initial commit, 4.5 stable

thirdparty/meshoptimizer/stripifier.cpp

@@ -0,0 +1,296 @@
+// This file is part of meshoptimizer library; see meshoptimizer.h for version/license details
+#include "meshoptimizer.h"
+
+#include <assert.h>
+#include <limits.h>
+#include <string.h>
+
+// This work is based on:
+// Francine Evans, Steven Skiena and Amitabh Varshney. Optimizing Triangle Strips for Fast Rendering. 1996
+namespace meshopt
+{
+
+static unsigned int findStripFirst(const unsigned int buffer[][3], unsigned int buffer_size, const unsigned char* valence)
+{
+	unsigned int index = 0;
+	unsigned int iv = ~0u;
+
+	for (size_t i = 0; i < buffer_size; ++i)
+	{
+		unsigned char va = valence[buffer[i][0]], vb = valence[buffer[i][1]], vc = valence[buffer[i][2]];
+		unsigned int v = (va < vb && va < vc) ? va : (vb < vc ? vb : vc);
+
+		if (v < iv)
+		{
+			index = unsigned(i);
+			iv = v;
+		}
+	}
+
+	return index;
+}
+
+static int findStripNext(const unsigned int buffer[][3], unsigned int buffer_size, unsigned int e0, unsigned int e1)
+{
+	for (size_t i = 0; i < buffer_size; ++i)
+	{
+		unsigned int a = buffer[i][0], b = buffer[i][1], c = buffer[i][2];
+
+		if (e0 == a && e1 == b)
+			return (int(i) << 2) | 2;
+		else if (e0 == b && e1 == c)
+			return (int(i) << 2) | 0;
+		else if (e0 == c && e1 == a)
+			return (int(i) << 2) | 1;
+	}
+
+	return -1;
+}
+
+} // namespace meshopt
+
+size_t meshopt_stripify(unsigned int* destination, const unsigned int* indices, size_t index_count, size_t vertex_count, unsigned int restart_index)
+{
+	assert(destination != indices);
+	assert(index_count % 3 == 0);
+
+	using namespace meshopt;
+
+	meshopt_Allocator allocator;
+
+	const size_t buffer_capacity = 8;
+
+	unsigned int buffer[buffer_capacity][3] = {};
+	unsigned int buffer_size = 0;
+
+	size_t index_offset = 0;
+
+	unsigned int strip[2] = {};
+	unsigned int parity = 0;
+
+	size_t strip_size = 0;
+
+	// compute vertex valence; this is used to prioritize starting triangle for strips
+	// note: we use 8-bit counters for performance; for outlier vertices the valence is incorrect but that just affects the heuristic
+	unsigned char* valence = allocator.allocate<unsigned char>(vertex_count);
+	memset(valence, 0, vertex_count);
+
+	for (size_t i = 0; i < index_count; ++i)
+	{
+		unsigned int index = indices[i];
+		assert(index < vertex_count);
+
+		valence[index]++;
+	}
+
+	int next = -1;
+
+	while (buffer_size > 0 || index_offset < index_count)
+	{
+		assert(next < 0 || (size_t(next >> 2) < buffer_size && (next & 3) < 3));
+
+		// fill triangle buffer
+		while (buffer_size < buffer_capacity && index_offset < index_count)
+		{
+			buffer[buffer_size][0] = indices[index_offset + 0];
+			buffer[buffer_size][1] = indices[index_offset + 1];
+			buffer[buffer_size][2] = indices[index_offset + 2];
+
+			buffer_size++;
+			index_offset += 3;
+		}
+
+		assert(buffer_size > 0);
+
+		if (next >= 0)
+		{
+			unsigned int i = next >> 2;
+			unsigned int a = buffer[i][0], b = buffer[i][1], c = buffer[i][2];
+			unsigned int v = buffer[i][next & 3];
+
+			// ordered removal from the buffer
+			memmove(buffer[i], buffer[i + 1], (buffer_size - i - 1) * sizeof(buffer[0]));
+			buffer_size--;
+
+			// update vertex valences for strip start heuristic
+			valence[a]--;
+			valence[b]--;
+			valence[c]--;
+
+			// find next triangle (note that edge order flips on every iteration)
+			// in some cases we need to perform a swap to pick a different outgoing triangle edge
+			// for [a b c], the default strip edge is [b c], but we might want to use [a c]
+			int cont = findStripNext(buffer, buffer_size, parity ? strip[1] : v, parity ? v : strip[1]);
+			int swap = cont < 0 ? findStripNext(buffer, buffer_size, parity ? v : strip[0], parity ? strip[0] : v) : -1;
+
+			if (cont < 0 && swap >= 0)
+			{
+				// [a b c] => [a b a c]
+				destination[strip_size++] = strip[0];
+				destination[strip_size++] = v;
+
+				// next strip has same winding
+				// ? a b => b a v
+				strip[1] = v;
+
+				next = swap;
+			}
+			else
+			{
+				// emit the next vertex in the strip
+				destination[strip_size++] = v;
+
+				// next strip has flipped winding
+				strip[0] = strip[1];
+				strip[1] = v;
+				parity ^= 1;
+
+				next = cont;
+			}
+		}
+		else
+		{
+			// if we didn't find anything, we need to find the next new triangle
+			// we use a heuristic to maximize the strip length
+			unsigned int i = findStripFirst(buffer, buffer_size, valence);
+			unsigned int a = buffer[i][0], b = buffer[i][1], c = buffer[i][2];
+
+			// ordered removal from the buffer
+			memmove(buffer[i], buffer[i + 1], (buffer_size - i - 1) * sizeof(buffer[0]));
+			buffer_size--;
+
+			// update vertex valences for strip start heuristic
+			valence[a]--;
+			valence[b]--;
+			valence[c]--;
+
+			// we need to pre-rotate the triangle so that we will find a match in the existing buffer on the next iteration
+			int ea = findStripNext(buffer, buffer_size, c, b);
+			int eb = findStripNext(buffer, buffer_size, a, c);
+			int ec = findStripNext(buffer, buffer_size, b, a);
+
+			// in some cases we can have several matching edges; since we can pick any edge, we pick the one with the smallest
+			// triangle index in the buffer. this reduces the effect of stripification on ACMR and additionally - for unclear
+			// reasons - slightly improves the stripification efficiency
+			int mine = INT_MAX;
+			mine = (ea >= 0 && mine > ea) ? ea : mine;
+			mine = (eb >= 0 && mine > eb) ? eb : mine;
+			mine = (ec >= 0 && mine > ec) ? ec : mine;
+
+			if (ea == mine)
+			{
+				// keep abc
+				next = ea;
+			}
+			else if (eb == mine)
+			{
+				// abc -> bca
+				unsigned int t = a;
+				a = b, b = c, c = t;
+
+				next = eb;
+			}
+			else if (ec == mine)
+			{
+				// abc -> cab
+				unsigned int t = c;
+				c = b, b = a, a = t;
+
+				next = ec;
+			}
+
+			if (restart_index)
+			{
+				if (strip_size)
+					destination[strip_size++] = restart_index;
+
+				destination[strip_size++] = a;
+				destination[strip_size++] = b;
+				destination[strip_size++] = c;
+
+				// new strip always starts with the same edge winding
+				strip[0] = b;
+				strip[1] = c;
+				parity = 1;
+			}
+			else
+			{
+				if (strip_size)
+				{
+					// connect last strip using degenerate triangles
+					destination[strip_size++] = strip[1];
+					destination[strip_size++] = a;
+				}
+
+				// note that we may need to flip the emitted triangle based on parity
+				// we always end up with outgoing edge "cb" in the end
+				unsigned int e0 = parity ? c : b;
+				unsigned int e1 = parity ? b : c;
+
+				destination[strip_size++] = a;
+				destination[strip_size++] = e0;
+				destination[strip_size++] = e1;
+
+				strip[0] = e0;
+				strip[1] = e1;
+				parity ^= 1;
+			}
+		}
+	}
+
+	return strip_size;
+}
+
+size_t meshopt_stripifyBound(size_t index_count)
+{
+	assert(index_count % 3 == 0);
+
+	// worst case without restarts is 2 degenerate indices and 3 indices per triangle
+	// worst case with restarts is 1 restart index and 3 indices per triangle
+	return (index_count / 3) * 5;
+}
+
+size_t meshopt_unstripify(unsigned int* destination, const unsigned int* indices, size_t index_count, unsigned int restart_index)
+{
+	assert(destination != indices);
+
+	size_t offset = 0;
+	size_t start = 0;
+
+	for (size_t i = 0; i < index_count; ++i)
+	{
+		if (restart_index && indices[i] == restart_index)
+		{
+			start = i + 1;
+		}
+		else if (i - start >= 2)
+		{
+			unsigned int a = indices[i - 2], b = indices[i - 1], c = indices[i];
+
+			// flip winding for odd triangles
+			if ((i - start) & 1)
+			{
+				unsigned int t = a;
+				a = b, b = t;
+			}
+
+			// although we use restart indices, strip swaps still produce degenerate triangles, so skip them
+			if (a != b && a != c && b != c)
+			{
+				destination[offset + 0] = a;
+				destination[offset + 1] = b;
+				destination[offset + 2] = c;
+				offset += 3;
+			}
+		}
+	}
+
+	return offset;
+}
+
+size_t meshopt_unstripifyBound(size_t index_count)
+{
+	assert(index_count == 0 || index_count >= 3);
+
+	return (index_count == 0) ? 0 : (index_count - 2) * 3;
+}