Swift2 为什么不'；我不能得到这个金属内核的结果吗

我试图了解金属计算着色器是如何工作的，因此我编写了以下代码：

class AppDelegate: NSObject, NSApplicationDelegate {


    var number:Float!
    var buffer:MTLBuffer!


    func applicationDidFinishLaunching(aNotification: NSNotification) {
        // Insert code here to initialize your application
        let metalDevice = MTLCreateSystemDefaultDevice()!
        let library = metalDevice.newDefaultLibrary()!
        let commandQueue = metalDevice.newCommandQueue()
        let commandBuffer = commandQueue.commandBuffer()
        let commandEncoder = commandBuffer.computeCommandEncoder()


        let pointlessFunction = library.newFunctionWithName("pointless")!
        let pipelineState = try! metalDevice.newComputePipelineStateWithFunction(pointlessFunction)
        commandEncoder.setComputePipelineState(pipelineState)
        number = 12

        buffer = metalDevice.newBufferWithBytes(&number, length: sizeof(Float), options: MTLResourceOptions.StorageModeShared)
        commandEncoder.setBuffer(buffer, offset: 0, atIndex: 0)


        commandEncoder.endEncoding()

        commandBuffer.commit()
        commandBuffer.waitUntilCompleted()

        let data = NSData(bytesNoCopy: buffer.contents(), length: sizeof(Float), freeWhenDone: false)
        var newResult:Float = 0
        data.getBytes(&newResult, length: sizeof(Float))
        print(newResult)




    }

通过使用StorageModeShared创建缓冲区，我希望对金属缓冲区所做的更改反映在我的Swift代码中，但是当我填充

newResult

变量时，看起来缓冲区的值仍然与开始时（12）的值相同，而它应该是125:

#include <metal_stdlib>
using namespace metal;



kernel void pointless (device float* outData [[ buffer(0) ]]) {

    *outData = 125.0;
}

#包括
使用金属；
内核无效无意义（设备浮点*outData[[buffer（0）]）{
*outData=125.0；
}

---

我做错了什么？

除非分派内核函数，否则它不会运行。我想你们是在假设，若你们有一个函数，那个么金属应该运行它一次，直到你们说不是，但这不会发生。相反，它根本不会运行。在

endEncoding

之前添加此项，您就可以开始了

let size = MTLSize(width: 1, height: 1, depth: 1)
commandEncoder.dispatchThreadgroups(size, threadsPerThreadgroup: size)