Added xatlas as alternative to thekla, forced it on.

Did some hacks to it to avoid it from failing on bad geometry.

thirdparty/xatlas/xatlas.h

@@ -0,0 +1,160 @@
+// This code is in the public domain -- castanyo@yahoo.es
+#pragma once
+#ifndef XATLAS_H
+#define XATLAS_H
+#include <float.h> // FLT_MAX
+#include <limits.h>
+#include <stdint.h>
+namespace xatlas {
+
+typedef void (*PrintFunc)(const char *, ...);
+
+struct Atlas;
+
+struct CharterOptions {
+	float proxyFitMetricWeight;
+	float roundnessMetricWeight;
+	float straightnessMetricWeight;
+	float normalSeamMetricWeight;
+	float textureSeamMetricWeight;
+	float maxChartArea;
+	float maxBoundaryLength;
+
+	CharterOptions() {
+		// These are the default values we use on The Witness.
+		proxyFitMetricWeight = 2.0f;
+		roundnessMetricWeight = 0.01f;
+		straightnessMetricWeight = 6.0f;
+		normalSeamMetricWeight = 4.0f;
+		textureSeamMetricWeight = 0.5f;
+		/*
+		proxyFitMetricWeight = 1.0f;
+		roundnessMetricWeight = 0.1f;
+		straightnessMetricWeight = 0.25f;
+		normalSeamMetricWeight = 1.0f;
+		textureSeamMetricWeight = 0.1f;
+		*/
+		maxChartArea = FLT_MAX;
+		maxBoundaryLength = FLT_MAX;
+	}
+};
+
+struct PackMethod {
+	enum Enum {
+		TexelArea, // texel_area determines resolution
+		ApproximateResolution, // guess texel_area to approximately match desired resolution
+		ExactResolution // run the packer multiple times to exactly match the desired resolution (slow)
+	};
+};
+
+struct PackerOptions {
+	PackMethod::Enum method;
+
+	// 0 - brute force
+	// 1 - 4096 attempts
+	// 2 - 2048
+	// 3 - 1024
+	// 4 - 512
+	// other - 256
+	// Avoid brute force packing, since it can be unusably slow in some situations.
+	int quality;
+
+	float texelArea; // This is not really texel area, but 1 / texel width?
+	uint32_t resolution;
+	bool blockAlign; // Align charts to 4x4 blocks.
+	bool conservative; // Pack charts with extra padding.
+	int padding;
+
+	PackerOptions() {
+		method = PackMethod::ApproximateResolution;
+		quality = 1;
+		texelArea = 8;
+		resolution = 512;
+		blockAlign = false;
+		conservative = false;
+		padding = 0;
+	}
+};
+
+struct AddMeshErrorCode {
+	enum Enum {
+		Success,
+		AlreadyAddedEdge, // index0 and index1 are the edge indices
+		DegenerateColocalEdge, // index0 and index1 are the edge indices
+		DegenerateEdge, // index0 and index1 are the edge indices
+		DuplicateEdge, // index0 and index1 are the edge indices
+		IndexOutOfRange, // index0 is the index
+		InvalidIndexCount, // not evenly divisible by 3 - expecting triangles
+		ZeroAreaFace,
+		ZeroLengthEdge // index0 and index1 are the edge indices
+	};
+};
+
+struct AddMeshError {
+	AddMeshErrorCode::Enum code;
+	uint32_t face;
+	uint32_t index0, index1;
+};
+
+struct IndexFormat {
+	enum Enum {
+		HalfFloat,
+		Float
+	};
+};
+
+struct InputMesh {
+	uint32_t vertexCount;
+	const void *vertexPositionData;
+	uint32_t vertexPositionStride;
+	const void *vertexNormalData; // optional
+	uint32_t vertexNormalStride; // optional
+
+	// optional
+	// The input UVs are provided as a hint to the chart generator.
+	const void *vertexUvData;
+	uint32_t vertexUvStride;
+
+	uint32_t indexCount;
+	const void *indexData;
+	IndexFormat::Enum indexFormat;
+
+	// optional. indexCount / 3 in length.
+	// Charter also uses material boundaries as a hint to cut charts.
+	const uint16_t *faceMaterialData;
+};
+
+struct OutputChart {
+	uint32_t *indexArray;
+	uint32_t indexCount;
+};
+
+struct OutputVertex {
+	float uv[2];
+	uint32_t xref; // Index of input vertex from which this output vertex originated.
+};
+
+struct OutputMesh {
+	OutputChart *chartArray;
+	uint32_t chartCount;
+	uint32_t *indexArray;
+	uint32_t indexCount;
+	OutputVertex *vertexArray;
+	uint32_t vertexCount;
+};
+
+void SetPrint(PrintFunc print);
+Atlas *Create();
+void Destroy(Atlas *atlas);
+// useColocalVertices - generates fewer charts (good), but is more sensitive to bad geometry.
+AddMeshError AddMesh(Atlas *atlas, const InputMesh &mesh, bool useColocalVertices = true);
+void Generate(Atlas *atlas, CharterOptions charterOptions = CharterOptions(), PackerOptions packerOptions = PackerOptions());
+uint32_t GetWidth(const Atlas *atlas);
+uint32_t GetHeight(const Atlas *atlas);
+uint32_t GetNumCharts(const Atlas *atlas);
+const OutputMesh *const *GetOutputMeshes(const Atlas *atlas);
+const char *StringForEnum(AddMeshErrorCode::Enum error);
+
+} // namespace xatlas
+
+#endif // XATLAS_H