使用 SceneKit 通过 Metal 计算管道渲染几何图形

Posted 2023-03-23

【中文标题】使用 SceneKit 通过 Metal 计算管道渲染几何图形

【英文标题】：Rendering geometry through a Metal compute pipeline using SceneKit

【发布时间】：2020-12-21 09:54:25

【问题描述】：

我是 Metal 新手，有以下问题。

我有一个简单的设置，可以在将几何图形通过计算管道后在屏幕上渲染一个三角形。我可以单独测试计算管道和渲染管道，但无法让它们一起工作。具体来说，我得到一个 GPU 挂起错误...

这是我试图通过一个三角形的尝试，除了通过如下所示的渲染命令之外，计算不做任何事情

这段代码大部分改编自Apple's sample 示例中的代码使用Metal View 并使用Objective-C 编写我展示的代码使用Swift 和SceneKit 作为基础。

我像这样构造一个简单的三角形，

// my swift variables in the ViewController
var vertexBuffer: MTLBuffer!
var renderPipelineState: MTLRenderPipelineState!
let sharedLibrary = sharedMetalRenderingDevice.device.makeDefaultLibrary()!
var _icbArgumentBuffer: MTLBuffer!
var _indirectCommandBuffer: MTLIndirectCommandBuffer!
var computePipelineState: MTLComputePipelineState!

// I call this inside viewDidLoad()
func setupMetalResources() 
    guard let device = sceneView.device else 
        assertionFailure()
        return
    
    
    struct TriangleVertex 
        var position: vector_float3
    
    
    let vertices: [TriangleVertex] = [
        TriangleVertex(position: vector_float3( 0.0, 0.5, 1)),
        TriangleVertex(position: vector_float3( -0.5, -0.5, 1)),
        TriangleVertex(position: vector_float3( 0.5, 0.5, 1))
    ]
    
    self.vertexBuffer = device.makeBuffer(
        bytes: vertices,
        length: MemoryLayout<TriangleVertex>.size * vertices.count,
        options: .cpuCacheModeWriteCombined)
    
    let vertexFunc = sharedLibrary.makeFunction(name: "passthrough_vertex")
    let fragmentFunc = sharedLibrary.makeFunction(name: "passthrough_fragment")
    
    let pipelineDescriptor = MTLRenderPipelineDescriptor()
    pipelineDescriptor.vertexFunction = vertexFunc
    pipelineDescriptor.fragmentFunction = fragmentFunc
    
    pipelineDescriptor.colorAttachments[0].pixelFormat = sceneView.colorPixelFormat
    pipelineDescriptor.depthAttachmentPixelFormat = sceneView.depthPixelFormat
    pipelineDescriptor.supportIndirectCommandBuffers = true
    
    guard let pipeline = try? device.makeRenderPipelineState(descriptor: pipelineDescriptor)
    else 
        assertionFailure()
        return
    
    
    self.renderPipelineState = pipeline
    
    let cullF = sharedLibrary.makeFunction(name: "testCull")
    let ag = cullF?.makeArgumentEncoder(bufferIndex: 1)
    
    let icbDesc = MTLIndirectCommandBufferDescriptor()
    icbDesc.commandTypes = .draw
    icbDesc.inheritBuffers = false
    icbDesc.maxVertexBufferBindCount = 3
    icbDesc.maxFragmentBufferBindCount = 0
    
    _indirectCommandBuffer = sharedMetalRenderingDevice.device.makeIndirectCommandBuffer(descriptor: icbDesc, maxCommandCount: 3, options: .storageModePrivate)
    
    _icbArgumentBuffer = sharedMetalRenderingDevice.device.makeBuffer(length: ag!.encodedLength, options: .storageModeShared)
    ag?.setArgumentBuffer(_icbArgumentBuffer, offset: 0)
    ag?.setIndirectCommandBuffer(_indirectCommandBuffer, index: 0)
    do 
        computePipelineState = try sharedMetalRenderingDevice.device.makeComputePipelineState(function: t!)
     catch 
        
    


// This is the SCNSceneRendererDelegate’s -> didRenderScene of SceneKit (my sceneview)
func renderer(_ renderer: SCNSceneRenderer, didRenderScene scene: SCNScene, atTime time: TimeInterval) 
    guard let renderEncoder = renderer.currentRenderCommandEncoder else  return 
    let myRange: Range = 0..<65536

    let commandBuffer = renderer.commandQueue?.makeCommandBuffer()
    let blit = commandBuffer?.makeBlitCommandEncoder()
    blit?.resetCommandsInBuffer(_indirectCommandBuffer, range: myRange)
    blit?.endEncoding()

    let computeEncoder = commandBuffer?.makeComputeCommandEncoder()
    computeEncoder!.setComputePipelineState(computePipelineState!)
    computeEncoder!.setBuffer(vertexBuffer, offset: 0, index: 0)
    computeEncoder!.setBuffer(_icbArgumentBuffer, offset: 0, index: 1)
    computeEncoder!.useResource( _indirectCommandBuffer, usage: .write)
    computeEncoder!.dispatchThreads(MTLSize(width: 1, height: 1, depth: 1), threadsPerThreadgroup: MTLSize(width: 1, height: 1, depth: 1))
    computeEncoder!.endEncoding()

    let optimBlit = commandBuffer?.makeBlitCommandEncoder()
    optimBlit?.optimizeIndirectCommandBuffer(_indirectCommandBuffer, range: myRange)
    optimBlit?.endEncoding()

    renderEncoder.setCullMode(.back)
    renderEncoder.setRenderPipelineState(renderPipelineState)
    renderEncoder.useResource(vertexBuffer, usage: .read)
    // If I comment the entire compute encoder and pass the vertex buffer to the render encoder, it works fine
    // The below 2 lines are how I pass the vertex buffer into the render pass 
    //        renderEncoder.setVertexBuffer(vertexBuffer, offset: 0, index: 0) 
    //        renderEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: 3)

    renderEncoder.executeCommandsInBuffer( _indirectCommandBuffer, range: myRange)
    //        renderEncoder.endEncoding() // uncommenting this causes "invalid usage because encoding has ended."
    commandBuffer?.commit() // I get a GPU Hang error 
    //        commandBuffer?.waitUntilCompleted() // uncommenting this causes the screen to go black and nothing shows  



// This is the Metal shader code
struct Vertex

    float4 position [[position]];
;
struct Vertex1

    float3 position;
;


vertex Vertex passthrough_vertex(const device Vertex1 *vertices [[buffer(0)]],
                                 constant simd_float4x4& modelViewProjectionTransform [[buffer(1)]],
                                 uint vid [[vertex_id]])

    Vertex out;
    out.position = modelViewProjectionTransform * float4(vertices[vid].position,1);
//    out.position = float4(vertices[vid].position.x, vertices[vid].position.y, vertices[vid].position.z, 1);
    return out;


fragment float4 passthrough_fragment(Vertex inVertex [[stage_in]])

    return float4(1,0,0,1);


typedef struct ICBContainer

    command_buffer commandBuffer [[ id(0) ]];
 ICBContainer;


kernel void
testCull(uint                      objectIndex   [[ thread_position_in_grid ]],
         device Vertex1            *vertices      [[ buffer(0) ]],
         device ICBContainer       *icb_container [[ buffer(1) ]])

    render_command cmd(icb_container->commandBuffer, objectIndex);
    
    cmd.set_vertex_buffer(vertices, 0);
    cmd.draw_primitives(primitive_type::triangle, 0, 3, 1, 1);

谁能指出错误或指出正确的方向来解决这个渲染问题？

【参考方案1】：

我有一个类似的问题/问题，这个链接帮助了我： https://gist.github.com/0xLeif/bc0d908bd7c5758d2f7766b8458ed4fd

我正在尝试使这项工作与我的特定应用程序一起工作，但我是金属新手，并且仍在努力使其与一堆不同的三角形一起工作......