Draw Triangle Polygon with Dynamic Display

Question

I'm trying to draw a custom polygon in Dynamic Display but its really not working at all. I can get it to work if I do this:

IPointCollection pc = seg.setRectangle( mapcontrol.map.extent.envelope) as IPointCollection; 

But I want a custom polygon. I tried this following code but I'm getting -2147220968

       IPoint p0 = new PointClass(); 
        IPoint p1 = new PointClass();
        IPoint p2 = new PointClass();
        p0.SpatialReference = gcs;
        p1.SpatialReference = gcs;
        p2.SpatialReference = gcs;

        p0.PutCoords(-94.569168d, 46.697493d);
        p1.PutCoords(-94.052811d, 46.711619d);
        p2.PutCoords(-94.51561d, 46.520131d);

        p0.Project(mapSP); 
        p1.Project(mapSP); 
        p2.Project(mapSP); 

        ILine line = new LineClass();
        ILine line2 = new LineClass();
        ILine line3 = new LineClass();

        line.SpatialReference = mapSP;
        line2.SpatialReference = mapSP;
        line3.SpatialReference = mapSP;

        line.FromPoint= p0; 
        line.ToPoint = p1;

        line2.FromPoint= p1; 
        line2.ToPoint = p2;

        line3.FromPoint= p2; 
        line3.ToPoint = p0;

        ISegmentCollection seg = new PolygonClass();
        seg.AddSegment(line as ISegment);
        seg.AddSegment(line2 as ISegment);
        seg.AddSegment(line3 as ISegment);
        pc = seg as IPointCollection;

                           dynamicSymbolProps.set_DynamicGlyph(esriDynamicSymbolType.esriDSymbolFill, fillGlyph);
try
{
  dynamicDisplay.DrawPolygon(pc);
}
catch (Exception ex)
{
  string m= ex.Message; 
}

Answer 1

Using the above code and adding the following will get it to work.

ITopologicalOperator toppy = seg as ITopologicalOperator;
toppy.Simplify();
IPointCollection4 pc4 = toppy as IPointCollection4;

dynamicSymbolProps.set_DynamicGlyph(esriDynamicSymbolType.esriDSymbolFill, fillGlyph);

dynamicDisplay.DrawPolygon(pc4);