[Interest] Improve ListView scrolling performance (many pictures)

[Bernhard B]

Hi Andy,

many thanks for your response! I am also using a QAbstractListModel-derived
class that gets exposed to the QML world which contains the images.

Yesterday I started to resize the images before feeding them to the
ListModel. According to the QML Profiler the delegate gets now created a
little bit faster, but fast scrolling is still a little bit sluggish. Today
I probably will play a little bit with different image codecs to see if
those have an impact. Currently I am using *.png files often which is
probably not the best choice.

Thanks a lot for your input, really appreciated!

Bernhard

Am Freitag, 11. August 2017 schrieb Andy :

> Bernhard:
>
> I don't use QML, but in my application I use a QAbstractItemModel-derived
> class and a QTreeView-derived class to display image thumbnails in the
> view. The way I make it speedy is to save the image as a thumbnail so the
> view items don't need to resize the image data at all.
>
> Maybe you could save a thumbnail of an appropriate size when you're adding
> them to your model?
>
> ---
> Andy Maloney  //  https://asmaloney.com
> twitter ~ @asmaloney <https://twitter.com/asmaloney>
>
>
> On Fri, Aug 11, 2017 at 3:33 AM, Bernhard B <schluchti at gmail.com
> <javascript:_e(%7B%7D,'cvml','schluchti at gmail.com');>> wrote:
>
>> Hi Vlad,
>>
>> you mean the QQuickAsyncImageProvider? That one sounds really promising.
>> Will definitely try that out. Many thanks for the suggestion!
>>
>> Bernhard
>>
>> 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>
>>> 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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>
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