Manifest "sizes" fallback logic

[laukstein]

Reference: https://lists.w3.org/Archives/Public/public-webapps/2015OctDec/0064.html

Does "sizes" has any fallback for device required different icon sizes?

{
    "icons": [
        {
            "src": "32x32.png",
            "sizes": "32x32"
        }, {
            "src": "48x48.png",
            "sizes": "48x48"
        }, {
            "src": "128x128.png",
            "sizes": "128x128"
        }
    ]
}

1. For example, would device request for 16x16 return scaled down image 32x32.png?
2. What about request 40x40 - would it scale up 32x32.png or scale down 48x48.png (40x40 is in middle of both those sizes (+8 = 48, -8 = 32))?
3. Would request 96x96 use 128x128.png?
4. Would request 192x192 and 512x512 use 128x128.png?

[marcoscaceres]

In Gecko, I'm just going to try to use HTMLPictureElement to do the selection (not sure if it will work, but going to try). That is, I just convert the JSON into a bunch of <source> elements and let the <picture> element tell me what the right thing is.

So, it might be nice to generalize the image selection algorithm to take a display context, and a bunch of sources, and let the algorithm pick one.

[laukstein]

Related issue #407 sizes="any".

[kenchris]

I think it is up to the platform (user agent) to decide how to best choose the icon, ie choosing a bigger one and scaling it down, which scaling algorithm to use etc.

[marcoscaceres]

I agree with @kenchris. We should do nothing here unless it becomes an issue.