How to edit already calculated buffers in the indicator?

[Mikołaj Gogola]

Hi,
I suppose my question is trivial, but I am strugglin with this. I want to draw straight lines on the chart when it hits specific hour and I want them to be longer than one bar. Lets say I have 1H Chart and when it is 12 o'clock I want lines drawn above 8:00, 9:00, 10:00 and 11:00 (I mean straight line from 8:00 to 11:00), but when I am trying to alter values in already calculated buffers everything on my chart disappears. Is there another way to achieve this? Should I call some "recalculate" function on my desired hour?

int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])
{
   MqlDateTime t;
   TimeToStruct(Time[0],t);
   if(t.hour == 12)
   {
      for( int i = 1; i <= 4; ++i )
      {
         buf0[i] = 150; // straight line at 150 height
      }  
   }
   return(rates_total);
}

[Marco vd Heijden]

Yes you can use a draw_once loop to draw the initial picture and then set a flag so that it doesn't run again.

Then on the next run you can overwrite the old picture with the new one.

[Amir Yacoby]

Why don't you use the time buffer passed to OnCalculate?

   TimeToStruct(Time[0],t); // should be TimeToStruct(time[0],t);

[Mikołaj Gogola]

Good point Amir time[0] sounds like more reasonable option.
Marco what do you mean exactly by draw_once loop? I tried to google it but couldn't find such thing as "draw_once".

[Jean Francois Le Bas]

use Objects

[Marco vd Heijden]

Mikołaj Gogola:

Good point Amir time[0] sounds like more reasonable option.
Marco what do you mean exactly by draw_once loop? I tried to google it but couldn't find such thing as "draw_once".

It's just a boolean flag you set.

Sometimes people use two loops one to draw history upon loading the expert and one that redraws a part of the current + n candles.

This is to prevent the indicator from redrawing all candles at every tick.

But i dont think it's applicable in your example.