Problem with twitching on axis-ends

[ghm]

Hi.

I have a problem with twitching in my plot. This twitching comes when the y-, or x-axis is swapping between having a value label at the end or having a tick at the end.

It's best demonstrated by these two screens:
screen2.PNGscreen1.PNG
If you test with the oscilloscope example, and adjust the displayed seconds, back and forth, you will see what I mean by twitching.

This is a bit annoying, especially when having live values thats going up and down.

I have based my widget on the refreshtest example, and managed to work around the problem by setting:

canvas()->setFrameStyle(QFrame::Box | QFrame::Plain );
canvas()->setLineWidth(5);

canvas()->setFrameStyle(QFrame::Box | QFrame::Plain );
canvas()->setLineWidth(5);

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But this adds a black border around the canvas, and I haven't figured out a way to make that border transparent, or inherit color from application.

If someone have a suggestion on how to workaround this, please let me know.

Gerhard

[Uwe]

What about setting a margin between the end of the scales and the canvas border: see QwtPlotLayout::setCanvasMargin().

The margin should be larger than half of the width of your tick labels. You could rotate the tick labels, so that you only need half of the font height - or something in between like in the cpuplot example.

Uwe

[ghm]

Thank you for your reply Uwe.

I managed to solve it by setting plotLayout()->setAlignCanvasToScales(false); for the vertical twitching.

But I also have the problem of twitching horizontally. Whenever a major tick on the y-axis appear that has a number of characters which is greater than the rest. For example you have a range from 0-2, and when the curve goes down to -1, you have one additional character, "-" and "1".

Example:

Y-axis
 ---
 |2|
 ---
 |1|
 ---
 |0|
----
|-1|
----

Y-axis
 ---
 |2|
 ---
 |1|
 ---
 |0|
----
|-1|
----

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Is there a way to set a fixed size for the label on the major tick? For instance setting it to 7 characters if you know your y-values ranges from -999999 to 9999999.

Example of wanted behaviour:

Y-axis
------
|   2|
------
|   1|
------
|   0|
------
|  -1|
------

Y-axis
------
|   2|
------
|   1|
------
|   0|
------
|  -1|
------

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Your help is greatly appreciated.

Gerhard

[Uwe]

This is one of the FAQs: grep for setMinimumExtent.

Also check the event_filter example.

Uwe

[ghm]

That did the trick.

Thank you Uwe, you've been very helpfull!

Gerhard