// compact triangles, compute edge error and build reference list
void Update_mesh(int iteration)
{
if (iteration > 0) // compact triangles
{
int dst = 0;
for (int i = 0; i < triangles.Count; i++)
{
if (triangles[i].deleted == 0)
{
triangles[dst++] = triangles[i];
}
}
}
//
// Init Quadrics by Plane & Edge Errors
//
// required at the beginning ( iteration == 0 )
// recomputing during the simplification is not required,
// but mostly improves the result for closed meshes
//
if (iteration == 0)
{
for (int i = 0; i < vertices.Count; i++)
{
Vertex v = vertices[i];
v.q = new SymetricMatrix(0.0);
vertices[i] = v;
}
for (int i = 0; i < triangles.Count; i++)
{
Triangle t = triangles[i];
Vector3 n = new Vector3();
Vector3[] p = new Vector3[3];
for (int j = 0; j < 3; j++)
{
p[j] = vertices[t.v[j]].p;
}
n = Vector3.Cross(p[1] - p[0], p[2] - p[0]);
n.Normalize();
t.n = n;
for (int j = 0; j < 3; j++)
{
Vertex v = vertices[t.v[j]];
v.q = vertices[t.v[j]].q + new SymetricMatrix(n.X, n.Y, n.Z, -Vector3.Dot(n, p[0]));
vertices[t.v[j]] = v;
}
triangles[i] = t;
}
for (int i = 0; i < triangles.Count; i++)
{
// Calc Edge Error
Triangle t = triangles[i];
Vector3 p = new Vector3();
for (int j = 0; j < 3; j++)
{
t.err[j] = Calculate_error(t.v[j], t.v[(j + 1) % 3], ref p);
}
t.err[3] = Math.Min(t.err[0], Math.Min(t.err[1], t.err[2]));
triangles[i] = t;
}
}
// Init Reference ID list
for (int i = 0; i < vertices.Count; i++)
{
Vertex v = vertices[i];
v.tstart = 0;
v.tcount = 0;
vertices[i] = v;
}
for (int i = 0; i < triangles.Count; i++)
{
Triangle t = triangles[i];
for (int j = 0; j < 3; i++)
{
Vertex v = vertices[t.v[j]];
v.tcount++;
vertices[t.v[j]] = v;
}
}
int tstart = 0;
for (int i = 0; i < vertices.Count; i++)
{
Vertex v = vertices[i];
v.tstart = tstart;
tstart += v.tcount;
v.tcount = 0;
vertices[i] = v;
}
// Write References
for (int i = 0; i < triangles.Count; i++)
{
Triangle t = triangles[i];
for (int j = 0; j < 3; j++)
{
Vertex v = vertices[t.v[j]];
Ref r = refs[v.tstart + v.tcount];
r.tid = i;
r.tvertex = j;
refs[v.tstart + v.tcount] = r;
v.tcount++;
vertices[t.v[j]] = v;
}
triangles[i] = t;
}
// Identify boundary : vertices[].border=0,1
if (iteration == 0)
{
ListHelper <int> vcount = new ListHelper <int>();
ListHelper <int> vids = new ListHelper <int>();
for (int i = 0; i < vertices.Count; i++)
{
Vertex v = vertices[i];
v.border = 0;
vertices[i] = v;
}
for (int i = 0; i < vertices.Count; i++)
{
Vertex v = vertices[i];
vcount.Clear();
vids.Clear();
for (int j = 0; j < v.tcount; j++)
{
int kb = refs[v.tstart + j].tid;
Triangle t = triangles[kb];
for (int k = 0; k < 3; k++)
{
int ofs = 0, id = t.v[k];
while (ofs < vcount.Count)
{
if (vids[ofs] == id)
{
break;
}
ofs++;
}
if (ofs == vcount.Count)
{
vcount.Add(1);
vids.Add(id);
}
else
{
vcount[ofs]++;
}
}
triangles[kb] = t;
}
for (int j = 0; j < vcount.Count; j++)
{
if (vcount[j] == 1)
{
Vertex vt = vertices[vids[j]];
vt.border = 1;
vertices[vids[j]] = vt;
}
}
}
}
}
// Main simplification function
//
// target_count : target nr. of triangles
// agressiveness : sharpness to increase the threashold.
// 5..8 are good numbers
// more iterations yield higher quality
//
void Simplify_mesh(int target_count, double agressiveness = 7)
{
// main iteration loop
int deleted_triangles = 0;
ListHelper <int> deleted0 = new ListHelper <int>();
ListHelper <int> deleted1 = new ListHelper <int>();
int triangle_count = triangles.Count;
for (int iteration = 0; iteration < 100; iteration++)
{
// target number of triangles reached ? Then break
if (triangle_count - deleted_triangles <= target_count)
{
break;
}
// update mesh once in a while
if (iteration % 5 == 0)
{
Update_mesh(iteration);
}
// clear dirty flag
for (int i = 0; i < triangles.Count; i++)
{
Triangle t = triangles[i];
t.dirty = 0;
triangles[i] = t;
}
//
// All triangles with edges below the threshold will be removed
//
// The following numbers works well for most models.
// If it does not, try to adjust the 3 parameters
//
double threshold = 0.000000001 * Math.Pow((double)(iteration + 3), agressiveness);
// remove vertices & mark deleted triangles
for (int i = 0; i < triangles.Count; i++)
{
Triangle t = triangles[i];
if (t.err[3] > threshold)
{
continue;
}
if (t.deleted != 0)
{
continue;
}
if (t.dirty != 0)
{
continue;
}
for (int j = 0; j < 3; j++)
{
if (t.err[j] < threshold)
{
int i0 = t.v[j];
Vertex v0 = vertices[i0];
int i1 = t.v[(j + 1) % 3];
Vertex v1 = vertices[i1];
// Border check
if (v0.border != v1.border)
{
continue;
}
// Compute vertex to collapse to
Vector3 p = new Vector3();
Calculate_error(i0, i1, ref p);
// dont remove if flipped
if (Flipped(p, i0, i1, ref v0, ref v1, ref deleted0))
{
continue;
}
if (Flipped(p, i1, i0, ref v1, ref v0, ref deleted1))
{
continue;
}
// not flipped, so remove edge
v0.p = p;
v0.q = v1.q + v0.q;
int tstart = refs.Count;
Update_triangles(i0, ref v0, ref deleted0, ref deleted_triangles);
Update_triangles(i0, ref v1, ref deleted1, ref deleted_triangles);
vertices[i0] = v0;
vertices[i1] = v1;
int tcount = refs.Count - tstart;
if (tcount <= v0.tcount)
{
// save ram
if (tcount != 0)
{
for (int f = 0; f < tcount; f++)
{
refs[v0.tstart + f] = refs[tstart];
}
}
}
else
{
// append
v0.tstart = tstart;
}
v0.tcount = tcount;
break;
}
}
triangles[i] = t;
// done?
if (triangle_count - deleted_triangles <= target_count)
{
break;
}
}
}
// clean up mesh
Compact_mesh();
}
