MTKView刷新问题

Question

我正在通过 MTKView 合成 UIImage 数组，并且我看到刷新问题仅在合成阶段显现出来，但一旦我与应用程序交互，这些问题就会消失。换句话说，复合材料按预期工作，但它们在屏幕上的外观看起来有点问题，直到我通过放大/平移等强制刷新。

我发布了两个视频来展示实际问题：Glitch1、Glitch2

我选择的复合方法是将每个 UIImage 转换为 MTLTexture，并将其提交到设置为“.load”的渲染缓冲区，该缓冲区会渲染带有此纹理的多边形，然后对 UIImage 中的每个图像重复该过程大批。

复合材料可以工作，但是屏幕反馈（正如您从视频中看到的那样）非常不稳定。

关于可能发生的事情有什么想法吗？任何建议，将不胜感激

一些相关代码：

for strokeDataCurrent in strokeDataArray {

        let strokeImage = UIImage(data: strokeDataCurrent.image)
        let strokeBbox = strokeDataCurrent.bbox
        let strokeType = strokeDataCurrent.strokeType
        self.brushStrokeMetal.drawStrokeImage(paintingViewMetal: self.canvasMetalViewPainting, strokeImage: strokeImage!, strokeBbox: strokeBbox, strokeType: strokeType)

} // end of for strokeDataCurrent in strokeDataArray

...

func drawStrokeUIImage (strokeUIImage: UIImage, strokeBbox: CGRect, strokeType: brushTypeMode) {

    // set up proper compositing mode fragmentFunction
    self.updateRenderPipeline(stampCompStyle: drawStampCompMode)

    let stampTexture = UIImageToMTLTexture(strokeUIImage: strokeUIImage)
    let stampColor = UIColor.white
    let stampCorners = self.stampSetVerticesFromBbox(bbox: strokeBbox)
    self.stampAppendToVertexBuffer(stampUse: stampUseMode.strokeBezier, stampCorners: stampCorners, stampColor: stampColor)
    self.renderStampSingle(stampTexture: stampTexture)


  } // end of func drawStrokeUIImage (strokeUIImage: UIImage, strokeBbox: CGRect)

func renderStampSingle(stampTexture: MTLTexture) {

    // this routine is designed to update metalDrawableTextureComposite one stroke at a time, taking into account
    // whatever compMode the stroke requires. Note that we copy the contents of metalDrawableTextureComposite to
    // self.currentDrawable!.texture because the goal will be to eventually display a resulting composite

    let renderPassDescriptorSingleStamp: MTLRenderPassDescriptor? = self.currentRenderPassDescriptor

    renderPassDescriptorSingleStamp?.colorAttachments[0].loadAction = .load
    renderPassDescriptorSingleStamp?.colorAttachments[0].clearColor = MTLClearColorMake(0, 0, 0, 0)
    renderPassDescriptorSingleStamp?.colorAttachments[0].texture = metalDrawableTextureComposite 

    // Create a new command buffer for each tessellation pass
    let commandBuffer: MTLCommandBuffer? = commandQueue.makeCommandBuffer()

    let renderCommandEncoder: MTLRenderCommandEncoder? = commandBuffer?.makeRenderCommandEncoder(descriptor: renderPassDescriptorSingleStamp!)

    renderCommandEncoder?.label = "Render Command Encoder"
    renderCommandEncoder?.setTriangleFillMode(.fill)
    defineCommandEncoder(
      renderCommandEncoder: renderCommandEncoder,
      vertexArrayStamps: vertexArrayStrokeStamps,
      metalTexture: stampTexture) // foreground sub-curve chunk

    renderCommandEncoder?.endEncoding() // finalize renderEncoder set up

    //begin presentsWithTransaction approach  (needed to better synchronize with Core Image scheduling
    copyTexture(buffer: commandBuffer!, from: metalDrawableTextureComposite, to: self.currentDrawable!.texture)
    commandBuffer?.commit() // commit and send task to gpu

    commandBuffer?.waitUntilScheduled()
    self.currentDrawable!.present()
    // end presentsWithTransaction approach
    self.initializeStampArray(stampUse: stampUseMode.strokeBezier) // clears out the stamp array in preparation of next draw call

  } // end of func renderStampSingle(stampTexture: MTLTexture)

Answer 1

首先，Metal 领域非常深入，并且它在 MTKView 构造中的使用记录很少，特别是对于任何不属于更传统的游戏范例的应用程序。在 @warrenm、@ken-thomases 和 @modj 等人的帮助下，我发现自己在 Metal 方面积累了有限的经验，他们的贡献对我和 Swift/Metal 社区都非常有价值在逃。非常感谢大家。

其次，对于任何对金属进行故障排除的人，请注意以下事项： 如果您收到消息：

[CAMetalLayerDrawable present] should not be called after already presenting this drawable. Get a nextDrawable instead

请不要忽视它。它可能看起来无害，特别是如果它只被报告一次。但请注意，这表明您的实现的一部分存在缺陷，必须先解决该问题，然后才能对应用程序的任何其他与 Metal 相关的方面进行故障排除。至少对我来说是这样。正如您从视频帖子中看到的那样，这个问题的症状非常严重，并导致了不可预测的行为，我很难查明其根源。对我来说特别难以看到的是，我在应用程序周期的早期只收到过一次这条消息，但是这个单一实例足以以我认为归因于 CoreImage 和/的方式使其他所有图形方式都变得混乱。或我所做的其他完全不相关的设计选择。

那么，我如何摆脱这个警告呢？好吧，就我而言，我假设具有以下设置：

self.enableSetNeedsDisplay = true // needed so we can call setNeedsDisplay()  to force a display update as soon as metal deems possible
self.isPaused = true // needed so the draw() loop does not get called once/fps
self.presentsWithTransaction = true // for better synchronization with CoreImage (such as simultaneously turning on a layer while also clearing MTKView)

这意味着每当我想刷新屏幕时我几乎都可以调用currentDrawable!.present()或直接调用。commandBuffer.presentDrawable(view.currentDrawable)嗯，事实并非如此。事实证明，这些调用只能在 draw() 循环内进行，并且只能通过调用来访问setNeedsDisplay()。一旦我做出了这个改变，我就很好地解决了我的刷新之谜。

此外，我发现该MTKView设置self.isPaused = true（以便我可以setNeedsDisplay()直接拨打电话）仍然会导致一些意外的行为。因此，我选择了：

self.enableSetNeedsDisplay = false // needed so we can call setNeedsDisplay()  to force a display update as soon as metal deems possible
self.isPaused = false // draw() loop gets called once/fps
self.presentsWithTransaction = true // for better synchronization with CoreImage

metalDrawableDriver以及修改我的draw()循环以驱动在设置标志并调用后执行哪种更新setNeedsDisplay()：

override func draw(_ rect: CGRect) {

autoreleasepool(invoking: { () -> () in

  switch metalDrawableDriver {

  case stampRenderMode.canvasRenderNoVisualUpdates:

    return

  case stampRenderMode.canvasRenderClearAll:

    renderClearCanvas()

  case stampRenderMode.canvasRenderPreComputedComposite:

    renderPreComputedComposite()

  case stampRenderMode.canvasRenderStampArraySubCurve:
      renderSubCurveArray()

  } // end of switch metalDrawableDriver

}) // end of autoreleasepool

} // end of draw()

这可能看起来很迂回，但这是我发现获得一致的用户驱动的显示更新的唯一机制。

我希望这篇文章描述了一个无错误且可行的解决方案，Metal 开发人员将来可能会发现有用。