[Development] The behaviour of Image / image provider are different from 5.5.1 to 5.6 in iOS

[Ben Lau]

Hi ekke,

I have tried. Image item will just ignore the devicePixelRatio set in
QImage.

Similar report: [QTBUG-38127] devicePixelRatio not supported by
QQmlImageProvider - Qt Bug Tracker
<https://bugreports.qt.io/browse/QTBUG-38127>


On 11 April 2016 at 20:47, ekke <ekke at ekkes-corner.org> wrote:

> perhaps devicePixelRatio is 3.0 - this would have the effect to get 170.666
> http://doc.qt.io/qt-5/qimage.html#setDevicePixelRatio
>
> ekke
> Am 11.04.16 um 14:36 schrieb Federico Buti:
>
> Hi Ben,
>
> I've solved the issue by multiplying width/height to
> qApp->devicePixelRatio(). That should be 3 on iPhone 6 and should provide
> the correct result.
> I'm not sure if that's a bug or it is intended behaviour and I actually
> didn't investigate the issue a lot since I was just testing stuff.
>
> Hope someone else can confirm it's a bug or expected.
>
> Cheers,
> F.
>
> On 11 April 2016 at 14:28, Ben Lau <xbenlau at gmail.com> wrote:
>
>>
>>
>> On 11 April 2016 at 20:19, ekke < <ekke at ekkes-corner.org>
>> ekke at ekkes-corner.org> wrote:
>>
>>> Am 11.04.16 um 14:07 schrieb Ben Lau:
>>>
>>>
>>> On 11 April 2016 at 19:59, ekke < <ekke at ekkes-corner.org>
>>> ekke at ekkes-corner.org> wrote:
>>>
>>>> Am 11.04.16 um 12:38 schrieb Ben Lau:
>>>>
>>>> Hi,
>>>>
>>>> I am writing an image provider that read all the images to memory at
>>>> startup. And I found that the behaviour is different from 5.5.1 to 5.6 in
>>>> iOS. Seems that it is undocumented. I wonder is it an expected behaviour or
>>>> a bug?
>>>>
>>>> That is the example project:
>>>> <https://github.com/benlau/quickcross/tree/master/tests/imageprovider>
>>>> https://github.com/benlau/quickcross/tree/master/tests/imageprovider
>>>>
>>>> That is the code of my image provider:
>>>>
>>>> QImage QCImageProvider::requestImage(const QString &id, QSize *size, <
>>>> /span>c
>>>> onst QSize &requestedSize)
>>>>
>>>> {
>>>>
>>>>     Q_UNUSED(requestedSize);
>>>>
>>>>     QCImageLoader* loader = QCImageLoader::instance();
>>>>
>>>>     QImage result;
>>>>
>>>>     if (loader->contains(id)) {
>>>>
>>>>         result = loader->image(id);
>>>>
>>>>         *size = result.size();
>>>>
>>>>     }
>>>>
>>>>     return result;
>>>>
>>>> }
>>>>
>>>> Code to display image:
>>>>
>>>> Image {
>>>>
>>>>   id: image
>>>>
>>>>   source: "image://arts/Lenna.png" // An 512x512 image
>>>>
>>>> }
>>>>
>>>> In Qt 5.5.1 with iPhone6, the property of image will be set to:
>>>>
>>>> width: 512
>>>>
>>>> height: 512
>>>>
>>>> sourceSize: Qt.size(512,512)
>>>>
>>>> However, in Qt 5.6 with iPhone6, it becomes:
>>>>
>>>> width: 170.66666
>>>>
>>>> height: 170.66666
>>>>
>>>> sourceSize: Qt.size(512,512)
>>>>
>>>> The display size of image is different.
>>>>
>>>>
>>>> now from Qt 5.6 HighDPI is supported for all platforms.
>>>> iPhone has scaling factor 3
>>>>
>>>> 170.66666 * 3 = 512
>>>>
>>>>
>>>> ekke
>>>>
>>>>
>>> But Qt 5.5 on iOS also support HighDPI. Their result are different.
>>>
>>>
>>> have you tried to explicitely set
>>>
>>> QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
>>>
>>>
>>> ekke
>>>
>>
>> I have tried to set / not-set this line. It don't make any different.
>>
>>
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