/// <summary>
/// Checks if polygon is valid for use in Box2d engine.
/// Last ditch effort to ensure no invalid polygons are
/// added to world geometry.
///
/// Performs a full check, for simplicity, convexity,
/// orientation, minimum angle, and volume. This won't
/// be very efficient, and a lot of it is redundant when
/// other tools in this section are used.
///
/// From Eric Jordan's convex decomposition library
/// </summary>
/// <param name="printErrors"></param>
/// <returns></returns>
public PolygonError CheckPolygon()
{
PolygonError error = PolygonError.None;
if (Count < 3 || Count > Point2DList.kMaxPolygonVertices)
{
error |= PolygonError.NotEnoughVertices;
// no other tests will be valid at this point, so just return
return(error);
}
if (IsDegenerate())
{
error |= PolygonError.Degenerate;
}
//bool bIsConvex = IsConvex();
//if (!IsConvex())
//{
// error |= PolygonError.NotConvex;
//}
if (!IsSimple())
{
error |= PolygonError.NotSimple;
}
if (GetArea() < MathUtil.EPSILON)
{
error |= PolygonError.AreaTooSmall;
}
// the following tests don't make sense if the polygon is not simple
if ((error & PolygonError.NotSimple) != PolygonError.NotSimple)
{
bool bReversed = false;
WindingOrderType expectedWindingOrder = WindingOrderType.CCW;
WindingOrderType reverseWindingOrder = WindingOrderType.CW;
if (WindingOrder == reverseWindingOrder)
{
WindingOrder = expectedWindingOrder;
bReversed = true;
}
//Compute normals
Point2D[] normals = new Point2D[Count];
Point2DList vertices = new Point2DList(Count);
for (int i = 0; i < Count; ++i)
{
vertices.Add(new Point2D(this[i].X, this[i].Y));
int i1 = i;
int i2 = NextIndex(i);
Point2D edge = new Point2D(this[i2].X - this[i1].X, this[i2].Y - this[i1].Y);
normals[i] = Point2D.Perpendicular(edge, 1.0);
normals[i].Normalize();
}
//Required side checks
for (int i = 0; i < Count; ++i)
{
int iminus = PreviousIndex(i);
//Parallel sides check
double cross = Point2D.Cross(normals[iminus], normals[i]);
cross = MathUtil.Clamp(cross, -1.0f, 1.0f);
float angle = (float)Math.Asin(cross);
if (Math.Abs(angle) <= Point2DList.kAngularSlop)
{
error |= PolygonError.SidesTooCloseToParallel;
break;
}
// For some reason, the following checks do not seem to work
// correctly in all cases - they return false positives.
// //Too skinny check - only valid for convex polygons
// if (bIsConvex)
// {
// for (int j = 0; j < Count; ++j)
// {
// if (j == i || j == NextIndex(i))
// {
// continue;
// }
// Point2D testVector = vertices[j] - vertices[i];
// testVector.Normalize();
// double s = Point2D.Dot(testVector, normals[i]);
// if (s >= -Point2DList.kLinearSlop)
// {
// error |= PolygonError.TooThin;
// }
// }
// Point2D centroid = vertices.GetCentroid();
// Point2D n1 = normals[iminus];
// Point2D n2 = normals[i];
// Point2D v = vertices[i] - centroid;
// Point2D d = new Point2D();
// d.X = Point2D.Dot(n1, v); // - toiSlop;
// d.Y = Point2D.Dot(n2, v); // - toiSlop;
// // Shifting the edge inward by toiSlop should
// // not cause the plane to pass the centroid.
// if ((d.X < 0.0f) || (d.Y < 0.0f))
// {
// error |= PolygonError.TooThin;
// }
// }
}
if (bReversed)
{
WindingOrder = reverseWindingOrder;
}
}
//if (error != PolygonError.None)
//{
// Console.WriteLine("Found invalid polygon: {0} {1}\n", Point2DList.GetErrorString(error), this.ToString());
//}
return(error);
}
