Axis won't stay at new scale setting

[Maxicatten]

Hi all,

After applying setAxisScale() to a QwtPlot and doing a replot() everything scales fine, but when I next call a plotzoomer moveBy() the plot moves but rescales back to the original. What is the proper way to permanently apply the axis rescaling?

Thanks!

[Uwe]

If you change the scales behind the back of the zoomer you have to adjust its internal zoom stack.

Uwe

[Maxicatten]

I will post some of my code shortly but does this approach sounds correct:

1) get the stack of the zoomer
2) pop the last rectangle
3) push an updated rectangle onto the stack
4) assign the updated stack to the zoomer

Or is there a more efficient way to update the zoomer after plot has been rescaled?

Rescaling should take effect only on the latest zoom rectangle, the previous ones in the stack don't need to be updated.

[Maxicatten]

Code below. The issue is I don't know how to get the current visible rescaled rectangle from the plot without going to the zoomer.

// rescale the main plot
setAxisScale(QwtPlot::yLeft,lowPlotY,highPlotY);
 
// how to get the current visible rescaled plot rectangle??
QwtDoubleRect boundRect = ????
 
// get the zoomer stack      
QStack<QwtDoubleRect> tmpStack = plot_zoomer->zoomStack();
 
// get rid of the latest non scaled rectangle
tmpStack.pop();
 
// add rescaled rectangle
tmpStack.push(boundRect);
 
plot_zoomer->setZoomStack(tmpStack);
 
replot();
 
// doesn't work, rescales back to original
plot_zoomer->moveBy(valdx,0);

// rescale the main plot
setAxisScale(QwtPlot::yLeft,lowPlotY,highPlotY);

// how to get the current visible rescaled plot rectangle??
QwtDoubleRect boundRect = ????

// get the zoomer stack      
QStack<QwtDoubleRect> tmpStack = plot_zoomer->zoomStack();

// get rid of the latest non scaled rectangle
tmpStack.pop();

// add rescaled rectangle
tmpStack.push(boundRect);

plot_zoomer->setZoomStack(tmpStack);
				
replot();

// doesn't work, rescales back to original
plot_zoomer->moveBy(valdx,0);

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[Maxicatten]

Anyone?

[Maxicatten]

Uwe,

Thanks again! I fixed the problem. A few notes for anyone else who may face
issues here:

1) setZoomStack() function does not take affect until setMaxStackDepth() is used
on a zoomer with some random value. This may be a bug that is fixed in a later
version.

2) Flicker issue fixed by removing zoom(-1) and instead grabbing the zoomer
stack, popping the top rectangle and pushing an updated ractangle, then doing
setZoomStack()

Some sample code below,

// setup zoomer
symbol_canvas = canvas();

plot_zoomer = new QwtPlotZoomer(symbol_canvas);

// set maxstackdepth to make setzoomstack function work
plot_zoomer->setMaxStackDepth(50);

QwtScaleDiv * xscalediv = axisScaleDiv(QwtPlot::xBottom);

double rleft = xscalediv->lBound(); // lowerBound() in later qwt version

double rtop = lowPlotY; // a variable set earlier

double rwidth = xscalediv->hBound() - xscalediv->lBound(); // upperBound() in
later qwt version

double rheight = highPlotY - lowPlotY;

// create a new rectangle
QwtDoubleRect boundRect(rleft, rtop, rwidth, rheight);

// grab the zoomer stack
QStack<QwtDoubleRect> tmpStack = plot_zoomer->zoomStack();

// get rid of the current rectangle
tmpStack.pop();

// push the updated rectangle
tmpStack.push(boundRect);

// set the new stack
plot_zoomer->setZoomStack(tmpStack);