Select mesh element

Questions & Answers
1

Hi! What is the approach to detect elements inside the mesh? Like, same to functionality that 3Ds Max Has - “select element”?
I can think of some ways, but looping all over and looping all over seems more like workaround then solution to me, so before posting any of my pseudo code I’ll gladly hear any advices on how to approach that task.

2

List<MeshExtrusion.Edge> _borders = MeshExtrusion.BuildManifoldEdges(_mm);
Dictionary<int, Color32> _colorKeys = new Dictionary<int, Color32>();

                         while (_borders.Count > 0)
                         {

                             List<MeshExtrusion.Edge> _takeusaway = new List<MeshExtrusion.Edge>();
                             List<int> _candidates = new List<int>();
                             _candidates.Add(_borders[0].vertexIndex[0]);
                             List<int> _openNewSearches = new List<int>();
                             List<int> _searched = new List<int>();
                             Color32 _startingColor = new Color32((byte)(UnityEngine.Random.value * 255), (byte)(UnityEngine.Random.value * 255), (byte)(UnityEngine.Random.value * 255), 255);


                             while (_candidates.Count > 0)
                             {
                                 for (int p = 0; p < _candidates.Count; p++)
                                 {
                                     if (!_searched.Contains(_candidates[p]))
                                     {
                                         for (int s = 0; s < _borders.Count; s++)
                                         {
                                             //_openNewSearches.Add(_candidates[p]);
                                             if (!_openNewSearches.Contains(_borders~~.vertexIndex[1]))~~

{
if (_borders~~.vertexIndex[0] == _candidates[p])
{
_openNewSearches.Add(_borders.vertexIndex[1]);~~

if (!_colorKeys.ContainsKey(_borders~~.vertexIndex[1]))
{
_colorKeys.Add(_borders.vertexIndex[1], _startingColor);
}~~

if (!_takeusaway .Contains(_borders~~))
{
_takeusaway .Add(_borders);
}~~

}
}
}

_searched.Add(_candidates[p]);

}

}

_candidates = new List();
for (int g = 0; g < _openNewSearches.Count; g++)
{
_candidates.Add(_openNewSearches[g]);
}
_openNewSearches = new List();
}

for (int i = 0; i < _takeusaway .Count; i++)
{
_borders.Remove(_takeusaway );
}

}

3

I think this is a more straight forward solution, less code without pre-calculating edges. Explanation on my blog:
http://dantefalcone.name/finding-linked-faces-elements-within-a-3d-model-mesh-with-unity3d-and-c/

/// <summary>
/// Given two faces, return whether they share any common vertices.
/// </summary>
/// <param name="faceA">Face represented as array of vertex indices.</param>
/// <param name="faceB">Face represented as array of vertex indices.</param>
/// <returns>bool - whether the faces are connected. </returns>
bool IsConnected(int[] faceA, int[] faceB)
{
    for (int i = 0; i < faceA.Length; i++)
        for (int j = 0; j < faceB.Length; j++)
            if (faceA *== faceB[j])*

return true;
return false;
}

///


/// Given a single triangle face of vertex indices,
/// returns a list of all the vertices of all linked faces.
///
/// A known triangle to start search.
/// Triangle index list of all vertices in mesh.
/// List - All triangle face indices that represent the surface element.
public List GetElement(int[] pickedTriangle, List triangles)
{
// Create the return result list,
// starting with the current picked face
List result = new List(pickedTriangle);

// Iterate through the triangle list index buffer
// by triangle (iterations of 3)
for (int i = 0; i < triangles.Count; i += 3)
{
// Select the (i)th triangle in the index buffer
int[] curTriangle = new int[3] {
triangles*,*
triangles[i + 1],
triangles[i + 2] };

// Check if faces are linked
if (IsConnected(curTriangle, pickedTriangle))
{
// Recursively add all the linked faces to the result
result.AddRange(GetElement(curTriangle, triangles));
}
}

return result;
}

4

Interesting but unfortunately the recursive call would iterate a billion times on complex objects so the connective test spot faces within a smoothing group only to extend by distances the time get quickly unacceptable …