Qt5.0b1 Location Map eats a lot of CPU while scrolling



  • Hello.

    I made a tiled based map geoservices plugin to work with custom offline source. There is nothing special and it works almost the same as tiled based Nokia Maps plugin but takes images from hard drive and not from network. GUI part created on Quick 2.

    When I quickly scroll my map (even if all images in RAM or using the static single image) I see jittering and my CPU go up to 100% on one core. Checked on MacBook Air (i5+GMA3000, OS X 10.8.1) and Nettop (Atom D525+nVidia Ion 2, Ubuntu 12.04).

    The same issue even when I use Nokia plugin with cached images - jittering and high CPU usage on scrolling. As I guess it is a question of adding ~20 new tiles (FullHD screen) when changing map center.

    But if I move Map component on the screen by changing scale, rotation or position everything goes smooth with low CPU load.

    Is it a bug -or a feature-? How it can be fixed?

    Thanks.



  • I've checked Qt 5.0 beta source and found that QGeoTileFetcher use mutex to queue tile requests. Can it be the reason of high CPU usage?



  • I think it will be great to have a lazy prefetch function that will prefetch with low priority in the background tiles for 2-4 area sizes. It is not so good for memory but such option can be good for smooth maps scrolling.

    What do you think?



  • Are there any information how to fix this issue?



  • Hi,

    This sounds like a feature suggestion which should be made via a bug report at bugreports.qt-project.org

    The QtLocation team used to be based in the Brisbane office, which no longer exists, although I assume that Digia are devoting some resources to that module going forward. Either way, tracking the issue via the bug tracker is the best way to ensure that it gets on somebody's radar to be fixed.

    Cheers,
    Chris.


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