在iOS中查找子网格的边界框
我正在从obj文件中绘制一个三维模型,如下所示。我需要找到该obj文件的每个子网格的边界框在iOS中查找子网格的边界框,ios,swift,metal,Ios,Swift,Metal,我正在从obj文件中绘制一个三维模型,如下所示。我需要找到该obj文件的每个子网格的边界框 let assetURL = Bundle.main.url(forResource: "train", withExtension: "obj")! let allocator = MTKMeshBufferAllocator(device: device) let asset = MDLAsset(url: assetURL, vertexDescriptor: vertexDescriptor
let assetURL = Bundle.main.url(forResource: "train", withExtension: "obj")!
let allocator = MTKMeshBufferAllocator(device: device)
let asset = MDLAsset(url: assetURL, vertexDescriptor: vertexDescriptor, bufferAllocator: meshAllocator)
let mdlMesh = asset.object(at: 0) as! MDLMesh
mesh = try! MTKMesh(mesh: mdlMesh, device: device)
for submesh in mesh.submeshes {
//I need to find the bounding box for each Submesh
}
我如何在iOS中实现这一点 这里有一个函数,它接受一个
MTKMesh
并在模型空间中生成一个mdlaxialignedboundingbox
es数组:
enum BoundingBoxError : Error {
case invalidIndexType(String)
}
func boundingBoxesForSubmeshes(of mtkMesh: MTKMesh, positionAttributeData: MDLVertexAttributeData) throws -> [MDLAxisAlignedBoundingBox]
{
struct VertexPosition {
var x, y, z: Float
}
var boundingBoxes = [MDLAxisAlignedBoundingBox]()
var minX = Float.greatestFiniteMagnitude
var minY = Float.greatestFiniteMagnitude
var minZ = Float.greatestFiniteMagnitude
var maxX = -Float.greatestFiniteMagnitude
var maxY = -Float.greatestFiniteMagnitude
var maxZ = -Float.greatestFiniteMagnitude
let positionsPtr = positionAttributeData.dataStart
for submesh in mtkMesh.submeshes {
let indexBuffer = submesh.indexBuffer
let mtlIndexBuffer = indexBuffer.buffer
let submeshIndicesRaw = mtlIndexBuffer.contents().advanced(by: indexBuffer.offset)
if submesh.indexType != .uint32 {
throw BoundingBoxError.invalidIndexType("Expected 32-bit indices")
}
let submeshIndicesPtr = submeshIndicesRaw.bindMemory(to: UInt32.self,
capacity: submesh.indexCount)
let submeshIndices = UnsafeMutableBufferPointer<UInt32>(start: submeshIndicesPtr,
count:submesh.indexCount)
for index in submeshIndices {
let positionPtr = positionsPtr.advanced(by: Int(index) * positionAttributeData.stride)
let position = positionPtr.assumingMemoryBound(to: VertexPosition.self).pointee
if position.x < minX { minX = position.x }
if position.y < minY { minY = position.y }
if position.z < minZ { minZ = position.z }
if position.x > maxX { maxX = position.x }
if position.y > maxY { maxY = position.y }
if position.z > maxZ { maxZ = position.z }
}
let min = SIMD3<Float>(x: minX, y: minY, z: minZ)
let max = SIMD3<Float>(x: maxX, y: maxY, z: maxZ)
let box = MDLAxisAlignedBoundingBox(maxBounds: max, minBounds: min)
boundingBoxes.append(box)
}
return boundingBoxes
}
我还没有彻底测试过这段代码,但它似乎在我有限的测试用例集上产生了合理的结果。用调试网格可视化框应该立即显示它们是否正确
let mesh = try! MTKMesh(mesh: mdlMesh, device: device)
let positionAttrData = mdlMesh.vertexAttributeData(forAttributeNamed: MDLVertexAttributePosition, as: .float3)!
let boundingBoxes = try? boundingBoxesForSubmeshes(of: mesh, positionAttributeData: positionAttrData)