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499 lines
14 KiB
C++
499 lines
14 KiB
C++
// This file is part of meshoptimizer library; see meshoptimizer.h for version/license details
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#include "meshoptimizer.h"
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#include <assert.h>
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#include <math.h>
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#include <string.h>
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// This work is based on:
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// Takio Kurita. An efficient agglomerative clustering algorithm using a heap. 1991
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namespace meshopt
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{
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struct ClusterAdjacency
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{
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unsigned int* offsets;
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unsigned int* clusters;
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unsigned int* shared;
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};
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static void filterClusterIndices(unsigned int* data, unsigned int* offsets, const unsigned int* cluster_indices, const unsigned int* cluster_index_counts, size_t cluster_count, unsigned char* used, size_t vertex_count, size_t total_index_count)
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{
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(void)vertex_count;
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(void)total_index_count;
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size_t cluster_start = 0;
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size_t cluster_write = 0;
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for (size_t i = 0; i < cluster_count; ++i)
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{
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offsets[i] = unsigned(cluster_write);
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// copy cluster indices, skipping duplicates
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for (size_t j = 0; j < cluster_index_counts[i]; ++j)
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{
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unsigned int v = cluster_indices[cluster_start + j];
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assert(v < vertex_count);
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data[cluster_write] = v;
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cluster_write += 1 - used[v];
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used[v] = 1;
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}
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// reset used flags for the next cluster
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for (size_t j = offsets[i]; j < cluster_write; ++j)
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used[data[j]] = 0;
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cluster_start += cluster_index_counts[i];
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}
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assert(cluster_start == total_index_count);
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assert(cluster_write <= total_index_count);
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offsets[cluster_count] = unsigned(cluster_write);
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}
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static void computeClusterBounds(float* cluster_bounds, const unsigned int* cluster_indices, const unsigned int* cluster_offsets, size_t cluster_count, const float* vertex_positions, size_t vertex_positions_stride)
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{
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size_t vertex_stride_float = vertex_positions_stride / sizeof(float);
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for (size_t i = 0; i < cluster_count; ++i)
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{
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float center[3] = {0, 0, 0};
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// approximate center of the cluster by averaging all vertex positions
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for (size_t j = cluster_offsets[i]; j < cluster_offsets[i + 1]; ++j)
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{
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const float* p = vertex_positions + cluster_indices[j] * vertex_stride_float;
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center[0] += p[0];
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center[1] += p[1];
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center[2] += p[2];
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}
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// note: technically clusters can't be empty per meshopt_partitionCluster but we check for a division by zero in case that changes
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if (size_t cluster_size = cluster_offsets[i + 1] - cluster_offsets[i])
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{
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center[0] /= float(cluster_size);
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center[1] /= float(cluster_size);
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center[2] /= float(cluster_size);
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}
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// compute radius of the bounding sphere for each cluster
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float radiussq = 0;
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for (size_t j = cluster_offsets[i]; j < cluster_offsets[i + 1]; ++j)
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{
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const float* p = vertex_positions + cluster_indices[j] * vertex_stride_float;
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float d2 = (p[0] - center[0]) * (p[0] - center[0]) + (p[1] - center[1]) * (p[1] - center[1]) + (p[2] - center[2]) * (p[2] - center[2]);
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radiussq = radiussq < d2 ? d2 : radiussq;
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}
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cluster_bounds[i * 4 + 0] = center[0];
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cluster_bounds[i * 4 + 1] = center[1];
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cluster_bounds[i * 4 + 2] = center[2];
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cluster_bounds[i * 4 + 3] = sqrtf(radiussq);
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}
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}
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static void buildClusterAdjacency(ClusterAdjacency& adjacency, const unsigned int* cluster_indices, const unsigned int* cluster_offsets, size_t cluster_count, size_t vertex_count, meshopt_Allocator& allocator)
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{
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unsigned int* ref_offsets = allocator.allocate<unsigned int>(vertex_count + 1);
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// compute number of clusters referenced by each vertex
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memset(ref_offsets, 0, vertex_count * sizeof(unsigned int));
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for (size_t i = 0; i < cluster_count; ++i)
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{
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for (size_t j = cluster_offsets[i]; j < cluster_offsets[i + 1]; ++j)
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ref_offsets[cluster_indices[j]]++;
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}
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// compute (worst-case) number of adjacent clusters for each cluster
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size_t total_adjacency = 0;
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for (size_t i = 0; i < cluster_count; ++i)
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{
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size_t count = 0;
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// worst case is every vertex has a disjoint cluster list
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for (size_t j = cluster_offsets[i]; j < cluster_offsets[i + 1]; ++j)
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count += ref_offsets[cluster_indices[j]] - 1;
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// ... but only every other cluster can be adjacent in the end
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total_adjacency += count < cluster_count - 1 ? count : cluster_count - 1;
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}
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// we can now allocate adjacency buffers
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adjacency.offsets = allocator.allocate<unsigned int>(cluster_count + 1);
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adjacency.clusters = allocator.allocate<unsigned int>(total_adjacency);
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adjacency.shared = allocator.allocate<unsigned int>(total_adjacency);
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// convert ref counts to offsets
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size_t total_refs = 0;
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for (size_t i = 0; i < vertex_count; ++i)
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{
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size_t count = ref_offsets[i];
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ref_offsets[i] = unsigned(total_refs);
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total_refs += count;
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}
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unsigned int* ref_data = allocator.allocate<unsigned int>(total_refs);
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// fill cluster refs for each vertex
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for (size_t i = 0; i < cluster_count; ++i)
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{
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for (size_t j = cluster_offsets[i]; j < cluster_offsets[i + 1]; ++j)
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ref_data[ref_offsets[cluster_indices[j]]++] = unsigned(i);
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}
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// after the previous pass, ref_offsets contain the end of the data for each vertex; shift it forward to get the start
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memmove(ref_offsets + 1, ref_offsets, vertex_count * sizeof(unsigned int));
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ref_offsets[0] = 0;
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// fill cluster adjacency for each cluster...
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adjacency.offsets[0] = 0;
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for (size_t i = 0; i < cluster_count; ++i)
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{
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unsigned int* adj = adjacency.clusters + adjacency.offsets[i];
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unsigned int* shd = adjacency.shared + adjacency.offsets[i];
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size_t count = 0;
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for (size_t j = cluster_offsets[i]; j < cluster_offsets[i + 1]; ++j)
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{
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unsigned int v = cluster_indices[j];
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// merge the entire cluster list of each vertex into current list
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for (size_t k = ref_offsets[v]; k < ref_offsets[v + 1]; ++k)
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{
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unsigned int c = ref_data[k];
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assert(c < cluster_count);
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if (c == unsigned(i))
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continue;
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// if the cluster is already in the list, increment the shared count
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bool found = false;
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for (size_t l = 0; l < count; ++l)
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if (adj[l] == c)
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{
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found = true;
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shd[l]++;
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break;
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}
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// .. or append a new cluster
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if (!found)
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{
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adj[count] = c;
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shd[count] = 1;
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count++;
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}
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}
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}
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// mark the end of the adjacency list; the next cluster will start there as well
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adjacency.offsets[i + 1] = adjacency.offsets[i] + unsigned(count);
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}
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assert(adjacency.offsets[cluster_count] <= total_adjacency);
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// ref_offsets can't be deallocated as it was allocated before adjacency
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allocator.deallocate(ref_data);
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}
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struct ClusterGroup
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{
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int group;
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int next;
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unsigned int size; // 0 unless root
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unsigned int vertices;
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};
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struct GroupOrder
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{
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unsigned int id;
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int order;
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};
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static void heapPush(GroupOrder* heap, size_t size, GroupOrder item)
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{
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// insert a new element at the end (breaks heap invariant)
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heap[size++] = item;
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// bubble up the new element to its correct position
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size_t i = size - 1;
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while (i > 0 && heap[i].order < heap[(i - 1) / 2].order)
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{
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size_t p = (i - 1) / 2;
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GroupOrder temp = heap[i];
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heap[i] = heap[p];
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heap[p] = temp;
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i = p;
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}
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}
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static GroupOrder heapPop(GroupOrder* heap, size_t size)
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{
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assert(size > 0);
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GroupOrder top = heap[0];
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// move the last element to the top (breaks heap invariant)
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heap[0] = heap[--size];
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// bubble down the new top element to its correct position
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size_t i = 0;
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while (i * 2 + 1 < size)
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{
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// find the smallest child
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size_t j = i * 2 + 1;
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j += (j + 1 < size && heap[j + 1].order < heap[j].order);
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// if the parent is already smaller than both children, we're done
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if (heap[j].order >= heap[i].order)
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break;
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// otherwise, swap the parent and child and continue
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GroupOrder temp = heap[i];
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heap[i] = heap[j];
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heap[j] = temp;
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i = j;
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}
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return top;
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}
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static unsigned int countShared(const ClusterGroup* groups, int group1, int group2, const ClusterAdjacency& adjacency)
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{
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unsigned int total = 0;
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for (int i1 = group1; i1 >= 0; i1 = groups[i1].next)
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for (int i2 = group2; i2 >= 0; i2 = groups[i2].next)
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{
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for (unsigned int adj = adjacency.offsets[i1]; adj < adjacency.offsets[i1 + 1]; ++adj)
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if (adjacency.clusters[adj] == unsigned(i2))
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{
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total += adjacency.shared[adj];
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break;
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}
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}
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return total;
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}
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static void mergeBounds(float* target, const float* source)
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{
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float r1 = target[3], r2 = source[3];
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float dx = source[0] - target[0], dy = source[1] - target[1], dz = source[2] - target[2];
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float d = sqrtf(dx * dx + dy * dy + dz * dz);
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if (d + r1 < r2)
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{
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memcpy(target, source, 4 * sizeof(float));
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return;
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}
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if (d + r2 > r1)
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{
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float k = d > 0 ? (d + r2 - r1) / (2 * d) : 0.f;
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target[0] += dx * k;
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target[1] += dy * k;
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target[2] += dz * k;
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target[3] = (d + r2 + r1) / 2;
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}
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}
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static float boundsScore(const float* target, const float* source)
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{
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float r1 = target[3], r2 = source[3];
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float dx = source[0] - target[0], dy = source[1] - target[1], dz = source[2] - target[2];
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float d = sqrtf(dx * dx + dy * dy + dz * dz);
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float mr = d + r1 < r2 ? r2 : (d + r2 < r1 ? r1 : (d + r2 + r1) / 2);
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return mr > 0 ? r1 / mr : 0.f;
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}
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static int pickGroupToMerge(const ClusterGroup* groups, int id, const ClusterAdjacency& adjacency, size_t max_partition_size, const float* cluster_bounds)
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{
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assert(groups[id].size > 0);
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float group_rsqrt = 1.f / sqrtf(float(int(groups[id].vertices)));
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int best_group = -1;
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float best_score = 0;
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for (int ci = id; ci >= 0; ci = groups[ci].next)
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{
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for (unsigned int adj = adjacency.offsets[ci]; adj != adjacency.offsets[ci + 1]; ++adj)
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{
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int other = groups[adjacency.clusters[adj]].group;
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if (other < 0)
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continue;
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assert(groups[other].size > 0);
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if (groups[id].size + groups[other].size > max_partition_size)
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continue;
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unsigned int shared = countShared(groups, id, other, adjacency);
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float other_rsqrt = 1.f / sqrtf(float(int(groups[other].vertices)));
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// normalize shared count by the expected boundary of each group (+ keeps scoring symmetric)
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float score = float(int(shared)) * (group_rsqrt + other_rsqrt);
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// incorporate spatial score to favor merging nearby groups
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if (cluster_bounds)
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score *= 1.f + 0.4f * boundsScore(&cluster_bounds[id * 4], &cluster_bounds[other * 4]);
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if (score > best_score)
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{
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best_group = other;
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best_score = score;
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}
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}
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}
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return best_group;
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}
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} // namespace meshopt
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size_t meshopt_partitionClusters(unsigned int* destination, const unsigned int* cluster_indices, size_t total_index_count, const unsigned int* cluster_index_counts, size_t cluster_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, size_t target_partition_size)
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{
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using namespace meshopt;
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assert((vertex_positions == NULL || vertex_positions_stride >= 12) && vertex_positions_stride <= 256);
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assert(vertex_positions_stride % sizeof(float) == 0);
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assert(target_partition_size > 0);
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size_t max_partition_size = target_partition_size + target_partition_size * 3 / 8;
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meshopt_Allocator allocator;
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unsigned char* used = allocator.allocate<unsigned char>(vertex_count);
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memset(used, 0, vertex_count);
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unsigned int* cluster_newindices = allocator.allocate<unsigned int>(total_index_count);
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unsigned int* cluster_offsets = allocator.allocate<unsigned int>(cluster_count + 1);
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// make new cluster index list that filters out duplicate indices
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filterClusterIndices(cluster_newindices, cluster_offsets, cluster_indices, cluster_index_counts, cluster_count, used, vertex_count, total_index_count);
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cluster_indices = cluster_newindices;
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// compute bounding sphere for each cluster if positions are provided
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float* cluster_bounds = NULL;
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if (vertex_positions)
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{
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cluster_bounds = allocator.allocate<float>(cluster_count * 4);
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computeClusterBounds(cluster_bounds, cluster_indices, cluster_offsets, cluster_count, vertex_positions, vertex_positions_stride);
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}
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// build cluster adjacency along with edge weights (shared vertex count)
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ClusterAdjacency adjacency = {};
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buildClusterAdjacency(adjacency, cluster_indices, cluster_offsets, cluster_count, vertex_count, allocator);
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ClusterGroup* groups = allocator.allocate<ClusterGroup>(cluster_count);
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GroupOrder* order = allocator.allocate<GroupOrder>(cluster_count);
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size_t pending = 0;
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// create a singleton group for each cluster and order them by priority
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for (size_t i = 0; i < cluster_count; ++i)
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{
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groups[i].group = int(i);
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groups[i].next = -1;
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groups[i].size = 1;
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groups[i].vertices = cluster_offsets[i + 1] - cluster_offsets[i];
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assert(groups[i].vertices > 0);
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GroupOrder item = {};
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item.id = unsigned(i);
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item.order = groups[i].vertices;
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heapPush(order, pending++, item);
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}
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// iteratively merge the smallest group with the best group
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while (pending)
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{
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GroupOrder top = heapPop(order, pending--);
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// this group was merged into another group earlier
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if (groups[top.id].size == 0)
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continue;
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// disassociate clusters from the group to prevent them from being merged again; we will re-associate them if the group is reinserted
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for (int i = top.id; i >= 0; i = groups[i].next)
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{
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assert(groups[i].group == int(top.id));
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groups[i].group = -1;
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}
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// the group is large enough, emit as is
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if (groups[top.id].size >= target_partition_size)
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continue;
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int best_group = pickGroupToMerge(groups, top.id, adjacency, max_partition_size, cluster_bounds);
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// we can't grow the group any more, emit as is
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if (best_group == -1)
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continue;
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// compute shared vertices to adjust the total vertices estimate after merging
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unsigned int shared = countShared(groups, top.id, best_group, adjacency);
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// combine groups by linking them together
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assert(groups[best_group].size > 0);
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for (int i = top.id; i >= 0; i = groups[i].next)
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if (groups[i].next < 0)
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{
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groups[i].next = best_group;
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break;
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}
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// update group sizes; note, the vertex update is a O(1) approximation which avoids recomputing the true size
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groups[top.id].size += groups[best_group].size;
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groups[top.id].vertices += groups[best_group].vertices;
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groups[top.id].vertices = (groups[top.id].vertices > shared) ? groups[top.id].vertices - shared : 1;
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groups[best_group].size = 0;
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groups[best_group].vertices = 0;
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// merge bounding spheres if bounds are available
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if (cluster_bounds)
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{
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mergeBounds(&cluster_bounds[top.id * 4], &cluster_bounds[best_group * 4]);
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memset(&cluster_bounds[best_group * 4], 0, 4 * sizeof(float));
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}
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// re-associate all clusters back to the merged group
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for (int i = top.id; i >= 0; i = groups[i].next)
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groups[i].group = int(top.id);
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top.order = groups[top.id].vertices;
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heapPush(order, pending++, top);
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}
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size_t next_group = 0;
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for (size_t i = 0; i < cluster_count; ++i)
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{
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if (groups[i].size == 0)
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continue;
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for (int j = int(i); j >= 0; j = groups[j].next)
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destination[j] = unsigned(next_group);
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next_group++;
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}
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assert(next_group <= cluster_count);
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return next_group;
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}
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