Transform slow?



  • Hi,

    I have a slow embedded device and I notice that the user interface could be more responsive. I have already used the Loader element to dynamically load/unload qml files and i'm trying to do some more optimalisations.

    I'm wondering about the transform element that I use to rotate my screens:

    @
    Rectangle {
    transform: { Rotation { origin.x: 120; origin.y: 120; angle 270 }
    showSomeStuyff
    }
    @

    Will this slow down my userinterface noticeable? I reckon for every change the cpu has to calculate the rotated rectangle?



  • I also use transform to rotate images:

    @
    Rectangle {
    transform: { Rotation { origin.x: 120; origin.y: 120; angle 270 }
    BorderImage {
    source: "myimage.png"
    }
    }
    @



  • What device do you use ?



  • Embedded linux, omap ARM 300 mhz. How does the transform function work?



  • What is your display device ?



  • It's an omap l138:

    Video Port Interface (VPIF):
    Two 8-bit SD (BT.656), Single 16-bit Video Display Channels



  • I'm not 100% certain, but I seem to recall someone saying that transform with QGV is much slower than with scenegraph rendering (ie, Qt 4.8 will be slower than Qt 5.0, in that QtQuick 1.1 will be slower than QtQuick 2.0, for transform operations) - although I can't remember why, now. Perhaps scenegraph allows partial-update and thus only the transformed element needs to be redrawn? Not sure.


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