private static void ComputeEdgeCostAtVertex(ProgMeshVertex v)
{
// compute the edge collapse cost for all edges that start
// from vertex v. Since we are only interested in reducing
// the object by selecting the min cost edge at each step, we
// only cache the cost of the least cost edge at this vertex
// (in member variable collapse) as well as the value of the
// cost (in member variable ObjDist).
if (v.Neighbor.Count == 0)
{
// v doesn't have neighbors so it costs nothing to collapse
v.Collapse = null;
v.ObjDist = -0.01f;
return;
}
v.ObjDist = Constants.FloatMax;
v.Collapse = null;
// search all neighboring edges for "least cost" edge
foreach (var neighbor in v.Neighbor)
{
var dist = ComputeEdgeCollapseCost(v, neighbor);
if (dist < v.ObjDist)
{
v.Collapse = neighbor; // candidate for edge collapse
v.ObjDist = dist; // cost of the collapse
}
}
}
private static float ComputeEdgeCollapseCost(ProgMeshVertex u, ProgMeshVertex v)
{
// if we collapse edge uv by moving u to v then how
// much different will the model change, i.e. how much "error".
// Texture, vertex normal, and border vertex code was removed
// to keep this demo as simple as possible.
// The method of determining cost was designed in order
// to exploit small and coplanar regions for
// effective polygon reduction.
// Is is possible to add some checks here to see if "folds"
// would be generated. i.e. normal of a remaining face gets
// flipped. I never seemed to run into this problem and
// therefore never added code to detect this case.
// find the "sides" triangles that are on the edge uv
var sides = new List <ProgMeshTriangle>(u.Face.Count);
foreach (var face in u.Face)
{
if (face.HasVertex(v))
{
sides.Add(face);
}
}
// use the triangle facing most away from the sides
// to determine our curvature term
var curvature = 0f;
foreach (var face in u.Face)
{
var minCurve = 1f; // curve for face i and closer side to it
foreach (var side in sides)
{
// use dot product of face normals.
var dotProd = face.Normal.Dot(side.Normal);
minCurve = MathF.Min(minCurve, (1f - dotProd) * 0.5f);
}
curvature = MathF.Max(curvature, minCurve);
}
// the more coplanar the lower the curvature term
var edgeLength = v.Position.Sub(u.Position).Magnitude();
return(edgeLength * curvature);
}
public void RemoveIfNonNeighbor(ProgMeshVertex n)
{
// removes n from neighbor Array if n isn't a neighbor.
if (!Neighbor.Contains(n))
{
return;
}
foreach (var face in Face)
{
if (face.HasVertex(n))
{
return;
}
}
ProgMeshUtil.RemoveFillWithBack(Neighbor, n);
}
private void Collapse(ProgMeshVertex u, ProgMeshVertex v)
{
int i;
// Collapse the edge uv by moving vertex u onto v
// Actually remove tris on uv, then update tris that
// have u to have v, and then remove u.
if (v == null)
{
// u is a vertex all by itself so just delete it
u.Dispose(this);
return;
}
var tmp = new ProgMeshVertex[u.Neighbor.Count];
// make tmp a Array of all the neighbors of u
for (i = 0; i < tmp.Length; i++)
{
tmp[i] = u.Neighbor[i];
}
// delete triangles on edge uv:
i = u.Face.Count;
while (i-- > 0)
{
if (u.Face[i].HasVertex(v))
{
u.Face[i].Dispose(this);
}
}
// update remaining triangles to have v instead of u
i = u.Face.Count;
while (i-- > 0)
{
u.Face[i].ReplaceVertex(u, v);
}
u.Dispose(this);
// recompute the edge collapse costs for neighboring vertices
foreach (var t in tmp)
{
ComputeEdgeCostAtVertex(t);
}
}
public void ReplaceVertex(ProgMeshVertex vOld, ProgMeshVertex vNew)
{
Debug.Assert(vOld != null && vNew != null, "[ProgMeshTriangle.ReplaceVertex] Arguments must not be null.");
Debug.Assert(vOld == _vertex[0] || vOld == _vertex[1] || vOld == _vertex[2], "[ProgMeshTriangle.replaceVertex] vOld must not be included in this.vertex.");
Debug.Assert(vNew != _vertex[0] && vNew != _vertex[1] && vNew != _vertex[2], "[ProgMeshTriangle.replaceVertex] vNew must not be included in this.vertex.");
if (vOld == _vertex[0])
{
_vertex[0] = vNew;
}
else if (vOld == _vertex[1])
{
_vertex[1] = vNew;
}
else
{
Debug.Assert(vOld == _vertex[2], "[ProgMeshTriangle.ReplaceVertex] vOld == vertex[2]");
_vertex[2] = vNew;
}
ProgMeshUtil.RemoveFillWithBack(vOld.Face, this);
Debug.Assert(!vNew.Face.Contains(this), "[ProgMeshTriangle.ReplaceVertex] !Contains(vNew->face, this)");
vNew.Face.Add(this);
for (var i = 0; i < 3; i++)
{
vOld.RemoveIfNonNeighbor(_vertex[i]);
_vertex[i].RemoveIfNonNeighbor(vOld);
}
for (var i = 0; i < 3; i++)
{
Debug.Assert(_vertex[i].Face.Count(f => f == this) == 1, "[ProgMeshTriangle.replaceVertex] Contains(vertex[i]->face, this) == 1");
for (var j = 0; j < 3; j++)
{
if (i != j)
{
ProgMeshUtil.AddUnique(_vertex[i].Neighbor, _vertex[j]);
}
}
}
ComputeNormal();
}
public ProgMeshTriangle(ProgMeshVertex v0, ProgMeshVertex v1, ProgMeshVertex v2)
{
Debug.Assert(v0 != null && v1 != null && v2 != null, "[ProgMeshTriangle] Vertices must not be null.");
Debug.Assert(v0 != v1 && v1 != v2 && v2 != v0, "[ProgMeshTriangle] Vertices must be different.");
_vertex = new[] { v0, v1, v2 };
ComputeNormal();
for (var i = 0; i < 3; i++)
{
_vertex[i].Face.Add(this);
for (var j = 0; j < 3; j++)
{
if (i != j)
{
ProgMeshUtil.AddUnique(_vertex[i].Neighbor, _vertex[j]);
}
}
}
}
public bool HasVertex(ProgMeshVertex v)
{
return(v == _vertex[0] || v == _vertex[1] || v == _vertex[2]);
}
