/// <summary>
/// Split brush polygons by a supplied plane, outputing the polygons on either side and capping the two halves on the plane
/// </summary>
/// <returns><c>true</c>, if splitting actually took place, <c>false</c> otherwise.</returns>
/// <param name="polygons">Source polygons.</param>
/// <param name="splitPlane">Split plane.</param>
/// <param name="excludeNewPolygons">If set to <c>true</c> the cap polygons will be marked as excludeFromBuild.</param>
/// <param name="polygonsFront">Generated polygons in front of the plane.</param>
/// <param name="polygonsBack">Generated polygons behind the plane.</param>
public static bool SplitPolygonsByPlane(List <Polygon> polygons, // Source polygons that will be split
Plane splitPlane,
bool excludeNewPolygons, // Whether new polygons should be marked as excludeFromBuild
out List <Polygon> polygonsFront,
out List <Polygon> polygonsBack)
{
polygonsFront = new List <Polygon>();
polygonsBack = new List <Polygon>();
// First of all make sure splitting actually needs to occur (we'll get bad issues if
// we try splitting geometry when we don't need to)
if (!GeometryHelper.PolygonsIntersectPlane(polygons, splitPlane))
{
return(false);
}
// For copying the material and color from the nearest polygons to the clipping to the generated polygons
Material newMaterial = polygons[0].Material;
Color newColor = polygons[0].Vertices[0].Color;
// These are the vertices that will be used in the new caps
List <Vertex> newVertices = new List <Vertex>();
for (int polygonIndex = 0; polygonIndex < polygons.Count; polygonIndex++)
{
Polygon.PolygonPlaneRelation planeRelation = Polygon.TestPolygonAgainstPlane(polygons[polygonIndex], splitPlane);
// Polygon has been found to span both sides of the plane, attempt to split into two pieces
if (planeRelation == Polygon.PolygonPlaneRelation.Spanning)
{
Polygon frontPolygon;
Polygon backPolygon;
Vertex newVertex1;
Vertex newVertex2;
// Attempt to split the polygon
if (Polygon.SplitPolygon(polygons[polygonIndex], out frontPolygon, out backPolygon, out newVertex1, out newVertex2, splitPlane))
{
// If the split algorithm was successful (produced two valid polygons) then add each polygon to
// their respective points and track the intersection points
polygonsFront.Add(frontPolygon);
polygonsBack.Add(backPolygon);
newVertices.Add(newVertex1);
newVertices.Add(newVertex2);
newMaterial = polygons[polygonIndex].Material;
newColor = polygons[0].Vertices[0].Color;
}
else
{
// Two valid polygons weren't generated, so use the valid one
if (frontPolygon != null)
{
planeRelation = Polygon.PolygonPlaneRelation.InFront;
}
else if (backPolygon != null)
{
planeRelation = Polygon.PolygonPlaneRelation.Behind;
}
else
{
Debug.LogError("Polygon splitting has resulted in two zero area polygons. This is unhandled.");
// Polygon.PolygonPlaneRelation secondplaneRelation = Polygon.TestPolygonAgainstPlane(polygons[polygonIndex], splitPlane);
}
}
}
// If the polygon is on one side of the plane or the other
if (planeRelation != Polygon.PolygonPlaneRelation.Spanning)
{
// Make sure any points that are coplanar on non-straddling polygons are still used in polygon
// construction
for (int vertexIndex = 0; vertexIndex < polygons[polygonIndex].Vertices.Length; vertexIndex++)
{
if (Polygon.ComparePointToPlane(polygons[polygonIndex].Vertices[vertexIndex].Position, splitPlane) == Polygon.PointPlaneRelation.On)
{
newVertices.Add(polygons[polygonIndex].Vertices[vertexIndex]);
}
}
if (planeRelation == Polygon.PolygonPlaneRelation.Behind)
{
polygonsBack.Add(polygons[polygonIndex]);
}
else
{
polygonsFront.Add(polygons[polygonIndex]);
}
}
}
// If any splits occured or coplanar vertices are found. (For example if you're splitting a sphere at the
// equator then no polygons will be split but there will be a bunch of coplanar vertices!)
if (newVertices.Count > 0)
{
// HACK: This code is awful, because we end up with lots of duplicate vertices
List <Vector3> positions = newVertices.Select(item => item.Position).ToList();
Polygon newPolygon = PolygonFactory.ConstructPolygon(positions, true);
// Assuming it was possible to create a polygon
if (newPolygon != null)
{
if (!MathHelper.PlaneEqualsLooser(newPolygon.Plane, splitPlane))
{
// Polygons are sometimes constructed facing the wrong way, possibly due to a winding order
// mismatch. If the two normals are opposite, flip the new polygon
if (Vector3.Dot(newPolygon.Plane.normal, splitPlane.normal) < -0.9f)
{
newPolygon.Flip();
}
}
newPolygon.ExcludeFromFinal = excludeNewPolygons;
// Copy the material and color from the nearest polygons to the new polygon
newPolygon.Material = newMaterial;
newPolygon.SetColor(newColor);
polygonsFront.Add(newPolygon);
newPolygon = newPolygon.DeepCopy();
newPolygon.Flip();
newPolygon.ExcludeFromFinal = excludeNewPolygons;
// Copy the material and color from the nearest polygons to the new polygon
newPolygon.Material = newMaterial;
newPolygon.SetColor(newColor);
if (newPolygon.Plane.normal == Vector3.zero)
{
Debug.LogError("Invalid Normal! Shouldn't be zero. This is unexpected since extraneous positions should have been removed!");
// Polygon fooNewPolygon = PolygonFactory.ConstructPolygon(positions, true);
}
polygonsBack.Add(newPolygon);
}
return(true);
}
else
{
// It wasn't possible to create the polygon, for example the constructed polygon was too small
// This could happen if you attempt to clip the tip off a long but thin brush, the plane-polyhedron test
// would say they intersect but in reality the resulting polygon would be near zero area
return(false);
}
}