Phasor Plotting with QwtPolar (drawing rays on a polar coordinate grid)

[bwnicewo]

Yeah, I wanted to attach an item to the plot, but I'm worried that I'll have to impliment my own plot item for just drawing a simple line from the origin, I would think there should just be a function to draw a line like drawLine or something that takes the length of the line and angle of the line.

[Uwe]

You can't simply draw to a widget - this is not how Qt works. On most platforms you can't event paint outside paint events at all. You also need to take care of the plot -> widget transformation, that is changing on different type of layout events or when zooming in/out. But having a class around a couple of lines of render code ( this is what your is plot item about) is nothing to be afraid of.

QwtPlotMarker has a mode for drawing such a line - but I simply forgot to add a similar feature to QwtPolarMarker.

Uwe

[bwnicewo]

What I have now to post the data is this:

d_grid = new QwtPolarGrid();
d_grid->setPen(QPen(Qt::white));
for ( int scaleId = 0; scaleId < QwtPolar::ScaleCount; scaleId++ )
{
d_grid->showGrid(scaleId);
d_grid->showMinorGrid(scaleId);

QPen minorPen(Qt::gray);
#if 0
minorPen.setStyle(Qt::DotLine);
#endif
d_grid->setMinorGridPen(scaleId, minorPen);
}
d_grid->setAxisPen(QwtPolar::AxisAzimuth, QPen(Qt::black));

d_grid->showAxis(QwtPolar::AxisAzimuth, true);
d_grid->showAxis(QwtPolar::AxisLeft, false);
d_grid->showAxis(QwtPolar::AxisRight, false);
d_grid->showAxis(QwtPolar::AxisTop, false);
d_grid->showAxis(QwtPolar::AxisBottom, false);
d_grid->showGrid(QwtPolar::Azimuth, true);
d_grid->showGrid(QwtPolar::Radius, true);
d_grid->attach(this);

// curves
m_curve = new QwtPolarCurve();
m_curve->setPen(QPen(Qt::red));
m_curve->setData(SinData(0,10));
m_curve->setPen(QPen(Qt::red));
m_curve->attach(this);
replot();

SinData is a class to return a QwtData pointer to setData, the arguments are an angle offset and amplitude of the line respectively. I'm attaching it to a QwtPolarPlot, the problem is I'm not seeing anything on the grid.

This wasn't my code, someone else wrote it.

[h-n-s]

bwnicewo, You solved it?