ARKIT-如何通过LiDAR从iPhone/iPad导出OBJ？

问题描述

如何将最新iPad Pro上新的SceneReconstruction接口生成的ARMeshGeometry导出到.obj文件？

以下是SceneReconstruction文档。

推荐答案

从苹果的Visualising Scene Scemantics示例应用开始，您可以从框架中的第一个锚检索ARMeshGeometry对象。

导出数据的最简单方法是首先将其转换为MDLMesh：

extension ARMeshGeometry {
    func toMDLMesh(device: MTLDevice) -> MDLMesh {
        let allocator = MTKMeshBufferAllocator(device: device);

        let data = Data.init(bytes: vertices.buffer.contents(), count: vertices.stride * vertices.count);
        let vertexBuffer = allocator.newBuffer(with: data, type: .vertex);

        let indexData = Data.init(bytes: faces.buffer.contents(), count: faces.bytesPerIndex * faces.count * faces.indexCountPerPrimitive);
        let indexBuffer = allocator.newBuffer(with: indexData, type: .index);

        let submesh = MDLSubmesh(indexBuffer: indexBuffer,
                                 indexCount: faces.count * faces.indexCountPerPrimitive,
                                 indexType: .uInt32,
                                 geometryType: .triangles,
                                 material: nil);

        let vertexDescriptor = MDLVertexDescriptor();
        vertexDescriptor.attributes[0] = MDLVertexAttribute(name: MDLVertexAttributePosition,
                                                            format: .float3,
                                                            offset: 0,
                                                            bufferIndex: 0);
        vertexDescriptor.layouts[0] = MDLVertexBufferLayout(stride: vertices.stride);

        return MDLMesh(vertexBuffer: vertexBuffer,
                       vertexCount: vertices.count,
                       descriptor: vertexDescriptor,
                       submeshes: [submesh]);
    }
}

一旦有了MDLMesh，导出到OBJ文件就轻而易举了：

    @IBAction func exportMesh(_ button: UIButton) {
        let meshAnchors = arView.session.currentFrame?.anchors.compactMap({ $0 as? ARMeshAnchor });

        DispatchQueue.global().async {

            let directory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0];
            let filename = directory.appendingPathComponent("MyFirstMesh.obj");

            guard let device = MTLCreateSystemDefaultDevice() else {
                print("metal device could not be created");
                return;
            };

            let asset = MDLAsset();

            for anchor in meshAnchors! {
                let mdlMesh = anchor.geometry.toMDLMesh(device: device);
                asset.add(mdlMesh);
            }

            do {
                try asset.export(to: filename);
            } catch {
                print("failed to write to file");
            }
        }
    }

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