, aTrack, aOther, aOtherPos,
                                  &track_stub_len ) )
    {
        return false;
    }
 
    // The start and end points must be different to calculate a valid polygon shape
    if( start == end )
        return false;
 
    VECTOR2D vecT = NormalizeVector(end - start);
 
    // find the 2 points on the track, sharp end of the teardrop
    int track_halfwidth = aTrack->GetWidth() / 2;
    VECTOR2I pointB = start + VECTOR2I( vecT.x * track_stub_len + vecT.y * track_halfwidth,
                                        vecT.y * track_stub_len - vecT.x * track_halfwidth );
    VECTOR2I pointA = start + VECTOR2I( vecT.x * track_stub_len - vecT.y * track_halfwidth,
                                        vecT.y * track_stub_len + vecT.x * track_halfwidth );
 
    PCB_LAYER_ID layer = aTrack->GetLayer();
 
    // To build a polygonal valid shape pointA and point B must be outside the pad
    // It can be inside with some pad shapes having very different X and X sizes
    if( !IsRound( aOther, layer ) )
    {
        PAD* pad = static_cast<PAD*>( aOther );
 
        if( pad->HitTest( pointA ) )
            return false;
 
        if( pad->HitTest( pointB ) )
            return false;
    }
 
    // Introduce a last point to cover the via centre to ensure it is seen as connected
    VECTOR2I pointD = aOtherPos;
    // add a small offset in order to have the aViaPad.m_Pos reference point inside
    // the teardrop area, just in case...
    int offset = pcbIUScale.mmToIU( 0.001 );
    pointD += VECTOR2I( int( -vecT.x*offset), int(-vecT.y*offset) );
 
    VECTOR2I pointC, pointE;     // Point on pad/via outlines
    std::vector<VECTOR2I> pts = { pointA, pointB, pointC, pointD, pointE };
 
    computeAnchorPoints( aParams, aTrack->GetLayer(), aOther, aOtherPos, pts );
 
    if( !aParams.IsCurved() )
    {
        aCorners = pts;
        return true;
    }
 
    // See if we can use curved teardrop shape
    if( IsRound( aOther, layer ) )
    {
        computeCurvedForRoundShape( aParams, aCorners, layer, track_halfwidth, vecT, aOther, aOtherPos, pts );
    }
    else
    {
        int td_width = KiROUND( GetWidth( aOther, layer ) * aParams.m_BestWidthRatio );
 
        if( aParams.m_TdMaxWidth > 0 && aParams.m_TdMaxWidth < td_width )
            td_width = aParams.m_TdMaxWidth;
 
        computeCurvedForRectShape( aParams, aCorners, td_width, track_halfwidth, pts, intersection );
    }
 
    return true;
}