ISymbol

public void Draw (IGeometry Geometry);

public void QueryBoundary (
    int hDC,
    ITransformation displayTransform,
    IGeometry Geometry,
    IPolygon boundary
);

Valid input Geometries are as follows:

For MarkerSymbols, the Geometry must be an IPoint.

For Fill Symbols, the Geometry can be either an IPolygon or an IEnvelope.

For Line Symbols, the Geometry must be an IPolyline.

esriScreenCache Constants

Esri screen caching flags.

Constant	Value	Description
esriNoScreenCache	-1	Apply action directly to window.
esriAllScreenCaches	-2	Apply action to all caches.
esriScreenRecording	-3	Apply action to recording.

private void DisplayArc(IMxApplication mxApplication, IScreenDisplay sreenDisplay,
    IEllipticArc ellipticArc, ISymbol lineSymbol)
{
    short oldActiveCache = sreenDisplay.ActiveCache;
    //Add the new arc to a segment collection.
    ISegment segment = ellipticArc as ISegment;
    ISegmentCollection polyline = new Polyline()as ISegmentCollection;
    object Missing = Type.Missing;
    polyline.AddSegment(segment, ref Missing, ref Missing);
    sreenDisplay.ActiveCache = (short)esriScreenCache.esriNoScreenCache;
    sreenDisplay.StartDrawing(mxApplication.Display.hDC, (short)
        esriScreenCache.esriNoScreenCache);
    sreenDisplay.SetSymbol(lineSymbol);
    sreenDisplay.DrawPolyline(polyline as IGeometry);
    sreenDisplay.FinishDrawing();
    sreenDisplay.ActiveCache = oldActiveCache;
}