Comment 21 for bug 1500282

(In reply to Karl Tomlinson (ni?:karlt) from comment #11)

> > Comparing this
> > to the Windows behaviour: the set scaling it read from the system as is,
> > with no rounding applied.
>
> Windows usually scales in steps, 1, 1.25, 1.5, 2 (and maybe higher).

The easily accessible UI only has a few choices (those sound about right), but there's other UI that lets the user set arbitrary scaling factors. And they've recommended supporting other oddball factors in the past (ISTR Metro guidelines had 133% and 180%, or something like that).

> Adding a 1.5 step makes sense, I think, especially because this is supported
> on Windows, and so has some chance of support from web authors.

I don't think _any_ of this should hinge on "support" from web authors.

> I'm not so keen on adding 1.25 because the benefits of a different size don't
> necessarily outweigh the disadvantage of likely interpolation.

1.25 is the most popular scaling factor on Windows (other than 100%, of course).

At one point we were greatly concerned about this for the browser chrome (some discussion in bug 1147702), but it's mostly been a non-issue. Providing a 2x image and downscaling works quite well in most cases, and we're already well along in starting to shift to SVG. The only thing that doesn't "just work" very well is tiny bitmaps, like 16x16 favicons. Interpolated upscaling doesn't look very good, and even in cases where we force nearest-neighbor it can still look a bit off when scaling to 20x20 (1.25x). (We also talked about special-casing this in the UI, e.g. by forcing them to display as 16x16 physical pixels + padding, but it hasn't been a significant issue.)

I think Linux should just follow what Windows is doing. If there's interest in pushing for snapping/rounding to certain levels, we should do that everywhere and be consistent.