Edge cut tool (#3629)

engine/Sandbox.Engine/Scene/Components/Mesh/PolygonMesh.cs

@@ -620,7 +620,7 @@ public sealed partial class PolygonMesh : IJsonConvert
 		pOutVertexB = GetVertexPosition( hVertexB );
 	}
 
-	private bool AreEdgesCoLinear( HalfEdgeHandle hEdgeA, HalfEdgeHandle hEdgeB, float flAngleToleranceInDegrees )
+	public bool AreEdgesCoLinear( HalfEdgeHandle hEdgeA, HalfEdgeHandle hEdgeB, float flAngleToleranceInDegrees )
 	{
 		float flTolerance = MathF.Cos( MathF.Min( flAngleToleranceInDegrees, 180.0f ).DegreeToRadian() );
 
@@ -653,6 +653,13 @@ public sealed partial class PolygonMesh : IJsonConvert
 		IsDirty = true;
 	}
 
+	public void DissolveEdge( HalfEdgeHandle edge )
+	{
+		Topology.DissolveEdge( edge, out _ );
+
+		IsDirty = true;
+	}
+
 	public void DissolveEdges( IReadOnlyList<HalfEdgeHandle> edges, bool bFaceMustBePlanar, DissolveRemoveVertexCondition removeCondition )
 	{
 		const float flColinearTolerance = 5.0f; // Edges may be at an angle of up to this many degrees and still be considered co-linear
@@ -727,6 +734,68 @@ public sealed partial class PolygonMesh : IJsonConvert
 		IsDirty = true;
 	}
 
+	public bool ComputeClosestPointOnEdge( VertexHandle hVertexA, VertexHandle hVertexB, Vector3 vTargetPoint, out float pOutBaseEdgeParam )
+	{
+		pOutBaseEdgeParam = 0.0f;
+		var hEdge = FindEdgeConnectingVertices( hVertexA, hVertexB );
+		if ( hEdge == HalfEdgeHandle.Invalid )
+			return false;
+
+		var vEdgePositions = new Vector3[2];
+		vEdgePositions[0] = GetVertexPosition( hVertexA );
+		vEdgePositions[1] = GetVertexPosition( hVertexB );
+		int nNumPositions = vEdgePositions.Length;
+
+		float flEdgeLength = 0.0f;
+		for ( int iPos = 1; iPos < nNumPositions; ++iPos )
+		{
+			flEdgeLength += vEdgePositions[iPos - 1].Distance( vEdgePositions[iPos] );
+		}
+
+		Vector3 vClosestPointOnEdge = Vector3.Zero;
+		float flClosestPointParam = 0.0f;
+		float flMinDistanceSqr = float.MaxValue;
+		float flClosestSegmentParam = 0.0f;
+		float flBaseEdgeParam = 0.0f;
+		int nClosestSegment = -1;
+
+		float flSegmentStart = 0.0f;
+		for ( int iPos = 1; iPos < nNumPositions; ++iPos )
+		{
+			var vEdgePosA = vEdgePositions[iPos - 1];
+			var vEdgePosB = vEdgePositions[iPos];
+
+			var vSegment = vEdgePosB - vEdgePosA;
+			float flSegmentLength = vSegment.Length;
+			float flSegmentEnd = flSegmentStart + flSegmentLength;
+
+			CalcClosestPointOnLineSegment( vTargetPoint, vEdgePosA, vEdgePosB, out var vClosestPointOnSegment, out var flSegmentParam );
+
+			float flDistSqr = vClosestPointOnSegment.DistanceSquared( vTargetPoint );
+			if ( flDistSqr < flMinDistanceSqr )
+			{
+				flMinDistanceSqr = flDistSqr;
+				vClosestPointOnEdge = vClosestPointOnSegment;
+				flClosestSegmentParam = flSegmentParam;
+				nClosestSegment = iPos - 1;
+				float flPointDistance = flSegmentStart + flSegmentParam * flSegmentLength;
+				flClosestPointParam = flPointDistance / flEdgeLength;
+
+				flBaseEdgeParam = MathX.Lerp( (iPos - 1) / (float)(nNumPositions - 1), iPos / (float)(nNumPositions - 1), flSegmentParam );
+			}
+
+			flSegmentStart = flSegmentEnd;
+		}
+
+		Assert.True( nClosestSegment >= 0 );
+		if ( nClosestSegment < 0 )
+			return false;
+
+		pOutBaseEdgeParam = flBaseEdgeParam;
+
+		return true;
+	}
+
 	private void RemoveVerticesFromColinearEdgesInFace( FaceHandle hFace, float flColinearAngleTolerance )
 	{
 		// Get all of the vertices in the face
@@ -743,23 +812,192 @@ public sealed partial class PolygonMesh : IJsonConvert
 		}
 	}
 
-	private bool RemoveColinearVertex( VertexHandle hVertex, float flColinearAngleTolerance )
+	bool RemoveColinearVertex( VertexHandle hVertex, float flColinearAngleTolerance )
+	{
+		return RemoveColinearVertexAndUpdateTable( hVertex, null, flColinearAngleTolerance );
+	}
+
+	public bool RemoveColinearVertexAndUpdateTable( VertexHandle hVertex, SortedSet<HalfEdgeHandle> edgeTable, float flColinearAngleTolerance = 5.0f )
 	{
 		Topology.GetFullEdgesConnectedToVertex( hVertex, out var edgesConnectedToVertex );
 
-		if ( edgesConnectedToVertex.Count == 2 )
+		if ( edgesConnectedToVertex is not null && edgesConnectedToVertex.Count == 2 )
 		{
 			if ( AreEdgesCoLinear( edgesConnectedToVertex[0], edgesConnectedToVertex[1], flColinearAngleTolerance ) )
 			{
+				// Were either of the edges in the table
+				bool bEdgeInTable = false;
+				if ( edgeTable is not null )
+				{
+					if ( edgeTable.Contains( edgesConnectedToVertex[0] ) ||
+						 edgeTable.Contains( edgesConnectedToVertex[1] ) )
+					{
+						bEdgeInTable = true;
+					}
+				}
+
+				// Get the vertices at the ends of each edge opposite the vertex about to be removed.
+				GetVerticesConnectedToEdge( edgesConnectedToVertex[0], out var hVertexA, out var hVertexB );
+				var hVertex0 = (hVertexA == hVertex) ? hVertexB : hVertexA;
+
+				GetVerticesConnectedToEdge( edgesConnectedToVertex[1], out hVertexA, out hVertexB );
+				var hVertex1 = (hVertexA == hVertex) ? hVertexB : hVertexA;
+
 				// Remove the vertex, combining the two edges into a single edge
 				if ( Topology.RemoveVertex( hVertex, true ) )
+				{
+					// Remove the two old edges from the table and add the new edge
+					if ( bEdgeInTable )
+					{
+						edgeTable.Remove( edgesConnectedToVertex[0] );
+						edgeTable.Remove( edgesConnectedToVertex[1] );
+						var hCombinedEdge = FindEdgeConnectingVertices( hVertex0, hVertex1 );
+						if ( hCombinedEdge != HalfEdgeHandle.Invalid )
+						{
+							edgeTable.Add( hCombinedEdge );
+						}
+					}
+
 					return true;
+				}
 			}
 		}
 
 		return false;
 	}
 
+	public bool GetEdgesConnectedToVertex( VertexHandle hVertex, out List<HalfEdgeHandle> edges )
+	{
+		return Topology.GetFullEdgesConnectedToVertex( hVertex, out edges );
+	}
+
+	static float CalcClosestPointToLineT( Vector3 P, Vector3 vLineA, Vector3 vLineB, out Vector3 vDir )
+	{
+		vDir = vLineB - vLineA;
+		var div = vDir.Dot( vDir );
+		return div < 0.00001f ? 0.0f : (vDir.Dot( P ) - vDir.Dot( vLineA )) / div;
+	}
+
+	static void CalcClosestPointOnLine( Vector3 P, Vector3 vLineA, Vector3 vLineB, out Vector3 vClosest, out float outT )
+	{
+		outT = CalcClosestPointToLineT( P, vLineA, vLineB, out var vDir );
+		vClosest = vLineA + vDir * outT;
+	}
+
+	public VertexHandle CreateEdgesConnectingVertexToPoint( VertexHandle hStartVertex, Vector3 vTargetPosition, out List<HalfEdgeHandle> pOutEdgeList, out bool pOutIsLastEdgeConnector, SortedSet<HalfEdgeHandle> pEdgeTable )
+	{
+		const float flTolerance = 0.001f;
+
+		pOutEdgeList = [];
+		pOutIsLastEdgeConnector = false;
+
+		var hCurrentVertex = hStartVertex;
+		var hTargetVertex = VertexHandle.Invalid;
+
+		while ( hTargetVertex == VertexHandle.Invalid )
+		{
+			var hNextVertex = VertexHandle.Invalid;
+
+			if ( FindCutEdgeIntersection( hCurrentVertex, vTargetPosition, out var hIntersectionEdge, out var hIntersectionFace, out var vIntersectionPoint ) )
+			{
+				GetVerticesConnectedToEdge( hIntersectionEdge, out var hVertexA, out var hVertexB );
+
+				var vPositionA = GetVertexPosition( hVertexA );
+				var vPositionB = GetVertexPosition( hVertexB );
+
+				CalcClosestPointOnLineSegment( vIntersectionPoint, vPositionA, vPositionB, out _, out var flParam );
+
+				if ( flParam < flTolerance )
+				{
+					hNextVertex = hVertexA;
+				}
+				else if ( flParam > (1.0f - flTolerance) )
+				{
+					hNextVertex = hVertexB;
+				}
+				else
+				{
+					AddVertexToEdgeAndUpdateTable( hVertexA, hVertexB, flParam, out hNextVertex, pEdgeTable );
+				}
+			}
+
+			if ( hNextVertex == VertexHandle.Invalid )
+				break;
+
+			var hTargetEdges = new HalfEdgeHandle[2];
+			hTargetEdges[0] = FindEdgeConnectingVertices( hCurrentVertex, hNextVertex );
+			hTargetEdges[1] = HalfEdgeHandle.Invalid;
+
+			if ( hTargetEdges[0] == HalfEdgeHandle.Invalid )
+			{
+				if ( IsLineBetweenVerticesInsideFace( hIntersectionFace, hCurrentVertex, hNextVertex ) )
+				{
+					AddEdgeToFace( hIntersectionFace, hCurrentVertex, hNextVertex, out hTargetEdges[0] );
+				}
+
+				if ( pEdgeTable is not null && (hTargetEdges[0] != HalfEdgeHandle.Invalid) )
+				{
+					pEdgeTable.Add( hTargetEdges[0] );
+				}
+			}
+
+			if ( hTargetEdges[0] != HalfEdgeHandle.Invalid )
+			{
+				var vPositionA = GetVertexPosition( hCurrentVertex );
+				var vPositionB = GetVertexPosition( hNextVertex );
+
+				CalcClosestPointOnLine( vTargetPosition, vPositionA, vPositionB, out _, out var flParam );
+				if ( (flParam > -flTolerance) && (flParam < (1.0f + flTolerance)) )
+				{
+					if ( flParam < flTolerance )
+					{
+						hTargetVertex = hCurrentVertex;
+					}
+					else if ( flParam > (1.0f - flTolerance) )
+					{
+						hTargetVertex = hNextVertex;
+					}
+					else
+					{
+						if ( AddVertexToEdgeAndUpdateTable( hCurrentVertex, hNextVertex, flParam, out hTargetVertex, pEdgeTable ) )
+						{
+							hTargetEdges[0] = FindEdgeConnectingVertices( hCurrentVertex, hTargetVertex );
+							hTargetEdges[1] = FindEdgeConnectingVertices( hTargetVertex, hNextVertex );
+
+							if ( pEdgeTable is not null && pEdgeTable.Contains( hTargetEdges[1] ) )
+							{
+								pOutIsLastEdgeConnector = true;
+							}
+						}
+						else
+						{
+							Assert.True( hTargetVertex != VertexHandle.Invalid );
+							break;
+						}
+					}
+				}
+			}
+
+			if ( hTargetEdges[0] != HalfEdgeHandle.Invalid )
+			{
+				pOutEdgeList.Add( hTargetEdges[0] );
+			}
+			if ( hTargetEdges[1] != HalfEdgeHandle.Invalid )
+			{
+				pOutEdgeList.Add( hTargetEdges[1] );
+			}
+
+			Assert.True( hNextVertex != hStartVertex );
+			Assert.True( hNextVertex != hCurrentVertex );
+			if ( (hNextVertex == hStartVertex) || (hNextVertex == hCurrentVertex) )
+				break;
+
+			hCurrentVertex = hNextVertex;
+		}
+
+		return hTargetVertex;
+	}
+
 	public enum DissolveRemoveVertexCondition
 	{
 		None,               // Never remove vertices
@@ -1396,6 +1634,43 @@ public sealed partial class PolygonMesh : IJsonConvert
 		return true;
 	}
 
+	public bool AddVertexToEdgeAndUpdateTable( VertexHandle hVertexA, VertexHandle hVertexB, float flParam, out VertexHandle pNewVertex, SortedSet<HalfEdgeHandle> pEdgeTable )
+	{
+		pNewVertex = VertexHandle.Invalid;
+
+		bool bOriginalEdgeInTable = false;
+		var hOriginalEdge = HalfEdgeHandle.Invalid;
+
+		if ( pEdgeTable is not null )
+		{
+			var hEdge = FindEdgeConnectingVertices( hVertexA, hVertexB );
+			if ( pEdgeTable.Contains( hEdge ) )
+			{
+				bOriginalEdgeInTable = true;
+			}
+		}
+
+		if ( AddVertexToEdge( hVertexA, hVertexB, flParam, out var hNewVertex ) )
+		{
+			if ( bOriginalEdgeInTable )
+			{
+				Topology.GetFullEdgesConnectedToVertex( hNewVertex, out var connectedEdges );
+				if ( connectedEdges.Count == 2 )
+				{
+					pEdgeTable.Remove( hOriginalEdge );
+					pEdgeTable.Add( connectedEdges[0] );
+					pEdgeTable.Add( connectedEdges[1] );
+				}
+			}
+
+			pNewVertex = hNewVertex;
+
+			return true;
+		}
+
+		return false;
+	}
+
 	public bool RemoveVertex( VertexHandle hVertex, bool removeFreeVerts )
 	{
 		return Topology.RemoveVertex( hVertex, removeFreeVerts );
@@ -2386,6 +2661,8 @@ public sealed partial class PolygonMesh : IJsonConvert
 				TextureCoord[hFaceVertex] = texCoord;
 			}
 		}
+
+		IsDirty = true;
 	}
 
 	private static bool CalcTextureBasisFromUVs( Vector3[] vVertPos, Vector2[] vTexCoord, out Vector3 vOutU, out Vector3 vOutV )
@@ -3039,7 +3316,7 @@ public sealed partial class PolygonMesh : IJsonConvert
 		return Topology.GetFullEdgesConnectedToFace( hFace, out edges );
 	}
 
-	private bool GetVerticesConnectedToEdge( HalfEdgeHandle hEdge, FaceHandle hFace, out VertexHandle hOutVertexA, out VertexHandle hOutVertexB )
+	public bool GetVerticesConnectedToEdge( HalfEdgeHandle hEdge, FaceHandle hFace, out VertexHandle hOutVertexA, out VertexHandle hOutVertexB )
 	{
 		hOutVertexA = VertexHandle.Invalid;
 		hOutVertexB = VertexHandle.Invalid;
@@ -3114,7 +3391,7 @@ public sealed partial class PolygonMesh : IJsonConvert
 		return HalfEdgeHandle.Invalid;
 	}
 
-	private bool GetVerticesConnectedToFace( FaceHandle hFace, out VertexHandle[] vertices )
+	public bool GetVerticesConnectedToFace( FaceHandle hFace, out VertexHandle[] vertices )
 	{
 		return Topology.GetVerticesConnectedToFace( hFace, out vertices );
 	}
@@ -4221,6 +4498,115 @@ public sealed partial class PolygonMesh : IJsonConvert
 					.ToArray();
 	}
 
+	bool FindCutEdgeIntersection( VertexHandle hVertex, Vector3 targetPosition, out HalfEdgeHandle outEdge, out FaceHandle outFace, out Vector3 outPosition )
+	{
+		outEdge = HalfEdgeHandle.Invalid;
+		outFace = FaceHandle.Invalid;
+		outPosition = default;
+
+		GetVertexPosition( hVertex, Transform.Zero, out var vCurrentPosition );
+		var vDir = (targetPosition - vCurrentPosition).Normal;
+
+		GetFacesConnectedToVertex( hVertex, out var connectedFaces );
+
+		var hBestFace = FaceHandle.Invalid;
+		var hBestVertexA = VertexHandle.Invalid;
+		var hBestVertexB = VertexHandle.Invalid;
+		var vBestPoint = Vector3.Zero;
+		var flMinDistance = float.MaxValue;
+
+		int nNumFaces = connectedFaces.Count;
+		for ( int iFace = 0; iFace < nNumFaces; ++iFace )
+		{
+			var hFace = connectedFaces[iFace];
+
+			ComputeFaceNormal( hFace, out var vFaceNormal );
+
+			if ( MathF.Abs( vFaceNormal.Dot( vDir ) ) > 0.5f )
+				continue;
+
+			var vCutPlaneNormal = vFaceNormal.Cross( vDir ).Normal;
+			var cutPlane = new Plane( vCurrentPosition, vCutPlaneNormal );
+			var basePlane = new Plane( vCurrentPosition, vDir );
+
+			var hStartFaceVertex = FindFaceVertexConnectedToVertex( hVertex, hFace );
+			var hFaceVertexA = GetNextVertexInFace( hStartFaceVertex );
+			var hFaceVertexB = GetNextVertexInFace( hFaceVertexA );
+
+			var hBestVertexForFaceA = VertexHandle.Invalid;
+			var hBestVertexForFaceB = VertexHandle.Invalid;
+			var vBestPointForFace = Vector3.Zero;
+			var flMinBasePlaneDistance = float.MaxValue;
+
+			while ( hFaceVertexB != hStartFaceVertex )
+			{
+				var hVertexA = GetVertexConnectedToFaceVertex( hFaceVertexA );
+				var hVertexB = GetVertexConnectedToFaceVertex( hFaceVertexB );
+
+				if ( (hVertexA != hVertex) && (hVertexB != hVertex) )
+				{
+					var vPositionA = GetVertexPosition( hVertexA );
+					var vPositionB = GetVertexPosition( hVertexB );
+					var vIntersection = cutPlane.IntersectLine( vPositionA, vPositionB );
+					if ( vIntersection.HasValue )
+					{
+						float flBasePlaneDistance = basePlane.GetDistance( vIntersection.Value );
+
+						if ( (flBasePlaneDistance >= 0) && (flBasePlaneDistance <= flMinBasePlaneDistance) )
+						{
+							var vAB = vPositionB - vPositionA;
+							var vCross = vDir.Cross( vAB );
+
+							if ( vCross.Dot( vFaceNormal ) > 0.0f )
+							{
+								hBestVertexForFaceA = hVertexA;
+								hBestVertexForFaceB = hVertexB;
+								vBestPointForFace = vIntersection.Value;
+							}
+							else if ( flBasePlaneDistance < flMinBasePlaneDistance )
+							{
+								hBestVertexForFaceA = VertexHandle.Invalid;
+								hBestVertexForFaceB = VertexHandle.Invalid;
+								vBestPointForFace = Vector3.Zero;
+							}
+
+							flMinBasePlaneDistance = flBasePlaneDistance;
+						}
+					}
+				}
+
+				hFaceVertexA = hFaceVertexB;
+				hFaceVertexB = GetNextVertexInFace( hFaceVertexB );
+			}
+
+			var flFaceTargetDistance = vBestPointForFace.Distance( targetPosition );
+			if ( (hBestVertexForFaceA != VertexHandle.Invalid) &&
+				 (hBestVertexForFaceB != VertexHandle.Invalid) &&
+				 (flFaceTargetDistance < flMinDistance) )
+			{
+				hBestFace = hFace;
+				hBestVertexA = hBestVertexForFaceA;
+				hBestVertexB = hBestVertexForFaceB;
+				vBestPoint = vBestPointForFace;
+				flMinDistance = flFaceTargetDistance;
+			}
+		}
+
+		if ( hBestFace == FaceHandle.Invalid )
+			return false;
+
+		outEdge = FindEdgeConnectingVertices( hBestVertexA, hBestVertexB );
+		outFace = hBestFace;
+		outPosition = vBestPoint;
+
+		return true;
+	}
+
+	public void GetFacesConnectedToEdge( HalfEdgeHandle hEdge, out FaceHandle hOutFaceA, out FaceHandle hOutFaceB )
+	{
+		Topology.GetFacesConnectedToFullEdge( hEdge, out hOutFaceA, out hOutFaceB );
+	}
+
 	private static readonly Vector3[] FaceNormals =
 	{
 		new( 0, 0, 1 ),

engine/Sandbox.System/Math/Plane.cs

@@ -179,11 +179,21 @@ public struct Plane : System.IEquatable<Plane>
 		float d1 = GetDistance( start );
 		float d2 = GetDistance( end );
 
-		if ( MathF.Abs( d1 ) < 0.001f ) return start;
+		const float eps = 0.001f;
-		if ( MathF.Abs( d1 - d2 ) < 0.001f ) return default;
+
+		if ( MathF.Abs( d1 - d2 ) < eps )
+		{
+			if ( MathF.Abs( d1 ) < eps )
+				return start;
+
+			return default;
+		}
 
 		float t = -d1 / (d2 - d1);
-		return (t is >= 0.0f and <= 1.0f) ? start + (end - start) * t : default;
+		if ( t >= 0.0f && t <= 1.0f )
+			return start + (end - start) * t;
+
+		return default;
 	}
 
 	/// <summary>

game/addons/tools/Code/Scene/Mesh/Tools/EdgeCutTool.Apply.cs

@@ -0,0 +1,293 @@
+using HalfEdgeMesh;
+using Sandbox.Diagnostics;
+
+namespace Editor.MeshEditor;
+
+partial class EdgeCutTool
+{
+	sealed class HalfEdgeHandleComparer : IComparer<HalfEdgeHandle>
+	{
+		public static readonly HalfEdgeHandleComparer Instance = new();
+
+		public int Compare( HalfEdgeHandle a, HalfEdgeHandle b )
+		{
+			return a.Index.CompareTo( b.Index );
+		}
+	}
+
+	void Cancel()
+	{
+		if ( _cutPoints.Count == 0 )
+		{
+			EditorToolManager.SetSubTool( _tool );
+		}
+
+		_cutPoints.Clear();
+	}
+
+	void Apply()
+	{
+		if ( _cutPoints.Count <= 1 ) return;
+
+		var components = new HashSet<MeshComponent>( _cutPoints.Count );
+		foreach ( var cutPoint in _cutPoints )
+		{
+			var component = cutPoint.Face.Component;
+			if ( component.IsValid() ) components.Add( component );
+		}
+
+		using var undoScope = SceneEditorSession.Active.UndoScope( "Apply Edge Cut" )
+			.WithComponentChanges( components )
+			.Push();
+
+		var vertices = new List<MeshVertex>();
+		var edges = new List<MeshEdge>();
+		if ( ApplyCut( vertices, edges ) == false ) return;
+
+		var selection = SceneEditorSession.Active.Selection;
+		selection.Clear();
+
+		foreach ( var vertex in vertices ) selection.Add( vertex );
+		foreach ( var edge in edges ) selection.Add( edge );
+
+		foreach ( var component in components )
+		{
+			var mesh = component.Mesh;
+			foreach ( var edge in edges )
+			{
+				mesh.GetFacesConnectedToEdge( edge.Handle, out var faceA, out var faceB );
+				selection.Add( new MeshFace( component, faceA ) );
+				selection.Add( new MeshFace( component, faceB ) );
+			}
+		}
+
+		EditorToolManager.SetSubTool( _tool );
+	}
+
+	bool ApplyCut( List<MeshVertex> outCutPathVertices, List<MeshEdge> outCutPathEdges )
+	{
+		var cutPoints = _cutPoints;
+		if ( cutPoints.Count == 0 ) return false;
+
+		var components = new List<MeshComponent>( cutPoints.Count );
+		var meshes = new List<PolygonMesh>( cutPoints.Count );
+
+		foreach ( var cp in cutPoints )
+		{
+			var component = cp.Face.Component;
+			if ( !component.IsValid() ) continue;
+
+			var mesh = component.Mesh;
+			if ( meshes.Contains( mesh ) ) continue;
+
+			meshes.Add( mesh );
+			components.Add( component );
+		}
+
+		var edgeTables = new List<SortedSet<HalfEdgeHandle>>( meshes.Count );
+		for ( int i = 0; i < meshes.Count; i++ ) edgeTables.Add( new SortedSet<HalfEdgeHandle>( HalfEdgeHandleComparer.Instance ) );
+
+		int startIndex = 0;
+		MeshVertex startVertex = default;
+		MeshEdge edgeToRemove = default;
+
+		while ( startIndex < cutPoints.Count )
+		{
+			while ( !startVertex.IsValid() && startIndex < cutPoints.Count )
+			{
+				var startPoint = cutPoints[startIndex];
+
+				if ( startPoint.IsValid() )
+				{
+					if ( startPoint.Edge.IsValid() )
+					{
+						var component = startPoint.Edge.Component;
+						int meshIndex = components.IndexOf( component );
+						Assert.True( meshIndex != -1 );
+
+						var hNewVertex = AddCutToEdge( startPoint.Edge, startPoint.BasePosition, edgeTables[meshIndex] );
+						startVertex = new MeshVertex( component, hNewVertex );
+						break;
+					}
+
+					if ( startPoint.Vertex.IsValid() )
+					{
+						startVertex = startPoint.Vertex;
+						break;
+					}
+				}
+
+				startIndex++;
+			}
+
+			int endIndex = startIndex + 1;
+			MeshVertex endVertex = default;
+
+			if ( endIndex < cutPoints.Count )
+			{
+				var endPoint = cutPoints[endIndex];
+				if ( endPoint.Face.IsValid() && endPoint.Face.Component == startVertex.Component )
+				{
+					var component = startVertex.Component;
+					var mesh = component.Mesh;
+					int meshIndex = components.IndexOf( component );
+					Assert.True( meshIndex != -1 );
+
+					var edgeTable = edgeTables[meshIndex];
+					var targetVertex = mesh.CreateEdgesConnectingVertexToPoint( startVertex.Handle, endPoint.BasePosition,
+						out var segmentEdges, out var isLastConnector, edgeTable );
+
+					if ( edgeToRemove.IsValid() && !segmentEdges.Contains( edgeToRemove.Handle ) )
+					{
+						mesh.GetVerticesConnectedToEdge( edgeToRemove.Handle, out var a, out var b );
+						mesh.DissolveEdge( edgeToRemove.Handle );
+						edgeTable.Remove( edgeToRemove.Handle );
+						mesh.RemoveColinearVertexAndUpdateTable( a, edgeTable );
+						mesh.RemoveColinearVertexAndUpdateTable( b, edgeTable );
+					}
+
+					if ( endPoint.Face.IsValid() && !endPoint.Vertex.IsValid() && !endPoint.Edge.IsValid() && segmentEdges.Count > 1 && isLastConnector )
+					{
+						edgeToRemove = new MeshEdge( component, segmentEdges[^1] );
+					}
+
+					endVertex = new MeshVertex( component, targetVertex );
+				}
+			}
+
+			startIndex = endIndex;
+			startVertex = endVertex;
+		}
+
+		if ( outCutPathEdges is not null || outCutPathVertices is not null )
+		{
+			var numMeshes = meshes.Count;
+			var totalEdgeCount = 0;
+
+			foreach ( var edgeTable in edgeTables )
+			{
+				totalEdgeCount += edgeTable.Count;
+			}
+
+			if ( outCutPathEdges is not null )
+			{
+				outCutPathEdges.Clear();
+				outCutPathEdges.EnsureCapacity( totalEdgeCount );
+			}
+
+			var vertexSet = new HashSet<MeshVertex>( totalEdgeCount * 2 );
+
+			for ( int i = 0; i < numMeshes; ++i )
+			{
+				var component = components[i];
+				var mesh = component.Mesh;
+				var edgeTable = edgeTables[i];
+
+				foreach ( var hEdge in edgeTable )
+				{
+					if ( hEdge.IsValid == false ) continue;
+
+					outCutPathEdges?.Add( new MeshEdge( component, hEdge ) );
+
+					if ( outCutPathVertices is not null )
+					{
+						mesh.GetVerticesConnectedToEdge( hEdge, out var hVertexA, out var hVertexB );
+						vertexSet.Add( new MeshVertex( component, hVertexA ) );
+						vertexSet.Add( new MeshVertex( component, hVertexB ) );
+					}
+				}
+			}
+
+			if ( outCutPathVertices is not null )
+			{
+				outCutPathVertices.Clear();
+				outCutPathVertices.EnsureCapacity( vertexSet.Count );
+
+				foreach ( var hVertex in vertexSet )
+				{
+					outCutPathVertices.Add( hVertex );
+				}
+			}
+		}
+
+		foreach ( var mesh in meshes )
+		{
+			mesh.ComputeFaceTextureCoordinatesFromParameters();
+		}
+
+		return true;
+	}
+
+	static MeshFace FindSharedFace( MeshCutPoint cutPointA, MeshCutPoint cutPointB )
+	{
+		if ( cutPointA.IsValid() == false ) return default;
+		if ( cutPointB.IsValid() == false ) return default;
+		if ( cutPointA.Component != cutPointB.Component ) return default;
+
+		cutPointA.GetConnectedFaces( out var connectedFacesA );
+		cutPointB.GetConnectedFaces( out var connectedFacesB );
+
+		foreach ( var face in connectedFacesA )
+		{
+			if ( face.IsValid && connectedFacesB.Contains( face ) )
+			{
+				return new MeshFace( cutPointA.Component, face );
+			}
+		}
+
+		return default;
+	}
+
+	static VertexHandle AddCutToEdge( MeshEdge edge, Vector3 targetPosition, SortedSet<HalfEdgeHandle> edgeTable )
+	{
+		if ( !edge.Component.IsValid() ) return VertexHandle.Invalid;
+
+		var mesh = edge.Component.Mesh;
+		var visited = new List<HalfEdgeHandle>( 32 );
+		var current = edge.Handle;
+		const float eps = 0.001f;
+
+		while ( current != HalfEdgeHandle.Invalid )
+		{
+			mesh.GetVerticesConnectedToEdge( current, out var a, out var b );
+			mesh.GetVertexPosition( a, Transform.Zero, out var pa );
+			mesh.GetVertexPosition( b, Transform.Zero, out var pb );
+			ClosestPointOnLine( targetPosition, pa, pb, out _, out var t );
+
+			VertexHandle next;
+			if ( t > 1f + eps ) next = b;
+			else if ( t < -eps ) next = a;
+			else if ( t <= eps ) return a;
+			else if ( t >= 1f - eps ) return b;
+			else
+			{
+				mesh.AddVertexToEdgeAndUpdateTable( a, b, t, out var v, edgeTable );
+				return v;
+			}
+
+			visited.Add( current );
+			var prev = current;
+			current = HalfEdgeHandle.Invalid;
+
+			mesh.GetEdgesConnectedToVertex( next, out var edges );
+			foreach ( var e in edges )
+			{
+				if ( !visited.Contains( e ) && mesh.AreEdgesCoLinear( e, prev, 1.0f ) )
+				{
+					current = e;
+					break;
+				}
+			}
+		}
+
+		return VertexHandle.Invalid;
+	}
+
+	static void ClosestPointOnLine( Vector3 p, Vector3 a, Vector3 b, out Vector3 closest, out float t )
+	{
+		var d = b - a;
+		var div = d.Dot( d );
+		t = div < 1e-5f ? 0f : (d.Dot( p ) - d.Dot( a )) / div;
+		closest = a + d * t;
+	}
+}

game/addons/tools/Code/Scene/Mesh/Tools/EdgeCutTool.Gizmo.cs

@@ -0,0 +1,118 @@
+
+namespace Editor.MeshEditor;
+
+partial class EdgeCutTool
+{
+	void DrawCutPoints()
+	{
+		using ( Gizmo.Scope( "Points" ) )
+		{
+			Gizmo.Draw.IgnoreDepth = true;
+
+			if ( _cutPoints.Count > 0 )
+			{
+				Gizmo.Draw.LineThickness = 2;
+				Gizmo.Draw.Color = new Color( 0.3137f, 0.7843f, 1.0f, 1f );
+				for ( int i = 1; i < _cutPoints.Count; i++ )
+				{
+					Gizmo.Draw.Line( _cutPoints[i - 1].WorldPosition, _cutPoints[i].WorldPosition );
+				}
+			}
+
+			Gizmo.Draw.Color = Color.White;
+
+			foreach ( var cutPoint in _cutPoints )
+			{
+				Gizmo.Draw.Sprite( cutPoint.WorldPosition, 10, null, false );
+			}
+		}
+	}
+
+	void DrawPreview()
+	{
+		if ( _previewCutPoint.IsValid() == false ) return;
+
+		var mesh = _previewCutPoint.Face.Component;
+		if ( _hoveredMesh != mesh ) _hoveredMesh = mesh;
+
+		var edge = _previewCutPoint.Edge;
+		if ( edge.IsValid() )
+		{
+			using ( Gizmo.Scope( "Edge Hover", _previewCutPoint.Edge.Transform ) )
+			{
+				Gizmo.Draw.IgnoreDepth = true;
+				Gizmo.Draw.Color = Color.Green;
+				Gizmo.Draw.LineThickness = 4;
+				Gizmo.Draw.Line( edge.Line );
+			}
+		}
+
+		using ( Gizmo.Scope( "Point" ) )
+		{
+			Gizmo.Draw.IgnoreDepth = true;
+
+			if ( _cutPoints.Count > 0 )
+			{
+				var lastCutPoint = _cutPoints.Last();
+				Gizmo.Draw.LineThickness = 4;
+				Gizmo.Draw.Color = Color.White;
+				Gizmo.Draw.Line( _previewCutPoint.WorldPosition, lastCutPoint.WorldPosition );
+			}
+
+			Gizmo.Draw.Color = Color.White;
+			Gizmo.Draw.Sprite( _previewCutPoint.WorldPosition, 10, null, false );
+		}
+	}
+
+	static void DrawMesh( MeshComponent mesh )
+	{
+		if ( mesh.IsValid() == false ) return;
+
+		using ( Gizmo.ObjectScope( mesh.GameObject, mesh.WorldTransform ) )
+		{
+			using ( Gizmo.Scope( "Edges" ) )
+			{
+				var edgeColor = new Color( 0.3137f, 0.7843f, 1.0f, 1f );
+
+				Gizmo.Draw.LineThickness = 1;
+				Gizmo.Draw.IgnoreDepth = true;
+				Gizmo.Draw.Color = edgeColor.Darken( 0.3f ).WithAlpha( 0.2f );
+
+				foreach ( var v in mesh.Mesh.GetEdges() )
+				{
+					Gizmo.Draw.Line( v );
+				}
+
+				Gizmo.Draw.Color = edgeColor;
+				Gizmo.Draw.IgnoreDepth = false;
+				Gizmo.Draw.LineThickness = 2;
+
+				foreach ( var v in mesh.Mesh.GetEdges() )
+				{
+					Gizmo.Draw.Line( v );
+				}
+			}
+
+			using ( Gizmo.Scope( "Vertices" ) )
+			{
+				var vertexColor = new Color( 1.0f, 1.0f, 0.3f, 1f );
+
+				Gizmo.Draw.IgnoreDepth = true;
+				Gizmo.Draw.Color = vertexColor.Darken( 0.3f ).WithAlpha( 0.2f );
+
+				foreach ( var v in mesh.Mesh.GetVertexPositions() )
+				{
+					Gizmo.Draw.Sprite( v, 8, null, false );
+				}
+
+				Gizmo.Draw.Color = vertexColor;
+				Gizmo.Draw.IgnoreDepth = false;
+
+				foreach ( var v in mesh.Mesh.GetVertexPositions() )
+				{
+					Gizmo.Draw.Sprite( v, 8, null, false );
+				}
+			}
+		}
+	}
+}

game/addons/tools/Code/Scene/Mesh/Tools/EdgeCutTool.Snapping.cs

@@ -0,0 +1,397 @@
+using HalfEdgeMesh;
+using System.Runtime.InteropServices;
+
+namespace Editor.MeshEditor;
+
+partial class EdgeCutTool
+{
+	enum EdgeCutAlignment { None, Grid, Perpendicular }
+	enum PolygonComponentType { Invalid = -1, Vertex, Edge, Face }
+
+	struct SnapPoint
+	{
+		public Vector3 Position;
+		public EdgeCutAlignment Alignment;
+		public PolygonComponentType Type;
+		public VertexHandle Vertex;
+		public HalfEdgeHandle Edge;
+
+		public SnapPoint( Vector3 pos, EdgeCutAlignment align )
+		{
+			Position = pos;
+			Alignment = align;
+			Type = PolygonComponentType.Face;
+			Vertex = default;
+			Edge = default;
+		}
+
+		public SnapPoint( VertexHandle v, Vector3 pos )
+		{
+			Position = pos;
+			Alignment = EdgeCutAlignment.None;
+			Type = PolygonComponentType.Vertex;
+			Vertex = v;
+			Edge = default;
+		}
+
+		public SnapPoint( HalfEdgeHandle e, Vector3 pos, EdgeCutAlignment align )
+		{
+			Position = pos;
+			Alignment = align;
+			Type = PolygonComponentType.Edge;
+			Vertex = default;
+			Edge = e;
+		}
+	}
+
+	static bool ShouldSnap() => Gizmo.Settings.SnapToGrid != Gizmo.IsCtrlPressed;
+
+	MeshCutPoint FindSnappedCutPoint()
+	{
+		var face = MeshTrace.TraceFace( SelectionSampleRadius, out var point );
+		if ( !face.IsValid() ) return default;
+
+		GenerateSnapPoints( face, point, out var snapPoints );
+		return SnapCutPoint( face, point, snapPoints );
+	}
+
+	static MeshCutPoint SnapCutPoint( MeshFace face, Vector3 target, List<SnapPoint> snaps )
+	{
+		if ( snaps.Count == 0 ) return default;
+
+		var best = snaps.OrderBy( s => target.DistanceSquared( s.Position ) ).First();
+		return best.Type switch
+		{
+			PolygonComponentType.Vertex => new( face, new MeshVertex( face.Component, best.Vertex ) ),
+			PolygonComponentType.Edge => new( face, new MeshEdge( face.Component, best.Edge ), best.Position ),
+			PolygonComponentType.Face => new( face, best.Position ),
+			_ => default
+		};
+	}
+
+	static void GenerateVertexSnapPoints( MeshFace face, List<SnapPoint> snaps )
+	{
+		if ( !face.IsValid() ) return;
+
+		var mesh = face.Component.Mesh;
+		var transform = face.Component.WorldTransform;
+
+		mesh.GetVerticesConnectedToFace( face.Handle, out var vertices );
+
+		foreach ( var v in vertices )
+		{
+			mesh.GetVertexPosition( v, transform, out var pos );
+			snaps.Add( new SnapPoint( v, pos ) );
+		}
+	}
+
+	void GenerateEdgeSnapPoints( MeshFace face, Vector3 target, List<SnapPoint> snaps )
+	{
+		if ( !face.IsValid() ) return;
+
+		var component = face.Component;
+		if ( !component.IsValid() ) return;
+
+		var mesh = component.Mesh;
+		var faceHandle = face.Handle;
+
+		var hasPrevious = _cutPoints.Count > 0;
+		var previous = hasPrevious ? _cutPoints.Last() : default;
+		var perpendicularNormal = Vector3.Zero;
+		var hasPerpendicular = hasPrevious && ComputePerpendicularPlaneNormalForCutPoint( previous, out perpendicularNormal );
+
+		mesh.GetEdgesConnectedToFace( faceHandle, out var edges );
+
+		for ( var i = 0; i < edges.Count; i++ )
+		{
+			var edge = edges[i];
+
+			mesh.GetVerticesConnectedToEdge( edge, out var vA, out var vB );
+			mesh.GetVertexPosition( vA, component.WorldTransform, out var p0 );
+			mesh.GetVertexPosition( vB, component.WorldTransform, out var p1 );
+
+			snaps.Add( new SnapPoint( edge, p0.LerpTo( p1, 0.5f ), EdgeCutAlignment.None ) );
+
+			if ( SnapToEdge( target, p0, p1, float.MaxValue, true, out var edgeSnap ) )
+				snaps.Add( new SnapPoint( edge, edgeSnap, EdgeCutAlignment.None ) );
+
+			if ( !hasPrevious || previous.Component != component )
+				continue;
+
+			var prevPos = previous.WorldPosition;
+
+			if ( ComputePlaneIntersectionSnapPoint( Vector3.Right, prevPos, target, p0, p1, out var hit ) )
+				snaps.Add( new SnapPoint( edge, hit, EdgeCutAlignment.Grid ) );
+
+			if ( ComputePlaneIntersectionSnapPoint( Vector3.Up, prevPos, target, p0, p1, out hit ) )
+				snaps.Add( new SnapPoint( edge, hit, EdgeCutAlignment.Grid ) );
+
+			if ( ComputePlaneIntersectionSnapPoint( Vector3.Forward, prevPos, target, p0, p1, out hit ) )
+				snaps.Add( new SnapPoint( edge, hit, EdgeCutAlignment.Grid ) );
+
+			if ( hasPerpendicular && ComputePlaneIntersectionSnapPoint( perpendicularNormal, prevPos, target, p0, p1, out hit ) )
+			{
+				snaps.Add( new SnapPoint( edge, hit, EdgeCutAlignment.Perpendicular ) );
+			}
+		}
+	}
+
+	static void GenerateFaceSnapPoints( MeshFace face, Vector3 target, List<SnapPoint> snaps )
+	{
+		if ( !face.IsValid() ) return;
+
+		var component = face.Component;
+		if ( !component.IsValid() ) return;
+
+		var mesh = component.Mesh;
+		var faceHandle = face.Handle;
+
+		var vertices = mesh.GetFaceVertexPositions( faceHandle, component.WorldTransform ).ToList();
+		var spacing = Gizmo.Settings.GridSpacing;
+
+		var min = new Vector3(
+			MathF.Floor( target.x / spacing ) * spacing,
+			MathF.Floor( target.y / spacing ) * spacing,
+			MathF.Floor( target.z / spacing ) * spacing );
+
+		var max = new Vector3(
+			MathF.Ceiling( target.x / spacing ) * spacing,
+			MathF.Ceiling( target.y / spacing ) * spacing,
+			MathF.Ceiling( target.z / spacing ) * spacing );
+
+		var gridEdges = new Line[]
+		{
+			new( new( min.x - 1, min.y, min.z ), new( max.x + 1, min.y, min.z ) ),
+			new( new( min.x - 1, min.y, max.z ), new( max.x + 1, min.y, max.z ) ),
+			new( new( min.x - 1, max.y, min.z ), new( max.x + 1, max.y, min.z ) ),
+			new( new( min.x - 1, max.y, max.z ), new( max.x + 1, max.y, max.z ) ),
+
+			new( new( min.x, min.y - 1, min.z ), new( min.x, max.y + 1, min.z ) ),
+			new( new( min.x, min.y - 1, max.z ), new( min.x, max.y + 1, max.z ) ),
+			new( new( max.x, min.y - 1, min.z ), new( max.x, max.y + 1, min.z ) ),
+			new( new( max.x, min.y - 1, max.z ), new( max.x, max.y + 1, max.z ) ),
+
+			new( new( min.x, min.y, min.z - 1 ), new( min.x, min.y, max.z + 1 ) ),
+			new( new( min.x, max.y, min.z - 1 ), new( min.x, max.y, max.z + 1 ) ),
+			new( new( max.x, min.y, min.z - 1 ), new( max.x, min.y, max.z + 1 ) ),
+			new( new( max.x, max.y, min.z - 1 ), new( max.x, max.y, max.z + 1 ) ),
+		};
+
+		var indices = Mesh.TriangulatePolygon( CollectionsMarshal.AsSpan( vertices ) );
+
+		for ( var i = 0; i < gridEdges.Length; i++ )
+		{
+			var e = gridEdges[i];
+			if ( PolygonIntersectLineSegment( vertices, indices, e.Start, e.End, out var hit ) )
+				snaps.Add( new SnapPoint( hit, EdgeCutAlignment.None ) );
+		}
+	}
+
+	void GenerateSnapPoints( MeshFace face, Vector3 target, out List<SnapPoint> snapPoints )
+	{
+		var alignedOnly = _cutPoints.Count > 0 && Gizmo.IsShiftPressed;
+
+		var all = new List<SnapPoint>();
+		GenerateVertexSnapPoints( face, all );
+		GenerateEdgeSnapPoints( face, target, all );
+
+		if ( _cutPoints.Count > 0 )
+			GenerateFaceSnapPoints( face, target, all );
+
+		snapPoints = new List<SnapPoint>( all.Count );
+
+		const float minDistSq = 0.01f * 0.01f;
+
+		foreach ( var snap in all )
+		{
+			if ( alignedOnly && snap.Alignment == EdgeCutAlignment.None )
+				continue;
+
+			var tooClose = false;
+			for ( var i = 0; i < snapPoints.Count; i++ )
+			{
+				if ( snapPoints[i].Position.DistanceSquared( snap.Position ) < minDistSq )
+				{
+					tooClose = true;
+					break;
+				}
+			}
+
+			if ( !tooClose )
+				snapPoints.Add( snap );
+		}
+	}
+
+	static bool ComputePerpendicularPlaneNormalForCutPoint( MeshCutPoint cutPoint, out Vector3 planeNormal )
+	{
+		planeNormal = default;
+
+		if ( !cutPoint.Component.IsValid() || !cutPoint.Face.IsValid() || !cutPoint.Edge.IsValid() )
+			return false;
+
+		var mesh = cutPoint.Component.Mesh;
+		mesh.GetVerticesConnectedToEdge( cutPoint.Edge.Handle, cutPoint.Face.Handle, out var a, out var b );
+		mesh.GetVertexPosition( a, Transform.Zero, out var pa );
+		mesh.GetVertexPosition( b, Transform.Zero, out var pb );
+
+		planeNormal = (pb - pa).Normal;
+		return true;
+	}
+
+	static bool SnapToEdge( Vector3 original, Vector3 a, Vector3 b, float maxDistance, bool gridSnap, out Vector3 snapped )
+	{
+		ClosestPointOnLineSegment( original, a, b, out var pointOnLine );
+
+		var maxDistSq = maxDistance < float.MaxValue ? maxDistance * maxDistance : float.MaxValue;
+		var snappedPoint = Vector3.Zero;
+		var snappedOk = false;
+
+		if ( pointOnLine.DistanceSquared( original ) < maxDistSq )
+		{
+			if ( gridSnap )
+			{
+				if ( IntersectRayWithGrid( pointOnLine, a, out var snapA ) &&
+					 snapA.DistanceSquared( original ) < maxDistSq )
+				{
+					snappedPoint = snapA;
+					snappedOk = true;
+				}
+
+				if ( IntersectRayWithGrid( pointOnLine, b, out var snapB ) &&
+					 snapB.DistanceSquared( original ) < maxDistSq &&
+					 pointOnLine.DistanceSquared( snapB ) < pointOnLine.DistanceSquared( snappedPoint ) )
+				{
+					snappedPoint = snapB;
+					snappedOk = true;
+				}
+			}
+			else
+			{
+				snappedPoint = pointOnLine;
+				snappedOk = true;
+			}
+		}
+
+		snapped = snappedOk ? snappedPoint : Vector3.Zero;
+		return snappedOk;
+	}
+
+	static float DistanceSqrToLine( Vector3 p, Vector3 a, Vector3 b, out float t )
+	{
+		ClosestPointOnLine( p, a, b, out var closest, out t );
+		return p.DistanceSquared( closest );
+	}
+
+	static bool ComputePlaneIntersectionSnapPoint( Vector3 vPlaneNormal, Vector3 vPlanePoint, Vector3 vOrginalPoint, Vector3 vEdgePointA, Vector3 vEdgePointB, out Vector3 pOutIntersectionPoint )
+	{
+		pOutIntersectionPoint = Vector3.Zero;
+
+		const float halfGridSize = 0.125f * 0.5f;
+
+		var vDelta = (vEdgePointA - vEdgePointB) * vPlaneNormal;
+
+		if ( vDelta.Length >= halfGridSize )
+		{
+			var plane = new Plane( vPlaneNormal, vPlaneNormal.Dot( vPlanePoint ) );
+			var vIntersection = plane.IntersectLine( vEdgePointA, vEdgePointB );
+			if ( vIntersection.HasValue )
+			{
+				pOutIntersectionPoint = vIntersection.Value;
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	static bool InsideTriangle( Vector3 a, Vector3 b, Vector3 c, Vector3 p, Vector3 normal )
+	{
+		const float eps = 1e-7f;
+		const float maxEdgeDistSq = eps * eps;
+
+		if ( Vector3.Dot( Vector3.Cross( b - a, p - a ), normal ) >= -eps &&
+			 Vector3.Dot( Vector3.Cross( c - b, p - b ), normal ) >= -eps &&
+			 Vector3.Dot( Vector3.Cross( a - c, p - c ), normal ) >= -eps
+		)
+			return true;
+
+		if ( DistanceSqrToLine( p, a, b, out var t ) < maxEdgeDistSq && t is >= 0f and <= 1f ) return true;
+		if ( DistanceSqrToLine( p, b, c, out t ) < maxEdgeDistSq && t is >= 0f and <= 1f ) return true;
+		if ( DistanceSqrToLine( p, c, a, out t ) < maxEdgeDistSq && t is >= 0f and <= 1f ) return true;
+
+		return false;
+	}
+
+	static bool PolygonIntersectLineSegment( List<Vector3> vertices, Span<int> indices, Vector3 a, Vector3 b, out Vector3 intersection )
+	{
+		intersection = Vector3.Zero;
+
+		for ( var i = 0; i + 2 < indices.Length; i += 3 )
+		{
+			var v0 = vertices[indices[i]];
+			var v1 = vertices[indices[i + 1]];
+			var v2 = vertices[indices[i + 2]];
+
+			var normal = Vector3.Cross( v1 - v0, v2 - v0 );
+			if ( normal.LengthSquared < 1e-8f ) continue;
+
+			normal = normal.Normal;
+			var plane = new Plane( v0, normal );
+
+			var hit = plane.IntersectLine( a, b );
+			if ( !hit.HasValue ) continue;
+
+			var p = hit.Value;
+			if ( InsideTriangle( v0, v1, v2, p, normal ) )
+			{
+				intersection = p;
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	static void ClosestPointOnLineSegment( Vector3 p, Vector3 a, Vector3 b, out Vector3 closest )
+	{
+		var d = b - a;
+		var len2 = d.Dot( d );
+		var t = len2 < 1e-5f ? 0f : Math.Clamp( d.Dot( p - a ) / len2, 0f, 1f );
+		closest = a + d * t;
+	}
+
+	static bool IntersectRayWithGrid( Vector3 origin, Vector3 end, out Vector3 intersection )
+	{
+		var spacing = Gizmo.Settings.GridSpacing;
+		var dir = end - origin;
+
+		var cell = new Vector3(
+			MathF.Floor( origin.x / spacing ) * spacing,
+			MathF.Floor( origin.y / spacing ) * spacing,
+			MathF.Floor( origin.z / spacing ) * spacing
+		);
+
+		var hit = false;
+		var closestT = 1f;
+
+		for ( var axis = 0; axis < 3; axis++ )
+		{
+			var d = dir[axis];
+			if ( d == 0f )
+				continue;
+
+			var sign = d > 0f ? 1f : -1f;
+			var plane = cell[axis] + (sign > 0f ? spacing : 0f);
+
+			var t = (plane - origin[axis]) / d;
+			if ( t > 0f && t <= closestT )
+			{
+				closestT = t;
+				hit = true;
+			}
+		}
+
+		intersection = hit ? origin + dir * closestT : Vector3.Zero;
+		return hit;
+	}
+}

game/addons/tools/Code/Scene/Mesh/Tools/EdgeCutTool.UI.cs

@@ -0,0 +1,45 @@
+
+namespace Editor.MeshEditor;
+
+partial class EdgeCutTool
+{
+	public override Widget CreateToolSidebar()
+	{
+		return new EdgeCutToolWidget( this );
+	}
+
+	public class EdgeCutToolWidget : ToolSidebarWidget
+	{
+		readonly EdgeCutTool _tool;
+
+		public EdgeCutToolWidget( EdgeCutTool tool ) : base()
+		{
+			_tool = tool;
+
+			AddTitle( "Edge Cut Tool", "content_cut" );
+
+			{
+				var row = Layout.AddRow();
+				row.Spacing = 4;
+
+				var apply = new Button( "Apply", "done" );
+				apply.Clicked = Apply;
+				apply.ToolTip = "[Apply " + EditorShortcuts.GetKeys( "mesh.edge-cut-apply" ) + "]";
+				row.Add( apply );
+
+				var cancel = new Button( "Cancel", "close" );
+				cancel.Clicked = Cancel;
+				cancel.ToolTip = "[Cancel " + EditorShortcuts.GetKeys( "mesh.edge-cut-cancel" ) + "]";
+				row.Add( cancel );
+			}
+
+			Layout.AddStretchCell();
+		}
+
+		[Shortcut( "mesh.edge-cut-apply", "enter", typeof( SceneDock ) )]
+		void Apply() => _tool.Apply();
+
+		[Shortcut( "mesh.edge-cut-cancel", "ESC", typeof( SceneDock ) )]
+		void Cancel() => _tool.Cancel();
+	}
+}

game/addons/tools/Code/Scene/Mesh/Tools/EdgeCutTool.cs

@@ -0,0 +1,174 @@
+using HalfEdgeMesh;
+
+namespace Editor.MeshEditor;
+
+[Alias( "tools.edge-cut-tool" )]
+public partial class EdgeCutTool( string tool ) : EditorTool
+{
+	static int SelectionSampleRadius => 8;
+
+	MeshComponent _hoveredMesh;
+	MeshCutPoint _previewCutPoint;
+	readonly List<MeshCutPoint> _cutPoints = [];
+
+	struct MeshCutPoint : IValid
+	{
+		public MeshFace Face;
+		public MeshVertex Vertex;
+		public MeshEdge Edge;
+		public Vector3 WorldPosition;
+		public Vector3 LocalPosition;
+		public Vector3 BasePosition;
+		public MeshComponent Component;
+
+		public readonly bool IsValid => Face.IsValid();
+
+		void SetWorldPosition( Vector3 position )
+		{
+			WorldPosition = position;
+			LocalPosition = Face.Component.WorldTransform.PointToLocal( position );
+
+			if ( Vertex.IsValid() )
+			{
+				BasePosition = Vertex.PositionLocal;
+			}
+			else if ( Edge.IsValid() )
+			{
+				var mesh = Edge.Component.Mesh;
+				mesh.GetVerticesConnectedToEdge( Edge.Handle, out var hVertexA, out var hVertexB );
+				mesh.ComputeClosestPointOnEdge( hVertexA, hVertexB, LocalPosition, out var flBaseParam );
+				mesh.GetVertexPosition( hVertexA, Transform.Zero, out var vPositionA );
+				mesh.GetVertexPosition( hVertexB, Transform.Zero, out var vPositionB );
+				BasePosition = vPositionA.LerpTo( vPositionB, flBaseParam );
+			}
+			else
+			{
+				BasePosition = LocalPosition;
+			}
+		}
+
+		public MeshCutPoint( MeshFace face, MeshVertex vertex )
+		{
+			Face = face;
+			Vertex = vertex;
+			Component = Face.Component;
+			SetWorldPosition( vertex.PositionWorld );
+		}
+
+		public MeshCutPoint( MeshFace face, MeshEdge edge, Vector3 point )
+		{
+			Face = face;
+			Edge = edge;
+			Component = Face.Component;
+			SetWorldPosition( point );
+		}
+
+		public MeshCutPoint( MeshFace face, Vector3 point )
+		{
+			Face = face;
+			Component = Face.Component;
+			SetWorldPosition( point );
+		}
+
+		public readonly void GetConnectedFaces( out List<FaceHandle> outFaces )
+		{
+			outFaces = [];
+
+			if ( Component.IsValid() == false ) return;
+
+			var mesh = Component.Mesh;
+
+			if ( Vertex.IsValid() )
+			{
+				mesh.GetFacesConnectedToVertex( Vertex.Handle, out outFaces );
+			}
+			else if ( Edge.IsValid() )
+			{
+				mesh.GetFacesConnectedToEdge( Edge.Handle, out var hFaceA, out var hFaceB );
+				outFaces.Add( hFaceA );
+				outFaces.Add( hFaceB );
+			}
+			else
+			{
+				outFaces.Add( Face.Handle );
+			}
+		}
+	}
+
+	readonly string _tool = tool;
+	bool _cancel;
+
+	public override void OnDisabled()
+	{
+		Cancel();
+	}
+
+	public override void OnUpdate()
+	{
+		var escape = Application.IsKeyDown( KeyCode.Escape );
+		if ( escape && !_cancel ) Cancel();
+		_cancel = escape;
+
+		_previewCutPoint = ShouldSnap() ? FindSnappedCutPoint() : FindCutPoint();
+
+		MeshCutPoint previousCutPoint = default;
+		if ( _cutPoints.Count > 0 )
+		{
+			previousCutPoint = _cutPoints.Last();
+		}
+
+		if ( previousCutPoint.IsValid() )
+		{
+			var sharedFace = FindSharedFace( previousCutPoint, _previewCutPoint );
+			if ( sharedFace.IsValid() == false )
+			{
+				_previewCutPoint = default;
+			}
+		}
+
+		if ( !Gizmo.Pressed.Any )
+		{
+			if ( Gizmo.WasLeftMousePressed )
+			{
+				PlaceCutPoint();
+			}
+		}
+
+		DrawCutPoints();
+		DrawPreview();
+		DrawMesh( _hoveredMesh );
+	}
+
+	void PlaceCutPoint()
+	{
+		if ( _previewCutPoint.IsValid() == false ) return;
+
+		_cutPoints.Add( _previewCutPoint );
+	}
+
+	MeshCutPoint FindCutPoint()
+	{
+		var trace = MeshTrace;
+		MeshCutPoint newCutPoint = default;
+		{
+			var vertex = trace.GetClosestVertex( SelectionSampleRadius, out var face );
+			if ( vertex.IsValid() ) newCutPoint = new MeshCutPoint( face, vertex );
+		}
+
+		if ( newCutPoint.IsValid() == false )
+		{
+			var edge = trace.GetClosestEdge( SelectionSampleRadius, out var face, out var hitPosition );
+			var transform = edge.Transform;
+			var pointOnEdge = edge.Line.ClosestPoint( transform.PointToLocal( hitPosition ) );
+			if ( edge.IsValid() ) newCutPoint = new MeshCutPoint( face, edge, transform.PointToWorld( pointOnEdge ) );
+		}
+
+		if ( _cutPoints.Count > 0 && newCutPoint.IsValid() == false )
+		{
+			var face = trace.TraceFace( out var hitPosition );
+			if ( face.IsValid() ) newCutPoint = new MeshCutPoint( face, hitPosition );
+		}
+
+		return newCutPoint;
+	}
+}

game/addons/tools/Code/Scene/Mesh/Tools/EdgeTool.UI.cs

@@ -43,7 +43,6 @@ partial class EdgeTool
 
 				CreateButton( "Dissolve", "blur_off", "mesh.dissolve", Dissolve, CanDissolve(), row.Layout );
 				CreateButton( "Collapse", "unfold_less", "mesh.collapse", Collapse, CanCollapse(), row.Layout );
-				CreateButton( "Bevel", "straighten", "mesh.edge-bevel", Bevel, CanBevel(), row.Layout );
 				CreateButton( "Connect", "link", "mesh.connect", Connect, CanConnect(), row.Layout );
 				CreateButton( "Extend", "call_made", "mesh.extend", Extend, CanExtend(), row.Layout );
 
@@ -107,9 +106,31 @@ partial class EdgeTool
 				group.Add( row );
 			}
 
+			{
+				var group = AddGroup( "Tools" );
+
+				var grid = Layout.Row();
+				grid.Spacing = 4;
+
+				CreateButton( "Bevel", "straighten", "mesh.edge-bevel", Bevel, CanBevel(), grid );
+				CreateButton( "Edge Cut Tool", "content_cut", "mesh.edge-cut-tool", OpenEdgeCutTool, true, grid );
+
+				grid.AddStretchCell();
+
+				group.Add( grid );
+			}
+
 			Layout.AddStretchCell();
 		}
 
+		[Shortcut( "mesh.edge-cut-tool", "C", typeof( SceneDock ) )]
+		void OpenEdgeCutTool()
+		{
+			var tool = new EdgeCutTool( nameof( EdgeTool ) );
+			tool.Manager = _tool.Manager;
+			_tool.CurrentTool = tool;
+		}
+
 		private void SetNormals( PolygonMesh.EdgeSmoothMode mode )
 		{
 			using ( SceneEditorSession.Active.UndoScope( "Set Normals" )

game/addons/tools/Code/Scene/Mesh/Tools/FaceTool.UI.cs

@@ -73,9 +73,31 @@ partial class FaceTool
 				group.Add( grid );
 			}
 
+			{
+				var group = AddGroup( "Tools" );
+
+				var grid = Layout.Row();
+				grid.Spacing = 4;
+
+				CreateButton( "Fast Texture Tool", "texture", "mesh.fast-texture-tool", OpenFastTextureTool, true, grid );
+				CreateButton( "Edge Cut Tool", "content_cut", "mesh.edge-cut-tool", OpenEdgeCutTool, true, grid );
+
+				grid.AddStretchCell();
+
+				group.Add( grid );
+			}
+
 			Layout.AddStretchCell();
 		}
 
+		[Shortcut( "mesh.edge-cut-tool", "C", typeof( SceneDock ) )]
+		void OpenEdgeCutTool()
+		{
+			var tool = new EdgeCutTool( nameof( FaceTool ) );
+			tool.Manager = _meshTool.Manager;
+			_meshTool.CurrentTool = tool;
+		}
+
 		[Shortcut( "mesh.fast-texture-tool", "CTRL+G", typeof( SceneDock ) )]
 		public void OpenFastTextureTool()
 		{

game/addons/tools/Code/Scene/Mesh/Tools/SceneTraceExtensions.cs

@@ -5,10 +5,12 @@ static class SceneTraceMeshExtensions
 {
 	static Vector2 RayScreenPosition => SceneViewportWidget.MousePosition;
 
-	public static MeshVertex GetClosestVertex( this SceneTrace trace, int radius )
+	public static MeshVertex GetClosestVertex( this SceneTrace trace, int radius ) => GetClosestVertex( trace, radius, out _ );
+
+	public static MeshVertex GetClosestVertex( this SceneTrace trace, int radius, out MeshFace bestFace )
 	{
 		var point = RayScreenPosition;
-		var bestFace = TraceFace( trace, out var bestHitDistance );
+		bestFace = TraceFace( trace, out var bestHitDistance, out _ );
 		var bestVertex = bestFace.GetClosestVertex( point, radius );
 
 		if ( bestFace.IsValid() && bestVertex.IsValid() )
@@ -34,11 +36,13 @@ static class SceneTraceMeshExtensions
 		return bestVertex;
 	}
 
-	public static MeshEdge GetClosestEdge( this SceneTrace trace, int radius )
+	public static MeshEdge GetClosestEdge( this SceneTrace trace, int radius ) => GetClosestEdge( trace, radius, out _, out _ );
+
+	public static MeshEdge GetClosestEdge( this SceneTrace trace, int radius, out MeshFace bestFace, out Vector3 hitPosition )
 	{
 		var point = RayScreenPosition;
-		var bestFace = TraceFace( trace, out var bestHitDistance );
+		bestFace = TraceFace( trace, out var bestHitDistance, out _ );
-		var hitPosition = Gizmo.CurrentRay.Project( bestHitDistance );
+		hitPosition = Gizmo.CurrentRay.Project( bestHitDistance );
 		var bestEdge = bestFace.GetClosestEdge( hitPosition, point, radius );
 
 		if ( bestFace.IsValid() && bestEdge.IsValid() )
@@ -66,14 +70,26 @@ static class SceneTraceMeshExtensions
 		return bestEdge;
 	}
 
-	static MeshFace TraceFace( this SceneTrace trace, out float distance )
+	public static MeshFace TraceFace( this SceneTrace trace )
+	{
+		return TraceFace( trace, out _, out _ );
+	}
+
+	public static MeshFace TraceFace( this SceneTrace trace, out Vector3 hitPosition )
+	{
+		return TraceFace( trace, out _, out hitPosition );
+	}
+
+	static MeshFace TraceFace( this SceneTrace trace, out float distance, out Vector3 hitPosition )
 	{
 		distance = default;
+		hitPosition = default;
 
 		var result = trace.Run();
 		if ( !result.Hit || result.Component is not MeshComponent component )
 			return default;
 
+		hitPosition = result.HitPosition;
 		distance = result.Distance;
 		var face = component.Mesh.TriangleToFace( result.Triangle );
 		return new MeshFace( component, face );
@@ -115,4 +131,40 @@ static class SceneTraceMeshExtensions
 
 		return faces;
 	}
+
+	public static MeshFace TraceFace( this SceneTrace trace, int radius, out Vector3 hitPosition )
+	{
+		MeshFace closest = default;
+		var closestDist = float.MaxValue;
+		var closestPoint = Vector3.Zero;
+		var point = RayScreenPosition;
+
+		void TestRay( Ray ray )
+		{
+			var result = trace.Ray( ray, Gizmo.RayDepth ).Run();
+			if ( !result.Hit || result.Distance >= closestDist )
+				return;
+
+			if ( result.Component is not MeshComponent component )
+				return;
+
+			closest = new MeshFace( component, component.Mesh.TriangleToFace( result.Triangle ) );
+			closestDist = result.Distance;
+			closestPoint = result.HitPosition;
+		}
+
+		TestRay( Gizmo.CurrentRay );
+
+		for ( var ring = 1; ring < radius; ring++ )
+		{
+			TestRay( Gizmo.Camera.GetRay( point + new Vector2( 0, ring ) ) );
+			TestRay( Gizmo.Camera.GetRay( point + new Vector2( ring, 0 ) ) );
+			TestRay( Gizmo.Camera.GetRay( point + new Vector2( 0, -ring ) ) );
+			TestRay( Gizmo.Camera.GetRay( point + new Vector2( -ring, 0 ) ) );
+		}
+
+		hitPosition = closestPoint;
+
+		return closest;
+	}
 }

game/addons/tools/Code/Scene/Mesh/Tools/VertexTool.UI.cs

@@ -14,6 +14,7 @@ partial class VertexTool
 		private readonly MeshVertex[] _vertices;
 		private readonly List<IGrouping<MeshComponent, MeshVertex>> _vertexGroups;
 		private readonly List<MeshComponent> _components;
+		readonly MeshTool _tool;
 
 		public enum MergeRange
 		{
@@ -39,6 +40,8 @@ partial class VertexTool
 
 		public VertexSelectionWidget( SerializedObject so, MeshTool tool ) : base()
 		{
+			_tool = tool;
+
 			AddTitle( "Vertex Mode", "workspaces" );
 
 			{
@@ -86,6 +89,7 @@ partial class VertexTool
 					CreateButton( "Weld UVs", "scatter_plot", "mesh.vertex-weld-uvs", WeldUVs, _vertices.Length > 0, row.Layout );
 					CreateButton( "Bevel", "straighten", "mesh.bevel", Bevel, _vertices.Length > 0, row.Layout );
 					CreateButton( "Connect", "link", "mesh.connect", Connect, _vertices.Length > 1, row.Layout );
+					CreateButton( "Edge Cut Tool", "content_cut", "mesh.edge-cut-tool", OpenEdgeCutTool, true, row.Layout );
 
 					row.Layout.AddStretchCell();
 
@@ -96,6 +100,14 @@ partial class VertexTool
 			Layout.AddStretchCell();
 		}
 
+		[Shortcut( "mesh.edge-cut-tool", "C", typeof( SceneDock ) )]
+		void OpenEdgeCutTool()
+		{
+			var tool = new EdgeCutTool( nameof( VertexTool ) );
+			tool.Manager = _tool.Manager;
+			_tool.CurrentTool = tool;
+		}
+
 		[Shortcut( "mesh.connect", "V", typeof( SceneDock ) )]
 		private void Connect()
 		{