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Make love.math.triangulate with any polygon winding order.

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vrld
2013-03-14 17:21:13 +01:00
parent d39cfbb4fa
commit db86fa4b83
1 changed files with 22 additions and 14 deletions
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src/modules/math/MathModule.cpp
+22 -14
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@@ -144,22 +144,30 @@ vector<Triangle> Math::triangulate(const vector<vertex> &polygon)
else if (polygon.size() == 3)
return vector<Triangle>(1, Triangle(polygon[0], polygon[1], polygon[2]));
vector<size_t> next_vertex(polygon.size()), prev_vertex(polygon.size());
// collect list of connections
// collect list of connections and record leftmost item to check if the polygon
// has the expected winding
vector<size_t> next_idx(polygon.size()), prev_idx(polygon.size());
size_t idx_lm = 0;
for (size_t i = 0; i < polygon.size(); ++i)
{
next_vertex[i] = i+1;
prev_vertex[i] = i-1;
const vertex &lm = polygon[idx_lm], &p = polygon[i];
if (p.x < lm.x || (p.x == lm.x && p.y < lm.y))
idx_lm = i;
next_idx[i] = i+1;
prev_idx[i] = i-1;
}
next_vertex[next_vertex.size()-1] = 0;
prev_vertex[0] = prev_vertex.size()-1;
next_idx[next_idx.size()-1] = 0;
prev_idx[0] = prev_idx.size()-1;
// check if the polygon has the expected winding and reverse polygon if needed
if (!is_oriented_ccw(polygon[prev_idx[idx_lm]], polygon[idx_lm], polygon[next_idx[idx_lm]]))
next_idx.swap(prev_idx);
// collect list of concave polygons
list<const vertex *> concave_vertices;
for (size_t i = 0; i < polygon.size(); ++i)
{
if (!is_oriented_ccw(polygon[prev_vertex[i]], polygon[i], polygon[next_vertex[i]]))
if (!is_oriented_ccw(polygon[prev_idx[i]], polygon[i], polygon[next_idx[i]]))
concave_vertices.push_back(&polygon[i]);
}
@@ -169,14 +177,14 @@ vector<Triangle> Math::triangulate(const vector<vertex> &polygon)
size_t current = 1, skipped = 0, next, prev;
while (n_vertices > 3)
{
next = next_vertex[current];
prev = prev_vertex[current];
next = next_idx[current];
prev = prev_idx[current];
const vertex &a = polygon[prev], &b = polygon[current], &c = polygon[next];
if (is_ear(a,b,c, concave_vertices))
{
triangles.push_back(Triangle(a,b,c));
next_vertex[prev] = next;
prev_vertex[next] = prev;
next_idx[prev] = next;
prev_idx[next] = prev;
concave_vertices.remove(&b);
--n_vertices;
skipped = 0;
@@ -187,8 +195,8 @@ vector<Triangle> Math::triangulate(const vector<vertex> &polygon)
}
current = next;
}
next = next_vertex[current];
prev = prev_vertex[current];
next = next_idx[current];
prev = prev_idx[current];
triangles.push_back(Triangle(polygon[prev], polygon[current], polygon[next]));
return triangles;