config/input: add cursor section

This should allow users to configure theme and size for the cursor,
as well as automatically set `XCURSOR_THEME` and `XCURSOR_SIZE` env
variables.

resources/default-config.kdl

@@ -67,6 +67,13 @@ focus-ring {
     inactive-color 0.3 0.3 0.3 1.0
 }
 
+cursor {
+    // Change the theme and size of the cursor as well as set the
+    // `XCURSOR_THEME` and `XCURSOR_SIZE` env variables.
+    // xcursor-theme "default"
+    // xcursor-size 24
+}
+
 // Uncomment this line to ask the clients to omit their client-side decorations if possible.
 // If the client will specifically ask for CSD, the request will be honored.
 // prefer-no-csd

src/config.rs

@@ -21,6 +21,8 @@ pub struct Config {
     #[knuffel(child, default)]
     pub prefer_no_csd: bool,
     #[knuffel(child, default)]
+    pub cursor: Cursor,
+    #[knuffel(child, default)]
     pub binds: Binds,
     #[knuffel(child, default)]
     pub debug: DebugConfig,
@@ -152,6 +154,23 @@ impl From<Color> for [f32; 4] {
     }
 }
 
+#[derive(knuffel::Decode, Debug, PartialEq)]
+pub struct Cursor {
+    #[knuffel(child, unwrap(argument), default = String::from("default"))]
+    pub xcursor_theme: String,
+    #[knuffel(child, unwrap(argument), default = 24)]
+    pub xcursor_size: u8,
+}
+
+impl Default for Cursor {
+    fn default() -> Self {
+        Self {
+            xcursor_theme: String::from("default"),
+            xcursor_size: 24,
+        }
+    }
+}
+
 #[derive(knuffel::Decode, Debug, Default, PartialEq, Eq)]
 pub struct Binds(#[knuffel(children)] pub Vec<Bind>);
 
@@ -366,6 +385,11 @@ mod tests {
 
             prefer-no-csd
 
+            cursor {
+                xcursor-theme "breeze_cursors"
+                xcursor-size 16
+            }
+
             binds {
                 Mod+T { spawn "alacritty"; }
                 Mod+Q { close-window; }
@@ -421,6 +445,10 @@ mod tests {
                     },
                 },
                 prefer_no_csd: true,
+                cursor: Cursor {
+                    xcursor_theme: String::from("breeze_cursors"),
+                    xcursor_size: 16,
+                },
                 binds: Binds(vec![
                     Bind {
                         key: Key {

src/cursor.rs

@@ -1,4 +1,5 @@
 use std::collections::HashMap;
+use std::env;
 use std::fs::File;
 use std::io::Read;
 
@@ -10,17 +11,22 @@ use smithay::utils::{Physical, Point, Transform};
 use xcursor::parser::{parse_xcursor, Image};
 use xcursor::CursorTheme;
 
-const CURSOR_SIZE: i32 = 24;
 static FALLBACK_CURSOR_DATA: &[u8] = include_bytes!("../resources/cursor.rgba");
 
 pub struct Cursor {
     images: Vec<Image>,
+    size: i32,
     cache: HashMap<i32, (TextureBuffer<GlesTexture>, Point<i32, Physical>)>,
 }
 
 impl Cursor {
-    pub fn load() -> Self {
-        let images = match load_xcursor() {
+    /// Load the said theme as well as set the `XCURSOR_THEME` and `XCURSOR_SIZE`
+    /// env variables.
+    pub fn load(theme: &str, size: u8) -> Self {
+        env::set_var("XCURSOR_THEME", theme);
+        env::set_var("XCURSOR_SIZE", size.to_string());
+
+        let images = match load_xcursor(theme) {
             Ok(images) => images,
             Err(err) => {
                 warn!("error loading xcursor default cursor: {err:?}");
@@ -40,6 +46,7 @@ impl Cursor {
 
         Self {
             images,
+            size: size as i32,
             cache: HashMap::new(),
         }
     }
@@ -54,7 +61,7 @@ impl Cursor {
             .or_insert_with_key(|scale| {
                 let _span = tracy_client::span!("create cursor texture");
 
-                let size = CURSOR_SIZE * scale;
+                let size = self.size * scale;
 
                 let nearest_image = self
                     .images
@@ -86,10 +93,10 @@ impl Cursor {
     }
 }
 
-fn load_xcursor() -> anyhow::Result<Vec<Image>> {
+fn load_xcursor(theme: &str) -> anyhow::Result<Vec<Image>> {
     let _span = tracy_client::span!();
 
-    let theme = CursorTheme::load("default");
+    let theme = CursorTheme::load(theme);
     let path = theme
         .load_icon("default")
         .ok_or_else(|| anyhow!("no default icon"))?;

src/niri.rs

@@ -262,7 +262,18 @@ impl State {
             }
         };
 
-        *self.niri.config.borrow_mut() = config;
+        let mut old_config = self.niri.config.borrow_mut();
+
+        if config.cursor != old_config.cursor {
+            self.niri.default_cursor =
+                Cursor::load(&config.cursor.xcursor_theme, config.cursor.xcursor_size);
+        }
+
+        *old_config = config;
+
+        // Release the borrow.
+        drop(old_config);
+
         self.niri.queue_redraw_all();
         // FIXME: apply output scale and whatnot.
         // FIXME: apply libinput device settings.
@@ -329,7 +340,8 @@ impl Niri {
         .unwrap();
         seat.add_pointer();
 
-        let default_cursor = Cursor::load();
+        let default_cursor =
+            Cursor::load(&config_.cursor.xcursor_theme, config_.cursor.xcursor_size);
 
         let socket_source = ListeningSocketSource::new_auto().unwrap();
         let socket_name = socket_source.socket_name().to_os_string();