MTK查看透明度

Question

我无法使MTKView清除其背景。我已经将视图及其层的isOpaque设置为false，将背景色设置为clear，并尝试了在google/sttackoverflow上找到的多种解决方案(下面的代码中大部分都是loadAction和clearColor的颜色附件(，但都不起作用。

所有背景色设置似乎都被忽略了。设置MTLRenderPassColorAttachmentDescriptor的loadAction和clearColor无效。

我想在MTKView下绘制我的常规UIView。我错过了什么？

// initialization
let metal = MTKView(frame: self.view.bounds)
metal.device = MTLCreateSystemDefaultDevice()
self.renderer = try! MetalRenderer(mtkView: metal)
metal.delegate = self.renderer
self.view.addSubview(metal);

import Foundation
import MetalKit
import simd
public enum MetalError: Error {
case mtkViewError
case renderError
}
internal class MetalRenderer: NSObject, MTKViewDelegate {
private let commandQueue: MTLCommandQueue;
private let pipelineState: MTLRenderPipelineState
private var viewportSize: SIMD2<UInt32> = SIMD2(x: 10, y: 10);
private weak var mtkView: MTKView?


init(mtkView: MTKView) throws {
guard let device = mtkView.device else { 
print("device not found error")
throw MetalError.mtkViewError 
}
self.mtkView = mtkView
// Load all the shader files with a .metal file extension in the project.
guard let defaultLibrary = device.makeDefaultLibrary() else {
print("Could not find library")
throw MetalError.mtkViewError
}
let vertexFunction = defaultLibrary.makeFunction(name: "vertexShader")
let fragmentFunction = defaultLibrary.makeFunction(name: "fragmentShader")
mtkView.layer.isOpaque = false;
mtkView.layer.backgroundColor = UIColor.clear.cgColor
mtkView.isOpaque = false;
mtkView.backgroundColor = .clear
let pipelineStateDescriptor = MTLRenderPipelineDescriptor();
pipelineStateDescriptor.label = "Pipeline";
pipelineStateDescriptor.vertexFunction = vertexFunction;
pipelineStateDescriptor.fragmentFunction = fragmentFunction;
pipelineStateDescriptor.isAlphaToCoverageEnabled = true
pipelineStateDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm;
pipelineStateDescriptor.colorAttachments[0].isBlendingEnabled = true;
pipelineStateDescriptor.colorAttachments[0].destinationRGBBlendFactor = .oneMinusSourceAlpha;
pipelineStateDescriptor.colorAttachments[0].destinationAlphaBlendFactor = .oneMinusSourceAlpha;
pipelineState = try! device.makeRenderPipelineState(descriptor: pipelineStateDescriptor);

guard let queue = device.makeCommandQueue() else { 
print("make command queue error")
throw MetalError.mtkViewError 
}
commandQueue = queue
}

func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {
viewportSize.x = UInt32(size.width)
viewportSize.y = UInt32(size.height)
}
func draw(in view: MTKView) {
let vertices: [Vertex] = [
Vertex(position: SIMD3<Float>(x: 250.0, y: -250.0, z: 0)),
Vertex(position: SIMD3<Float>(x: -250.0, y: -250.0, z: 0)),
Vertex(position: SIMD3<Float>(x: 0.0, y: 250.0, z: 0)),
]

guard let commandBuffer = commandQueue.makeCommandBuffer() else { 
print("Couldn't create command buffer")
return 
}
// Create a new command buffer for each render pass to the current drawable.
commandBuffer.label = "MyCommand";
// Obtain a renderPassDescriptor generated from the view's drawable textures.
guard let renderPassDescriptor = view.currentRenderPassDescriptor else {
print("Couldn't create render pass descriptor")
return
}

guard let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor) else {
print("Couldn't create render encoder")
return
}
renderPassDescriptor.colorAttachments[0].loadAction = .clear
renderPassDescriptor.colorAttachments[0].clearColor = MTLClearColorMake(1.0, 0.0, 0.0, 0.5)
renderEncoder.label = "MyRenderEncoder";
// Set the region of the drawable to draw into.
renderEncoder.setViewport(MTLViewport(originX: 0.0, originY: 0.0, width: Double(viewportSize.x), height: Double(viewportSize.y), znear: 0.0, zfar: 1.0))
renderEncoder.setRenderPipelineState(pipelineState)
// Pass in the parameter data.
renderEncoder.setVertexBytes(vertices, length: MemoryLayout<Vertex>.size * vertices.count, index: Int(VertexInputIndexVertices.rawValue))
renderEncoder.setVertexBytes(&viewportSize, length: MemoryLayout<SIMD2<UInt32>>.size, index: Int(VertexInputIndexViewportSize.rawValue))
renderEncoder.drawPrimitives(type: MTLPrimitiveType.triangle, vertexStart: 0, vertexCount: 3)
renderEncoder.endEncoding()
// Schedule a present once the framebuffer is complete using the current drawable.
guard let drawable = view.currentDrawable else {
print("Couldn't get current drawable")
return
}
commandBuffer.present(drawable)
// Finalize rendering here & push the command buffer to the GPU.
commandBuffer.commit()
}
}

Answer 1

多亏了Frank，答案只是设置了视图本身的clearColor属性，但我错过了。我还删除了MTLRenderPipelineDDescriptor中的大多数调整，现在的代码是：

let pipelineStateDescriptor = MTLRenderPipelineDescriptor();
pipelineStateDescriptor.label = "Pipeline";
pipelineStateDescriptor.vertexFunction = vertexFunction;
pipelineStateDescriptor.fragmentFunction = fragmentFunction;
pipelineStateDescriptor.colorAttachments[0].pixelFormat = 
mtkView.colorPixelFormat;

也不需要从currentRenderPassDescriptor更改MTLRenderPass描述符。

EDIT：还要确保将MTKView的isOpaque属性也设置为false。