Picture flickering

Question

Hallo all,
I'm working on a small research project on motion learning in humans.
What I'm trying to do is a simple 'game' where the player has to try to follow a track moving on the screen with the cursor.
The player move the cursor acting with his forefinger on a slider connected to a DAQ card.
I'm having troubles with the track display. I'm not able to avoid some disturbing flickering effect.
I've found an old discussion (2002) with a similar problem but with no solution.
May be in this time a solution have been found or some new features of  LV have solved this issue.
I attach a simple example that on my laptop generate the flickering.
My track is an array of points that I draw on the screen with DrawMultiplesLines.vi
In this example I use sine function do generate the track, in the real application we have more complex tracks.
thank you
Gianpiero
LV 8.5
Message Edited by htdev on 12-13-2007 05:32 AM
Message Edited by htdev on 12-13-2007 05:34 AM
Attachments:
flickr2.vi ‏21 KB

Answer 1

The most important setting would be "right-click...advanced...Smooth updates".
from the LabVIEW help:
When LabVIEW updates an object with smooth updates off, it erases the contents of the object and draws the new value, which results in a noticeable flicker. Using smooth updates avoids the flicker that erasing and drawing causes.
I am not sure if synchronous display (as suggested above) would really help, it just forces a front panel update of the indicator with every write to the indicator terminal. This could significantly slow down your code.
from the LabVIEW help:
By default, controls and indicators use asynchronous displays, which means that after the execution system passes data to front panel controls and indicators, it can immediately continue execution. At some point thereafter, the user interface system notices that the control or indicator needs to be updated, and it redraws to show the new data. If the execution system attempts to update the control multiple times in rapid succession, you might not see some of the intervening updates.
In most applications, asynchronous displays significantly speed up execution without affecting what the user sees. For example, you can update a Boolean value hundreds of times in a second, which is more updates than the human eye can discern. Asynchronous displays permit the execution system to spend more time executing VIs, with updates automatically reduced to a slower rate by the user interface thread.
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