为什么此金属代码无法产生正确的三角形几何形状?

埃文·埃斯科巴尔

我正在遵循Metal by Example的Metal教程,并将代码转换为Swift。

我正在运行第二个示例,由于某种原因,此代码无法正常工作。


import UIKit
import Metal
import MetalKit
import simd

class MBEMetalView: UIView {

     // // // // // MAIN // // // // //
     var metalDevice: MTLDevice! = nil
     var metalLayer: CAMetalLayer! = nil
     var commandQueue: MTLCommandQueue! = nil
     var vertexBuffer: MTLBuffer! = nil
     var pipelineState: MTLRenderPipelineState! = nil
     var displayLink: CADisplayLink! = nil

     override class var layerClass : AnyClass {
          return CAMetalLayer.self
     }
//     override func didMoveToWindow() {
//          self.redraw()
//     }
     override func didMoveToSuperview() {
          super.didMoveToSuperview()
          if self.superview != nil {
               self.displayLink = CADisplayLink(target: self, selector: #selector(displayLinkFired))
               self.displayLink.add(to: RunLoop.main, forMode: .common)
          } else {
               self.displayLink.invalidate()
          }
     }
     @objc func displayLinkFired() {
          self.redraw()
     }





     // // // // // INIT // // // // //
     required init?(coder aDecoder: NSCoder) {
          super.init(coder: aDecoder)
          self.prepareDeviceLayerAndQueue()
          self.makeBuffers()
          self.makePipeline()
     }

     func prepareDeviceLayerAndQueue() {
          metalLayer = (self.layer as! CAMetalLayer)
          metalDevice = MTLCreateSystemDefaultDevice()
          metalLayer.device = metalDevice
          metalLayer.pixelFormat = .bgra8Unorm
          commandQueue = metalDevice.makeCommandQueue()
     }

     func makeBuffers() {
          var vertices: [MBEVertex] = [
               MBEVertex(position: vector_float4(0, 0.5, 0, 1) , color: vector_float4(1, 0, 0, 1)),
               MBEVertex(position: vector_float4(-0.5, -0.5, 0, 1)  , color: vector_float4(0, 1, 0, 1)),
               MBEVertex(position: vector_float4(0.5, -0.5, 0, 1)  , color: vector_float4(0, 0, 1, 1))
          ]
          self.vertexBuffer = metalDevice.makeBuffer(bytes: &vertices, length: 56, options: .storageModeShared)
     }

     func makePipeline() {
          guard let library = metalDevice.makeDefaultLibrary() else { print("COULD NOT CREATE LIBRARY") ; return }
          guard let vertexFunction = library.makeFunction(name: "vertex_main") else { print("COULD NOT CREATE A VERTEX FUNCTION") ; return }
          guard let fragmentFunction = library.makeFunction(name: "fragment_main") else { print("COULD NOT CREATE LIBRARY") ; return }

          let pipelineDescriptor = MTLRenderPipelineDescriptor()
          pipelineDescriptor.vertexFunction = vertexFunction
          pipelineDescriptor.fragmentFunction = fragmentFunction
          pipelineDescriptor.colorAttachments[0].pixelFormat = metalLayer.pixelFormat

          pipelineState = try? metalDevice.makeRenderPipelineState(descriptor: pipelineDescriptor)
          if pipelineState == nil { print("COULD NOT CREATE PIPELINE STATE") ; return }

     }





     // // // // // FUNCTIONS // // // // //
     func redraw() {
          guard let drawable = metalLayer.nextDrawable() else { print("COULD NOT CREATE A DRAWABLE") ; return }
          let texture = drawable.texture
          let renderPassDescriptor = MTLRenderPassDescriptor()
          renderPassDescriptor.colorAttachments[0].texture = texture
          renderPassDescriptor.colorAttachments[0].loadAction = .clear
          renderPassDescriptor.colorAttachments[0].storeAction = .store
          renderPassDescriptor.colorAttachments[0].clearColor = MTLClearColor(red: 0.1, green: 0.1, blue: 0.1, alpha: 1)

          guard let commandBuffer = commandQueue.makeCommandBuffer() else { print("COULD NOT CREATE A COMMAND BUFFER") ; return }
          guard let commandEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor) else { print("COULD NOT CREATE AN ENCODER") ; return }

          commandEncoder.setRenderPipelineState(pipelineState)
          commandEncoder.setVertexBuffer(vertexBuffer, offset: 0, index: 0)
          commandEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: 3)

          commandEncoder.endEncoding()
          commandBuffer.present(drawable)
          commandBuffer.commit()
     }





     // // // // // TYPES // // // // //
     struct MBEVertex {
          var position: vector_float4
          var color: vector_float4
     }

}

我非常确定着色器不是问题,因为顶点着色器仅接收顶点缓冲区并返回顶点。

片段着色器仅获取顶点着色器的输出和并返回颜色。

视图控制器是默认的-没碰过。

我将控制器视图的类更改为此MBEMetalView类。

我确实偶然发现了一行用顶点指针,长度和“ storageModeShared”选项创建顶点缓冲区的代码错误。

最初,我将length =设置为,MemoryLayout.size(of: vertices)但是根据控制台消息,仅在缓冲区需要32长度时才创建8长度。

我只是增加了长度,错误就消失了……

但是,三角形变形了而不是正确的颜色。看起来前两个顶点具有正确的位置,但第三个顶点没有。

没有一种颜色是正确的。有任何想法吗?

当我更改缓冲区的长度时,三角形将改变形状或从屏幕上消失。

华伦

无需猜测缓冲区的长度。您可以将其计算为顶点数乘以每个顶点占用的字节数:

let bufferLength = MemoryLayout<MBEVertex>.stride * vertices.count
self.vertexBuffer = metalDevice.makeBuffer(bytes: &vertices, length: bufferLength, options: .storageModeShared)

在这种情况下,结果实际上是96。

通常,这比硬编码常量更好。

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