在 iOS 设备上在 Swift 3 中设置 Metal

Question

我一直在尝试将 Apple 的 MetalBasicTessellation 项目转换为在 iPad Air 3 上的 swift 3 中工作，但到目前为止还没有成功。令人沮丧的是，该项目附带了一个 iOS 实现（用 ObjectiveC 和一个 Swift Playground 编写），但没有 Swift 3 实现。

我已获得要编译的代码，但无法在我的 iPad 上运行并出现以下错误：

2017-05-14 14:25:54.268400-0700 MetalBasicTessellation[2436:570250] -[MTLRenderPipelineDescriptorInternal validateWithDevice:], line 1728: error 'tessellation is only supported on MTLFeatureSet_iOS_GPUFamily3_v1 and later'

我很确定 iPad Air 2 是合规的，但我感觉错误是由于 MetalKitView 配置不正确造成的。我已经对项目的 Objective-c 和 Playground 文件进行了逆向工程，但我已经达到了我目前的专业知识所能理解的程度。

//
//  ViewController.swift
//  MetalBasicTessellation
//
//  Created by vladimir sierra on 5/10/17.
//  
//

import UIKit
import Metal
import MetalKit

class ViewController: UIViewController {

  @IBOutlet weak var mtkView: MTKView!

  // Seven steps required to set up metal for rendering:

  // 1. Create a MTLDevice
  // 2. Create a CAMetalLayer
  // 3. Create a Vertex Buffer

  // 4. Create a Vertex Shader
  // 5. Create a Fragment Shader

  // 6. Create a Render Pipeline
  // 7. Create a Command Queue

  var device: MTLDevice! // to be initialized in viewDidLoad
  //var metalLayer: CAMetalLayer! // to be initialized in viewDidLoad
  var vertexBuffer: MTLBuffer! // to be initialized in viewDidLoad
  var library: MTLLibrary!

  // once we create a vertex and fragment shader, we combine them in an object called render pipeline. In Metal the shaders are precompiled, and the render pipeline configuration is compiled after you first set it up. This makes everything extremely efficient

  var renderPipeline: MTLRenderPipelineState! // to be initialized in viewDidLoad
  var commandQueue: MTLCommandQueue! // to be initialized in viewDidLoad

  //var timer: CADisplayLink! // function to be called every time the device screen refreshes so we can redraw the screen



  override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    /*
    if let window = view.window {
      let scale = window.screen.nativeScale // (2 for iPhone 5s, 6 and iPads;  3 for iPhone 6 Plus)
      let layerSize = view.bounds.size
      // apply the scale to increase the drawable texture size.
      view.contentScaleFactor = scale
      //metalLayer.frame = CGRect(x: 0, y: 0, width: layerSize.width, height: layerSize.height)
      //metalLayer.drawableSize = CGSize(width: layerSize.width * scale, height: layerSize.height * scale)
    } */
  }

  override func viewDidLoad() {
    super.viewDidLoad()

    device = MTLCreateSystemDefaultDevice() // returns a reference to the default MTLDevice

    //device.supportsFeatureSet(MTLFeatureSet_iOS_GPUFamily3_v2)



    // set up layer to display metal content
    //metalLayer = CAMetalLayer()          // initialize metalLayer
    //metalLayer.device = device           // device the layer should use
    //metalLayer.pixelFormat = .bgra8Unorm // normalized 8 bit rgba
    //metalLayer.framebufferOnly = true    // set to true for performance issues
    //view.layer.addSublayer(metalLayer)   // add sublayer to main view's layer

    // precompile custom metal functions

    let defaultLibrary = device.newDefaultLibrary()! // MTLLibrary object with precompiled shaders


    let fragmentProgram = defaultLibrary.makeFunction(name: "tessellation_fragment")
    let vertexProgram = defaultLibrary.makeFunction(name: "tessellation_vertex_triangle")

    // Setup Compute Pipeline
    let kernelFunction = defaultLibrary.makeFunction(name: "tessellation_kernel_triangle")
    var computePipeline: MTLComputePipelineState?
    do {
      computePipeline = try device.makeComputePipelineState(function: kernelFunction!)
    } catch let error as NSError {
      print("compute pipeline error: " + error.description)
    }

    // Setup Vertex Descriptor
    let vertexDescriptor = MTLVertexDescriptor()
    vertexDescriptor.attributes[0].format = .float4
    vertexDescriptor.attributes[0].offset = 0
    vertexDescriptor.attributes[0].bufferIndex = 0;
    vertexDescriptor.layouts[0].stepFunction = .perPatchControlPoint
    vertexDescriptor.layouts[0].stepRate = 1
    vertexDescriptor.layouts[0].stride = 4*MemoryLayout<Float>.size

    // Setup Render Pipeline
    let renderPipelineDescriptor = MTLRenderPipelineDescriptor()
    renderPipelineDescriptor.vertexDescriptor = vertexDescriptor
    //renderPipelineDescriptor.fragmentFunction = defaultLibrary.makeFunction(name: "tessellation_fragment")
    renderPipelineDescriptor.fragmentFunction = fragmentProgram
    //renderPipelineDescriptor.vertexFunction = defaultLibrary.makeFunction(name: "tessellation_vertex_triangle")
    renderPipelineDescriptor.vertexFunction = vertexProgram

    //renderPipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm // normalized 8 bit rgba
    renderPipelineDescriptor.colorAttachments[0].pixelFormat = mtkView.colorPixelFormat

    renderPipelineDescriptor.isTessellationFactorScaleEnabled = false
    renderPipelineDescriptor.tessellationFactorFormat = .half
    renderPipelineDescriptor.tessellationControlPointIndexType = .none
    renderPipelineDescriptor.tessellationFactorStepFunction = .constant
    renderPipelineDescriptor.tessellationOutputWindingOrder = .clockwise
    renderPipelineDescriptor.tessellationPartitionMode = .fractionalEven
    renderPipelineDescriptor.maxTessellationFactor = 64;

    // Compile renderPipeline
    do {
      renderPipeline = try device.makeRenderPipelineState(descriptor: renderPipelineDescriptor)
    } catch let error as NSError {
      print("render pipeline error: " + error.description)
    }

    // Setup Buffers
    let tessellationFactorsBuffer = device.makeBuffer(length: 256, options: MTLResourceOptions.storageModePrivate)
    let controlPointPositions: [Float] = [
      -0.8, -0.8, 0.0, 1.0,   // lower-left
      0.0,  0.8, 0.0, 1.0,   // upper-middle
      0.8, -0.8, 0.0, 1.0,   // lower-right
    ]
    let controlPointsBuffer = device.makeBuffer(bytes: controlPointPositions, length:256 , options: [])

    // Tessellation Pass
    let commandBuffer = commandQueue.makeCommandBuffer()

    let computeCommandEncoder = commandBuffer.makeComputeCommandEncoder()
    computeCommandEncoder.setComputePipelineState(computePipeline!)

    let edgeFactor: [Float] = [16.0]
    let insideFactor: [Float] = [8.0]
    computeCommandEncoder.setBytes(edgeFactor, length: MemoryLayout<Float>.size, at: 0)
    computeCommandEncoder.setBytes(insideFactor, length: MemoryLayout<Float>.size, at: 1)
    computeCommandEncoder.setBuffer(tessellationFactorsBuffer, offset: 0, at: 2)
    computeCommandEncoder.dispatchThreadgroups(MTLSizeMake(1, 1, 1), threadsPerThreadgroup: MTLSizeMake(1, 1, 1))
    computeCommandEncoder.endEncoding()

    let renderPassDescriptor = mtkView.currentRenderPassDescriptor
    let renderCommandEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor!)
    renderCommandEncoder.setRenderPipelineState(renderPipeline!)
    renderCommandEncoder.setVertexBuffer(controlPointsBuffer, offset: 0, at: 0)
    renderCommandEncoder.setTriangleFillMode(.lines)
    renderCommandEncoder.setTessellationFactorBuffer(tessellationFactorsBuffer, offset: 0, instanceStride: 0)
    renderCommandEncoder.drawPatches(numberOfPatchControlPoints: 3, patchStart: 0, patchCount: 1, patchIndexBuffer: nil, patchIndexBufferOffset: 0, instanceCount: 1, baseInstance: 0)
    renderCommandEncoder.endEncoding()

    commandBuffer.present(mtkView.currentDrawable!)
    commandBuffer.commit()
    commandBuffer.waitUntilCompleted()
    /*
    // finally create an ordered list of commands forthe GPU to execute
    commandQueue = device.makeCommandQueue()

    timer = CADisplayLink(target: self, selector: #selector(ViewController.gameloop)) // call gameloop every time the screen refreshes
    timer.add(to: RunLoop.main, forMode: RunLoopMode.defaultRunLoopMode)

    */



  }

  override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
  }

  /*
  func render() {
    guard let drawable = metalLayer?.nextDrawable() else { return } // returns the texture to draw into in order for something to appear on the screen
    //objectToDraw.render(commandQueue: commandQueue, renderPipeline: renderPipeline, drawable: drawable, clearColor: nil)
  }

  // this is the routine that gets run every time the screen refreshes
  func gameloop() {
    autoreleasepool {
      self.render()
    }
  } */


}

整个git可以找到here

有什么金属大师之魂能帮忙吗？那里的文档非常稀少。

Answer 1

docs for MTLFeatureSet_iOS_GPUFamily3_v1 说：

与 Apple A9 GPU 和 iOS 9.0 一起推出。

（已添加重点。）

同时，iOS Device Compatibility Reference: Hardware GPU Information 文章称 iPad Air 2 具有 A8 GPU。

我不相信你的设备有能力。

一般来说，MTKView 的配置不会影响支持的功能集。这是设备固有的（硬件和操作系统版本的组合）。您可以使用supportsFeatureSet(_:) method of MTLDevice 查询设备是否支持给定的功能集。由于可以（并且通常）独立于任何其他对象（例如 MTKView）获取设备，因此功能集支持不能依赖于此类其他对象。