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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。

+BIT祝威+悄悄在此留下版了个权的信息说：

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<T>

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         }

public static void Sort(this UnmanagedArray array, bool descending)

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         }

public static void Sort(this UnmanagedArray array, bool descending) where T : struct, IComparable

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。

+BIT祝威+悄悄在此留下版了个权的信息说：

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 }

Teamplate method

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。

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原文地址：https://www.cnblogs.com/bitzhuwei/p/CSharpGL-36-generic-unmanaged-array-sorting.html