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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V2.0//EN" "document-v20.dtd">
<document>
<header>
<title>HPSF THUMBNAIL HOW-TO</title>
<authors>
<person name="Drew Varner" email="Drew.Varner@-deleteThis-sc.edu" />
</authors>
</header>
<body>
<section><title>The VT_CF Format</title>
<p>Thumbnail information is stored as a VT_CF, or Thumbnail Variant. The
Thumbnail Variant is used to store various types of information in a
clipboard. The VT_CF can store information in formats for the Macintosh or
Windows clipboard.</p>
<p>There are many types of data that can be copied to the clipboard, but the
only types of information needed for thumbnail manipulation are the image
formats.</p>
<p>The <code>VT_CF</code> structure looks like this:</p>
<table>
<tr>
<th>Element:</th>
<td>Clipboard Size</td>
<td>Clipboard Format Tag</td>
<td>Clipboard Data</td>
</tr>
<tr>
<th>Size:</th>
<td>32 bit unsigned integer (DWord)</td>
<td>32 bit signed integer (DWord)</td>
<td>variable length (byte array)</td>
</tr>
</table>
<p>The Clipboard Size refers to the size (in bytes) of Clipboard Data
(variable size) plus the Clipboard Format (four bytes).</p>
<p>Clipboard Format Tag has four possible values:</p>
<table>
<tr>
<th>Value</th>
<th>Identifier</th>
<th>Description</th>
</tr>
<tr>
<td><code>-1L</code></td>
<td><code>CFTAG_WINDOWS</code></td>
<td>a built-in Windows© clipboard format value</td>
</tr>
<tr>
<td><code>-2L</code></td>
<td><code>CFTAG_MACINTOSH</code></td>
<td>a Macintosh clipboard format value</td>
</tr>
<tr>
<td><code>-3L</code></td>
<td><code>CFTAG_FMTID</code></td>
<td>a format identifier (FMTID) This is rarely used.</td>
</tr>
<tr>
<td><code>0L</code></td>
<td><code>CFTAG_NODATA</code></td>
<td>No data This is rarely used.</td>
</tr>
</table>
</section>
<section><title>Windows Clipboard Data</title>
<p>Windows clipboard data has four image formats for thumbnails:</p>
<table>
<tr>
<th>Value</th>
<th>Identifier</th>
<th>Description</th>
</tr>
<tr>
<td>3</td>
<td><code>CF_METAFILEPICT</code></td>
<td>Windows metafile format - recommended</td>
</tr>
<tr>
<td>8</td>
<td><code>CF_DIB</code></td>
<td>Device Independent Bitmap</td>
</tr>
<tr>
<td>14</td>
<td><code>CF_ENHMETAFILE</code></td>
<td>Enhanced Windows metafile format</td>
</tr>
<tr>
<td>2</td>
<td><code>CF_BITMAP</code></td>
<td>Bitmap - Obsolete - Use <code>CF_DIB</code> instead</td>
</tr>
</table>
</section>
<section><title>Windows Metafile Format</title>
<p>The most common format for thumbnails on the Windows platform is the
Windows metafile format. The Clipboard places and extra header in front of
a the standard Windows Metafile Format data.</p>
<p>The Clipboard Data byte array looks like this when an image is stored in
Windows' Clipboard WMF format.</p>
<table>
<tr>
<th>Identifier</th>
<td>CF_METAFILEPICT</td>
<td>mm</td>
<td>width</td>
<td>height</td>
<td>handle</td>
<td>WMF data</td>
</tr>
<tr>
<th>Size</th>
<td>32 bit unsigned int</td>
<td>16 bit unsigned(?) int</td>
<td>16 bit unsigned(?) int</td>
<td>16 bit unsigned(?) int</td>
<td>16 bit unsigned(?) int</td>
<td>byte array - variable length</td>
</tr>
<tr>
<th>Description</th>
<td>Clipboard WMF</td>
<td>Mapping Mode</td>
<td>Image Width</td>
<td>Image Height</td>
<td>handle to the WMF data array in memory, or 0</td>
<td>standard WMF byte stream</td>
</tr>
</table>
</section>
<section><title>Device Independent Bitmap</title>
<p><strong>FIXME:</strong> Describe the Device Independent Bitmap
format!</p>
</section>
<section><title>Macintosh Clipboard Data</title>
<p><strong>FIXME:</strong> Describe the Macintosh clipboard formats!</p>
</section>
</body>
</document>
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