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finding price on a trendline ( equation of a straight line)

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I came across this solution while searching for trendline strategies. 
https://www.iexpertadvisor.com/metatrader-mql-course-module-13-using-a-trendline-in-an-expert-advisor/

But I am having a slight issue with the code and I do not know why the problem exist. The logic of the code seems correct.
I am interested in this function from the code: ( i have inserted the code)
'int fnGetTrendLineSignal(string strName, int type),'  

I have tested this function,
1. I manually drew a trendline on the chart.
2. I entered the trendline name
3. I checked the calculated price( or y value) for the current time (time now). But the calculated price doesn't match the actual price on the trendline for the current time. 

I have attached a screenshot of the problem. 

i am losing sleep over this.
Thank you very much
double fnGetTrendLineSignal(string strName)
  {
// get the four coordinates
   double x1 = ObjectGet( strName, OBJPROP_TIME1);
   double y1 = ObjectGet( strName, OBJPROP_PRICE1);
   double x2 = ObjectGet( strName, OBJPROP_TIME2);
   double y2 = ObjectGet( strName, OBJPROP_PRICE2);
   
   

// calculate the slope of the line (m)
        double m = (y2-y1)/(x2-x1);
  

// calcualte the offset (b)
   double b=y1 -m*x1;

// get the current x value
   double time=TimeCurrent();
 

// calculate the value (y) of the projected trendline at (x): y = mx + b
   double value=m*time+b;
 

   return value;
  }


Will Kene:
But I am having a slight issue with the code and I do not know why the problem exist. The logic of the code seems correct.
https://docs.mql4.com/objects/objectgetvaluebyshift
Will Kene: . I checked the calculated price( or y value) for the current time (time now). But the calculated price doesn't match the actual price on the trendline for the current time.
   double x1 = ObjectGet( strName, OBJPROP_TIME1);
   double y1 = ObjectGet( strName, OBJPROP_PRICE1);
   double x2 = ObjectGet( strName, OBJPROP_TIME2);
   double y2 = ObjectGet( strName, OBJPROP_PRICE2);
   double m = (y2-y1)/(x2-x1);
   double b=y1 -m*x1;
   double time=TimeCurrent();
   double value=m*time+b;

Your problem is the assumption of continuous time. You have missing bars (weekend.) Therefor the trendline doesn't have constant slope in time.
          "Free-of-Holes" Charts - MQL4 Articles
          No candle if open = close ? - MQL4 and MetaTrader 4 - MQL4 programming forum

Compare to

   double x1 = iBarShift(_Symbol, PERIOD_CURRENT, ObjectGet( strName, OBJPROP_TIME1) );
   double y1 = ObjectGet( strName, OBJPROP_PRICE1);
   double x2 = iBarShift(_Symbol, PERIOD_CURRENT, ObjectGet( strName, OBJPROP_TIME2) );
   double y2 = ObjectGet( strName, OBJPROP_PRICE2);
   double m = (y2-y1)/(x2-x1);
   double b=y1 -m*x1;
   double time=iBarShift(_Symbol, PERIOD_CURRENT, TimeCurrent() );
   double value=m*time+b;
whro
Mohamad Zulhairi Baba:
https://docs.mql4.com/objects/objectgetvaluebyshift
Thank you. solves the problem
whroeder1:

Your problem is the assumption of continuous time. You have missing bars (weekend.) Therefor the trendline doesn't have constant slope in time.
          "Free-of-Holes" Charts - MQL4 Articles
          No candle if open = close ? - MQL4 and MetaTrader 4 - MQL4 programming forum

Compare to

Makes sense. Really grateful. Thank you. Now I can sleep. happy pips
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