feat: add optional background blur via image crate

Gaussian blur applied at texture load time when `background_blur` is
set in moonset.toml. Blur runs once, result is shared across monitors.

Cargo.lock

@@ -2,6 +2,12 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "adler2"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "320119579fcad9c21884f5c4861d16174d0e06250625266f50fe6898340abefa"
+
 [[package]]
 name = "aho-corasick"
 version = "1.1.4"
@@ -79,6 +85,18 @@ version = "2.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "843867be96c8daad0d758b57df9392b6d8d271134fce549de6ce169ff98a92af"
 
+[[package]]
+name = "bytemuck"
+version = "1.25.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c8efb64bd706a16a1bdde310ae86b351e4d21550d98d056f22f8a7f7a2183fec"
+
+[[package]]
+name = "byteorder-lite"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f1fe948ff07f4bd06c30984e69f5b4899c516a3ef74f34df92a2df2ab535495"
+
 [[package]]
 name = "cairo-rs"
 version = "0.22.0"
@@ -130,6 +148,15 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1d07550c9036bf2ae0c684c4297d503f838287c83c53686d05370d0e139ae570"
 
+[[package]]
+name = "crc32fast"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9481c1c90cbf2ac953f07c8d4a58aa3945c425b7185c9154d67a65e4230da511"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "dirs"
 version = "6.0.0"
@@ -196,6 +223,15 @@ version = "2.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
 
+[[package]]
+name = "fdeflate"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e6853b52649d4ac5c0bd02320cddc5ba956bdb407c4b75a2c6b75bf51500f8c"
+dependencies = [
+ "simd-adler32",
+]
+
 [[package]]
 name = "field-offset"
 version = "0.3.6"
@@ -206,6 +242,16 @@ dependencies = [
  "rustc_version",
 ]
 
+[[package]]
+name = "flate2"
+version = "1.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "843fba2746e448b37e26a819579957415c8cef339bf08564fe8b7ddbd959573c"
+dependencies = [
+ "crc32fast",
+ "miniz_oxide",
+]
+
 [[package]]
 name = "foldhash"
 version = "0.1.5"
@@ -630,6 +676,21 @@ version = "2.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3d3067d79b975e8844ca9eb072e16b31c3c1c36928edf9c6789548c524d0d954"
 
+[[package]]
+name = "image"
+version = "0.25.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85ab80394333c02fe689eaf900ab500fbd0c2213da414687ebf995a65d5a6104"
+dependencies = [
+ "bytemuck",
+ "byteorder-lite",
+ "moxcms",
+ "num-traits",
+ "png",
+ "zune-core",
+ "zune-jpeg",
+]
+
 [[package]]
 name = "indexmap"
 version = "2.13.0"
@@ -732,9 +793,19 @@ dependencies = [
  "autocfg",
 ]
 
+[[package]]
+name = "miniz_oxide"
+version = "0.8.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fa76a2c86f704bdb222d66965fb3d63269ce38518b83cb0575fca855ebb6316"
+dependencies = [
+ "adler2",
+ "simd-adler32",
+]
+
 [[package]]
 name = "moonset"
-version = "0.1.0"
+version = "0.1.1"
 dependencies = [
  "dirs",
  "env_logger",
@@ -744,6 +815,7 @@ dependencies = [
  "glib-build-tools",
  "gtk4",
  "gtk4-layer-shell",
+ "image",
  "log",
  "nix",
  "serde",
@@ -751,6 +823,16 @@ dependencies = [
  "toml 0.8.23",
 ]
 
+[[package]]
+name = "moxcms"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb85c154ba489f01b25c0d36ae69a87e4a1c73a72631fc6c0eb6dde34a73e44b"
+dependencies = [
+ "num-traits",
+ "pxfm",
+]
+
 [[package]]
 name = "nix"
 version = "0.29.0"
@@ -763,6 +845,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "num-traits"
+version = "0.2.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "071dfc062690e90b734c0b2273ce72ad0ffa95f0c74596bc250dcfd960262841"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "once_cell"
 version = "1.21.4"
@@ -817,6 +908,19 @@ version = "0.3.32"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7edddbd0b52d732b21ad9a5fab5c704c14cd949e5e9a1ec5929a24fded1b904c"
 
+[[package]]
+name = "png"
+version = "0.18.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60769b8b31b2a9f263dae2776c37b1b28ae246943cf719eb6946a1db05128a61"
+dependencies = [
+ "bitflags",
+ "crc32fast",
+ "fdeflate",
+ "flate2",
+ "miniz_oxide",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.13.1"
@@ -860,6 +964,12 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "pxfm"
+version = "0.1.28"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b5a041e753da8b807c9255f28de81879c78c876392ff2469cde94799b2896b9d"
+
 [[package]]
 name = "quote"
 version = "1.0.45"
@@ -1004,6 +1114,12 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "simd-adler32"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "703d5c7ef118737c72f1af64ad2f6f8c5e1921f818cdcb97b8fe6fc69bf66214"
+
 [[package]]
 name = "slab"
 version = "0.4.12"
@@ -1394,3 +1510,18 @@ name = "zmij"
 version = "1.0.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b8848ee67ecc8aedbaf3e4122217aff892639231befc6a1b58d29fff4c2cabaa"
+
+[[package]]
+name = "zune-core"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb8a0807f7c01457d0379ba880ba6322660448ddebc890ce29bb64da71fb40f9"
+
+[[package]]
+name = "zune-jpeg"
+version = "0.5.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "27bc9d5b815bc103f142aa054f561d9187d191692ec7c2d1e2b4737f8dbd7296"
+dependencies = [
+ "zune-core",
+]

Cargo.toml

@@ -15,6 +15,7 @@ toml = "0.8"
 dirs = "6"
 serde = { version = "1", features = ["derive"] }
 nix = { version = "0.29", features = ["user"] }
+image = { version = "0.25", default-features = false, features = ["jpeg", "png"] }
 log = "0.4"
 env_logger = "0.11"
 

DECISIONS.md

@@ -2,6 +2,13 @@
 
 Architectural and design decisions for Moonset, in reverse chronological order.
 
+## 2026-03-28 – Optional background blur via `image` crate
+
+- **Who**: Hekate, Dom
+- **Why**: Blurred wallpaper as background is a common UX pattern for overlay menus
+- **Tradeoffs**: Adds `image` crate dependency (~15 transitive crates); CPU-side Gaussian blur at load time adds startup latency proportional to image size and sigma. Acceptable because blur runs once and the texture is shared across monitors.
+- **How**: `load_background_texture(bg_path, blur_radius)` loads texture, optionally applies `imageops::blur()`, returns `gdk::Texture`. Config option `background_blur: Option<f32>` in TOML.
+
 ## 2026-03-28 – Use absolute paths for system binaries
 
 - **Who**: Hekate, Dom

src/config.rs

@@ -20,6 +20,7 @@ fn default_config_paths() -> Vec<PathBuf> {
 #[derive(Debug, Clone, Default, Deserialize)]
 pub struct Config {
     pub background_path: Option<String>,
+    pub background_blur: Option<f32>,
 }
 
 /// Load config from TOML files. Later paths override earlier ones.
@@ -34,6 +35,9 @@ pub fn load_config(config_paths: Option<&[PathBuf]>) -> Config {
                 if parsed.background_path.is_some() {
                     merged.background_path = parsed.background_path;
                 }
+                if parsed.background_blur.is_some() {
+                    merged.background_blur = parsed.background_blur;
+                }
             }
         }
     }
@@ -76,6 +80,7 @@ mod tests {
     fn default_config_has_none_background() {
         let config = Config::default();
         assert!(config.background_path.is_none());
+        assert!(config.background_blur.is_none());
     }
 
     #[test]
@@ -95,6 +100,28 @@ mod tests {
         assert_eq!(config.background_path.as_deref(), Some("/custom/wallpaper.jpg"));
     }
 
+    #[test]
+    fn load_config_reads_background_blur() {
+        let dir = tempfile::tempdir().unwrap();
+        let conf = dir.path().join("moonset.toml");
+        fs::write(&conf, "background_blur = 20.0\n").unwrap();
+        let paths = vec![conf];
+        let config = load_config(Some(&paths));
+        assert_eq!(config.background_blur, Some(20.0));
+    }
+
+    #[test]
+    fn load_config_blur_override() {
+        let dir = tempfile::tempdir().unwrap();
+        let conf1 = dir.path().join("first.toml");
+        let conf2 = dir.path().join("second.toml");
+        fs::write(&conf1, "background_blur = 10.0\n").unwrap();
+        fs::write(&conf2, "background_blur = 25.0\n").unwrap();
+        let paths = vec![conf1, conf2];
+        let config = load_config(Some(&paths));
+        assert_eq!(config.background_blur, Some(25.0));
+    }
+
     #[test]
     fn load_config_later_paths_override_earlier() {
         let dir = tempfile::tempdir().unwrap();
@@ -124,6 +151,7 @@ mod tests {
         fs::write(&wallpaper, "fake").unwrap();
         let config = Config {
             background_path: Some(wallpaper.to_str().unwrap().to_string()),
+            ..Config::default()
         };
         assert_eq!(
             resolve_background_path_with(&config, Path::new("/nonexistent")),
@@ -135,6 +163,7 @@ mod tests {
     fn resolve_ignores_config_path_when_file_missing() {
         let config = Config {
             background_path: Some("/nonexistent/wallpaper.jpg".to_string()),
+            ..Config::default()
         };
         let result = resolve_background_path_with(&config, Path::new("/nonexistent"));
         // Falls through to gresource fallback

src/main.rs

@@ -56,7 +56,7 @@ fn activate(app: &gtk::Application) {
     // Resolve wallpaper once, decode texture once, share across all windows
     let config = config::load_config(None);
     let bg_path = config::resolve_background_path(&config);
-    let texture = panel::load_background_texture(&bg_path);
+    let texture = panel::load_background_texture(&bg_path, config.background_blur);
 
     // Panel on focused output (no set_monitor → compositor picks focused)
     let panel = panel::create_panel_window(&texture, app);

src/panel.rs

@@ -6,6 +6,7 @@ use gdk_pixbuf::Pixbuf;
 use glib::clone;
 use gtk4::prelude::*;
 use gtk4::{self as gtk, gio};
+use image::imageops;
 use std::cell::RefCell;
 use std::path::Path;
 use std::rc::Rc;
@@ -80,10 +81,11 @@ pub fn action_definitions() -> Vec<ActionDef> {
 }
 
 /// Load the wallpaper as a texture once, for sharing across all windows.
-pub fn load_background_texture(bg_path: &Path) -> gdk::Texture {
+/// When `blur_radius` is `Some(sigma)` with sigma > 0, a Gaussian blur is applied.
+pub fn load_background_texture(bg_path: &Path, blur_radius: Option<f32>) -> gdk::Texture {
     let fallback = format!("{}/wallpaper.jpg", crate::GRESOURCE_PREFIX);
 
-    if bg_path.starts_with(crate::GRESOURCE_PREFIX) {
+    let texture = if bg_path.starts_with(crate::GRESOURCE_PREFIX) {
         let resource_path = bg_path.to_str().unwrap_or(&fallback);
         gdk::Texture::from_resource(resource_path)
     } else {
@@ -91,9 +93,37 @@ pub fn load_background_texture(bg_path: &Path) -> gdk::Texture {
         gdk::Texture::from_file(&file).unwrap_or_else(|_| {
             gdk::Texture::from_resource(&fallback)
         })
+    };
+
+    match blur_radius {
+        Some(sigma) if sigma > 0.0 => apply_blur(&texture, sigma),
+        _ => texture,
     }
 }
 
+/// Apply Gaussian blur to a texture and return a blurred texture.
+fn apply_blur(texture: &gdk::Texture, sigma: f32) -> gdk::Texture {
+    let width = texture.width() as u32;
+    let height = texture.height() as u32;
+    let stride = width as usize * 4;
+    let mut pixel_data = vec![0u8; stride * height as usize];
+    texture.download(&mut pixel_data, stride);
+
+    let img = image::RgbaImage::from_raw(width, height, pixel_data)
+        .expect("pixel buffer size matches texture dimensions");
+    let blurred = imageops::blur(&image::DynamicImage::ImageRgba8(img), sigma);
+
+    let bytes = glib::Bytes::from(blurred.as_raw());
+    let mem_texture = gdk::MemoryTexture::new(
+        width as i32,
+        height as i32,
+        gdk::MemoryFormat::B8g8r8a8Premultiplied,
+        &bytes,
+        stride,
+    );
+    mem_texture.upcast()
+}
+
 /// Create a wallpaper-only window for secondary monitors.
 pub fn create_wallpaper_window(texture: &gdk::Texture, app: &gtk::Application) -> gtk::ApplicationWindow {
     let window = gtk::ApplicationWindow::builder()