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  step line chart zoom in/out and scroll
Posted by jungryul kim on Feb-19-2024 11:54
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I am trying to add a zoom function to the step line chart.

The x-axis of each line has CTime data and the y-axis values are 0 to 7.
The range of the x-axis may be different for each line and the quantity may also be different.

The output results are drawn as a step line chart as follows.
The x-axis displays the CTiem format in seconds, such as '2024-02-01 02:22:33'.

When trying to add zoom in/out function, it is difficult to implement in the code below.

///////////////////////////////////////////////////// ///////////////

void CSimpleZoomScrollDlg::initChartViewer(CChartViewer *viewer)
{
      viewer->setFullRange("x", m_timeStamps[0], m_timeStamps[m_timeStamps.len - 1]);

      viewer->setViewPortWidth(0.2);
     viewer->setViewPortLeft(1 - viewer->getViewPortWidth());

      viewer->setZoomInWidthLimit(10.0 / m_timeStamps.len);

     viewer->setMouseWheelZoomRatio(1.1);

      m_PointerPB.SetCheck(1);
     viewer->setMouseUsage(Chart::MouseUsageScroll);
}

///////////////////////////////////////////////////// ///////////////////

Sample data is generated as follows:
    m_timeStamps = m_ranSeries->getDateSeries(1827, Chart::chartTime(2007, 1, 1), 86400);
     m_dataSeriesA = m_ranSeries->getSeries(1827, 150, -10, 10);
     m_dataSeriesB = m_ranSeries->getSeries(1827, 200, -10, 10);
     m_dataSeriesC = m_ranSeries->getSeries(1827, 250, -8, 8);


You can zoom only if the number of x-axis data and the actual data are the same.

In reality, the data I have has different numbers and x-axis ranges for each line, so I don't know how to apply the above example.
I would like to inquire.
chart.png

  Re: step line chart zoom in/out and scroll
Posted by jungryul kim on Feb-19-2024 13:19
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Below are the database search results and step line chart code.
A layer is assigned to each line, and the x-axis range is also assigned separately.
chart2.png

  Re: step line chart zoom in/out and scroll
Posted by Peter Kwan on Feb-19-2024 17:09
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Hi Jungryul Kim

The chart can work even if the x data range for the lines are different. You just need to modify the code to determine the viewPortTimeStamps and viewPortDataSeries separately. Also, you need to compute the full x-axis range by considering all the x data series.

In the original code, there is a line to configure the x-axis range:

viewer->setFullRange("x", m_timeStamps[0], m_timeStamps[m_timeStamps.len - 1]);

Even though you have multiple x data series, the entire chart still contains only one x-axis at the bottom of the plot area. The min and max values should be:

// Get the min/max x value by considered all x data series
double minX = m_pChartX[0][0];
double maxX = m_pChartX[0][m_nChartYSize[0] - 1];
for (int i = 1; i < m_nLineSize; ++i) {
    minX = std::min(minX, m_pChartX[i][0]);
    maxX = std::max(maxX, m_pChartX[i][m_nChartYSize[i] - 1]);
}

// This is the full range
viewer->setFullRange("x", minX, maxX);


Then in the charting code, in the original sample code, the viewPortTimeStamps are determined using:

// Get the array indexes that corresponds to the visible start and end dates
int startIndex = (int)floor(Chart::bSearch(m_timeStamps, viewPortStartDate));
int endIndex = (int)ceil(Chart::bSearch(m_timeStamps, viewPortEndDate));
int noOfPoints = endIndex - startIndex + 1;

// Extract the part of the data array that are visible.
DoubleArray viewPortTimeStamps = DoubleArray(m_timeStamps.data + startIndex, noOfPoints);
DoubleArray viewPortDataSeriesA = DoubleArray(m_dataSeriesA.data + startIndex, noOfPoints);
DoubleArray viewPortDataSeriesB = DoubleArray(m_dataSeriesB.data + startIndex, noOfPoints);
DoubleArray viewPortDataSeriesC = DoubleArray(m_dataSeriesC.data + startIndex, noOfPoints);


Because you have multiple x data series, you need to change it to a loop like:

std::vector<DoubleArray> viewPortTimeSeries;
std::vector<DoubleArray> viewPortDataSeries;

for (int i = 0; i < m_nLineSize; i++)
{
DoubleArray dataX(m_pChartX[i], m_nChartYSize[i]);
DoubleArray dataY(m_pChartY[i], m_nChartYSize[i]);

// Get the array indexes that corresponds to the visible start and end dates
int startIndex = (int)floor(Chart::bSearch(dataX, viewPortStartDate));
int endIndex = (int)ceil(Chart::bSearch(dataX, viewPortEndDate));
int noOfPoints = endIndex - startIndex + 1;

// Extract the part of the data array that are visible.
viewPortTimeSeries.push_back(DoubleArray(dataX.data + startIndex, noOfPoints));
viewPortDataSeries.push_back(DoubleArray(dataY.data + startIndex, noOfPoints));
}


Then you can add the layers using:

You need to change it to a loop:

for (int i = 0; i < m_nLineSize; i++)
{
    layer[i] = c->addStepLineLayer();

    layer[i]->addDataSet(viewPortDataSeries[i]);
    layer[i]->setXData(viewPortTimeSeries[i]);
    layer[i]->setLineWidth(2);
}


Best Regards
Peter Kwan

  Re: step line chart zoom in/out and scroll
Posted by jungryul kim on Feb-20-2024 10:06
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The problem was resolved by applying the code you provided.
I learned how to zoom in/out scroll sufficiently even for unevenly shaped lines.
Thank you very much.
chart3.png