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Thread: Problem with canvas()->update()

  1. #1
    Join Date
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    Default Problem with canvas()->update()

    Hello everyone. Got a problem.

    I know you can handle rapidly-updating plot information by subclassing QwtPlot and setting update() to invalidate the paint cache and update the canvas. The idea behind this, as I'm sure you all know, is to make it so that a data processor in its own thread won't try to force the table(s) to redraw for every block of data, as this is impossible to keep up. Instead, all these incoming redraw requests do is set up the plot to redraw on the next main loop.

    For some reason when I attempted to implement this, i get massive slowdowns when I attempt canvas()->update() from the plot's update function. Nothing else causes the slow down - not the dispatching of information, not QwtPlot::drawCanvas, not invalidating the paint cache. Everything else seems fine. Our lead programmer isn't even sure why this would be a problem.

    I guess I'm just hoping this rings bells and someone knows why that call causes such massive overhead. I apologize that there is no source code I am able to show, as this is proprietary work.

  2. #2
    Join Date
    Feb 2006
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    Default Re: Problem with canvas()->update()

    Quote Originally Posted by jblovloss View Post
    I apologize that there is no source code I am able to show, as this is proprietary work.
    Nobody will have a look at trillions lines of code - you always have to strip your code down to an independent small piece of code demonstrating your problem. Isolating such a problem can be a cumbersome job, but it has nothing to do with "proprietary".

    Uwe

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