William's % R Gradient Indicator for Amibroker (AFL)

_SECTION_BEGIN("William's % R Gradient");
function PercentR( periods )
{
 return -100 * ( HHV( H, periods ) - C )/( HHV( H, periods ) - LLV( L, periods ) ); 
}
Plot( PercentR( Param("Periods", 14, 2, 100 ) ),_DEFAULT_NAME(),IIf( C > O, ParamColor("Up Color", colorBrightGreen ), ParamColor("Down Color", colorDarkRed ) ),ParamStyle( "Style", styleLine , maskHistogram  ), 1 );
_SECTION_END();

_SECTION_BEGIN("Background_Setting");
SetChartBkGradientFill( ParamColor("BgTop", colorDarkOliveGreen),
ParamColor("BgBottom", colorCustom2),ParamColor("titleblock",colorCustom4 ));
Plot( -20 , "", colorGreen,styleDashed);
Plot( -80 , "", colorRed,styleDashed);
_SECTION_END();