# using Subdiv2D to find quad problem

I'm trying to make some free form deformation and some algorithms says they need quad instead of triangle. So I try to modify the triangle finding code copyied from somewhere into the quad one. I make a subclass

```
class MyDelauny : public Subdiv2D
and do something like:
void fourVertex(vector<int> &triangleList) const
{
{
vector<int> clean;
triangleList.swap(clean);
}
int i, total = (int)(qedges.size() * 4);
std::vector<bool> edgemask(total, false);
const bool filterPoints = true;
Rect2f rect(topLeft.x, topLeft.y, bottomRight.x - topLeft.x, bottomRight.y - topLeft.y);
for (i = 4; i < total; i += 2)
{
if (edgemask[i])
continue;
Point2f a, b, c,d;
int edge_a = i;
int indexA = edgeOrg(edge_a, &a) - 4;
if (filterPoints && !rect.contains(a))
continue;
int edge_b = getEdge(edge_a, NEXT_AROUND_LEFT);
int indexB = edgeOrg(edge_b, &b) - 4;
if (filterPoints && !rect.contains(b))
continue;
int edge_c = getEdge(edge_b, NEXT_AROUND_LEFT);
int indexC = edgeOrg(edge_c, &c) - 4;
if (filterPoints && !rect.contains(c))
continue;
int edge_d = getEdge(edge_a, NEXT_AROUND_RIGHT);
int indexD = edgeOrg(edge_d, &d) - 4;;
if (filterPoints && !rect.contains(d))
continue;
edgemask[edge_a] = true;
edgemask[edge_b] = true;
edgemask[edge_c] = true;
edgemask[edge_d] = true;
triangleList.push_back(indexA);
triangleList.push_back(indexB);
triangleList.push_back(indexC);
triangleList.push_back(indexD);
}
}
```

Since I already can get the triangle form 2 NEXT_AROUND_LEFT (blue) , If I add another NEXT_AROUND_RIGHT (red) then I can get a quad.

After outputting the vectors, I draw the points and link they together

looks not bad but actually the quad drew twice becasue I just add an edge to a triangle.

I tried to record which vertex I have alread used and not to use it to find quad but it results in too few quad .

needs help for better ways to find quads.thanks a lot!