Knowing pixel distance between consecutive ticks

[kalos80]

Hi all,

is there a way to know the distance in pixels between two ticks?

Thank you very much for your help!

[Uwe]

With plot->axisScaleDiv(...) you find the list of all ticks. With plot_canvasMap(...) you can translate them into pixel positions.

Uwe

[kalos80]

Uwe, thank you very much for your hints.

[frankiefrank]

Could anyone please expand on this? I can't understand how to use the QwtScaleMap object to perform said conversion.

[d_stranz]

Could anyone please expand on this? I can't understand how to use the QwtScaleMap object to perform said conversion.

QwtScaleMap * scaleMap = myPlot->canvasMap( QwtPlot::xBottom );
int distance_in_pixels = scaleMap->transform( xTick2 ) - scaleMap->transform( xTick1 );

QwtScaleMap * scaleMap = myPlot->canvasMap( QwtPlot::xBottom );
int distance_in_pixels = scaleMap->transform( xTick2 ) - scaleMap->transform( xTick1 );

To copy to clipboard, switch view to plain text mode 

(From Qwt 5.2; may be different in 6.0 but probably not).

[barrygp]

is there a way to define or set the distance in pixels between consecutive ticks?

[Uwe]

is there a way to define or set the distance in pixels between consecutive ticks?

Unfortunately - no.

Uwe

[barrygp]

Thanks. If not precise pixels then, is there anyway to change the distance or relative distance between consecutive ticks?

[Uwe]

Well the ticks even might not be equidistant because of rounding up/down to the closest pixel position ( doubles -> integers ! ).

In general the ticks are related to scale values - never to widget coordinates. So you have to set up an event filter for the plot canvas adjusting the ticks somehow to the geometry of the canvas.

Uwe

[barrygp]

Thanks Uwe, that makes sense. I used QwtPlot::setAxisScale() with a defined step number and seems I may be able to work with that.

[Uwe]

Don't know if it helps, but maybe QwtPlotRescaler offers something useful for you.
At least it does something similar: QwtPlot::setAxisScale according to resize events of the canvas.

Uwe