/// <summary>
/// Classifies an edge w.r.t a plane, adding it to inFrontEdges or behindEdges. If the plane intersects the edge, it's split,
/// and the two resulting edges are added to inFrontEdges or behindEdges instead
/// </summary>
private static void ClassifyEdge( Plane2 plane, Edge edge, ICollection< Edge > inFrontEdges, ICollection< Edge > behindEdges )
{
PlaneClassification startClass = plane.ClassifyPoint( edge.Start, OnPlaneTolerance );
PlaneClassification endClass = plane.ClassifyPoint( edge.End, OnPlaneTolerance );
if ( startClass == PlaneClassification.On )
{
startClass = endClass;
}
if ( endClass == PlaneClassification.On )
{
endClass = startClass;
}
if ( startClass == endClass )
{
// Edge endpoints on the same side of the splitter plane - no split required
if ( startClass == PlaneClassification.Behind )
{
AddEdge( behindEdges, edge );
}
else if ( startClass == PlaneClassification.InFront )
{
AddEdge( inFrontEdges, edge );
}
// Don't care about edges that are on the splitter plane
return;
}
Point2 midPt = Intersections2.GetLinePlaneIntersection( edge.Start, edge.End, plane ).IntersectionPosition;
Edge startToMid = new Edge( edge.Start, midPt, edge.IsDoubleSided, edge.SourceEdge );
Edge midToEnd = new Edge( midPt, edge.End, edge.IsDoubleSided, edge.SourceEdge );
if ( startClass == PlaneClassification.Behind )
{
AddEdge( behindEdges, startToMid );
AddEdge( inFrontEdges, midToEnd );
}
else
{
AddEdge( inFrontEdges, startToMid );
AddEdge( behindEdges, midToEnd );
}
}
/// <summary>
/// Splits a source polygon along a plane, returning the sub-poly behind the plane in "behind"
/// and the sub-poly in-front of the plane in "inFront"
/// </summary>
public void Split( Plane2 plane, Polygon source, out Polygon behind, out Polygon inFront )
{
float tolerance = 0.001f;
int firstDefiniteClassIndex = -1;
PlaneClassification[] classifications = new PlaneClassification[ source.Indices.Length ];
for ( int index = 0; index < source.Indices.Length; ++index )
{
classifications[ index ] = plane.ClassifyPoint( m_Points[ source.Indices[ index ] ], tolerance );
if ( ( firstDefiniteClassIndex == -1 ) && ( classifications[ index ] != PlaneClassification.On ) )
{
firstDefiniteClassIndex = index;
}
}
if ( firstDefiniteClassIndex > 1 )
{
// The first two points are on the split plane. This means that we
// can easily classify the polygon as either behind or in front depending on the first
// definite class
if ( classifications[ firstDefiniteClassIndex ] == PlaneClassification.Behind )
{
behind = new Polygon( source.Indices );
inFront = null;
}
else
{
behind = null;
inFront = new Polygon( source.Indices );
}
return;
}
int lastPtIndex = firstDefiniteClassIndex;
int curPtIndex = ( lastPtIndex + 1 ) % source.Indices.Length;
Point2 lastPt = m_Points[ source.Indices[ lastPtIndex ] ];
PlaneClassification lastClass = classifications[ lastPtIndex ];
List< int > behindPoints = new List< int >( source.Indices.Length + 2 );
List< int > inFrontPoints = new List< int >( source.Indices.Length + 2 );
for ( int count = 0; count < source.Indices.Length; ++count )
{
Point2 curPt = m_Points[ source.Indices[ curPtIndex ] ];
PlaneClassification curClass = classifications[ curPtIndex ];
if ( curClass == PlaneClassification.On )
{
curClass = lastClass;
}
if ( curClass != lastClass )
{
// Split line on plane
Line2Intersection intersection = Intersections2.GetLinePlaneIntersection( lastPt, curPt, plane );
int newPtIndex = AddPoint( intersection.IntersectionPosition );
behindPoints.Add( newPtIndex );
inFrontPoints.Add( newPtIndex );
}
if ( curClass == PlaneClassification.Behind )
{
behindPoints.Add( source.Indices[ curPtIndex ] );
}
else
{
inFrontPoints.Add( source.Indices[ curPtIndex ] );
}
lastClass = curClass;
lastPt = curPt;
curPtIndex = ( curPtIndex + 1 ) % source.Indices.Length;
}
behind = ( behindPoints.Count == 0 ) ? null : new Polygon( behindPoints.ToArray( ) );
inFront = ( inFrontPoints.Count == 0 ) ? null : new Polygon( inFrontPoints.ToArray( ) );
}