Chrome Version : 52.0.2743.82 (Official Build) beta (64-bit)

This is two feature requests regarding the list of zoom levels available.

1. Change 0.333 and 0.666 to be more precisely 1/3 and 2/3.
2. Add an 80% zoom level.

The goal is to allow zooming out on a HiDPI display to more precisely align to pixels. To ensure that devicePixelRatio is a whole number or nice fraction. If you’re convinced as to why this is desirable, you may stop reading now.

Windows users who are accustomed to the old behavior of ignoring 125% zoom will be able to set the default page zoom to 80% in preferences. Adding this item to the list is certainly the simplest way of restoring this feature for those users.

This mainly applies on Windows and Linux, as well as Chrome OS, which ships certain devices at 1.25dppx. Mac OS only scales in integer multiples, but a hypothetical 3x (virtual, like iPhone Plus) display would still benefit from exact 1/3 zoom.

Current behavior:
At 1.5x scale and 0.666 zoom, the product of zoom and dsf should be 0.999. (It’s actually 0.9990000128746033 because apparently this number is converted to single precision at some point.)
At 1.25x scale and 0.666 zoom, the product of zoom and dsf should be 0.8325 (actually 0.8324999809265137). Under these conditions I can reliably produce a blurry image.

Desired behavior:
At 1.5x scale and 0.666666666666666 zoom, the product of zoom and dsf should be exactly 1.
At 1.25x scale and 0.666666666666666 zoom, the product of zoom and dsf should be 0.8(3) repeating, which behaves nicely (it's exactly 80 dpi).

Potential drawbacks:

1. Most media queries should be using a range and not checking if devicePixelRatio is exactly 1; there’s little purpose to this. Even though 0.999 will cause an error of 1 pixel every 1000, I can’t actually get a consistently blurry picture under these circumstances. Still, this is already a floating-point constant, so changing it should not be an issue. The benefits are more noticeable for 1.25x users than for 1.5x.

2. Adding 0.8 puts the zoom steps closer together. I believe this is OK; it actually makes the consecutive ratios in that range match the ratios at the larger end, and I really think having multiplicative inverses is beneficial.

With enable-use-zoom-for-dsf launching, my test page is a lot less blurry than it was in the past, but it’s still noticeable. Visit https://twister.43foldrs.com/dp/dp.html and zoom the page in and out to see. The picture is consistently blurry with dsf set to 1.25 and zoom set to 0.666, and using an extension to set the zoom to exactly 2/3 cleans up the image. In principle, this same improvement will be seen on any image whose dimensions are a multiple of 6, in this case.