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Unity - "NativeArray<T> where T:struct" の要素を "T[] where T:struct" へ高速にコピーする

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Marsha.CopyTo() には IntPtr -> IntPtr のコピーメソッドがないので、kernel32.dll にある CopyMemory() を使う。

public static class Kern32 {
    [DllImport("kernel32.dll", EntryPoint = "CopyMemory", SetLastError = false)]
    public static extern void CopyMemory(System.IntPtr dest, System.IntPtr src, uint count);
}

"T[] where T:struct" は Generic なので fixed ブロックでポインタに変換できない。Marsha.UnsafeAddrOfPinnedArrayElement() で配列の最初のポインタが取れるのでそれを利用する。その前に、GC されないように Pinned データに指定しておく。

public static class NativeArrayExtension {
    public static void UnsafeCopyTo<T>(this NativeArray<T> src, T[] dst) where T:struct {
        unsafe {
            var pSrc = (System.IntPtr)src.GetUnsafePtr();
            var hDst = GCHandle.Alloc(dst, GCHandleType.Pinned);
            try {
                var pDst = Marshal.UnsafeAddrOfPinnedArrayElement(dst, 0);
                Kern32.CopyMemory(pDst, pSrc, (uint)(dst.Length * Marshal.SizeOf<T>()));
            } finally {
                hDst.Free();
            }
        }
    }
}
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