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Hi,

I'm currently trying to implement Volo in a C# application, but running into a problem when trying to set the image to decode. I'm using the below code, pretty much copied from your C# sample:

System.Drawing.Imaging.BitmapData bmpData = bmp8bpp.LockBits(
                            new Rectangle(0, 0, bmp8bpp.Width, bmp8bpp.Height),
                            System.Drawing.Imaging.ImageLockMode.ReadOnly,
                            System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
voloret = Volo.Set(volo, Volo.PROP_IMAGE_POINTER, bmpData.Scan0);
voloret = Volo.Set(volo, Volo.PROP_IMAGE_WIDTH, bmpData.Width);
voloret = Volo.Set(volo, Volo.PROP_IMAGE_LINE_DELTA, bmpData.Stride);
voloret = Volo.Set(volo, Volo.PROP_IMAGE_HEIGHT, bmpData.Height);
voloret = Volo.Set(volo, Volo.PROP_CALLBACK_RESULT, new Volo.Callback(Volo_CBResult));

However, the PROP_IMAGE_LINE_DELTA set returns 0 if bmpData.Stride is negative (which is a perfectly acceptable value). Does Volo not support upside-down bitmaps?

Thanks,

David
 

OK, I discovered the mirrored property and am now trying the following code:

if (bmpData.Stride < 0)
{
    voloret = Volo.Set(volo, Volo.PROP_IMAGE_LINE_DELTA, -bmpData.Stride);
    voloret = Volo.Set(volo, Volo.PROP_IMAGE_MIRRORED, Volo.CONST_ENABLED);
}
else
    voloret = Volo.Set(volo, Volo.PROP_IMAGE_LINE_DELTA, bmpData.Stride);

But now I just get an access violation when I call Decode. (I don't change any other Volo properties before I call Decode, it essentially gets called immediately after the above-posted code.)

Reading the C# documentation, it looks like the Scan0 property will point to the last line of the data array for an upside down bitmap. SwiftDecoder expects the image pointer to point to the first byte of the data array, with a positive line delta. When you get a negative stride, you need to subtract (Height - 1)*Stride from the Scan0 pointer to point to the base of the image data.

Regards,

Bob Dunphy
 

 Nice catch, worked great. Thanks!