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demo: Implement an initial version of Metis clusterizer
We might need to split this into a separate option because, while this seems to work, it also results in disjoint clusters and in addition to this doesn't fill the clusters very well; at the minimum this will need further tweaks.
This commit is contained in:
Arseny Kapoulkine
+127
-1
@@ -99,8 +99,134 @@ static float boundsError(const LODBounds& bounds, float x, float y, float z)
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return d <= 0 ? FLT_MAX : bounds.error / d;
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}
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#ifdef METIS
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static void clusterizeMetisRec(std::vector<Cluster>& result, const std::vector<unsigned int>& indices, const std::vector<int>& triidx, const std::vector<int>& triadj)
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{
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assert(triadj.size() == triidx.size() * 3);
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if (triidx.size() <= kClusterSize)
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{
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Cluster cluster;
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for (size_t i = 0; i < triidx.size(); ++i)
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{
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cluster.indices.push_back(indices[triidx[i] * 3 + 0]);
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cluster.indices.push_back(indices[triidx[i] * 3 + 1]);
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cluster.indices.push_back(indices[triidx[i] * 3 + 2]);
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}
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cluster.parent.error = FLT_MAX;
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result.push_back(cluster);
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return;
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}
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std::vector<int> xadj(triidx.size() + 1);
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std::vector<int> adjncy;
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std::vector<int> part(triidx.size());
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for (size_t i = 0; i < triidx.size(); ++i)
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{
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for (int j = 0; j < 3; ++j)
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if (triadj[i * 3 + j] != -1)
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adjncy.push_back(triadj[i * 3 + j]);
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xadj[i + 1] = adjncy.size();
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}
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int options[METIS_NOPTIONS];
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METIS_SetDefaultOptions(options);
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options[METIS_OPTION_SEED] = 42;
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options[METIS_OPTION_UFACTOR] = triidx.size() > 8 * kClusterSize ? 100 : 10;
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int nvtxs = int(triidx.size());
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int ncon = 1;
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int nparts = 2;
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int edgecut = 0;
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int r = METIS_PartGraphRecursive(&nvtxs, &ncon, &xadj[0], &adjncy[0], NULL, NULL, NULL, &nparts, NULL, NULL, options, &edgecut, &part[0]);
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assert(r == METIS_OK);
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(void)r;
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int partsize[2] = {};
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std::vector<int> partoff(part.size());
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for (size_t i = 0; i < part.size(); ++i)
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partoff[i] = partsize[part[i]]++;
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for (int p = 0; p < 2; ++p)
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{
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std::vector<int> partidx, partadj;
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partidx.reserve(partsize[p]);
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partadj.reserve(partsize[p] * 3);
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for (size_t i = 0; i < triidx.size(); ++i)
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{
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if (part[i] != p)
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continue;
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partidx.push_back(triidx[i]);
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for (int j = 0; j < 3; ++j)
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{
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if (triadj[i * 3 + j] >= 0 && part[triadj[i * 3 + j]] == p)
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partadj.push_back(partoff[triadj[i * 3 + j]]);
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else
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partadj.push_back(-1);
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}
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}
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clusterizeMetisRec(result, indices, partidx, partadj);
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}
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}
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static std::vector<Cluster> clusterizeMetis(const std::vector<Vertex>& vertices, const std::vector<unsigned int>& indices)
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{
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(void)vertices; // for now
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std::map<std::pair<unsigned int, unsigned int>, unsigned int> edges;
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for (size_t i = 0; i < indices.size(); ++i)
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{
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unsigned int v0 = indices[i + 0];
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unsigned int v1 = indices[i + (i % 3 == 2 ? -2 : 1)];
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// we don't track adjacency fully on non-manifold edges for now
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edges[std::make_pair(v0, v1)] = unsigned(i / 3);
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}
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std::vector<int> triadj(indices.size(), -1);
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for (size_t i = 0; i < indices.size(); i += 3)
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{
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unsigned int v0 = indices[i + 0], v1 = indices[i + 1], v2 = indices[i + 2];
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std::map<std::pair<unsigned int, unsigned int>, unsigned int>::iterator oab = edges.find(std::make_pair(v1, v0));
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std::map<std::pair<unsigned int, unsigned int>, unsigned int>::iterator obc = edges.find(std::make_pair(v2, v1));
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std::map<std::pair<unsigned int, unsigned int>, unsigned int>::iterator oca = edges.find(std::make_pair(v0, v2));
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triadj[i + 0] = oab != edges.end() ? int(oab->second) : -1;
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triadj[i + 1] = obc != edges.end() ? int(obc->second) : -1;
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triadj[i + 2] = oca != edges.end() ? int(oca->second) : -1;
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}
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std::vector<int> triidx(indices.size() / 3);
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for (size_t i = 0; i < indices.size(); i += 3)
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triidx[i / 3] = int(i / 3);
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std::vector<Cluster> result;
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clusterizeMetisRec(result, indices, triidx, triadj);
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return result;
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}
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#endif
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static std::vector<Cluster> clusterize(const std::vector<Vertex>& vertices, const std::vector<unsigned int>& indices)
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{
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#ifdef METIS
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static const char* metis = getenv("METIS");
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if (metis && atoi(metis))
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return clusterizeMetis(vertices, indices);
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#endif
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const size_t max_vertices = 192; // TODO: depends on kClusterSize, also may want to dial down for mesh shaders
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const size_t max_triangles = kClusterSize;
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@@ -208,8 +334,8 @@ static std::vector<std::vector<int> > partitionMetis(const std::vector<Cluster>&
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else
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{
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int r = METIS_PartGraphKway(&nvtxs, &ncon, &xadj[0], &adjncy[0], NULL, NULL, &adjwgt[0], &nparts, NULL, NULL, options, &edgecut, &part[0]);
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(void)r;
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assert(r == METIS_OK);
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(void)r;
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result.resize(nparts);
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for (size_t i = 0; i < part.size(); ++i)
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