In this tutorial, we’ll create an Auto TrendLines Indicator to automatically draw TrendLines in TradeStation and MultiCharts using EasyLanguage and PowerLanguage,
Firstly, we calculate the maximum and the minimum of the last X candles or days.
This is only an example, you can create your trendline indicator simply replacing the HighestHigh and LowestLow value.
In EasyLanguage is possible to determine the Min-Max with two functions:
HighestHigh = Highest(High,BackHigh);
LowestLow = Lowest(Low,BackLow);
Drawing TrendLines by hand could be a boring activity. With TradeStation, you can create a Trendline Indicator that automated the process.
TLID = TL_New(StartDate, StartTime, StartValue, EndDate, EndTime, EndValue);
TLID is a variable that contains the TrendLine ID. This is a unique identifier and is useful if you will draw many trendlines in your chart.
TL_New is a reserved word that uses six parameters to draw a new trendline.
Inputs:
BackHigh (20),
BackLow (20);
Vars:
TL_HIGH(1),
TL_LOW(2),
HighestHigh(0),
LowestLow(0);
HighestHigh = Highest(High,BackHigh);
LowestLow = Lowest(Low,BackLow);
If lastbaronchart or lastbaronchartEX then
Begin
TL_HIGH = TL_New(Date[BackHigh], Time[BackHigh], HighestHigh, Date, Time, HighestHigh);
TL_LOW = TL_New(Date[BackHigh], Time[BackHigh], LowestLow, Date, Time, LowestLow);
End;

TrendLine Indicator Tradestation
Very simple! Do you like to personalize the TrendLines?
You can choose the color, the size, and the style.
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TradeStation EasyLanguage TrendLine Indicator Code:
Inputs:
BackHigh (20),
BackLow (20),
TL_HIGH_COLOR(DarkGreen),
TL_LOW_COLOR(DarkRed),
TL_HIGH_SIZE(2),
TL_LOW_SIZE(2),
TL_HIGH_STYLE(2),
TL_LOW_STYLE(2);
Vars:
TL_HIGH(1),
TL_LOW(2),
HighestHigh(0),
LowestLow(0),
TimeStorage(0);
HighestHigh = Highest(High,BackHigh);
LowestLow = Lowest(Low,BackLow);
If lastbaronchart or lastbaronchartEX then
Begin
TL_HIGH = TL_New(Date[BackHigh], Time[BackHigh], HighestHigh, Date, Time, HighestHigh);
TL_SetColor(TL_HIGH,TL_HIGH_COLOR);
TL_SetSize(TL_HIGH,TL_HIGH_SIZE);
TL_SetStyle(TL_HIGH,TL_HIGH_STYLE);
TL_LOW = TL_New(Date[BackHigh], Time[BackHigh], LowestLow, Date, Time, LowestLow);
TL_SetColor(TL_LOW,TL_LOW_COLOR);
TL_SetSize(TL_LOW,TL_LOW_SIZE);
TL_SetStyle(TL_LOW,TL_LOW_STYLE);
End;

With the TradeStation TrendLine Indicator in Easyanguage you have to refresh the chart (Ctrl+R) when you want to redraw the trendlines.
Resources: