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Thread: QwtDial works slowly in QWS

  1. #1
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    Question QwtDial works slowly in QWS

    Hi there,

    I was trying to use QwtDial to display things under Qt for Embedded Linux. Then I found it's painfully slow to move the needle, therefore, to change a value of a dial. After searching Google I found it's not a good choice to embed QWidget-based things into QGraphicsView via QGraphicsProxyWidgetItem. Then I abandoned the Graphics View framework and straightly place a QwtDial in a single QMainWindow, but it didn't improve at all.

    Can you tell me a if there's someway to make the needle move more pliably and even in the QGraphicsView? Thanks.

    My development board is mini2440 which is based on sumsang s3c2440 arm920t cpu.
    Kernel version 2.6.31
    Cross gcc compiler version 4.1.2 with EABI support
    Kernel and userspace software are all compiled with EABI.

  2. #2
    Join Date
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    Default Re: QwtDial works slowly in QWS

    Well, I don't believe, that QGraphicsView is the source of the problem.

    Please try to find out if painting the dial to the backing store is the reason or if it is the blitting of the backingstore to your hardware. If it is the blitting ( what I wouldn't expect ) it might help to paint the bounding rect of the previous + new needle positions only.

    What about the performance, when you disable antialiasing ( removing the line in QwtDial::paintEvent ) ? Also try to paint parts of the dial only ( also by removing lines in QwtDial::paintEvent ) - can you identify one of these parts being the bottleneck ?

    ?

    Uwe

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