`--scale` requires more precision than is displayed

On my laptop running GNOME Shell 45.5 with Wayland and fractional scaling enabled, x1.75 is listed as an available scale factor, but --scale=1.75 is not accepted. Instead, I need to provide many more decimals: --scale=1.7518248 works. But there’s no way to discover this without patching out the 2-decimal rounding from impl Display for Mode.

Ideally gnome-randr would automatically select the closest of the available scale factors within some tolerance, rather than passing the provided value directly to GNOME which requires the excessive precision.

$ gnome-randr
supports-mirroring: true
layout-mode: logical
supports-changing-layout-mode: true
global-scale-required: false
legacy-ui-scaling-factor: 1

logical monitor 0:
x: 0, y: 0, scale: 1.7518248558044434, rotation: normal, primary: yes
associated physical monitors:
    eDP-1 BOE 0x07c8 0x00000000

eDP-1 BOE 0x07c8 0x00000000
              3840x2160@60.000  3840x2160   60.00*+     [x1.00, x1.25, x1.50, x1.75, x2.00, x2.20, x2.50+, x2.76, x3.00, x3.24, x3.48, x3.75, x4.00]
              3840x2160@48.000  3840x2160   48.00       [x1.00, x1.25, x1.50, x1.75, x2.00, x2.20, x2.50+, x2.76, x3.00, x3.24, x3.48, x3.75, x4.00]
              3200x1800@59.956  3200x1800   59.96       [x1.00, x1.25, x1.50, x1.75, x2.00+, x2.25, x2.50, x2.74, x2.99, x3.23, x3.51, x3.77]
              2880x1620@59.960  2880x1620   59.96       [x1.00, x1.25, x1.50, x1.75+, x2.00, x2.25, x2.50, x2.77, x3.00, x3.27]
              2560x1600@59.987  2560x1600   59.99       [x1.00, x1.25, x1.50+, x1.75, x2.00, x2.25, x2.50, x2.76, x2.99, x3.23]
              2560x1440@59.961  2560x1440   59.96       [x1.00, x1.25, x1.50+, x1.76, x2.00, x2.25, x2.50, x2.76, x3.02]
              2048x1536@59.954  2048x1536   59.95       [x1.00, x1.25+, x1.50, x1.75, x2.00, x2.25, x2.50, x2.75]
              2048x1152@59.903  2048x1152   59.90       [x1.00, x1.24+, x1.51, x1.75, x2.00, x2.25]
              1920x1440@59.968  1920x1440   59.97       [x1.00, x1.25+, x1.50, x1.75, x2.00, x2.25, x2.50]
              1920x1200@59.885  1920x1200   59.88       [x1.00, x1.25+, x1.50, x1.75, x2.00, x2.24]
              1920x1080@59.963  1920x1080   59.96       [x1.00, x1.25+, x1.50, x1.74, x2.00, x2.31]
              1680x1050@59.954  1680x1050   59.95       [x1.00+, x1.25, x1.50, x1.75, x2.00]
              1600x1200@59.869  1600x1200   59.87       [x1.00+, x1.25, x1.50, x1.75, x2.00]
               1600x900@59.946  1600x900    59.95       [x1.00+, x1.25, x1.49, x1.75]
              1440x1080@59.989  1440x1080   59.99       [x1.00+, x1.25, x1.50, x1.75, x2.00]
               1440x900@59.887  1440x900    59.89       [x1.00+, x1.25, x1.50, x1.75]
              1400x1050@59.978  1400x1050   59.98       [x1.00+, x1.25, x1.50, x1.75]
               1368x768@59.882  1368x768    59.88       [x1.00+, x1.26, x1.50]
               1280x960@59.939  1280x960    59.94       [x1.00+, x1.25, x1.50, x1.75]
               1280x800@59.810  1280x800    59.81       [x1.00+, x1.25, x1.50]
               1280x720@59.855  1280x720    59.86       [x1.00+, x1.25, x1.51]
               1152x864@59.959  1152x864    59.96       [x1.00+, x1.25, x1.50]
               1024x768@59.920  1024x768    59.92       [x1.00+, x1.25]
                800x600@59.861  800x600     59.86       [x1.00+]
is-builtin: true
display-name: "Built-in display"

$ gnome-randr modify eDP-1 --mode=3840x2160@60.000 --scale=1.75
setting mode to 3840x2160@60.000
setting scale to 1.75
D-Bus error: Scale 1.75 not valid for resolution 3840x2160 (org.freedesktop.DBus.Error.InvalidArgs)
Scale 1.75 not valid for resolution 3840x2160

$ gnome-randr modify eDP-1 --mode=3840x2160@60.000 --scale=1.7518248
setting mode to 3840x2160@60.000
setting scale to 1.7518248

maxwellainatchi / gnome-randr-rust

`--scale` requires more precision than is displayed #26