There is a problem when trying to optimally[*] show an Image with PreserveAspectCrop fillMode. [*]optimally => as best looking as possible while using as litte memory as possible
You can see that problem in the screenshot at http://i.imgur.com/LSSlFEB.png that corresponds with the code at http://paste.ubuntu.com/19480453/ As you can see when displaying a landscape (width > height) image in a square Image Item the optimal way is to set the source size height only, but if the image is portrait (height > width) then the optimal way is to set the source size width only. The requirement my program has is to have the best rendering quality and memory usage for Image Items using PreserveAspectCrop. Image sources are totally arbitrary, they can be from disk, from the internet or even from QQuickImageProviders (since we are plugin based and plugins can bring their own QQuickImageProvider) This can be fixed in several ways. Workaround A ********** Changing the Image Item source size comparing the aspect ratio of the image file with the one Image Item. You can see an implementation of that workaround at http://bazaar.launchpad.net/~unity-team/unity8/trunk/view/head:/plugins/Dash/CroppedImageMinimumSourceSize.qml The problem with this workaround is that half of the times you end up loading the image a second time. This means extra CPU and potentially network usage. Workaround B ********** Implementing your own image provider that does compare the aspect ratios before loading the image. You can see a partial implementation of this workaround at https://code.launchpad.net/~aacid/unity8/croppedImageMinimumSourceSizeProvider/+merge/300176 There are two problems with this workaround: * You end up implementing quite a bit of duplicated functionality from qquickpixmapcache.cpp * For the chained image providers (i.e. the original source was an image provider url) you still have to query the image provider twice half of the times Solution ******** Implementing the change in QtQuick internals so that when PreserveAspectCrop fillMode is used together with a sourceSize that has both width and height it does return the optimal image You can see a work in progress implementation of this solution at https://codereview.qt-project.org/#/c/165299/ And how the previews could would look at http://i.imgur.com/NRoXNzy.png (notice how the last column now is good in both cases) There are two issues with this solution: * It's a small behaviour change (but in my opinion for the better) * Needs new api for the QQuickImageProvider to be able to implement it, so we either need the proposed QQuickImageProviderV2 or with a new "bool shouldPreserveAspectRatioCrop(url, requestSize)" getter in the existing QQuickImageProvider API All in all I think the solution i propose for QtQuick is acceptable but i would like some agreeing that is fine adding new API before finishing the patch. _______________________________________________ Development mailing list Development@qt-project.org http://lists.qt-project.org/mailman/listinfo/development
