# Finding the vertices of each edge on mesh

I’m fairly new to unity and game development is general so sorry in advance if this is a stupid question!
Basically i’d like to know how i can get all of the vertices of a mesh along each of the sides (its a flat plane with a height map applied to it) and then stitch them to the adjacent mesh.

Just ran this and I think it does the job…

``````/// Builds an array of edges that connect to only one triangle.
/// In other words, the outline of the mesh
public static Edge[] BuildManifoldEdges(Mesh mesh)
{
// Build a edge list for all unique edges in the mesh
Edge[] edges = BuildEdges(mesh.vertexCount, mesh.triangles);

// We only want edges that connect to a single triangle
ArrayList culledEdges = new ArrayList();
foreach (Edge edge in edges)
{
if (edge.faceIndex[0] == edge.faceIndex[1])
{
}
}

return culledEdges.ToArray(typeof(Edge)) as Edge[];
}

/// Builds an array of unique edges
/// This requires that your mesh has all vertices welded. However on import, Unity has to split
/// vertices at uv seams and normal seams. Thus for a mesh with seams in your mesh you
/// will get two edges adjoining one triangle.
/// Often this is not a problem but you can fix it by welding vertices
/// and passing in the triangle array of the welded vertices.
public static Edge[] BuildEdges(int vertexCount, int[] triangleArray)
{
int maxEdgeCount = triangleArray.Length;
int[] firstEdge = new int[vertexCount + maxEdgeCount];
int nextEdge = vertexCount;
int triangleCount = triangleArray.Length / 3;

for (int a = 0; a < vertexCount; a++)
firstEdge[a] = -1;

// First pass over all triangles. This finds all the edges satisfying the
// condition that the first vertex index is less than the second vertex index
// when the direction from the first vertex to the second vertex represents
// a counterclockwise winding around the triangle to which the edge belongs.
// For each edge found, the edge index is stored in a linked list of edges
// belonging to the lower-numbered vertex index i. This allows us to quickly
// find an edge in the second pass whose higher-numbered vertex index is i.
Edge[] edgeArray = new Edge[maxEdgeCount];

int edgeCount = 0;
for (int a = 0; a < triangleCount; a++)
{
int i1 = triangleArray[a * 3 + 2];
for (int b = 0; b < 3; b++)
{
int i2 = triangleArray[a * 3 + b];
if (i1 < i2)
{
Edge newEdge = new Edge();
newEdge.vertexIndex[0] = i1;
newEdge.vertexIndex[1] = i2;
newEdge.faceIndex[0] = a;
newEdge.faceIndex[1] = a;
edgeArray[edgeCount] = newEdge;

int edgeIndex = firstEdge[i1];
if (edgeIndex == -1)
{
firstEdge[i1] = edgeCount;
}
else
{
while (true)
{
int index = firstEdge[nextEdge + edgeIndex];
if (index == -1)
{
firstEdge[nextEdge + edgeIndex] = edgeCount;
break;
}

edgeIndex = index;
}
}

firstEdge[nextEdge + edgeCount] = -1;
edgeCount++;
}

i1 = i2;
}
}

// Second pass over all triangles. This finds all the edges satisfying the
// condition that the first vertex index is greater than the second vertex index
// when the direction from the first vertex to the second vertex represents
// a counterclockwise winding around the triangle to which the edge belongs.
// For each of these edges, the same edge should have already been found in
// the first pass for a different triangle. Of course we might have edges with only one triangle
// in that case we just add the edge here
// So we search the list of edges
// for the higher-numbered vertex index for the matching edge and fill in the
// second triangle index. The maximum number of comparisons in this search for
// any vertex is the number of edges having that vertex as an endpoint.

for (int a = 0; a < triangleCount; a++)
{
int i1 = triangleArray[a * 3 + 2];
for (int b = 0; b < 3; b++)
{
int i2 = triangleArray[a * 3 + b];
if (i1 > i2)
{
bool foundEdge = false;
for (int edgeIndex = firstEdge[i2]; edgeIndex != -1; edgeIndex = firstEdge[nextEdge + edgeIndex])
{
Edge edge = edgeArray[edgeIndex];
if ((edge.vertexIndex[1] == i1) && (edge.faceIndex[0] == edge.faceIndex[1]))
{
edgeArray[edgeIndex].faceIndex[1] = a;
foundEdge = true;
break;
}
}

if (!foundEdge)
{
Edge newEdge = new Edge();
newEdge.vertexIndex[0] = i1;
newEdge.vertexIndex[1] = i2;
newEdge.faceIndex[0] = a;
newEdge.faceIndex[1] = a;
edgeArray[edgeCount] = newEdge;
edgeCount++;
}
}

i1 = i2;
}
}

Edge[] compactedEdges = new Edge[edgeCount];
for (int e = 0; e < edgeCount; e++)
compactedEdges[e] = edgeArray[e];

return compactedEdges;
}
}

public class Edge
{
// The indiex to each vertex
public int[] vertexIndex = new int[2];
// The index into the face.
// (faceindex[0] == faceindex[1] means the edge connects to only one triangle)
public int[] faceIndex = new int[2];
}
``````