C 語言獲取任意文件的縮略圖

因為用shell取縮略圖時，對於損壞的文件，讀出來的圖有黑邊，所以就誕生了以下方法，不過這個效率要比用shell取的低3-4倍（耗時主要是在將黑色背景轉為透明的過程）。

1.添加類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("shell32.dll", CharSet = CharSet.Unicode, SetLastError =

    true

    )]

17. internal

    static

    extern

    int

    SHCreateItemFromParsingName(

18. [MarshalAs(UnmanagedType.LPWStr)]

    string

    path,
19. // The following parameter is not used - binding context.
20. IntPtr pbc,

21. ref

    Guid riid,
22. [MarshalAs(UnmanagedType.Interface)]

    out

    IShellItem shellItem);
24. [DllImport("gdi32.dll")]
25. [

    return

    : MarshalAs(UnmanagedType.Bool)]

26. internal

    static

    extern

    bool

    DeleteObject(IntPtr hObject);
28. [ComImport]
29. [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
30. [Guid("43826d1e-e718-42ee-bc55-a1e261c37bfe")]

31. internal

    interface

    IShellItem

32. {

33. void

    BindToHandler(IntPtr pbc,
34. [MarshalAs(UnmanagedType.LPStruct)]Guid bhid,
35. [MarshalAs(UnmanagedType.LPStruct)]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(ComInterfaceType.InterfaceIsIUnknown)]

76. internal

    interface

    IShellItemImageFactory
77. {
78. [PreserveSig]
79. HResult GetImage(
80. [In, MarshalAs(UnmanagedType.Struct)] NativeSize size,
81. [In] ThumbnailOptions flags,
82. [Out]

    out

    IntPtr phbm);
83. }
85. [StructLayout(LayoutKind.Sequential)]

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. [StructLayout(LayoutKind.Sequential)]

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 = GetHBitmap(Path.GetFullPath(fileName), width, height, options);

108. try

109. {
110. // return a System.Drawing.Bitmap 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 = Bitmap.FromHbitmap(nativeHBitmap);

124. if

     (Bitmap.GetPixelFormatSize(bmp.PixelFormat) < 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

     Bitmap(srcBitmap.Width, srcBitmap.Height, targetPixelFormat);
134. Rectangle bmpBounds =

     new

     Rectangle(0, 0, srcBitmap.Width, srcBitmap.Height);
136. BitmapData srcData = srcBitmap.LockBits(bmpBounds, ImageLockMode.ReadOnly, srcBitmap.PixelFormat);

138. bool

     isAlplaBitmap =

     false

     ;

140. try

141. {

142. for

     (

     int

     y = 0; y <= srcData.Height - 1; y++)
143. {

144. for

     (

     int

     x = 0; x <= srcData.Width - 1; x++)
145. {
146. Color pixelColor = Color.FromArgb(
147. Marshal.ReadInt32(srcData.Scan0, (srcData.Stride * y) + (4 * x)));

149. if

     (pixelColor.A > 0 & pixelColor.A < 255)
150. {
151. isAlplaBitmap =

     true

     ;
152. }
154. result.SetPixel(x, y, pixelColor);
155. }
156. }
157. }

158. finally

159. {
160. srcBitmap.UnlockBits(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, IntPtr.Zero,

     ref

     shellItem2Guid,

     out

     nativeShellItem);

179. if

     (retCode != 0)

180. throw

     Marshal.GetExceptionForHR(retCode);
182. NativeSize nativeSize =

     new

     NativeSize();
183. nativeSize.Width = width;
184. nativeSize.Height = height;
186. IntPtr hBitmap;
187. HResult hr = ((IShellItemImageFactory)nativeShellItem).GetImage(nativeSize, options,

     out

     hBitmap);
189. Marshal.ReleaseComObject(nativeShellItem);

191. if

     (hr == HResult.Ok)

     return

     hBitmap;

193. throw

     Marshal.GetExceptionForHR((

     int

     )hr);
194. }
195. }

2.使用方法：[csharp] view plain copy

1. int

   pic_size = 256;
3. Bitmap bm = WindowsThumbnailProvider.GetThumbnail(path, pic_size, pic_size, ThumbnailOptions.None);

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