How to create images from symbol in ArcObjects?

Question

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;
 }
 }

• MathiasWestin: Yes, when I tried to loop through layers of the IMultiLayerFillSymbol and drawing the individual IPictureFillSymbol it throws the same exception.

Answer 1

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.

• MathiasWestin: Great! Adding a ITransformation solved the problem!
• vinayan: @seems that the url is broken :(
• Kirk Kuykendall: @vinayan looks like Richie also uses SymboltoBitmap here kiwigis.blogspot.com/2009/05/…