HTPC — magic4pc (LG Magic Remote)

Go-client for using the LG Magic Remote (webOS TV app) as HTPC mouse/keyboard input. Fork: mallexxx/magic4pc_altclient branch bazzite-linux.

LG TV: 192.168.1.75, HTPC: 192.168.1.86.

Architecture

TV server: webOS app on LG TV → sends UDP to fixed source port 9106
HTPC client: /usr/local/bin/magic4pc, UDP listener
xdotool: single persistent process via stdin pipe (mouse + keyboard)
ydotool: gamescope-specific keys (Ctrl+1, Ctrl+2) via /run/user/1000/.ydotool_socket

Session detection:

isGamescopeSession() — scans /proc/*/cmdline for kwin_wayland; if absent → gamescope (Steam Big Picture mode)
activeDisplay() — KDE uses Xwayland display from kwin args; gamescope uses :1 (game) if visible windows present, else :0 (Steam BP)

Button Mapping

Button	Keycode	Gamescope	KDE Desktop
Red	403	Ctrl+1 (Steam menu)	Super
Green	404	Escape	Escape
Yellow	405	Ctrl+2 (Steam QAM)	Middle click
Blue	406	Right click	Right click
Back	461	Mouse X1	Mouse X1
D-pad	37-40	Arrow keys	Arrow keys
Ch+/Ch-	33/34	PageUp/Down	PageUp/Down
Play/Stop/Pause	415/413/19	XF86Audio*	XF86Audio*
Touch (swipe)	—	mousemove (scaled)	mousemove
Tap	—	Left click	Left click

Mouse Coordinate Mapping

TV sends coordinates in 0–1920 × 0–1080 space.

In gamescope: uses letterbox algorithm.

Find active window: (a) under cursor via getmouselocation, or (b) largest bounding-box window (non-popup, highest ID)
Compute 16:9 letterbox viewport from window width: lb_h = win_w * 9/16
Compute offset: off_y = -(lb_h - win_h) / 2
Map: x11_x = tv_x * scale + off_x; clip negatives to 0

In KDE: getdisplaygeometry → scale = display / 1920×1080.

Key Pitfalls

Problem	Fix
TV "service error" / won't reconnect	Fixed source UDP port 9106
TV stuck "waiting for client"	Server keepalive timeout 10s
KDE XTest prompt on every click	Single persistent xdotool process
KDE XTest prompt after xdotool restart	`XwaylandEisNoPrompt=true` in kwinrc
Wrong mouse coordinates	Dynamic scale via `xdotool getdisplaygeometry`
Binary lost after `rpm-ostree upgrade`	Rebuild and redeploy

Deploy

# Build on Mac
cd ~/Developer/magic4pc_altclient
GOOS=linux GOARCH=amd64 go build -o magic4pc .

# Copy + restart on HTPC
scp magic4pc htpc:/home/bazzite/magic4pc/magic4pc
echo bazzite | sudo -S systemctl stop magic4pc.service
echo bazzite | sudo -S cp /home/bazzite/magic4pc/magic4pc \
  /usr/local/bin/magic4pc
echo bazzite | sudo -S systemctl start magic4pc.service

Sudoers rule (no-password systemctl):

bazzite ALL=(ALL) NOPASSWD: /usr/bin/systemctl

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