/// <summary>
/// Update a vertex as it can change from reflex to convex and convex vertices may
/// become ears when other ears are removed.
/// </summary>
/// <param name="prev">Previous vertex.</param>
/// <param name="curr">Current vertex.</param>
/// <param name="next">Next vertex.</param>
private void UpdateVertex(Vector3 prev, Vector3 curr, Vector3 next)
{
// Check if vertex became convex and update if so
if (reflex.Contains(curr))
{
if (Maths2D.IsConvex(prev, curr, next))
{
reflex.Remove(curr);
convex.AddLast(curr);
}
}
// Check if the vertex is convex and if so, check if it is an ear.
if (convex.Contains(curr))
{
if (CheckIfEar(prev, curr, next))
{
if (!ears.Contains(curr))
{
ears.AddLast(curr);
}
}
else if (ears.Contains(curr))
{
ears.Remove(curr);
}
}
}
/// <summary>
/// Check if a vertex is an ear by iterating over reflex vertices and checking
/// containment inside triangle formed by vertex and neighbours.
/// </summary>
/// <param name="prev">Previous vertex.</param>
/// <param name="curr">Current vertex.</param>
/// <param name="next">Next vertex.</param>
/// <returns>Ear or not.</returns>
private bool CheckIfEar(Vector3 prev, Vector3 curr, Vector3 next)
{
// If any reflex point is inside, it's not an ear.
foreach (var vertex in reflex)
{
if (Maths2D.PointInTriangle(prev.ToXZ(), curr.ToXZ(), next.ToXZ(), vertex.ToXZ()) &&
vertex != prev && vertex != curr && vertex != next)
{
return(false);
}
}
return(true);
}
/// <summary>
/// Construct the necessary lists for triangulation with ear clipping.
/// </summary>
private void PrepareLists()
{
// Get reflex/convex vertices
var j = vertices.Count - 1;
var i = j - 1;
for (int k = 0; k < vertices.Count; k++)
{
if (!Maths2D.IsConvex(vertices[i], vertices[j], vertices[k]))
{
reflex.AddLast(vertices[j]);
}
else
{
convex.AddLast(vertices[j]);
}
i = j;
j = k;
}
// Get ears
var curr = convex.First;
var prev = verts.Find(curr.Value).Previous ?? verts.Last;
var next = verts.Find(curr.Value).Next ?? verts.First;
while (curr != verts.First)
{
if (CheckIfEar(prev.Value, curr.Value, next.Value))
{
ears.AddLast(curr.Value);
}
curr = curr.Next;
if (curr == null)
{
break;
}
prev = verts.Find(curr.Value).Previous ?? verts.Last;
next = verts.Find(curr.Value).Next ?? verts.First;
}
}