[Interest] QML Image size vs sourceSize strange things

[Jérôme Godbout]

Do you really need to same memory by reducing the source size? I think you should left the source size alone and sample the image from the full source. Source size for SVG doesn’t make any sense, it’s vectoriel, doesn’t have any size, it can scale to any dimension. When playing with the image size (not the source) it will sample the source for each pixel, not sure about the algorithm but you might need an higher source resolution to get a proper image without artifact. I would at least take the Screen.devicePixelRatio into the source size into account and even add a x2 to ensure proper sampling, but I don’t see any real advantage to play with the source size unless you really are consuming way too much memory.

This might slow you down if the same image is using different sourceSize:

Note: Changing this property dynamically causes the image source to be reloaded, potentially even from the network, if it is not in the disk cache.


On Mar 23, 2021, at 3:31 AM, Alexander Dyagilev <alervdvcw at gmail.com<mailto:alervdvcw at gmail.com>> wrote:


Hello,

We had a strange problem with blurred images under Retina displays. Left part of the image - before, right one - after the fix.

<pjcgokflkeakcklh.png>

Our QML code was using with to show images:

Image {

        anchors.verticalCenter: parent.verticalCenter

        sourceSize.width: 25

        sourceSize.height: 25

        source: preview.url

    }



I've tried to multiply sourceSize by Screen.devicePixelRatio - images became bigger so they did not fit their places.

Then I've replaced sourceSize.width with just width and the same for height. And it works fine now.

My questions is:

1) Is it required to multiply sourceSize by devicePixelRatio? Or is it managed automatically? It seems that it is managed automatically for PNG and NOT managed for SVG.

2) If it is already managed automatically for PNG (these images preview.url are PNGs) then why was it blurred? The original PNG image is of size 64x64 pixels under Retina displays.

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Jerome Godbout
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