cosmic-hot-corners

A native Hot Corners daemon for the COSMIC™ Desktop (Pop!_OS), built entirely with libcosmic and iced.

Overview

cosmic-hot-corners runs as a background daemon with no visible window. It places four invisible 10×10 px wlr-layer-shell surfaces — one at each screen corner — using Layer::Overlay. When the pointer enters a corner and remains there longer than the configured delay, a configurable action is triggered.

The project is fully integrated with the COSMIC ecosystem: configuration is stored and watched via cosmic-config, and all Wayland interaction is handled through libcosmic's iced_winit + cctk (COSMIC Client Toolkit) backend.

Architecture

main.rs
├── cosmic-hot-corners            // opens settings GUI (default)
└── cosmic-hot-corners --daemon   // runs the daemon (no visible window)

app.rs
├── init()         Loads config; waits for Wayland output events to create surfaces.
├── subscription() Listens to OutputEvent (Added/Removed) to manage surfaces per monitor,
│                  CursorMoved/CursorLeft for pointer detection, and watch_config() for
│                  live config reload without restarting the daemon.
├── update()
│   ├── OutputAdded   → creates 4 layer-shell surfaces (10×10 px, Overlay) for that output
│   ├── OutputRemoved → destroys the 4 surfaces for that output
│   ├── CursorMoved   → increments pending_generation, schedules tokio::time::sleep(delay_ms)
│   ├── TriggerCorner → fires action only if generation still matches
│   │                   (cancellation-safe — rapid movement never triggers)
│   └── ConfigUpdated → hot-reloads config; next trigger uses new settings
└── execute_action() Dispatches CornerAction variants via D-Bus or sh -c.

config.rs
└── Config (cosmic-config v1)
    ├── delay_ms: u64          // activation delay in milliseconds
    ├── top_left: CornerAction
    ├── top_right: CornerAction
    ├── bottom_left: CornerAction
    └── bottom_right: CornerAction

settings_app.rs
└── GUI settings window (libcosmic, follows COSMIC light/dark theme automatically)
    ├── Activation delay field
    └── 2×2 grid of corner cards, each with action dropdown + optional command input

Corner Actions

Variant	Behavior
Disabled	No-op
ShowWorkspaces	Opens the workspaces overview via D-Bus (com.system76.CosmicWorkspaces)
OpenLauncher	Opens the app launcher via D-Bus (com.system76.CosmicLauncher)
RunCommand(String)	Executes an arbitrary shell command via sh -c

Configuration

GUI (recommended)

After installing, open Hot Corners Settings from the COSMIC app drawer, or right-click the daemon's entry in the launcher and choose Configure Hot Corners.

The settings window lets you assign an action to each corner and adjust the activation delay. Changes are saved instantly — no restart required.

Manual (advanced)

Configuration is also stored as plain files managed by cosmic-config, under:

~/.config/cosmic/io.github.cosmic-hot-corners/v1/

Each field is a separate file. Example — enable workspace overview on the top-left corner with a 400 ms delay:

mkdir -p ~/.config/cosmic/io.github.cosmic-hot-corners/v1
echo '400' > ~/.config/cosmic/io.github.cosmic-hot-corners/v1/delay_ms
echo 'ShowWorkspaces' > ~/.config/cosmic/io.github.cosmic-hot-corners/v1/top_left

Requirements

• COSMIC Desktop (Wayland compositor with wlr-layer-shell support)
• libxkbcommon-dev, libwayland-dev, pkg-config
• Rust toolchain (edition 2024)

Installation

1. Install build dependencies

sudo apt install libxkbcommon-dev libwayland-dev pkg-config

2. Clone and install

git clone https://github.com/your-username/cosmic-hotcorners
cd cosmic-hotcorners
just build-release
sudo just install

3. Open the settings

Launch the settings GUI to configure each corner:

cosmic-hot-corners

Or open Hot Corners Settings from the COSMIC app drawer.

4. Autostart

To start the daemon automatically on login:

just autostart

To disable autostart:

just autostart-disable

This installs/removes a .desktop file in ~/.config/autostart/. The daemon does not run as a systemd service — it is launched by the COSMIC session manager alongside other autostart applications.

Configuration changes made in the settings GUI are applied instantly — the running daemon reloads config automatically without needing a restart.

To stop a running instance:

pkill -f cosmic-hot-corners

For distribution packaging:

just vendor
just build-vendored
just rootdir=debian/cosmic-hot-corners prefix=/usr install

Flatpak

The project ships a Flatpak manifest at io.github.cosmic-hot-corners.yml.

Build and test locally

1. Install dependencies:

sudo apt install flatpak flatpak-builder
flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
flatpak install flathub org.freedesktop.Platform//25.08 org.freedesktop.Sdk//25.08 \
    org.freedesktop.Sdk.Extension.rust-stable//25.08

2. Generate cargo sources (required once, and again after Cargo.lock changes):

pip install aiohttp toml
just flatpak-sources

3. Build and install locally:

just flatpak-build

4. Test:

just flatpak-run-settings   # open settings GUI
just flatpak-run            # run daemon

Submit to Flathub

1. Create a GitHub repo named io.github.cosmic-hot-corners under the flathub org (via a PR to flathub/flathub)
2. In that repo: copy io.github.cosmic-hot-corners.yml and generated-sources.json, adjusting the source from type: dir to a versioned archive or git tag
3. The Flathub CI builds and validates the manifest — the team reviews and merges

Development

Install rustup and configure your editor with rust-analyzer. To reduce compile times, disable LTO in the release profile and use mold + sccache.

License

MPL-2.0