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);