获取c语言随机文件的缩略图

使用shell导入缩览图时，读取到的关于受损文件的图片有黑色边缘，因此诞生了以下方法，但效率比使用shell高3 ~ 4倍(耗时主要是将黑色背景转换为透明的过程)。

1.添加类WindowsThumbnailProvider

[csharp] view plain copy

1. [Flags]
2. public enum ThumbnailOptions
3. {
4. None = 0x00,
5. BiggerSizeOk = 0x01,
6. InMemoryOnly = 0x02,
7. IconOnly = 0x04,
8. ThumbnailOnly = 0x08,
9. InCacheOnly = 0x10,
10. }
12. public class WindowsThumbnailProvider
13. {
14. private const string IShellItem2Guid = "7E9FB0D3-919F-4307-AB2E-9B1860310C93";
16. [dllImport(";, CharSet = C, SetLastError = true)]
17. internal static extern int SHCreateItemFromParsingName(
18. [MarshalA)] string path,
19. // The following parameter is not used - binding context.
20. IntPtr pbc,
21. ref Guid riid,
22. [MarshalA)] out IShellItem shellItem);
24. [DllImport("gdi32.dll")]
25. [return: MarshalA)]
26. internal static extern bool DeleteObject(IntPtr hObject);
28. [ComImport]
29. [InterfaceType)]
30. [Guid("43826d1e-e718-42ee-bc55-a1e261c37bfe")]
31. internal interface IShellItem
32. {
33. void BindToHandler(IntPtr pbc,
34. [MarshalA)]Guid bhid,
35. [MarshalA)]Guid riid,
36. out IntPtr ppv);
38. void GetParent(out IShellItem ppsi);
39. void GetDisplayName(SIGDN sigdnName, out IntPtr ppszName);
40. void GetAttributes(uint sfgaoMask, out uint psfgaoAttribs);
41. void Compare(IShellItem psi, uint hint, out int piOrder);
42. };
44. internal enum SIGDN : uint
45. {
46. NORMALDISPLAY = 0,
47. PARENTRELATIVEPARSING = 0x80018001,
48. PARENTRELATIVEFORADDRESSBAR = 0x8001c001,
49. DESKTOPABSOLUTEPARSING = 0x80028000,
50. PARENTRELATIVEEDITING = 0x80031001,
51. DESKTOPABSOLUTEEDITING = 0x8004c000,
52. FILESYSPATH = 0x80058000,
53. URL = 0x80068000
54. }
56. internal enum HResult
57. {
58. Ok = 0x0000,
59. False = 0x0001,
60. InvalidArguments = unchecked((int)0x80070057),
61. OutOfMemory = unchecked((int)0x8007000E),
62. NoInterface = unchecked((int)0x80004002),
63. Fail = unchecked((int)0x80004005),
64. ElementNotFound = unchecked((int)0x80070490),
65. TypeElementNotFound = unchecked((int)0x8002802B),
66. NoObject = unchecked((int)0x800401E5),
67. Win32ErrorCanceled = 1223,
68. Canceled = unchecked((int)0x800704C7),
69. ResourceInUse = unchecked((int)0x800700AA),
70. AccessDenied = unchecked((int)0x80030005)
71. }
73. [ComImportAttribute()]
74. [GuidAttribute("bcc18b79-ba16-442f-80c4-8a59c30c463b")]
75. [InterfaceTypeAttribute)]
76. internal interface IShellItemImageFactory
77. {
78. [PreserveSig]
79. HResult GetImage(
80. [In, MarshalA)] NativeSize size,
81. [In] ThumbnailOptions flags,
82. [Out] out IntPtr phbm);
83. }
85. [StructLayou)]
86. internal struct NativeSize
87. {
88. private int width;
89. private int height;
91. public int Width { set { width = value; } }
92. public int Height { set { height = value; } }
93. };
95. [StructLayou)]
96. public struct RGBQUAD
97. {
98. public byte rgbBlue;
99. public byte rgbGreen;
100. public byte rgbRed;
101. public byte rgbReserved;
102. }
104. public static Bitmap GetThumbnail(string fileName, int width, int height, ThumbnailOptions options)
105. {
106. IntPtr hBitmap = GetHBitma(fileName), width, height, options);
108. try
109. {
110. // return a Sy from the hBitmap
111. return GetBitmapFromHBitmap(hBitmap);
112. }
113. finally
114. {
115. // delete HBitmap to avoid memory leaks
116. DeleteObject(hBitmap);
117. }
118. }
120. public static Bitmap GetBitmapFromHBitmap(IntPtr nativeHBitmap)
121. {
122. Bitmap bmp = Bi(nativeHBitmap);
124. if ) < 32)
125. return bmp;
127. return CreateAlphaBitmap(bmp, PixelFormat.Format32bppArgb);
128. }
130. public static Bitmap CreateAlphaBitmap(Bitmap srcBitmap, PixelFormat targetPixelFormat)
131. {
132. Bitmap result = new Bitma, , targetPixelFormat);
134. Rectangle bmpBounds = new Rectangle(0, 0, , );
136. BitmapData srcData = (bmpBounds, ImageLockMode.ReadOnly, );
138. bool isAlplaBitmap = false;
140. try
141. {
142. for (int y = 0; y <= - 1; y++)
143. {
144. for (int x = 0; x <= - 1; x++)
145. {
146. Color pixelColor = Color.FromArgb(
147. Mar, * y) + (4 * x)));
149. if > 0 & < 255)
150. {
151. isAlplaBitmap = true;
152. }
154. re(x, y, pixelColor);
155. }
156. }
157. }
158. finally
159. {
160. (srcData);
161. }
163. if (isAlplaBitmap)
164. {
165. return result;
166. }
167. else
168. {
169. return srcBitmap;
170. }
171. }
173. private static IntPtr GetHBitmap(string fileName, int width, int height, ThumbnailOptions options)
174. {
175. IShellItem nativeShellItem;
176. Guid shellItem2Guid = new Guid(IShellItem2Guid);
177. int retCode = SHCreateItemFromParsingName(fileName, In, ref shellItem2Guid, out nativeShellItem);
179. if (retCode != 0)
180. throw Mar(retCode);
182. NativeSize nativeSize = new NativeSize();
183. na = width;
184. na = height;
186. IntPtr hBitmap;
187. HResult hr = ((IShellItemImageFactory)nativeShellItem).GetImage(nativeSize, options, out hBitmap);
189. Mar(nativeShellItem);
191. if (hr == HRe) return hBitmap;
193. throw Mar((int)hr);
194. }
195. }

2.使用方法：[csharp] view plain copy

1. int pic_size = 256;
3. Bitmap bm = Window(path, pic_size, pic_size, T);