// Split a polygon by a plane, this is a bit faster than clipping twice with the flipped
// plane, and will guarantee that points are exact
public static SplitPolygon SplitPolygonByPlane(IEnumerable <IVertex> vertList, ClipPlane plane)
{
if (plane == null)
{
throw new ArgumentNullException("plane");
}
if (vertList == null)
{
throw new ArgumentNullException("vertList");
}
List <IVertex> front_list = new List <IVertex>();
List <IVertex> back_list = new List <IVertex>();
ClipSide firstPointSide = ClipSide.CoPlanar;
ClipSide lastPointSide = ClipSide.CoPlanar;
IVertex lastVertex = null;
IVertex firstVertex = null;
bool isCoPlanar = true;
foreach (var v in vertList)
{
if (lastVertex == null)
{
// This is the first vertex in the list, so it is specially handled
// because we have no prior state, and, we'll need to refer to it with
// regards to the final vertex
firstVertex = lastVertex = v;
firstPointSide = lastPointSide = plane.ClassifyPoint(v.Position);
isCoPlanar = isCoPlanar && firstPointSide == ClipSide.CoPlanar;
// Emit the point to both sides if coplanar, otherwise emit
// it to the particular side it is
if (firstPointSide == ClipSide.CoPlanar)
{
front_list.Add(v);
back_list.Add(v);
}
else if (firstPointSide == ClipSide.Back)
{
back_list.Add(v);
}
else
{
front_list.Add(v);
}
continue;
}
// Classify the current point to the plane
ClipSide currPointSide = plane.ClassifyPoint(v.Position);
isCoPlanar = isCoPlanar && currPointSide == ClipSide.CoPlanar;
// One thing to be mindful of is to generate the intersection points in a consistent manner by
// calling the intersection function with the verts in the same order.
if (lastPointSide == ClipSide.CoPlanar)
{
// The last point was on the split plane
if (currPointSide == ClipSide.CoPlanar)
{
// Still on the split plane
front_list.Add(v);
back_list.Add(v);
}
else if (currPointSide == ClipSide.Back)
{
// Going from the split plane to the backside
back_list.Add(v);
}
else
{
// Going from the split plane to the frontside
front_list.Add(v);
}
}
else if (lastPointSide == ClipSide.Front)
{
// Last point was in the front
if (currPointSide == ClipSide.CoPlanar)
{
// Front -> coplanar
front_list.Add(v);
back_list.Add(v);
}
else if (currPointSide == ClipSide.Back)
{
// Front -> Back
var intersected_pt = plane.IntersectEdge(lastVertex, v);
front_list.Add(intersected_pt);
back_list.Add(intersected_pt);
back_list.Add(v);
}
else
{
// Front -> Front
front_list.Add(v);
}
}
else
{
// Last point was in the back
if (currPointSide == ClipSide.CoPlanar)
{
// Back -> coplanar
front_list.Add(v);
back_list.Add(v);
}
else if (currPointSide == ClipSide.Back)
{
// Back -> Back
back_list.Add(v);
}
else
{
// Back -> Front
var intersected_pt = plane.IntersectEdge(v, lastVertex);
back_list.Add(intersected_pt);
front_list.Add(intersected_pt);
front_list.Add(v);
}
}
lastPointSide = currPointSide;
lastVertex = v;
}
// To finish up we need to handle the edge from the last vertex back to the first vertex
// This is only necessary if the last point and the first point were on different sides of the plane
if (firstPointSide != lastPointSide)
{
// We ended up in a different area then the first point
if (firstPointSide == ClipSide.CoPlanar || lastPointSide == ClipSide.CoPlanar)
{
// If we started or ended on a co-planar point, then we don't have to add more
}
else if (firstPointSide == ClipSide.Back)
{
// We started in the back, we ended in the front
var intersection_pt = plane.IntersectEdge(lastVertex, firstVertex);
front_list.Add(intersection_pt);
back_list.Add(intersection_pt);
}
else if (firstPointSide == ClipSide.Front)
{
// We started in the front, we ended in the back
var intersection_pt = plane.IntersectEdge(firstVertex, lastVertex);
front_list.Add(intersection_pt);
back_list.Add(intersection_pt);
}
}
var res = new SplitPolygon();
if (isCoPlanar)
{
front_list = CleanDegenerates(front_list).ToList();
res.coplaner = front_list.Count > 2 ? front_list.ToArray() : null;
res.front = null;
res.back = null;
}
else
{
// If there we some verts co-planar, but not all, and the remaining
// verts are on one side, then the other side will have some verts, but not a full triangle
front_list = CleanDegenerates(front_list).ToList();
back_list = CleanDegenerates(back_list).ToList();
res.front = front_list.Count > 2 ? front_list.ToArray() : null;
res.back = back_list.Count > 2 ? back_list.ToArray() : null;
res.coplaner = null;
}
return(res);
}
/// <summary>
/// Generic implementation of Sutherland–Hodgman clipping algorithm
/// </summary>
/// <param name="vertList"></param>
/// <returns></returns>
public static IEnumerable <IVertex> ClipToPlaneRaw(IEnumerable <IVertex> vertList, ClipPlane plane)
{
if (plane == null)
{
throw new ArgumentNullException("plane");
}
if (vertList == null)
{
yield break;
}
ClipSide firstPointSide = ClipSide.CoPlanar;
ClipSide lastPointSide = ClipSide.CoPlanar;
IVertex lastVertex = null;
IVertex firstVertex = null;
foreach (var v in vertList)
{
if (lastVertex == null)
{
// This is the first vertex in the list, so it is specially handled
// because we have no prior state, and, we'll need to refer to it with
// regards to the final vertex
firstVertex = lastVertex = v;
firstPointSide = lastPointSide = plane.ClassifyPoint(v.Position);
// If this point is in front of the plane, emit it
if (firstPointSide != ClipSide.Back)
{
yield return(v);
}
continue;
}
// Classify the current point to the plane
ClipSide currPointSide = plane.ClassifyPoint(v.Position);
// We have 4 possible situations:
// 1) Last point in front of the plane, current point in front of the plane:
// In this situation emit the current point
// 2) Last point in front of the plane, current point is behind the plane:
// In this situation emit the intersection point of the plane and the edge (last, curr)
// 3) Last point in back of the plane, current point is behind the plane:
// In this situation do not emit anything
// 4) Last point in back of the plane, current point in front of the plane:
// In this situation emit the intersection point of the plane and the edge (curr, last), and
// then emit the current point
//
// One thing to be mindful of is to generate the intersection points in a consistent manner by
// calling the intersection function with the verts in the same order.
if (lastPointSide != ClipSide.Back)
{
if (currPointSide != ClipSide.Back)
{
// Situation 1
yield return(v);
}
else
{
// Situation 2
yield return(plane.IntersectEdge(lastVertex, v));
}
}
else
{
if (currPointSide != ClipSide.Back)
{
// Situation 4
yield return(plane.IntersectEdge(v, lastVertex));
yield return(v);
}
}
lastPointSide = currPointSide;
lastVertex = v;
}
// To finish up we need to handle the edge from the last vertex back to the first vertex
// This is only necessary if the last point and the first point were on different sides of the plane
bool firstInFront = firstPointSide != ClipSide.Back;
bool lastInFront = lastPointSide != ClipSide.Back;
if (firstInFront != lastInFront)
{
if (firstInFront)
{
yield return(plane.IntersectEdge(firstVertex, lastVertex));
}
else
{
yield return(plane.IntersectEdge(lastVertex, firstVertex));
}
}
}