gltfpack: Switch to SimplifyInternalDebug for debugSimplify

This code reworks the debug visualization for simplification to use new
internal feature that communicates metadata via index data.

For now we draw loops even for locked vertices and don't make an attempt
to deduplicate points or lines, as visualization performance is not
critical, and locked loops actually make it easier to debug in some
cases.

gltf/mesh.cpp

@@ -527,8 +527,13 @@ static Stream* getStream(Mesh& mesh, cgltf_attribute_type type, int index = 0)
 	return NULL;
 }
 
-static void simplifyMesh(Mesh& mesh, float threshold, bool attributes, bool aggressive, bool lock_borders)
+static void simplifyMesh(Mesh& mesh, float threshold, bool attributes, bool aggressive, bool lock_borders, bool debug = false)
 {
+	enum
+	{
+		meshopt_SimplifyInternalDebug = 1 << 30
+	};
+
 	assert(mesh.type == cgltf_primitive_type_triangles);
 
 	if (mesh.indices.empty())
@@ -543,7 +548,11 @@ static void simplifyMesh(Mesh& mesh, float threshold, bool attributes, bool aggr
 	size_t target_index_count = size_t(double(mesh.indices.size() / 3) * threshold) * 3;
 	float target_error = 1e-2f;
 	float target_error_aggressive = 1e-1f;
-	unsigned int options = lock_borders ? meshopt_SimplifyLockBorder : 0;
+	unsigned int options = 0;
+	if (lock_borders)
+		options |= meshopt_SimplifyLockBorder;
+	if (debug)
+		options |= meshopt_SimplifyInternalDebug;
 
 	const Stream* attr = getStream(mesh, cgltf_attribute_type_color);
 	attr = attr ? attr : getStream(mesh, cgltf_attribute_type_normal);
@@ -784,10 +793,6 @@ void processMesh(Mesh& mesh, const Settings& settings)
 }
 
 #ifndef NDEBUG
-extern MESHOPTIMIZER_API unsigned char* meshopt_simplifyDebugKind;
-extern MESHOPTIMIZER_API unsigned int* meshopt_simplifyDebugLoop;
-extern MESHOPTIMIZER_API unsigned int* meshopt_simplifyDebugLoopBack;
-
 void debugSimplify(const Mesh& source, Mesh& kinds, Mesh& loops, float ratio, bool attributes)
 {
 	Mesh mesh = source;
@@ -799,27 +804,9 @@ void debugSimplify(const Mesh& source, Mesh& kinds, Mesh& loops, float ratio, bo
 	reindexMesh(mesh);
 	filterTriangles(mesh);
 
-	// before simplification we need to setup target kind/loop arrays
 	size_t vertex_count = mesh.streams[0].data.size();
 
-	std::vector<unsigned char> kind(vertex_count);
-	std::vector<unsigned int> loop(vertex_count);
-	std::vector<unsigned int> loopback(vertex_count);
-	std::vector<unsigned char> live(vertex_count);
-
-	meshopt_simplifyDebugKind = &kind[0];
-	meshopt_simplifyDebugLoop = &loop[0];
-	meshopt_simplifyDebugLoopBack = &loopback[0];
-
-	simplifyMesh(mesh, ratio, attributes, /* aggressive= */ false, /* lock_borders= */ false);
-
-	meshopt_simplifyDebugKind = NULL;
-	meshopt_simplifyDebugLoop = NULL;
-	meshopt_simplifyDebugLoopBack = NULL;
-
-	// fill out live info
-	for (size_t i = 0; i < mesh.indices.size(); ++i)
-		live[mesh.indices[i]] = true;
+	simplifyMesh(mesh, ratio, attributes, /* aggressive= */ false, /* lock_borders= */ false, /* debug= */ true);
 
 	// color palette for display
 	static const Attr kPalette[] = {
@@ -850,38 +837,37 @@ void debugSimplify(const Mesh& source, Mesh& kinds, Mesh& loops, float ratio, bo
 
 	// transform kind/loop data into lines & points
 	Stream colors = {cgltf_attribute_type_color};
-	colors.data.resize(vertex_count);
-
-	for (size_t i = 0; i < vertex_count; ++i)
-		colors.data[i] = kPalette[kind[i]];
+	colors.data.resize(vertex_count, kPalette[0]);
 
 	kinds.type = cgltf_primitive_type_points;
-
-	kinds.streams.push_back(colors);
-
-	for (size_t i = 0; i < vertex_count; ++i)
-		if (live[i] && kind[i] != 0)
-			kinds.indices.push_back(unsigned(i));
-
 	loops.type = cgltf_primitive_type_lines;
 
-	loops.streams.push_back(colors);
-
-	for (size_t i = 0; i < vertex_count; ++i)
-		if (live[i] && (kind[i] == 1 || kind[i] == 2))
+	for (size_t i = 0; i < mesh.indices.size(); i += 3)
+	{
+		for (int k = 0; k < 3; ++k)
 		{
-			if (loop[i] != ~0u && live[loop[i]])
+			const unsigned int mask = (1 << 28) - 1;
+			unsigned int v = mesh.indices[i + k];
+			unsigned int next = mesh.indices[i + (k + 1) % 3];
+			unsigned int vk = (v >> 28) & 7;
+			unsigned int vl = v >> 31;
+
+			if (vk)
 			{
-				loops.indices.push_back(unsigned(i));
-				loops.indices.push_back(loop[i]);
+				colors.data[v & mask] = kPalette[vk];
+				kinds.indices.push_back(v & mask);
 			}
 
-			if (loopback[i] != ~0u && live[loopback[i]])
+			if (vl)
 			{
-				loops.indices.push_back(loopback[i]);
-				loops.indices.push_back(unsigned(i));
+				loops.indices.push_back(v & mask);
+				loops.indices.push_back(next & mask);
 			}
 		}
+	}
+
+	kinds.streams.push_back(colors);
+	loops.streams.push_back(colors);
 }
 
 void debugMeshlets(const Mesh& source, Mesh& meshlets, int max_vertices, bool scan)