From e6036680231a36e0793794f33ef7ef70e36a1a27 Mon Sep 17 00:00:00 2001
From: Vladyslav Baranovskyi <int17ist@gmail.com>
Date: Thu, 6 Feb 2025 11:28:14 +0200
Subject: [PATCH] STL exporting using assimp

---
 openVulkanoCpp/Scene/Export/MeshWriter.cpp | 88 ++++++++++++++++++++++
 openVulkanoCpp/Scene/Export/MeshWriter.hpp |  1 +
 2 files changed, 89 insertions(+)

diff --git a/openVulkanoCpp/Scene/Export/MeshWriter.cpp b/openVulkanoCpp/Scene/Export/MeshWriter.cpp
index c748015..399c1ca 100644
--- a/openVulkanoCpp/Scene/Export/MeshWriter.cpp
+++ b/openVulkanoCpp/Scene/Export/MeshWriter.cpp
@@ -183,6 +183,94 @@ namespace OpenVulkano::Scene
 		}
 #else
 		throw std::runtime_error("Unable to convert the scene to FBX: Assimp is not available!");
+#endif
+	}
+
+	void MeshWriter::WriteAsSTL(Geometry* geometry, const std::string& filePath, bool binary)
+	{
+#if __has_include("assimp/Exporter.hpp")
+		aiNode rootNode;
+
+		aiScene scene;
+		scene.mRootNode = &rootNode;
+
+		aiMesh mesh;
+		mesh.mNumVertices = geometry->vertexCount;
+		mesh.mMaterialIndex = 0;
+		mesh.mPrimitiveTypes = aiPrimitiveType_TRIANGLE;
+		
+		std::unique_ptr<aiVector3D[]> vertices = std::make_unique<aiVector3D[]>(geometry->vertexCount);
+		mesh.mVertices = vertices.get();
+
+		std::unique_ptr<aiVector3D[]> normals = std::make_unique<aiVector3D[]>(geometry->vertexCount);
+		mesh.mNormals = normals.get();
+		
+		for (int i = 0; i < geometry->vertexCount; ++i)
+		{
+			const Vertex& vertex = geometry->vertices[i];
+			mesh.mVertices[i] = aiVector3D(vertex.position.x, vertex.position.y, vertex.position.z);
+			mesh.mNormals[i] = aiVector3D(vertex.normal.x, vertex.normal.y, vertex.normal.z);
+		}
+
+		mesh.mNumFaces = geometry->indexCount / 3;
+		std::unique_ptr<aiFace[]> faces = std::make_unique<aiFace[]>(mesh.mNumFaces);
+		mesh.mFaces = faces.get();
+
+		std::unique_ptr<unsigned int[]> indices = std::make_unique<unsigned int[]>(geometry->indexCount);
+		size_t lastUsedIndex = 0;
+
+		for (int i = 0; i < mesh.mNumFaces; ++i)
+		{
+			aiFace& face = mesh.mFaces[i];
+			face.mNumIndices = 3;
+			face.mIndices = &indices[lastUsedIndex];
+
+			face.mIndices[0] = geometry->GetIndex(i * 3 + 0);
+			face.mIndices[1] = geometry->GetIndex(i * 3 + 1);
+			face.mIndices[2] = geometry->GetIndex(i * 3 + 2);
+
+			lastUsedIndex += face.mNumIndices;
+		}
+
+		aiMesh* meshes[1] = { &mesh };
+		scene.mMeshes = meshes;
+		scene.mNumMeshes = 1;
+
+		unsigned int meshIndices[1];
+		scene.mRootNode->mMeshes = meshIndices;
+		scene.mRootNode->mMeshes[0] = 0;
+		scene.mRootNode->mNumMeshes = 1;
+
+		// STL doesn't use materials, but Assimp requires at least one
+		aiMaterial material;
+		aiMaterial* materials[1] = { &material };
+		scene.mMaterials = materials;
+		scene.mNumMaterials = 1;
+
+		Assimp::Exporter exporter;
+		const char* formatId = binary ? "stlb" : "stl";
+		aiReturn result = exporter.Export(&scene, formatId, filePath);
+
+		mesh.mVertices = nullptr;
+		mesh.mNormals = nullptr;
+		for (int i = 0; i < mesh.mNumFaces; ++i)
+		{
+			aiFace& face = mesh.mFaces[i];
+			face.mIndices = nullptr;
+		}
+		mesh.mFaces = nullptr;
+
+		rootNode.mMeshes = nullptr;
+		scene.mRootNode = nullptr;
+		scene.mMeshes = nullptr;
+		scene.mMaterials = nullptr;
+
+		if (result != aiReturn_SUCCESS)
+		{
+			throw std::runtime_error("Unable to write STL file to " + filePath + ": " + exporter.GetErrorString());
+		}
+#else
+		throw std::runtime_error("Unable to export to STL: Assimp is not available!");
 #endif
 	}
 }
\ No newline at end of file
diff --git a/openVulkanoCpp/Scene/Export/MeshWriter.hpp b/openVulkanoCpp/Scene/Export/MeshWriter.hpp
index ba24bce..3b9255b 100644
--- a/openVulkanoCpp/Scene/Export/MeshWriter.hpp
+++ b/openVulkanoCpp/Scene/Export/MeshWriter.hpp
@@ -19,5 +19,6 @@ namespace OpenVulkano::Scene
 		static void WriteObjAsZip(Geometry* geometry, const std::string& texturePath, const std::string& zipPath);
 		static void WriteAsUSDZ(Geometry* geometry, const std::string& texturePath, const std::string& usdzPath);
 		static void WriteAsFBX(Geometry* geometry, const std::string& texturePath, const std::string& fbxPath);
+		static void WriteAsSTL(Geometry* geometry, const std::string& filePath, bool binary);
 	};
 }
\ No newline at end of file