Created
April 26, 2020 21:35
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Triangulate function to extract the triangles from a list of vertices to construct a mesh in Unity
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public class Triangulator | |
{ | |
private List<Vector2> m_points = new List<Vector2>(); | |
public Triangulator (Vector2[] points) { | |
m_points = new List<Vector2>(points); | |
} | |
public int[] Triangulate() { | |
List<int> indices = new List<int>(); | |
int n = m_points.Count; | |
if (n < 3) | |
return indices.ToArray(); | |
int[] V = new int[n]; | |
if (Area() > 0) { | |
for (int v = 0; v < n; v++) | |
V[v] = v; | |
} | |
else { | |
for (int v = 0; v < n; v++) | |
V[v] = (n - 1) - v; | |
} | |
int nv = n; | |
int count = 2 * nv; | |
for (int v = nv - 1; nv > 2; ) { | |
if ((count--) <= 0) | |
return indices.ToArray(); | |
int u = v; | |
if (nv <= u) | |
u = 0; | |
v = u + 1; | |
if (nv <= v) | |
v = 0; | |
int w = v + 1; | |
if (nv <= w) | |
w = 0; | |
if (Snip(u, v, w, nv, V)) { | |
int a, b, c, s, t; | |
a = V[u]; | |
b = V[v]; | |
c = V[w]; | |
indices.Add(a); | |
indices.Add(b); | |
indices.Add(c); | |
for (s = v, t = v + 1; t < nv; s++, t++) | |
V[s] = V[t]; | |
nv--; | |
count = 2 * nv; | |
} | |
} | |
indices.Reverse(); | |
return indices.ToArray(); | |
} | |
private float Area () { | |
int n = m_points.Count; | |
float A = 0.0f; | |
for (int p = n - 1, q = 0; q < n; p = q++) { | |
Vector2 pval = m_points[p]; | |
Vector2 qval = m_points[q]; | |
A += pval.x * qval.y - qval.x * pval.y; | |
} | |
return (A * 0.5f); | |
} | |
private bool Snip (int u, int v, int w, int n, int[] V) { | |
int p; | |
Vector2 A = m_points[V[u]]; | |
Vector2 B = m_points[V[v]]; | |
Vector2 C = m_points[V[w]]; | |
if (Mathf.Epsilon > (((B.x - A.x) * (C.y - A.y)) - ((B.y - A.y) * (C.x - A.x)))) | |
return false; | |
for (p = 0; p < n; p++) { | |
if ((p == u) || (p == v) || (p == w)) | |
continue; | |
Vector2 P = m_points[V[p]]; | |
if (InsideTriangle(A, B, C, P)) | |
return false; | |
} | |
return true; | |
} | |
private bool InsideTriangle (Vector2 A, Vector2 B, Vector2 C, Vector2 P) { | |
float ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy; | |
float cCROSSap, bCROSScp, aCROSSbp; | |
ax = C.x - B.x; ay = C.y - B.y; | |
bx = A.x - C.x; by = A.y - C.y; | |
cx = B.x - A.x; cy = B.y - A.y; | |
apx = P.x - A.x; apy = P.y - A.y; | |
bpx = P.x - B.x; bpy = P.y - B.y; | |
cpx = P.x - C.x; cpy = P.y - C.y; | |
aCROSSbp = ax * bpy - ay * bpx; | |
cCROSSap = cx * apy - cy * apx; | |
bCROSScp = bx * cpy - by * cpx; | |
return ((aCROSSbp >= 0.0f) && (bCROSScp >= 0.0f) && (cCROSSap >= 0.0f)); | |
} | |
} |
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