metal &object c

https://developer.apple.com/documentation/metal/mtlcommandencoder/1458041-pushdebuggroup

PushDebugGroups

https://developer.apple.com/documentation/metal/mtlcommandencoder

这个encoder我之前在其它api里没见过 就对应我tbdr里面提到的renderpass

有四种

MTLRenderCommandEncoder	An encoder used for graphics rendering tasks.
MTLComputeCommandEncoder	An encoder used for computational tasks.
MTLBlitCommandEncoder	An encoder used for memory management tasks.
MTLParallelRenderCommandEncoder	An encoder used for multiple graphics rendering tasks encoded in parallel.

https://developer.apple.com/documentation/metal/mtlcommandbuffer/1639924-gpustarttime

https://developer.apple.com/documentation/metal/mtlcommandbuffer/1442997-addcompletedhandler

https://developer.apple.com/documentation/metal/mtlcommandbuffer?language=objc

看了下cmdqueue和cmdbuffer和其它是一致的 只是往cmdbuffer上写命令的时候需要用到以上四种不同encoder来写不同功能的命令并且它们可以

按照次序（一次只能用一种）多个encoder写到一块cmdbuffer上 这样是不是我还是没法用cmd的 

commandBuffer.addCompletedHandler { cb in
    let executionDuration = cb.gpuEndTime - cb.gpuStartTime
    /* ... */
}
拿到renderpass的时间。。。