chart position resets on window interaction

[jwkelly]

I have a chart in our system that is providing real-time data visualization, but the scope position frequently resets to zero before completing each sweep. I've attached an extremely simple example that reproduces this problem whenever you make any interactions with the window (click the title bar, click a scroll bar, resize the window, etc.). In our system there are other, unavoidable things that are causing this, but I haven't been able to identify them yet due to the large number of components running at once. Has anyone else seen this problem and been able to resolve it? This basically makes the chart display unusable in our system.

I'm currently running 64-bit LV 2011 on Windows 7. This problem also occurs on 32-bit LV 2011 on Windows 7, but I don't recall it happening when we were using LV 2010. A few changes have been made to our system since then, but nothing I would expect to have an effect on this. So I can't conclusively say it's a LV 2011 problem, but that seems to be a good suspect.

[Joseph_Loo]

I am running widows xp with 2011. The reset occurs only when I resize the window. Scroll bars has no affect.

a temporary fix is to remove the scroll bars and not allow a window resize. in Labview.

[jwkelly]

Thanks for trying it out, but no resizing, scrolling, or moving happens when our system is actually running. The problem still occurs, though, and I'm not sure if it's a write to a property node or what that is causing it at this point. I suspect that if the problem didn't occur on window interactions that it wouldn't occur at other times for us either. The chart display is one of LabVIEW's basic functions and this problem should not even occur when you move, scroll, or resize the window.

[Alisha_P]

Hi,

I've looked into the behavior you are seeing and found that odd chart behavior upon window resize was reported to R&D (CAR# #336245) for further investigation. Thanks for the feedback!

As Joseph said, a workaround for the behavior seen upon window resize would be to not allow anyone to resize the window. I know, though, that you said other things in your program are causing the odd behavior. If you are able to pinpoint the  parts of the code that are causing this behavior, we can possibly recommend a workaround and pass along the additional information to R&D.

[jwkelly]

I actually just figured out today that if you place a ForceRedraw Inovke Node for the chart inside the loop, that the problem goes away. I'm not exactly sure why, though. The best thing I can think of is that maybe if the loop iterates again without redrawing that the next time it does redraw, there's a gap between what's on the chart and what it has in the buffer so it resets the scope to zero. I would expect the chart to be able to handle this type of situation, though, and still would consider this issue a bug.

[jwkelly]

I should have also mentioned that a sequence structure or some other method needs to be used to ensure that the ForceRedraw occurs before or after the chart update each iteration (it doesn't matter which, just that there's a ForceRedraw between chart updates)

[Alisha_P]

Thanks for the workaround information! I agree that it still seems like a bug. However, I've now tested it with our newest version of LabVIEW, LabVIEW 2011 SP1, and the behavior (strange waveform chart resetting when you resize the window) seems to be fixed in the later version.