[Interest] Improve ListView scrolling performance (many pictures)

Bernhard B schluchti at gmail.com
Fri Aug 11 09:33:59 CEST 2017

Hi Vlad,

you mean the QQuickAsyncImageProvider? That one sounds really promising.
Will definitely try that out. Many thanks for the suggestion!


Am Donnerstag, 10. August 2017 schrieb Vlad Stelmahovsky :

> threaded image provider might help
> On Thu, Aug 10, 2017 at 12:36 PM, Bernhard B <schluchti at gmail.com
> <javascript:_e(%7B%7D,'cvml','schluchti at gmail.com');>> wrote:
>> Hi,
>> yesterday, I also tried to replace the Base64ImageProvider approach with
>> a subclassed QQuickPaintedItem which paints the image in it's paint method.
>> I imagined that this approach might be faster es no bade64 decoding needs
>> to be done. But unfortunately it looks like as it's performing even worse
>> that way.
>> Bernhard
>> Am Mittwoch, 9. August 2017 schrieb Bernhard B :
>>> Hi,
>>> I would need some help from you guys on how to improve the ListView's
>>> performance. The problem is, that scrolling through my ListView sometimes
>>> feels a little bit sluggish.
>>> If I only display some text in the ListView's delegate I can scroll
>>> smoothly through my list. But as soon as there is a picture in the
>>> ListView's delegate I notice that I can't scroll smoothly through my list
>>> anymore. That's especially noticable if I try to scroll fast through my
>>> list. Every time I hit a picture while scrolling through the list I can see
>>> that there is a noticable delay until the picture is fully loaded. My
>>> assumption is, that those pictures are the reason why he scrolling feels so
>>> sluggish.
>>> My application currently works like this:
>>> * load 20 pictures via REST (pictures are base64 encoded)
>>> * populate list model
>>> * the Image component in the delegate uses a Base64ImageProvider (self
>>> written) to access the model's base64 encoded content and displays the image
>>> * if the user scrolls past a threshold another batch of base64 encoded
>>> pictures is fetched from the server
>>> I also found this document: http://doc.qt.io/qt-
>>> 5/qtquick-performance.html#rendering and tried to apply as much as
>>> possible. In detail I applied the following changes:
>>> * removed complex bindings from delegate
>>> * set sourceSize property for Image
>>> * increased cacheBuffer a bit
>>> * profiled with QML profiler and improved a few things
>>> But still, the ListView feels a bit sluggish. The strange thing is, that
>>> it's most noticable on Android whereas on Windows and iOs it is better.
>>> Does anyone have an idea on how to improve that?
>>> Any help is really appreciated.
>>> Thanks a lot!
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> --
> Best regards,
> Vlad
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