我想要做什么
我正在尝试使用金属视图在相机提要上显示过滤器：MTKView。我正在密切关注 Apple 示例代码的方法 -通过利用 TrueDepth 相机数据增强实时视频（链接）。
到目前为止我所拥有的
以下代码效果很好（主要从上述示例代码中解释）：
class MetalObject: NSObject, MTKViewDelegate {
private var metalBufferView : MTKView?
private var metalDevice = MTLCreateSystemDefaultDevice()
private var metalCommandQueue : MTLCommandQueue!
private var ciContext : CIContext!
private let colorSpace = CGColorSpaceCreateDeviceRGB()
private var videoPixelBuffer : CVPixelBuffer?
private let syncQueue = DispatchQueue(label: "Preview View Sync Queue", qos: .userInitiated, attributes: [], autoreleaseFrequency: .workItem)
private var textureWidth : Int = 0
private var textureHeight : Int = 0
private var textureMirroring = false
private var sampler : MTLSamplerState!
private var renderPipelineState : MTLRenderPipelineState!
private var vertexCoordBuffer : MTLBuffer!
private var textCoordBuffer : MTLBuffer!
private var internalBounds : CGRect!
private var textureTranform : CGAffineTransform?
private var previewImage : CIImage?
init(with frame: CGRect) {
super.init()
self.metalBufferView = MTKView(frame: frame, device: self.metalDevice)
self.metalBufferView!.contentScaleFactor = UIScreen.main.nativeScale
self.metalBufferView!.framebufferOnly = true
self.metalBufferView!.colorPixelFormat = .bgra8Unorm
self.metalBufferView!.isPaused = true
self.metalBufferView!.enableSetNeedsDisplay = false
self.metalBufferView!.delegate = self
self.metalCommandQueue = self.metalDevice!.makeCommandQueue()
self.ciContext = CIContext(mtlDevice: self.metalDevice!)
//Configure Metal
let defaultLibrary = self.metalDevice!.makeDefaultLibrary()!
let pipelineDescriptor = MTLRenderPipelineDescriptor()
pipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm
pipelineDescriptor.vertexFunction = defaultLibrary.makeFunction(name: "vertexPassThrough")
pipelineDescriptor.fragmentFunction = defaultLibrary.makeFunction(name: "fragmentPassThrough")
// To determine how our textures are sampled, we create a sampler descriptor, which
// will be used to ask for a sampler state object from our device below.
let samplerDescriptor = MTLSamplerDescriptor()
samplerDescriptor.sAddressMode = .clampToEdge
samplerDescriptor.tAddressMode = .clampToEdge
samplerDescriptor.minFilter = .linear
samplerDescriptor.magFilter = .linear
sampler = self.metalDevice!.makeSamplerState(descriptor: samplerDescriptor)
do {
renderPipelineState = try self.metalDevice!.makeRenderPipelineState(descriptor: pipelineDescriptor)
} catch {
fatalError("Unable to create preview Metal view pipeline state. (\(error))")
}
}
final func update (newVideoPixelBuffer: CVPixelBuffer?) {
self.syncQueue.async {
var filteredImage : CIImage
self.videoPixelBuffer = newVideoPixelBuffer
//---------
//Core image filters
//Strictly CIFilters, chained together
//---------
self.previewImage = filteredImage
//Ask Metal View to draw
self.metalBufferView?.draw()
}
}
//MARK: - Metal View Delegate
final func draw(in view: MTKView) {
print (Thread.current)
guard let drawable = self.metalBufferView!.currentDrawable,
let currentRenderPassDescriptor = self.metalBufferView!.currentRenderPassDescriptor,
let previewImage = self.previewImage else {
return
}
// create a texture for the CI image to render to
let textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(
pixelFormat: .bgra8Unorm,
width: Int(previewImage.extent.width),
height: Int(previewImage.extent.height),
mipmapped: false)
textureDescriptor.usage = [.shaderWrite, .shaderRead]
let texture = self.metalDevice!.makeTexture(descriptor: textureDescriptor)!
if texture.width != textureWidth ||
texture.height != textureHeight ||
self.metalBufferView!.bounds != internalBounds {
setupTransform(width: texture.width, height: texture.height, mirroring: mirroring, rotation: rotation)
}
// Set up command buffer and encoder
guard let commandQueue = self.metalCommandQueue else {
print("Failed to create Metal command queue")
return
}
guard let commandBuffer = commandQueue.makeCommandBuffer() else {
print("Failed to create Metal command buffer")
return
}
// add rendering of the image to the command buffer
ciContext.render(previewImage,
to: texture,
commandBuffer: commandBuffer,
bounds: previewImage.extent,
colorSpace: self.colorSpace)
guard let commandEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: currentRenderPassDescriptor) else {
print("Failed to create Metal command encoder")
return
}
// add vertex and fragment shaders to the command buffer
commandEncoder.label = "Preview display"
commandEncoder.setRenderPipelineState(renderPipelineState!)
commandEncoder.setVertexBuffer(vertexCoordBuffer, offset: 0, index: 0)
commandEncoder.setVertexBuffer(textCoordBuffer, offset: 0, index: 1)
commandEncoder.setFragmentTexture(texture, index: 0)
commandEncoder.setFragmentSamplerState(sampler, index: 0)
commandEncoder.drawPrimitives(type: .triangleStrip, vertexStart: 0, vertexCount: 4)
commandEncoder.endEncoding()
commandBuffer.present(drawable) // Draw to the screen
commandBuffer.commit()
}
final func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {
}
}
笔记
MTKViewDelegate使用而不是子类化的原因是MTKView当它被子类化时，在主线程上调用了绘图调用。使用上面显示的委托方法，似乎是一个不同的金属相关线程调用每个循环。上述方法似乎提供了更好的性能。CIFilter必须编辑有关上述更新方法的使用细节。这一切都是一个沉重的链条CIFilters堆叠。不幸的是，这些过滤器没有任何调整的余地。
问题
上面的代码似乎大大减慢了主线程的速度，导致应用程序 UI 的其余部分不稳定。例如，滚动 a UIScrollviewget 似乎很慢且不稳定。
目标
调整 Metal 视图以减轻 CPU 负担并轻松处理主线程，从而为 UI 的其余部分留下足够的汁液。
根据上图，命令缓冲区的准备工作都是在 CPU 中完成的，直到提交并提交（？）。有没有办法从 CPU 中卸载它？
任何提高绘图效率的提示、反馈、提示等将不胜感激。