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  Odd behaviour with zoom and aggregated data
Posted by Mauricio on Sep-22-2012 07:51
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Hi Peter,

I'm going crazy with a very odd behavior while zooming in/out and using aggregated data.
Since I have too many points to plot, I have 3 versions of the data: the first with all the
points, the second with a tenth
of the points and the third with a hundredth of the points.

The array size that I display is always the same size, 10,000 samples, but depending on
the zoom value I take those 10,000 samples from one of the 3 versions of the data.
Obviously, when I change from one
data set to another, I set the x-axis full range again and I set the viewportWidth and
viewPortLeft to appropriate values.

For reference, every sample represents 1 millimeter (you will see the plot in meters).

It works well for the most part. HOWEVER, I noticed a very odd and reproducible behavior
a couple days ago:
If I zoom in with the mouse in a position to the right of the screen, then the data is
shown shifted in the y-axis. It's hard to explain, so I attached a word document with
pictures.

The code is as follows:

BOOL CZoomscrolltrackDlg::OnMouseWheel(UINT nFlags, short zDelta, CPoint pt)  //
nothing fancy here, taken straight out of an example
{
   // Process the mouse wheel only if the mouse is over the plot area
   if (!m_ChartViewer.isMouseOnPlotArea())
      return FALSE;

    // We zoom in or out by 10% depending on the mouse wheel direction.
   double newVpWidth = m_ChartViewer.getViewPortWidth() * (zDelta > 0 ? 0.9 : 1 /
0.9);
   double newVpHeight = m_ChartViewer.getViewPortHeight() * (zDelta > 0 ? 0.9 : 1 /
0.9);

    // We do not zoom beyond the zoom width or height limits.

   double maxHeight = m_ChartViewer.getZoomOutHeightLimit();
   double minHeight = m_ChartViewer.getZoomInHeightLimit();
   double maxWidth = m_ChartViewer.getZoomOutWidthLimit();
   double minWidth = m_ChartViewer.getZoomInWidthLimit();

    newVpWidth = max(m_ChartViewer.getZoomInWidthLimit(), min(newVpWidth,
m_ChartViewer.getZoomOutWidthLimit()));
    newVpHeight = max(m_ChartViewer.getZoomInHeightLimit(), min(newVpHeight,
m_ChartViewer.getZoomOutHeightLimit()));

   if ((newVpWidth != m_ChartViewer.getViewPortWidth()) ||
      (newVpHeight != m_ChartViewer.getViewPortHeight()))
   {
      // Set the view port position and size so that the point under the mouse remains
under
      // the mouse after zooming.

      double deltaX = (m_ChartViewer.getPlotAreaMouseX() -
m_ChartViewer.getPlotAreaLeft()) * (m_ChartViewer.getViewPortWidth() - newVpWidth)
/ m_ChartViewer.getPlotAreaWidth();
      m_ChartViewer.setViewPortLeft(m_ChartViewer.getViewPortLeft() + deltaX);
      m_ChartViewer.setViewPortWidth(newVpWidth);

      double deltaY = (m_ChartViewer.getPlotAreaMouseY() -
m_ChartViewer.getPlotAreaTop()) * (m_ChartViewer.getViewPortHeight() - newVpHeight)
/ m_ChartViewer.getPlotAreaHeight();
      m_ChartViewer.setViewPortTop(m_ChartViewer.getViewPortTop() + deltaY);
      m_ChartViewer.setViewPortHeight(newVpHeight);

      m_ChartViewer.updateViewPort(true, true);
   }

   return TRUE;
}

void CZoomscrolltrackDlg::OnViewPortChanged()
{
    // Update the chart if necessary
    //if (m_ChartViewer.needUpdateChart())
        drawChart(&m_ChartViewer);
}

void CZoomscrolltrackDlg::drawChart(CChartViewer *viewer)
{
      XYChart *c = new XYChart(kPlotWidth, kPlotHeight, 0xffffff, 0xaaaaaa);

      // Set the plotaarea
      c->setSize(kPlotWidth, kPlotHeight);
      c->setPlotArea(kPlotOriginX, kPlotOriginY, kPlotWidth-kPlotMargin, kPlotHeight-
kPlotMargin, c->linearGradientColor(0, 55, 0, c->getHeight() - 35, 0xf0f6ff, 0xa0c0ff), -1,
Chart::Transparent,
Chart::Transparent,Chart::Transparent); //0xffffff, 0xffffff);

      // As the data can lie outside the plotarea in a zoomed chart, we need enable
clipping.
      c->setClipping();

      // Set legend icon style to use line style icon, sized for 8pt font
      c->getLegend()->setLineStyleKey();
      c->getLegend()->setFontSize(8);

      // Set the axis stem to transparent
      c->xAxis()->setColors(Chart::Transparent); //, Chart::Transparent,
Chart::Transparent, Chart::Transparent);
      c->yAxis()->setColors(Chart::Transparent); //,Chart::Transparent,
Chart::Transparent, Chart::Transparent);
      c->setBackground(0x99CCFF);

      // Add axis title using 10pts Arial Bold Italic font
      c->yAxis()->setTitle("Channel", "arialbi.ttf", 10);

      ///////////////////////////////////////////////////////////////////////////////////////
      // Add data to chart
      ///////////////////////////////////////////////////////////////////////////////////////
      // Add a line layer for the channels
      LineLayer *chLayer = c->addLineLayer();
      chLayer->setLineWidth(1);
      chLayer->setFastLineMode();

      // Get the start index and end index that are visible on the chart.
      double mmStart = viewer->getValueAtViewPort("x", viewer->getViewPortLeft());
      double mmEnd = viewer->getValueAtViewPort("x", viewer->getViewPortLeft() +
viewer->getViewPortWidth());

      // Get the start channel and end channel that are visible on the chart.
      m_chEnd   = (int)floor(m_databaseManager.getNumChannels() - viewer-
>getValueAtViewPort("y", viewer->getViewPortTop()) );
      m_chStart = (int)ceil (m_databaseManager.getNumChannels() - viewer-
>getValueAtViewPort("y", viewer->getViewPortTop() + viewer->getViewPortHeight()) );

      // Now we add the data series to the layer.
      m_channelManager.addDataSets(chLayer, mmStart, mmEnd, m_chStart, m_chEnd,
viewer->needUpdateImageMap());

      ///////////////////////////////////////////////////////////////////////////////////////
      // Configure axis scale and labelling
      ///////////////////////////////////////////////////////////////////////////////////////

      // set data xAxis full range (according to the loaded data chunk) (the Y axis full
range is always all the channels
      double minX = m_channelManager.getXAxisStart();
      double maxX = m_channelManager.getXAxisEnd();
      viewer->setFullRange("x", minX, maxX);

      // set the viewPortWidth and viewPortLeft
      double viewPortPercent = (mmEnd-mmStart) / (maxX-minX);
      viewer->setViewPortWidth(viewPortPercent);
      viewer->setViewPortLeft( (mmStart-minX) / (maxX-minX) );

      // Set the x-axis as numeric axis with the scale according to the view port x range.
      viewer->syncLinearAxisWithViewPort("x", c->xAxis());
      viewer->syncLinearAxisWithViewPort("y", c->yAxis());

      // Configure the x-axis depending on the zoom value to show mm, m, or km
      c->xAxis()->setFormatCondition("align", 500000);
      c->xAxis()->setLabelFormat("{={value}/1000000} km");
      c->xAxis()->setFormatCondition("align", 1);
      c->xAxis()->setLabelFormat("{={value}/1000} m");


      ///////////////////////////////////////////////////////////////////////////////////////
      // Output the chart
      ///////////////////////////////////////////////////////////////////////////////////////
      delete viewer->getChart();
      viewer->setChart(c);
}

Any ideas??
Odd behavior with zoom and aggregated data.zip
Odd behavior with zoom and aggregated data.zip
234.67 Kb

  Re: Odd behaviour with zoom and aggregated data
Posted by Mauricio on Sep-22-2012 10:13
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Never mind. I found the issue... shame on me... it was a problem with integer arithmetic vs
floating point arithmetic while calculating the indexes to get the data.