Xwayland screen and get_outputs have different sizes when using scale.

[jameswalmsley]

Overview

When setting some output scales, the sway rect and the Xwayland screen
have different sizes:

E.g. for my 2560x1440 resolution screen at 1.4 scale.

$ swaymsg -t get_outputs | jq -r '.[] | select(.focused).rect'
{
  "x": 0,
  "y": 0,
  "width": 1828,
  "height": 1028
}

$ xrandr
Screen 0: minimum 16 x 16, current 1828 x 1028, maximum 32767 x 32767
XWAYLAND0 connected 1824x1028+0+0 (normal left inverted right x axis y axis) 310mm x 170mm
   1824x1028     59.92*+

XWAYLAND0 width of 1824 when it should be 1828.

Other scales will create a matching size.

Is there a way to get the Xwayland screen ID of an output?

Git-sha's

wayland 1.17.0-43-ge7d88f3
wayland-protocols 1.18-6-g733de76
xwayland xorg-server-1.20.0-569-gb1ee4036b
wlroots 0.9.0-1-g5bbb4448
sway 1.2-rc1-162-g1e44247b

[jameswalmsley]

Further Findings

When using kanshi:

# Thinkpad Carbon X1 6th Gen - Alone.
{
	output "Unknown 0x2036 0x00000000" mode 2560x1440 position 0,0 scale 1.333333
	exec swaymsg output \"Unknown 0x2036 0x00000000\" scale_filter linear
}

$ swaymsg -t get_outputs | jq -r '.[] | select(.focused).rect'
{
  "x": 0,
  "y": 0,
  "width": 1921,
  "height": 1081
}

$ swaymsg output eDP-1 scale 1.333333
$ swaymsg -t get_outputs | jq -r '.[] | select(.focused).rect'
{
  "x": 0,
  "y": 0,
  "width": 1920,
  "height": 1080
}

Adding an exec line to kanshi works:

# Thinkpad Carbon X1 6th Gen - Alone.
{
	output "Unknown 0x2036 0x00000000" mode 2560x1440 position 0,0 scale 1.333333
	exec swaymsg output \"Unknown 0x2036 0x00000000\" scale_filter linear
	exec swaymsg output \"Unknown 0x2036 0x00000000\" scale 1.333333
}

Why is there a difference between kanshi, and a direct swaymsg? Numerical precision?

This fixes my case of 1.333... but not for e.g. 1.4.

[jameswalmsley]

Using issue #4896 for investigating the kanshi vs swaymsg difference.
Will look a bit deeper at why Xwayland and wlr have different rect sizes.