Viewing Thumbnails

Sep 17, 2009

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Update for Vault 2012: Additional image formats supported. This post applies to Vault 2011 and earlier. Go here for the Vault 2012 code.

Here is how you view thumbnail data from Vault.

Background:
Thumbnails are stored as metafiles, which must be rendered to a display context. This is a bit different from a jpeg because metafiles have no fixed size. This is nice because the image can be scaled to any size without loss of detail.

Sample Code:
Once you have found the PropInst object with the thumbnail value, here is how you can render it to a System.Drawing.Image object.

C#:

/// <summary>
/// Takes a thumbnail property from Vault and renders it to an Image
/// </summary>
private System.Drawing.Image RenderThumbnailToImage(Document.PropInst propInst, int width, int height)
{
// convert the property value to a byte array
byte[] thumbnailRaw = (byte[])propInst.Val;

// load the data into a stream but skip the first 12 bytes
Stream stream = new MemoryStream(thumbnailRaw, 12, thumbnailRaw.Length – 12);

// create the Metafile object
System.Drawing.Imaging.Metafile metafile = new System.Drawing.Imaging.Metafile(stream);

    // render the Metafile to an Image object and display in the picture box
    Image retVal = metafile.GetThumbnailImage(width, height, new Image.GetThumbnailImageAbort(GetThumbnailImageAbort), IntPtr.Zero);
    stream.Close();
    return retVal;
}

/// <summary>
/// Delagate for the GetThumnailImage function.
/// </summary>
private static bool GetThumbnailImageAbort()
{
return false; // do nothing
}

VB.NET:

''' <summary>
''' Takes a thumbnail property from Vault and renders it to an Image
''' </summary>
Private Function RenderThumbnailToImage(ByVal propInst As Document.PropInst, ByVal width As Integer, ByVal height As Integer) As System.Drawing.Image

' convert the property value to a byte array
Dim thumbnailRaw As Byte() = CType(propInst.Val, Byte())

' load the data into a stream but skip the first 12 bytes
Dim stream As System.IO.Stream = New System.IO.MemoryStream(thumbnailRaw, 12, thumbnailRaw.Length – 12)

' create the Metafile object
Dim metafile As System.Drawing.Imaging.Metafile = New System.Drawing.Imaging.Metafile(stream)

' render the Metafile to an Image object and display in the picture box
Dim retVal As Image = metafile.GetThumbnailImage(width, height, New Image.GetThumbnailImageAbort(AddressOf GetThumbnailImageAbort), IntPtr.Zero)

    stream.Close()
    Return retVal
End Function

''' <summary>
''' Delagate for the GetThumnailImage function.
''' </summary>
Private Shared Function GetThumbnailImageAbort() As Boolean
    Return False ' do nothing
End Function

sample code Thumbnail

Comments

3 responses to “Viewing Thumbnails”

J. Daniel Smith

September 30, 2009

Your C# can be simplified slightly with a lambda; you also can use “using” rather than an explicit close. I also wonder whether the Metafile should be Dispose()d too:
private System.Drawing.Image RenderThumbnailToImage(Document.PropInst propInst, int width, int height)
{
// convert the property value to a byte array
var thumbnailRaw = (byte[])propInst.Val;
// load the data into a stream but skip the first 12 bytes
const int bytesToSkip = 12;
using (var stream = new MemoryStream(thumbnailRaw, bytesToSkip, thumbnailRaw.Length – bytesToSkip))
{
// create the Metafile object
using (var metafile = new System.Drawing.Imaging.Metafile(stream))
{
// render the Metafile to an Image object and display in the picture box
return metafile.GetThumbnailImage(width, height, () => false, IntPtr.Zero);
}
}
}
I’m enjoying the articles; the File Associations – Part 1 was very nice.

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Reply
varinder Singh

January 21, 2010

Is there a way to create thumbnail for non-CAD files, like image files.

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Reply
Doug Redmond

January 22, 2010

Answered on the Vault newsgroup:
http://discussion.autodesk.com/forums/thread.jspa?threadID=759609&tstart=0

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