CSharpGL(36)通用的非托管数组排序方法
如果OpenGL要渲染半透明物体，一个方法是根据顶点到窗口的距离排序，按照从远到近的顺序依次渲染。所以本篇介绍对 UnmanagedArray<T> 进行排序的几种方法。
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UnmanagedArray<T>
首先重新介绍一下非托管数组这个东西。一个 UnmanagedArray<float> 与一个 float[] 是一样的用处，只不过 UnmanagedArray<float> 是用 Marshal.AllocHGlobal(memSize); 在非托管内存上申请的空间。
1 namespace CSharpGL 2 { 3 /// <summary> 4 /// unmanaged huge array. 5 /// <para>Check http://www.cnblogs.com/bitzhuwei/p/huge-unmanged-array-in-csharp.html </para> 6 /// </summary> 7 /// <typeparam name="T">sbyte, byte, char, short, ushort, int, uint, long, ulong, float, double, decimal, bool or other struct types. enum not supported.</typeparam> 8 public sealed unsafe class UnmanagedArray<T> : UnmanagedArrayBase where T : struct 9 { 10 public UnmanagedArray(int count) 11 : base(count, Marshal.SizeOf(typeof(T))) 12 { 13 } 14 } 15 16 /// <summary> 17 /// Base type of unmanaged array. 18 /// <para>Similar to array in <code>int array[Length];</code></para> 19 /// </summary> 20 public abstract class UnmanagedArrayBase : IDisposable 21 { 22 /// <summary> 23 /// 此非托管数组中的数据在内存中的起始地址 24 /// Start position of array; Head of array; first element's position of array. 25 /// <para>Similar to <code>array</code> in <code>int array[Length];</code></para> 26 /// </summary> 27 public IntPtr Header { get; private set; } 28 29 /// <summary> 30 /// How many elements? 31 /// <para>Similar to <code>Length</code> in <code>int array[Length];</code></para> 32 /// </summary> 33 public int Length { get; private set; } 34 35 /// <summary> 36 /// 单个元素的字节数。 37 /// <para>How manay bytes for one element of array?</para> 38 /// </summary> 39 protected int elementSize; 40 41 /// <summary> 42 /// 申请到的字节数。（元素的总数 * 单个元素的字节数）。 43 /// <para>How many bytes for total array?</para> 44 /// <para>Length * elementSize</para> 45 /// </summary> 46 public int ByteLength 47 { 48 get { return (this.Length * this.elementSize); } 49 } 50 51 protected UnmanagedArrayBase(int elementCount, int elementSize) 52 { 53 this.Length = elementCount; 54 this.elementSize = elementSize; 55 int memSize = this.Length * this.elementSize; 56 this.Header = Marshal.AllocHGlobal(memSize); 57 } 58 } 59 }
UnmanagedArray<float>
下面我们以 UnmanagedArray<float> 为例，实现对非托管数组的排序。（下面是快速排序算法）
1 public static void Sort(this UnmanagedArray<float> array, bool descending) 2 { 3 QuickSort(array, 0, array.Length - 1, descending); 4 } 5 6 public static void Sort(UnmanagedArray<float> array, int start, int length, bool descending) 7 { 8 QuickSort(array, start, start + length - 1, descending); 9 } 10 11 private static void QuickSort(UnmanagedArray<float> array, int start, int end, bool descending) 12 { 13 if (start >= end) { return; } 14 15 Stack<int> stack = new Stack<int>(); 16 stack.Push(end); 17 stack.Push(start); 18 QuickSort(array, descending, stack); 19 } 20 21 private static void QuickSort(UnmanagedArray<float> array, bool descending, Stack<int> stack) 22 { 23 while (stack.Count > 0) 24 { 25 int start = stack.Pop(); 26 int end = stack.Pop(); 27 int index = QuickSortPartion(array, start, end, descending); 28 if (start < index - 1) 29 { 30 stack.Push(index - 1); stack.Push(start); 31 } 32 if (index + 1 < end) 33 { 34 stack.Push(end); stack.Push(index + 1); 35 } 36 } 37 } 38 39 private static unsafe int QuickSortPartion(UnmanagedArray<float> array, int start, int end, bool descending) 40 { 41 float* pointer = (float*)array.Header.ToPointer(); 42 float pivot, startValue, endValue; 43 pivot = pointer[start]; 44 while (start < end) 45 { 46 startValue = pointer[start]; 47 while ((start < end) 48 && ((descending && (startValue.CompareTo(pivot) > 0)) 49 || (!descending) && (startValue.CompareTo(pivot) < 0))) 50 { 51 start++; 52 startValue = pointer[start]; 53 } 54 55 endValue = pointer[end]; 56 while ((start < end) 57 && ((descending && (endValue.CompareTo(pivot) < 0)) 58 || (!descending) && (endValue.CompareTo(pivot) > 0))) 59 { 60 end--; 61 endValue = pointer[end]; 62 } 63 64 if (start < end) 65 { 66 pointer[end] = startValue; 67 pointer[start] = endValue; 68 } 69 } 70 71 return start; 72 }
原本我以为把这个方法改写一下，用 T代替具体的 float ，就可以实现对任意 T where T : struct,IComparable<T> 的排序，但是VS报了这样的编译错误：无法获取托管类型(“T”)的地址和大小，或无法声明指向它的指针。
看来C#不允许将泛型T作为unsafe里的数组的类型。那么只能用下面的几种方式变通一下。
Marshal
Marshal 有这样2个方法：
1 // 从非托管数组中读取一个元素 2 public static object PtrToStructure(IntPtr ptr, Type structureType); 3 // 向非托管数组写入一个元素 4 public static void StructureToPtr(object structure, IntPtr ptr, bool fDeleteOld);
用这2个方法就可以实现对非托管数组的读写操作。于是泛型版本( UnmagedArray<T> )的排序算法就实现了。
1 public static void Sort<T>(this UnmanagedArray<T> array, bool descending) where T : struct, IComparable<T> 2 { 3 QuickSort(array, 0, array.Length - 1, descending); 4 } 5 6 public static void Sort<T>(this UnmanagedArray<T> array, int start, int length, bool descending) where T : struct, IComparable<T> 7 { 8 QuickSort(array, start, start + length - 1, descending); 9 } 10 11 private static void QuickSort<T>(UnmanagedArray<T> array, int start, int end, bool descending) where T : struct, IComparable<T> 12 { 13 if (start >= end) { return; } 14 15 var stack = new Stack<int>(); 16 stack.Push(end); 17 stack.Push(start); 18 QuickSort(array, descending, stack); 19 } 20 21 private static void QuickSort<T>(UnmanagedArray<T> array, bool descending, Stack<int> stack) where T : struct, IComparable<T> 22 { 23 IntPtr pointer = array.Header; 24 Type type = typeof(T); 25 int elementSize = Marshal.SizeOf(type); 26 27 while (stack.Count > 0) 28 { 29 int start = stack.Pop(); 30 int end = stack.Pop(); 31 int index = QuickSortPartion(array, start, end, descending, type, elementSize); 32 if (start < index - 1) 33 { 34 stack.Push(index - 1); stack.Push(start); 35 } 36 if (index + 1 < end) 37 { 38 stack.Push(end); stack.Push(index + 1); 39 } 40 } 41 } 42 43 private static int QuickSortPartion<T>(UnmanagedArray<T> array, int start, int end, bool descending, Type type, int elementSize) where T : struct, IComparable<T> 44 { 45 IntPtr pointer = array.Header; 46 IntPtr pivotIndex, startIndex, endIndex; 47 T pivot, startValue, endValue; 48 pivotIndex = new IntPtr((int)pointer + start * elementSize); 49 pivot = (T)Marshal.PtrToStructure(pivotIndex, type); 50 while (start < end) 51 { 52 startIndex = new IntPtr((int)pointer + start * elementSize); 53 startValue = (T)Marshal.PtrToStructure(startIndex, type); 54 while ((start < end) 55 && ((descending && (startValue.CompareTo(pivot) > 0)) 56 || ((!descending) && (startValue.CompareTo(pivot) < 0)))) 57 { 58 start++; 59 startIndex = new IntPtr((int)pointer + start * elementSize); 60 startValue = (T)Marshal.PtrToStructure(startIndex, type); 61 } 62 63 endIndex = new IntPtr((int)pointer + end * elementSize); 64 endValue = (T)Marshal.PtrToStructure(endIndex, type); 65 while ((start < end) 66 && ((descending && (endValue.CompareTo(pivot) < 0)) 67 || ((!descending) && (endValue.CompareTo(pivot) > 0)))) 68 { 69 end--; 70 endIndex = new IntPtr((int)pointer + end * elementSize); 71 endValue = (T)Marshal.PtrToStructure(endIndex, type); 72 } 73 74 if (start < end) 75 { 76 Marshal.StructureToPtr(endValue, startIndex, true); 77 Marshal.StructureToPtr(startValue, endIndex, true); 78 } 79 } 80 81 return start; 82 }
虽然可用，但是用Marshal读写非托管数组效率比较低（使用了装箱拆箱操作）。于是我有了下面这个思路。
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CodeProvider
我们知道C#现有的类库是支持动态生成和调用C#代码的。因此，我可以在调用 Sort<T>(this UnmanagedArray<T> array, bool descending) 时，临时为具体的T生成一个排序方法，然后去调用这个方法。这就不需要使用 Marshal 了。
具体步骤如下。
准备模板
为了便于编码、维护，我们先准备一个排序代码的模板。模板里的TemplateStructType纯属一个占位符，在使用的时候我们先用具体的类型把它替换掉，就成了我们需要的源代码。
1 using System; 2 using System.Collections.Generic; 3 using System.Runtime.InteropServices; 4 5 namespace CSharpGL 6 { 7 /// <summary> 8 /// Helper class for sorting unmanaged array. 9 /// </summary> 10 public static partial class SortingHelper 11 { 12 ///// <summary> 13 ///// Sort unmanaged array specified with <paramref name="array"/> at specified area. 14 ///// </summary> 15 ///// <param name="array"></param> 16 ///// <param name="descending">true for descending sort; otherwise false.</param> 17 //public static void Sort(this UnmanagedArray<TemplateStructType> array, bool descending) 18 //{ 19 // QuickSort(array, 0, array.Length - 1, descending); 20 //} 21 22 /// <summary> 23 /// Sort unmanaged array specified with <paramref name="array"/> at specified area. 24 /// </summary> 25 /// <param name="array"></param> 26 /// <param name="start">index of first value to be sorted.</param> 27 /// <param name="length">length of <paramref name="array"/> to bo sorted.</param> 28 /// <param name="descending">true for descending sort; otherwise false.</param> 29 public static void Sort(UnmanagedArray<TemplateStructType> array, int start, int length, bool descending) 30 { 31 QuickSort(array, start, start + length - 1, descending); 32 } 33 34 private static void QuickSort(UnmanagedArray<TemplateStructType> array, int start, int end, bool descending) 35 { 36 if (start >= end) { return; } 37 38 Stack<int> stack = new Stack<int>(); 39 stack.Push(end); 40 stack.Push(start); 41 QuickSort(array, descending, stack); 42 } 43 44 private static void QuickSort(UnmanagedArray<TemplateStructType> array, bool descending, Stack<int> stack) 45 { 46 while (stack.Count > 0) 47 { 48 int start = stack.Pop(); 49 int end = stack.Pop(); 50 int index = QuickSortPartion(array, start, end, descending); 51 if (start < index - 1) 52 { 53 stack.Push(index - 1); stack.Push(start); 54 } 55 if (index + 1 < end) 56 { 57 stack.Push(end); stack.Push(index + 1); 58 } 59 } 60 } 61 62 private static unsafe int QuickSortPartion(UnmanagedArray<TemplateStructType> array, int start, int end, bool descending) 63 { 64 TemplateStructType* pointer = (TemplateStructType*)array.Header.ToPointer(); 65 TemplateStructType pivot, startValue, endValue; 66 pivot = pointer[start]; 67 while (start < end) 68 { 69 startValue = pointer[start]; 70 while ((start < end) 71 && ((descending && (startValue.CompareTo(pivot) > 0)) 72 || (!descending) && (startValue.CompareTo(pivot) < 0))) 73 { 74 start++; 75 startValue = pointer[start]; 76 } 77 78 endValue = pointer[end]; 79 while ((start < end) 80 && ((descending && (endValue.CompareTo(pivot) < 0)) 81 || (!descending) && (endValue.CompareTo(pivot) > 0))) 82 { 83 end--; 84 endValue = pointer[end]; 85 } 86 87 if (start < end) 88 { 89 pointer[end] = startValue; 90 pointer[start] = endValue; 91 } 92 } 93 94 return start; 95 } 96 } 97 }
嵌入的资源
然后把这个模板文件设置为嵌入的资源，以便于调用。
动态生成和调用代码
利用CSharpCodeProvider来把源代码编译为Assembly并调用。
1 public static void Sort<T>(this UnmanagedArray<T> array, bool descending) where T : struct, IComparable<T> 2 { 3 Type type = typeof(T); 4 string order = ManifestResourceLoader.LoadTextFile(@"ResourcesSortingHelper.Order`1.cs"); 5 order = order.Replace("TemplateStructType", type.FullName); 6 var codeProvider = new CSharpCodeProvider(); 7 var option = new CompilerParameters(); 8 option.GenerateInMemory = true; 9 option.CompilerOptions = "/unsafe"; 10 option.ReferencedAssemblies.Add("System.dll"); 11 option.ReferencedAssemblies.Add("CSharpGL.dll"); 12 CompilerResults result = codeProvider.CompileAssemblyFromSource(option, 13 order); 14 Assembly asm = result.CompiledAssembly; 15 Type sortingHelper = asm.GetType("CSharpGL.SortingHelper"); 16 Type unmanagedArrayGeneric = typeof(UnmanagedArray<>); 17 Type unmanagedArray = unmanagedArrayGeneric.MakeGenericType(type); 18 MethodInfo method = sortingHelper.GetMethod("Sort", new Type[] { unmanagedArray, typeof(int), typeof(int), typeof(bool) }); 19 method.Invoke(null, new object[] { array, 0, array.Length, descending }); 20 }
+BIT祝威+悄悄在此留下版了个权的信息说：
总结
还有一种利用emit的方法，我就暂时不研究了。