为什么我不能读取那些MTLTexture像素？

我试图通过MTLTexture这种方式获得像素:

let pixelCount = compareTexture.width * compareTexture.height

let region = MTLRegionMake2D(0, 0, compareTexture.width, compareTexture.height)  

var textureComponentsArray = Array(repeating: float4(0), count: pixelCount)

textureComponentsArray.withUnsafeMutableBytes {
   compareTexture.getBytes($0.baseAddress!, bytesPerRow: (MemoryLayout.size * compareTexture.width), from: region, mipmapLevel: 0)
}

print(textureComponentsArray.first!)

不幸的是,大多数元素要么是NaN,要么等于我初始化textureComponentsArray的值.例如,此代码打印:

float4(nan, nan, nan, nan)

我在macOS上,我的MTLTexture有这些属性:

let textureDescriptor = MTLTextureDescriptor()
textureDescriptor.width = imageTexture.width
textureDescriptor.height = imageTexture.height
textureDescriptor.pixelFormat = imageTexture.pixelFormat
textureDescriptor.resourceOptions = .storageModeManaged
textureDescriptor.storageMode = .managed
textureDescriptor.usage = [.renderTarget, .shaderRead, .shaderWrite]

我确实使用托管存储模式,因此数据应该可供CPU使用,我不明白为什么它不起作用.

谢谢.

编辑:
我正在尝试使用:

blitCommandEncoder.synchronize(resource: compareTexture)

我确实等待命令缓冲区完成,但仍然存在问题.