更改为MTLTexture时，透明png变黑

Question

我正在将Asset文件夹中的png格式更改为MTLTexture。它在透明边缘变黑。

 func loadTexture(device: MTLDevice, textureName: String) throws -> MTLTexture {
        let textureLoader = MTKTextureLoader(device: device)
        return try textureLoader.newTexture(name: textureName, scaleFactor: 1.0, bundle: nil,  options: nil)
    }

管道描述符是

  let pipelineDescriptor = MTLRenderPipelineDescriptor()
        pipelineDescriptor.fragmentFunction = fragmentFunction
        pipelineDescriptor.vertexFunction = vertexFunction
        pipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm
        pipelineDescriptor.sampleCount = 4

        pipelineDescriptor.colorAttachments[0].isBlendingEnabled = true
        pipelineDescriptor.colorAttachments[0].rgbBlendOperation = .add
        pipelineDescriptor.colorAttachments[0].alphaBlendOperation = .add
        pipelineDescriptor.colorAttachments[0].sourceRGBBlendFactor = .one
        pipelineDescriptor.colorAttachments[0].sourceAlphaBlendFactor = .one
        pipelineDescriptor.colorAttachments[0].destinationRGBBlendFactor = .oneMinusSourceAlpha
        pipelineDescriptor.colorAttachments[0].destinationAlphaBlendFactor = .oneMinusSourceAlpha