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  How to get the index value of dataset when tracking a finance chart
Posted by James on Feb-09-2021 10:09
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Hi,
   I'm confused with the index value of Drawing and Tracking.

   In function drawchart:
   //-----------------------------------
    // After determining the extra points, we can obtain the data
int startIndex = (int)floor(viewer->getValueAtViewPort("x", viewer->getViewPortLeft()));
int endIndex = (int)ceil(viewer->getValueAtViewPort("x", viewer->getViewPortLeft() + viewer->getViewPortWidth()));

// Add the extra points (adjust the extra points if there are insufficient data)
extraPoints = min(extraPoints, startIndex);
startIndex -= extraPoints;
int duration = endIndex - startIndex + 1;
TRACE("start index = %d , end index = %d for plot arean", startIndex,endIndex);
   //--------------------------------------
    the debug information is :
    start index = 143 , end index = 221 for plot area
    that means there are 79 data point to draw

    But in the tracking function trackFinance, I add a debugger code:
   //---------------------------------------
    TRACE("index X =%d, and value =%fn", xIndex,value);
  //-----------------------------------------

    Then I found that index=0 at the left of chart, and index = 48 at the right of chart.
    Why the max index !=(79-1) ？ What's the index value in dataset at this moment?
    How to get the index value of dataset when tracking a chart?

   Thanks

    Regards

   James

  Re: How to get the index value of dataset when tracking a finance chart
Posted by James on Feb-09-2021 14:08
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Hi，
   I noticed that code in drawChart:
   //-----------------------------------------
startIndex -= extraPoints;
   //-----------------------------------------

    That menas the startIndex has negtive offset refer to plot data point.
    So the actual index in dataset is:
    startIndex + extraPoints + index of tracking = 143 +30 + 48 = 221, at right of plot area and the right of dataset.

    Regards