perf: cache blurred wallpaper to disk to avoid re-blur on startup

First launch with blur blurs and saves to ~/.cache/moonlock/.
Subsequent starts load the cached PNG directly. Cache invalidates
when wallpaper path, size, mtime, or sigma changes.
Adds dirs crate for cache directory resolution.

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 = "anyhow"
 version = "1.0.102"
@@ -20,6 +26,18 @@ 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"
@@ -65,6 +83,36 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
 
+[[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"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3e8aa94d75141228480295a7d0e7feb620b1a5ad9f12bc40be62411e38cce4e"
+dependencies = [
+ "dirs-sys",
+]
+
+[[package]]
+name = "dirs-sys"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e01a3366d27ee9890022452ee61b2b63a67e6f13f58900b651ff5665f0bb1fab"
+dependencies = [
+ "libc",
+ "option-ext",
+ "redox_users",
+ "windows-sys",
+]
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -87,6 +135,15 @@ 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"
@@ -97,6 +154,16 @@ 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"
@@ -223,6 +290,17 @@ dependencies = [
  "system-deps",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff2abc00be7fca6ebc474524697ae276ad847ad0a6b3faa4bcb027e9a4614ad0"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.4.2"
@@ -510,6 +588,21 @@ 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"
@@ -546,6 +639,15 @@ version = "0.2.183"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b5b646652bf6661599e1da8901b3b9522896f01e736bad5f723fe7a3a27f899d"
 
+[[package]]
+name = "libredox"
+version = "0.1.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7ddbf48fd451246b1f8c2610bd3b4ac0cc6e149d89832867093ab69a17194f08"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.12.1"
@@ -574,9 +676,20 @@ dependencies = [
 ]
 
 [[package]]
-name = "moonlock"
+name = "miniz_oxide"
-version = "0.4.2"
+version = "0.8.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fa76a2c86f704bdb222d66965fb3d63269ce38518b83cb0575fca855ebb6316"
 dependencies = [
+ "adler2",
+ "simd-adler32",
+]
+
+[[package]]
+name = "moonlock"
+version = "0.5.0"
+dependencies = [
+ "dirs",
  "gdk-pixbuf",
  "gdk4",
  "gio",
@@ -584,6 +697,7 @@ dependencies = [
  "glib-build-tools",
  "gtk4",
  "gtk4-session-lock",
+ "image",
  "libc",
  "log",
  "nix",
@@ -594,6 +708,16 @@ dependencies = [
  "zeroize",
 ]
 
+[[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"
@@ -606,12 +730,27 @@ 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"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9f7c3e4beb33f85d45ae3e3a1792185706c8e16d043238c593331cc7cd313b50"
 
+[[package]]
+name = "option-ext"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "04744f49eae99ab78e0d5c0b603ab218f515ea8cfe5a456d7629ad883a3b6e7d"
+
 [[package]]
 name = "pango"
 version = "0.22.0"
@@ -648,6 +787,19 @@ 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 = "prettyplease"
 version = "0.2.37"
@@ -676,6 +828,12 @@ 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"
@@ -691,6 +849,17 @@ version = "6.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
 
+[[package]]
+name = "redox_users"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4e608c6638b9c18977b00b475ac1f28d14e84b27d8d42f70e0bf1e3dec127ac"
+dependencies = [
+ "getrandom 0.2.17",
+ "libredox",
+ "thiserror",
+]
+
 [[package]]
 name = "rustc_version"
 version = "0.4.1"
@@ -780,6 +949,12 @@ 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"
@@ -839,12 +1014,32 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
 dependencies = [
  "fastrand",
- "getrandom",
+ "getrandom 0.4.2",
  "once_cell",
  "rustix",
  "windows-sys",
 ]
 
+[[package]]
+name = "thiserror"
+version = "2.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4288b5bcbc7920c07a1149a35cf9590a2aa808e0bc1eafaade0b80947865fbc4"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "2.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ebc4ee7f67670e9b64d05fa4253e753e016c6c95ff35b89b7941d6b856dec1d5"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "toml"
 version = "0.8.23"
@@ -964,6 +1159,12 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "03c2856837ef78f57382f06b2b8563a2f512f7185d732608fd9176cb3b8edf0e"
 
+[[package]]
+name = "wasi"
+version = "0.11.1+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
+
 [[package]]
 name = "wasip2"
 version = "1.0.2+wasi-0.2.9"
@@ -1168,3 +1369,18 @@ 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

@@ -14,9 +14,11 @@ gdk-pixbuf = "0.22"
 gio = "0.22"
 toml = "0.8"
 serde = { version = "1", features = ["derive"] }
+dirs = "6"
 nix = { version = "0.29", features = ["user"] }
 zeroize = { version = "1", features = ["derive"] }
 libc = "0.2"
+image = { version = "0.25", default-features = false, features = ["jpeg", "png"] }
 log = "0.4"
 systemd-journal-logger = "2.2"
 

DECISIONS.md

@@ -0,0 +1,17 @@
+# Decisions
+
+Architectural and design decisions for Moonlock, in reverse chronological order.
+
+## 2026-03-28 – Optional background blur via `image` crate
+
+- **Who**: Nyx, Dom
+- **Why**: Consistent with moonset/moongreet — blurred wallpaper as lockscreen background is a common UX pattern
+- **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 – Shared wallpaper texture pattern (aligned with moonset/moongreet)
+
+- **Who**: Nyx, Dom
+- **Why**: Previously loaded wallpaper per-window via `Picture::for_filename()`. Multi-monitor setups decoded the JPEG redundantly. Blur feature requires texture pixel access anyway.
+- **Tradeoffs**: Slightly more code in main.rs (texture loaded before window creation), but avoids redundant decoding and enables the blur feature.
+- **How**: `load_background_texture()` in lockscreen.rs decodes once, `create_background_picture()` wraps shared `gdk::Texture` in `gtk::Picture`. Same pattern as moonset/moongreet.

src/config.rs

@@ -21,6 +21,7 @@ fn default_config_paths() -> Vec<PathBuf> {
 #[derive(Debug, Clone, Default, Deserialize)]
 struct RawConfig {
     pub background_path: Option<String>,
+    pub background_blur: Option<f32>,
     pub fingerprint_enabled: Option<bool>,
 }
 
@@ -28,6 +29,7 @@ struct RawConfig {
 #[derive(Debug, Clone)]
 pub struct Config {
     pub background_path: Option<String>,
+    pub background_blur: Option<f32>,
     pub fingerprint_enabled: bool,
 }
 
@@ -35,6 +37,7 @@ impl Default for Config {
     fn default() -> Self {
         Config {
             background_path: None,
+            background_blur: None,
             fingerprint_enabled: true,
         }
     }
@@ -48,6 +51,7 @@ pub fn load_config(config_paths: Option<&[PathBuf]>) -> Config {
         if let Ok(content) = fs::read_to_string(path) {
             if let Ok(parsed) = toml::from_str::<RawConfig>(&content) {
                 if parsed.background_path.is_some() { merged.background_path = parsed.background_path; }
+                if parsed.background_blur.is_some() { merged.background_blur = parsed.background_blur; }
                 if let Some(fp) = parsed.fingerprint_enabled { merged.fingerprint_enabled = fp; }
             }
         }
@@ -72,7 +76,7 @@ pub fn resolve_background_path_with(config: &Config, moonarch_wallpaper: &Path)
 mod tests {
     use super::*;
 
-    #[test] fn default_config() { let c = Config::default(); assert!(c.background_path.is_none()); assert!(c.fingerprint_enabled); }
+    #[test] fn default_config() { let c = Config::default(); assert!(c.background_path.is_none()); assert!(c.background_blur.is_none()); assert!(c.fingerprint_enabled); }
     #[test] fn load_default_fingerprint_true() {
         let dir = tempfile::tempdir().unwrap();
         let conf = dir.path().join("moonlock.toml");
@@ -83,15 +87,23 @@ mod tests {
     #[test] fn load_background() {
         let dir = tempfile::tempdir().unwrap();
         let conf = dir.path().join("moonlock.toml");
-        fs::write(&conf, "background_path = \"/custom/bg.jpg\"\nfingerprint_enabled = false\n").unwrap();
+        fs::write(&conf, "background_path = \"/custom/bg.jpg\"\nbackground_blur = 15.0\nfingerprint_enabled = false\n").unwrap();
         let c = load_config(Some(&[conf]));
         assert_eq!(c.background_path.as_deref(), Some("/custom/bg.jpg"));
+        assert_eq!(c.background_blur, Some(15.0));
         assert!(!c.fingerprint_enabled);
     }
+    #[test] fn load_blur_optional() {
+        let dir = tempfile::tempdir().unwrap();
+        let conf = dir.path().join("moonlock.toml");
+        fs::write(&conf, "background_path = \"/bg.jpg\"\n").unwrap();
+        let c = load_config(Some(&[conf]));
+        assert!(c.background_blur.is_none());
+    }
     #[test] fn resolve_config_path() {
         let dir = tempfile::tempdir().unwrap();
         let wp = dir.path().join("bg.jpg"); fs::write(&wp, "fake").unwrap();
-        let c = Config { background_path: Some(wp.to_str().unwrap().to_string()), fingerprint_enabled: true };
+        let c = Config { background_path: Some(wp.to_str().unwrap().to_string()), ..Config::default() };
         assert_eq!(resolve_background_path_with(&c, Path::new("/nonexistent")), wp);
     }
     #[test] fn empty_user_config_preserves_system_fingerprint() {

src/lockscreen.rs

@@ -6,9 +6,14 @@ 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::fs;
+use std::io::Write;
+use std::os::unix::fs::OpenOptionsExt;
+use std::path::{Path, PathBuf};
 use std::rc::Rc;
+use std::time::SystemTime;
 
 use zeroize::Zeroizing;
 
@@ -41,7 +46,7 @@ struct LockscreenState {
 /// Create a lockscreen window for a single monitor.
 /// Fingerprint is not initialized here — use `wire_fingerprint()` after async init.
 pub fn create_lockscreen_window(
-    bg_path: &Path,
+    bg_texture: &gdk::Texture,
     _config: &Config,
     app: &gtk::Application,
     unlock_callback: Rc<dyn Fn()>,
@@ -82,7 +87,7 @@ pub fn create_lockscreen_window(
     window.set_child(Some(&overlay));
 
     // Background wallpaper
-    let background = create_background_picture(bg_path);
+    let background = create_background_picture(bg_texture);
     overlay.set_child(Some(&background));
 
     // Centered vertical box
@@ -413,13 +418,159 @@ pub fn start_fingerprint(
     });
 }
 
-/// Create a Picture widget for the wallpaper background.
+/// Load the wallpaper as a texture once, for sharing across all windows.
-fn create_background_picture(bg_path: &Path) -> gtk::Picture {
+/// When `blur_radius` is `Some(sigma)` with sigma > 0, a Gaussian blur is applied.
-    let background = if bg_path.starts_with("/dev/moonarch/moonlock") {
+pub fn load_background_texture(bg_path: &Path, blur_radius: Option<f32>) -> gdk::Texture {
-        gtk::Picture::for_resource(bg_path.to_str().unwrap_or(""))
+    let fallback = "/dev/moonarch/moonlock/wallpaper.jpg";
+
+    let texture = if bg_path.starts_with("/dev/moonarch/moonlock") {
+        let resource_path = bg_path.to_str().unwrap_or(fallback);
+        gdk::Texture::from_resource(resource_path)
     } else {
-        gtk::Picture::for_filename(bg_path.to_str().unwrap_or(""))
+        let file = gio::File::for_path(bg_path);
+        gdk::Texture::from_file(&file).unwrap_or_else(|_| {
+            gdk::Texture::from_resource(fallback)
+        })
     };
+
+    match blur_radius {
+        Some(sigma) if sigma > 0.0 => load_blurred_with_cache(bg_path, &texture, sigma),
+        _ => texture,
+    }
+}
+
+// -- Blur cache ----------------------------------------------------------------
+
+const CACHE_PNG: &str = "blur-cache.png";
+const CACHE_META: &str = "blur-cache.meta";
+
+fn blur_cache_dir() -> Option<PathBuf> {
+    dirs::cache_dir().map(|d| d.join("moonlock"))
+}
+
+/// Build the cache key string for the current wallpaper + sigma.
+fn build_cache_meta(bg_path: &Path, sigma: f32) -> Option<String> {
+    if bg_path.starts_with("/dev/moonarch/") {
+        let binary = std::env::current_exe().ok()?;
+        let binary_mtime = fs::metadata(&binary)
+            .ok()?
+            .modified()
+            .ok()?
+            .duration_since(SystemTime::UNIX_EPOCH)
+            .ok()?
+            .as_secs();
+        Some(format!(
+            "path={}\nbinary_mtime={}\nsigma={}\n",
+            bg_path.display(), binary_mtime, sigma,
+        ))
+    } else {
+        let meta = fs::metadata(bg_path).ok()?;
+        let mtime = meta
+            .modified()
+            .ok()?
+            .duration_since(SystemTime::UNIX_EPOCH)
+            .ok()?
+            .as_secs();
+        Some(format!(
+            "path={}\nsize={}\nmtime={}\nsigma={}\n",
+            bg_path.display(), meta.len(), mtime, sigma,
+        ))
+    }
+}
+
+/// Try to load a cached blurred texture if the cache key matches.
+fn load_cached_blur(cache_dir: &Path, expected_meta: &str) -> Option<gdk::Texture> {
+    let stored_meta = fs::read_to_string(cache_dir.join(CACHE_META)).ok()?;
+    if stored_meta != expected_meta {
+        log::debug!("Blur cache meta mismatch, will re-blur");
+        return None;
+    }
+    let file = gio::File::for_path(cache_dir.join(CACHE_PNG));
+    match gdk::Texture::from_file(&file) {
+        Ok(texture) => {
+            log::debug!("Loaded blurred wallpaper from cache");
+            Some(texture)
+        }
+        Err(e) => {
+            log::debug!("Failed to load cached blur PNG: {e}");
+            None
+        }
+    }
+}
+
+/// Save a blurred texture to the cache directory.
+fn save_blur_cache(cache_dir: &Path, texture: &gdk::Texture, meta: &str) {
+    if let Err(e) = save_blur_cache_inner(cache_dir, texture, meta) {
+        log::debug!("Failed to save blur cache: {e}");
+    }
+}
+
+fn save_blur_cache_inner(
+    cache_dir: &Path,
+    texture: &gdk::Texture,
+    meta: &str,
+) -> Result<(), Box<dyn std::error::Error>> {
+    fs::create_dir_all(cache_dir)?;
+
+    let png_bytes = texture.save_to_png_bytes();
+
+    let mut f = fs::OpenOptions::new()
+        .create(true).write(true).truncate(true).mode(0o600)
+        .open(cache_dir.join(CACHE_PNG))?;
+    f.write_all(&png_bytes)?;
+
+    let mut f = fs::OpenOptions::new()
+        .create(true).write(true).truncate(true).mode(0o600)
+        .open(cache_dir.join(CACHE_META))?;
+    f.write_all(meta.as_bytes())?;
+
+    log::debug!("Saved blur cache to {}", cache_dir.display());
+    Ok(())
+}
+
+/// Load blurred texture, using disk cache when available.
+fn load_blurred_with_cache(bg_path: &Path, texture: &gdk::Texture, sigma: f32) -> gdk::Texture {
+    if let Some(cache_dir) = blur_cache_dir() {
+        if let Some(meta) = build_cache_meta(bg_path, sigma) {
+            if let Some(cached) = load_cached_blur(&cache_dir, &meta) {
+                return cached;
+            }
+            let blurred = apply_blur(texture, sigma);
+            save_blur_cache(&cache_dir, &blurred, &meta);
+            return blurred;
+        }
+    }
+    apply_blur(texture, sigma)
+}
+
+// -- Blur implementation -------------------------------------------------------
+
+/// 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 Picture widget for the wallpaper background from a shared texture.
+fn create_background_picture(texture: &gdk::Texture) -> gtk::Picture {
+    let background = gtk::Picture::for_paintable(texture);
     background.set_content_fit(gtk::ContentFit::Cover);
     background.set_hexpand(true);
     background.set_vexpand(true);
@@ -576,4 +727,60 @@ mod tests {
     fn avatar_size_matches_css() {
         assert_eq!(AVATAR_SIZE, 128);
     }
+
+    // -- Blur cache tests --
+
+    #[test]
+    fn build_cache_meta_for_file() {
+        let dir = tempfile::tempdir().unwrap();
+        let file = dir.path().join("wallpaper.jpg");
+        fs::write(&file, b"fake image").unwrap();
+        let meta = build_cache_meta(&file, 20.0);
+        assert!(meta.is_some());
+        let meta = meta.unwrap();
+        assert!(meta.contains("path="));
+        assert!(meta.contains("size=10"));
+        assert!(meta.contains("sigma=20"));
+    }
+
+    #[test]
+    fn build_cache_meta_for_gresource() {
+        let path = Path::new("/dev/moonarch/moonlock/wallpaper.jpg");
+        let meta = build_cache_meta(path, 15.0);
+        assert!(meta.is_some());
+        let meta = meta.unwrap();
+        assert!(meta.contains("binary_mtime="));
+        assert!(meta.contains("sigma=15"));
+        assert!(!meta.contains("size="));
+    }
+
+    #[test]
+    fn build_cache_meta_missing_file() {
+        let meta = build_cache_meta(Path::new("/nonexistent/wallpaper.jpg"), 20.0);
+        assert!(meta.is_none());
+    }
+
+    #[test]
+    fn cache_meta_mismatch_returns_none() {
+        let dir = tempfile::tempdir().unwrap();
+        fs::write(
+            dir.path().join(CACHE_META),
+            "path=/old.jpg\nsize=100\nmtime=1\nsigma=20\n",
+        ).unwrap();
+        let result = load_cached_blur(
+            dir.path(),
+            "path=/new.jpg\nsize=200\nmtime=2\nsigma=20\n",
+        );
+        assert!(result.is_none());
+    }
+
+    #[test]
+    fn cache_missing_meta_returns_none() {
+        let dir = tempfile::tempdir().unwrap();
+        let result = load_cached_blur(
+            dir.path(),
+            "path=/any.jpg\nsize=1\nmtime=1\nsigma=20\n",
+        );
+        assert!(result.is_none());
+    }
 }

src/main.rs

@@ -14,7 +14,6 @@ use gtk4::prelude::*;
 use gtk4::{self as gtk, gio};
 use gtk4_session_lock;
 use std::cell::RefCell;
-use std::path::PathBuf;
 use std::rc::Rc;
 
 use crate::fingerprint::FingerprintListener;
@@ -42,14 +41,15 @@ fn activate(app: &gtk::Application) {
 
     let config = config::load_config(None);
     let bg_path = config::resolve_background_path(&config);
+    let bg_texture = lockscreen::load_background_texture(&bg_path, config.background_blur);
 
     if gtk4_session_lock::is_supported() {
-        activate_with_session_lock(app, &display, &bg_path, &config);
+        activate_with_session_lock(app, &display, &bg_texture, &config);
     } else {
         #[cfg(debug_assertions)]
         {
             log::warn!("ext-session-lock-v1 not supported — running in development mode");
-            activate_without_lock(app, &bg_path, &config);
+            activate_without_lock(app, &bg_texture, &config);
         }
         #[cfg(not(debug_assertions))]
         {
@@ -62,7 +62,7 @@ fn activate(app: &gtk::Application) {
 fn activate_with_session_lock(
     app: &gtk::Application,
     display: &gdk::Display,
-    bg_path: &PathBuf,
+    bg_texture: &gdk::Texture,
     config: &config::Config,
 ) {
     let lock = gtk4_session_lock::Instance::new();
@@ -87,7 +87,7 @@ fn activate_with_session_lock(
             .and_then(|obj| obj.downcast::<gdk::Monitor>().ok())
         {
             let handles = lockscreen::create_lockscreen_window(
-                bg_path,
+                bg_texture,
                 config,
                 app,
                 unlock_callback.clone(),
@@ -144,7 +144,7 @@ fn init_fingerprint_async(all_handles: Vec<lockscreen::LockscreenHandles>) {
 #[cfg(debug_assertions)]
 fn activate_without_lock(
     app: &gtk::Application,
-    bg_path: &PathBuf,
+    bg_texture: &gdk::Texture,
     config: &config::Config,
 ) {
     let app_clone = app.clone();
@@ -153,7 +153,7 @@ fn activate_without_lock(
     });
 
     let handles = lockscreen::create_lockscreen_window(
-        bg_path,
+        bg_texture,
         config,
         app,
         unlock_callback,