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I'm trying to create images from symbols so that I can create a custom symbol dialog. Found this sample code on the ESRI forums and it workes great on almost all symbols. I'm having problems with a IMultiLayerFillSymbol that has a IPictureFillSymbol on one of it's layers. It's throwing an exception on symbol.Draw(geometry);

Does anyone know if there is any additional steps that has to taken to get it to work with a IMultiLayerFillSymbol?

static public Image ImageFromSymbol(ISymbol symbol, Int32 width, Int32 height)
{
    try
    {
        Bitmap bitmap = new Bitmap(width, height);
        Graphics g = Graphics.FromImage(bitmap);
        IntPtr hdc = g.GetHdc();

        IGeometry geometry = null;
        if (symbol is IMarkerSymbol)
        {
            IPoint point = new PointClass();
            point.X = (width / 2);
            point.Y = (height / 2);
            geometry = point;
        }
        else if (symbol is ILineSymbol)
        {
            IPolyline line = new PolylineClass();
            IPoint ptFrom = new PointClass();
            IPoint ptTo = new PointClass();
            ptFrom.X = 3; ptFrom.Y = (height / 2);
            ptTo.X = (width - 3); ptTo.Y = ptFrom.Y;
            line.FromPoint = ptFrom;
            line.ToPoint = ptTo;
            geometry = line;
        }
        else
        {
            IEnvelope bounds = new EnvelopeClass();
            bounds.XMin = 1; bounds.XMax = width - 1;
            bounds.YMin = 1; bounds.YMax = height - 1;
            geometry = bounds;
        }

        symbol.SetupDC(hdc.ToInt32(), null);
        symbol.Draw(geometry);
        symbol.ResetDC();
        g.ReleaseHdc(hdc);
        g.Dispose();

        return bitmap as Image;
    }
    catch (Exception ex)
    {
        Debug.Print(ex.Message);
        return null;
    }
}

Update, Added the following code to make it work:

Updated the ImageFromSymbol metod with:

ITransformation pTransformation = CreateTransFromDC(
                       hDC, size.Width, size.Height);
pSymbol.SetupDC(hDC.ToInt32(), pTransformation);

Added:

 private const int LOGPIXELSY = 90;

[DllImport("GDI32.dll", EntryPoint = "GetDeviceCaps",
           ExactSpelling = true, SetLastError = true)]
       private static extern int GetDeviceCaps(IntPtr hdc, int nIndex);


private static ITransformation CreateTransFromDC(IntPtr hDC,
           int lWidth, int lHeight) {
           // Calculate the parameters for the new transformation,
           // based on the dimensions passed to this function.
           try {
               IEnvelope pBoundsEnvelope = new EnvelopeClass();
               pBoundsEnvelope.PutCoords(0.0, 0.0, (double)lWidth,
                   (double)lHeight);

               tagRECT deviceRect;
               deviceRect.left = 0;
               deviceRect.top = 0;
               deviceRect.right = lWidth;
               deviceRect.bottom = lHeight;

               int dpi = GetDeviceCaps(hDC, LOGPIXELSY);
               if (dpi == 0) {
                   throw new Exception(
                     "Could not retrieve Resolution from device context.");
               }

               // Create a new display transformation and set its properties
               IDisplayTransformation newTrans =
                   new DisplayTransformationClass();
               newTrans.VisibleBounds = pBoundsEnvelope;
               newTrans.Bounds = pBoundsEnvelope;
               newTrans.set_DeviceFrame(ref deviceRect);
               newTrans.Resolution = dpi;

               return newTrans;
           }
           catch {
               return null;
           }
       }
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  • Yes, when I tried to loop through layers of the IMultiLayerFillSymbol and drawing the individual IPictureFillSymbol it throws the same exception. Oct 6 '10 at 14:54
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I'd try creating a new DisplayTransformation class and passing it to SetupDC (instead of null). I think you'll need to set the device frame to match the pixel extent, along with visible extent. Then pass an envelope to Draw that matches the visible extent.

Update: try Richie Carmichael's SymbolToBitmap function here.

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