time at x axis in a real time data plot

pencky

Hey

I'm trying to plot real time data in a graph.
So I copied the code from the example:

static double lastPointKey = 0;
if (key-lastPointKey > 0.01) // at most add point every 10 ms
{
  double value0 = qSin(key); //qSin(key*1.6+qCos(key*1.7)*2)*10 + qSin(key*1.2+0.56)*20 + 26;
  double value1 = qCos(key); //qSin(key*1.3+qCos(key*1.2)*1.2)*7 + qSin(key*0.9+0.26)*24 + 26;
  // add data to lines:
  ui->customPlot->graph(0)->addData(key, value0);
  ui->customPlot->graph(1)->addData(key, value1);
  // set data of dots:
  ui->customPlot->graph(2)->clearData();
  ui->customPlot->graph(2)->addData(key, value0);
  ui->customPlot->graph(3)->clearData();
  ui->customPlot->graph(3)->addData(key, value1);
  // remove data of lines that's outside visible range:
  ui->customPlot->graph(0)->removeDataBefore(key-8);
  ui->customPlot->graph(1)->removeDataBefore(key-8);
  // rescale value (vertical) axis to fit the current data:
  ui->customPlot->graph(0)->rescaleValueAxis();
  ui->customPlot->graph(1)->rescaleValueAxis(true);
  lastPointKey = key;
}
// make key axis range scroll with the data (at a constant range size of 8):
ui->customPlot->xAxis->setRange(key+0.25, 8, Qt::AlignRight);
ui->customPlot->replot();

Now I have the current time at the x axis.
I want to start measuring by 0 seconds and then go further every second.

So I defined two variables

double starttime = QDataTime::currentDateTime().toTime_t(); // at the beginning
double now=QDataTime::currentDateTime().toTime_t(); // time, every loop

ui->customPlot->xAxis->setRange(now-starttime,8,Qt::AlignRight);
//also in the addData function?

But now I get something like that:

1:00:00 1:00:01 1:00:02 1:00:03 1:00:04

and the data between every second is interpolated linear, so that it looks very ugly and react slowly.
Is there a way to fix it?