/// <summary>
/// 对vertices组成的多边形三角形化.
/// <para>earTips为当前的耳朵的索引.</para>
static List<Vertex> DoTriangulate(ArrayLinkedList<EarVertex> vertices, ArrayLinkedList<int> earTips)
{
// N边行, 形成N-2个三角形, 共3*(N-2)个顶点.
List<Vertex> answer = new List<Vertex>((vertices.Count - 2) * 3);
// 被移除的耳朵.
EarVertex[] removedEars = new EarVertex[2];
int removedEarCount = 0;
// 需要被移除的耳朵的在earTips中的索引.
int earTipIndex = -1;
for (var e = earTips.GetEnumerator(); e.MoveNext(); )
{
if (earTipIndex >= 0) { earTips.RemoveAt(earTipIndex); }
earTipIndex = e.CurrentIndex;
// 需要移除的耳朵的在vertices中的索引.
int earTipVertexIndex = earTips[earTipIndex];
// 需要移除的耳朵节点.
EarVertex earTipVertex = vertices[earTipVertexIndex];
// 耳朵节点的上一个节点.
int prevIndex = vertices.PrevIndex(earTipVertexIndex);
EarVertex prevVertex = vertices.PrevValue(earTipVertexIndex);
// 耳朵节点的下一个节点.
int nextIndex = vertices.NextIndex(earTipVertexIndex);
EarVertex nextVertex = vertices.NextValue(earTipVertexIndex);
// 构成新的三角形.
answer.Add(prevVertex.vertex);
answer.Add(earTipVertex.vertex);
answer.Add(nextVertex.vertex);
// 以该节点为耳尖的耳朵已被"切掉", 移除这个节点.
vertices.RemoveAt(earTipVertexIndex);
// 更新该节点的上节点的状态.
int state = UpdateEarVertexState(vertices, prevIndex);
// 加入新的耳朵.
if (state > 0)
{
prevVertex.earListIndex = earTips.Add(prevIndex);
}
// 收集之前是, 而现在不再是耳朵的节点.
else if (state < 0)
{
removedEars[removedEarCount++] = prevVertex;
}
// 更新该节点的下节点的状态.
state = UpdateEarVertexState(vertices, nextIndex);
if (state > 0)
{
nextVertex.earListIndex = earTips.Add(nextIndex);
}
else if (state < 0)
{
removedEars[removedEarCount++] = nextVertex;
}
// 在earTips中移除之前是, 现在不是耳朵的节点.
for (int i = 0; i < removedEarCount; ++i)
{
Utility.Verify(removedEars[i].earListIndex >= 0);
earTips.RemoveAt(removedEars[i].earListIndex);
removedEars[i].earListIndex = -1;
}
removedEarCount = 0;
}
// 移除最后一个耳朵, 清空earTips.
if (earTipIndex >= 0) { earTips.RemoveAt(earTipIndex); }
return answer;
}
/// <summary>
/// 检查vertices[index]的内角, 是否为优角.
/// </summary>
/// <param name="vertices"></param>
/// <param name="index"></param>
/// <returns></returns>
static bool CheckIsReflex(ArrayLinkedList<EarVertex> vertices, int index)
{
Vertex current = vertices[index].vertex;
Vertex prev = vertices.PrevValue(index).vertex;
Vertex next = vertices.NextValue(index).vertex;
return next.Position.cross2(prev.Position, current.Position) < 0f;
}
