indexgenerator: Share buildPositionRemap across two new generators

This code is identical and self-sufficient so it's easy to extract.
Building the edge table is more specialized due to the need for storing
the opposite vertex, and the hasher along with other data is necessary
during lookup, so it's better to leave that duplicated for now.

src/indexgenerator.cpp

@@ -160,6 +160,26 @@ static T* hashLookup(T* table, size_t buckets, const Hash& hash, const T& key, c
 	return 0;
 }
 
+static void buildPositionRemap(unsigned int* remap, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride, meshopt_Allocator& allocator)
+{
+	VertexHasher vertex_hasher = {reinterpret_cast<const unsigned char*>(vertex_positions), 3 * sizeof(float), vertex_positions_stride};
+
+	size_t vertex_table_size = hashBuckets(vertex_count);
+	unsigned int* vertex_table = allocator.allocate<unsigned int>(vertex_table_size);
+	memset(vertex_table, -1, vertex_table_size * sizeof(unsigned int));
+
+	for (size_t i = 0; i < vertex_count; ++i)
+	{
+		unsigned int index = unsigned(i);
+		unsigned int* entry = hashLookup(vertex_table, vertex_table_size, vertex_hasher, index, ~0u);
+
+		if (*entry == ~0u)
+			*entry = index;
+
+		remap[index] = *entry;
+	}
+}
+
 } // namespace meshopt
 
 size_t meshopt_generateVertexRemap(unsigned int* destination, const unsigned int* indices, size_t index_count, const void* vertices, size_t vertex_count, size_t vertex_size)
@@ -399,25 +419,9 @@ void meshopt_generateAdjacencyIndexBuffer(unsigned int* destination, const unsig
 
 	static const int next[4] = {1, 2, 0, 1};
 
-	VertexHasher vertex_hasher = {reinterpret_cast<const unsigned char*>(vertex_positions), 3 * sizeof(float), vertex_positions_stride};
-
-	size_t vertex_table_size = hashBuckets(vertex_count);
-	unsigned int* vertex_table = allocator.allocate<unsigned int>(vertex_table_size);
-	memset(vertex_table, -1, vertex_table_size * sizeof(unsigned int));
-
 	// build position remap: for each vertex, which other (canonical) vertex does it map to?
 	unsigned int* remap = allocator.allocate<unsigned int>(vertex_count);
-
-	for (size_t i = 0; i < vertex_count; ++i)
-	{
-		unsigned int index = unsigned(i);
-		unsigned int* entry = hashLookup(vertex_table, vertex_table_size, vertex_hasher, index, ~0u);
-
-		if (*entry == ~0u)
-			*entry = index;
-
-		remap[index] = *entry;
-	}
+	buildPositionRemap(remap, vertex_positions, vertex_count, vertex_positions_stride, allocator);
 
 	// build edge set; this stores all triangle edges but we can look these up by any other wedge
 	EdgeHasher edge_hasher = {remap};
@@ -486,25 +490,9 @@ void meshopt_generateTessellationIndexBuffer(unsigned int* destination, const un
 
 	static const int next[3] = {1, 2, 0};
 
-	VertexHasher vertex_hasher = {reinterpret_cast<const unsigned char*>(vertex_positions), 3 * sizeof(float), vertex_positions_stride};
-
-	size_t vertex_table_size = hashBuckets(vertex_count);
-	unsigned int* vertex_table = allocator.allocate<unsigned int>(vertex_table_size);
-	memset(vertex_table, -1, vertex_table_size * sizeof(unsigned int));
-
 	// build position remap: for each vertex, which other (canonical) vertex does it map to?
 	unsigned int* remap = allocator.allocate<unsigned int>(vertex_count);
-
-	for (size_t i = 0; i < vertex_count; ++i)
-	{
-		unsigned int index = unsigned(i);
-		unsigned int* entry = hashLookup(vertex_table, vertex_table_size, vertex_hasher, index, ~0u);
-
-		if (*entry == ~0u)
-			*entry = index;
-
-		remap[index] = *entry;
-	}
+	buildPositionRemap(remap, vertex_positions, vertex_count, vertex_positions_stride, allocator);
 
 	// build edge set; this stores all triangle edges but we can look these up by any other wedge
 	EdgeHasher edge_hasher = {remap};