//
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// MetalPixelConverter.swift
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// LiveProject
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//
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// Created by 倪路朋 on 7/1/25.
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//
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import Metal
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import MetalKit
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import CoreVideo
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final class MetalPixelConverter {
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// MARK: - Properties
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private let device: MTLDevice
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private var textureCache: CVMetalTextureCache?
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private var commandQueue: MTLCommandQueue?
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private var computePipeline: MTLComputePipelineState?
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// MARK: - Initialization
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init?(metalDevice: MTLDevice? = MTLCreateSystemDefaultDevice()) {
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guard let device = metalDevice else {
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print("⚠️ Metal 不可用")
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return nil
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}
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self.device = device
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// 1. 创建纹理缓存
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guard CVMetalTextureCacheCreate(
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kCFAllocatorDefault,
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nil,
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device,
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nil,
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&textureCache
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) == kCVReturnSuccess else {
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print("❌ 创建 Metal 纹理缓存失败")
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return nil
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}
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// 2. 创建命令队列
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self.commandQueue = device.makeCommandQueue()
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// 3. 加载着色器
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do {
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self.computePipeline = try makeComputePipeline(device: device)
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} catch {
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print("❌ 加载着色器失败: \(error)")
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return nil
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}
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}
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// MARK: - Public Methods
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/// 将 BGRA CVPixelBuffer 转换为 NV12 CVPixelBuffer
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func convertBGRAtoNV12(
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_ inputBuffer: CVPixelBuffer,
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completion: @escaping (Result<CVPixelBuffer, Error>) -> Void
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) {
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// 0. 验证输入格式
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guard CVPixelBufferGetPixelFormatType(inputBuffer) == kCVPixelFormatType_32BGRA else {
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completion(.failure(ConversionError.invalidInputFormat))
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return
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}
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// 1. 创建输出 NV12 Buffer
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let (width, height) = (CVPixelBufferGetWidth(inputBuffer), CVPixelBufferGetHeight(inputBuffer))
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guard let outputBuffer = createNV12PixelBuffer(width: width, height: height) else {
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completion(.failure(ConversionError.outputBufferCreationFailed))
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return
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}
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// 2. 异步处理（避免阻塞主线程）
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DispatchQueue.global(qos: .userInitiated).async { [weak self] in
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guard let self = self else { return }
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do {
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let result = try self.performConversion(
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inputBuffer: inputBuffer,
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outputBuffer: outputBuffer
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)
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DispatchQueue.main.async {
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completion(.success(result))
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}
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} catch {
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DispatchQueue.main.async {
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completion(.failure(error))
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}
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}
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}
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}
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// MARK: - Private Methods
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private func makeComputePipeline(device: MTLDevice) throws -> MTLComputePipelineState {
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// 1. 获取默认 Metal 库（需在项目中添加 .metal 文件）
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let library = try device.makeDefaultLibrary(bundle: Bundle(for: Self.self))
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// 2. 加载着色器函数
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guard let kernelFunction = library.makeFunction(name: "bgraToNV12") else {
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throw ConversionError.shaderNotFound
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}
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// 3. 创建计算管线
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return try device.makeComputePipelineState(function: kernelFunction)
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}
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private func createNV12PixelBuffer(width: Int, height: Int) -> CVPixelBuffer? {
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var pixelBuffer: CVPixelBuffer?
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let status = CVPixelBufferCreate(
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kCFAllocatorDefault,
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width,
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height,
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kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange,
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nil,
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&pixelBuffer
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)
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return status == kCVReturnSuccess ? pixelBuffer : nil
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}
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private func performConversion(
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inputBuffer: CVPixelBuffer,
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outputBuffer: CVPixelBuffer
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) throws -> CVPixelBuffer {
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// 1. 锁定缓冲区
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CVPixelBufferLockBaseAddress(inputBuffer, .readOnly)
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CVPixelBufferLockBaseAddress(outputBuffer, [])
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defer {
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CVPixelBufferUnlockBaseAddress(inputBuffer, .readOnly)
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CVPixelBufferUnlockBaseAddress(outputBuffer, [])
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}
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// 2. 创建 Metal 纹理
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guard let textureCache = textureCache,
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let inputTexture = createMetalTexture(
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from: inputBuffer,
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pixelFormat: .bgra8Unorm,
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textureCache: textureCache
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),
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let yTexture = createMetalTexture(
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from: outputBuffer,
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planeIndex: 0,
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pixelFormat: .r8Unorm,
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textureCache: textureCache
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),
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let uvTexture = createMetalTexture(
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from: outputBuffer,
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planeIndex: 1,
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pixelFormat: .rg8Unorm,
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textureCache: textureCache
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) else {
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throw ConversionError.textureCreationFailed
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}
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// 3. 执行 Metal 计算
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guard let commandBuffer = commandQueue?.makeCommandBuffer(),
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let encoder = commandBuffer.makeComputeCommandEncoder() else {
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throw ConversionError.metalCommandFailed
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}
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encoder.setComputePipelineState(computePipeline!)
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encoder.setTexture(inputTexture, index: 0)
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encoder.setTexture(yTexture, index: 1)
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encoder.setTexture(uvTexture, index: 2)
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// 4. 调度计算任务
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let threadgroupSize = MTLSize(width: 16, height: 16, depth: 1)
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let threadgroupCount = MTLSize(
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width: (inputTexture.width + threadgroupSize.width - 1) / threadgroupSize.width,
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height: (inputTexture.height + threadgroupSize.height - 1) / threadgroupSize.height,
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depth: 1
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)
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encoder.dispatchThreadgroups(threadgroupCount, threadsPerThreadgroup: threadgroupSize)
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encoder.endEncoding()
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// 5. 提交并等待完成
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commandBuffer.commit()
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commandBuffer.waitUntilCompleted()
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return outputBuffer
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}
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private func createMetalTexture(
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from pixelBuffer: CVPixelBuffer,
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planeIndex: Int = 0,
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pixelFormat: MTLPixelFormat,
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textureCache: CVMetalTextureCache
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) -> MTLTexture? {
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let width = CVPixelBufferGetWidthOfPlane(pixelBuffer, planeIndex)
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let height = CVPixelBufferGetHeightOfPlane(pixelBuffer, planeIndex)
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var cvMetalTexture: CVMetalTexture?
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let status = CVMetalTextureCacheCreateTextureFromImage(
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nil,
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textureCache,
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pixelBuffer,
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nil,
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pixelFormat,
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width,
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height,
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planeIndex,
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&cvMetalTexture
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)
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guard status == kCVReturnSuccess, let texture = cvMetalTexture else {
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return nil
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}
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return CVMetalTextureGetTexture(texture)
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}
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// MARK: - Error Handling
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enum ConversionError: Error, LocalizedError {
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case invalidInputFormat
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case outputBufferCreationFailed
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case shaderNotFound
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case textureCreationFailed
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case metalCommandFailed
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var errorDescription: String? {
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switch self {
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case .invalidInputFormat: return "输入格式必须是 BGRA"
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case .outputBufferCreationFailed: return "无法创建 NV12 输出缓冲区"
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case .shaderNotFound: return "找不到 Metal 着色器"
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case .textureCreationFailed: return "无法创建 Metal 纹理"
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case .metalCommandFailed: return "Metal 命令执行失败"
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}
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}
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}
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}
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