// E.M.Pottasch, Jul 2010
// from Metastock formula, link: http://stocata.org/metastock/stop_trail_atr.html
// added separate parameters for upward and downward market environment

function vstop_func(trBull,trBear)
{
	trailArray[ 0 ] = C[ 0 ]; // initialize
	for( i = 1; i < BarCount; i++ )
	{
		prev = trailArray[ i - 1 ];
 
		if (C[ i ] > prev AND C[ i - 1 ] > prev)
		{
			trailArray[ i ] = Max(prev,C[ i ] - trBull[ i ]);
		}
		else if (C[ i ] < prev AND C[ i - 1 ] < prev)
		{
			trailArray[ i ] = Min(prev,C[ i ] + trBear[ i ]);
		}
		else if (C[ i ] > prev)
		{
			trailArray[ i ] = C[ i ] - trBull[ i ];
		}
		else
		{
			trailArray[ i ] = C[ i ] + trBear[ i ];	
		}
	}
	return trailArray;
}

per = Param("per",20, 1, 150, 1);
multBull = Param("multBull",2, 1, 4, 0.05);
multBear = Param("multBear",2, 1, 4, 0.05);

trBull = multBull * ATR(per);
trBear = multBear * ATR(per);

trailArray = vstop_func(trBull,trBear);

SetChartBkColor( ParamColor("ColorBG", ColorRGB( 0, 0, 0 ) ) );
GraphXSpace = 5;
SetChartOptions(0, chartShowDates);
Plot(IIf(trailArray > C,trailArray,Null),"\ntrailShort",ParamColor("ColorTrailShort",ColorRGB(255,0,0)),styleStaircase);
Plot(IIf(trailArray < C,trailArray,Null),"\ntrailLong",ParamColor("ColorTrailLong",ColorRGB(0,255,0)),styleStaircase);
Plot( C, "\nCandle",colorWhite, styleCandle );