implement always_center_single_column layout option

niri-config/src/lib.rs

@@ -397,6 +397,8 @@ pub struct Layout {
     pub default_column_width: Option<DefaultColumnWidth>,
     #[knuffel(child, unwrap(argument), default)]
     pub center_focused_column: CenterFocusedColumn,
+    #[knuffel(child)]
+    pub always_center_single_column: bool,
     #[knuffel(child, unwrap(argument), default = Self::default().gaps)]
     pub gaps: FloatOrInt<0, 65535>,
     #[knuffel(child, default)]
@@ -411,6 +413,7 @@ impl Default for Layout {
             preset_column_widths: Default::default(),
             default_column_width: Default::default(),
             center_focused_column: Default::default(),
+            always_center_single_column: false,
             gaps: FloatOrInt(16.),
             struts: Default::default(),
         }
@@ -3057,6 +3060,7 @@ mod tests {
                         bottom: FloatOrInt(0.),
                     },
                     center_focused_column: CenterFocusedColumn::OnOverflow,
+                    always_center_single_column: false,
                 },
                 spawn_at_startup: vec![SpawnAtStartup {
                     command: vec!["alacritty".to_owned(), "-e".to_owned(), "fish".to_owned()],

src/layout/mod.rs

@@ -236,6 +236,7 @@ pub struct Options {
     pub focus_ring: niri_config::FocusRing,
     pub border: niri_config::Border,
     pub center_focused_column: CenterFocusedColumn,
+    pub always_center_single_column: bool,
     /// Column widths that `toggle_width()` switches between.
     pub preset_widths: Vec<ColumnWidth>,
     /// Initial width for new columns.
@@ -255,6 +256,7 @@ impl Default for Options {
             focus_ring: Default::default(),
             border: Default::default(),
             center_focused_column: Default::default(),
+            always_center_single_column: false,
             preset_widths: vec![
                 ColumnWidth::Proportion(1. / 3.),
                 ColumnWidth::Proportion(0.5),
@@ -297,6 +299,7 @@ impl Options {
             focus_ring: layout.focus_ring,
             border: layout.border,
             center_focused_column: layout.center_focused_column,
+            always_center_single_column: layout.always_center_single_column,
             preset_widths,
             default_width,
             animations: config.animations.clone(),
@@ -4455,11 +4458,13 @@ mod tests {
             focus_ring in arbitrary_focus_ring(),
             border in arbitrary_border(),
             center_focused_column in arbitrary_center_focused_column(),
+            always_center_single_column in any::<bool>(),
         ) -> Options {
             Options {
                 gaps,
                 struts,
                 center_focused_column,
+                always_center_single_column,
                 focus_ring,
                 border,
                 ..Default::default()

src/layout/workspace.rs

@@ -459,6 +459,11 @@ impl<W: LayoutElement> Workspace<W> {
         self.scale
     }
 
+    pub fn is_centering_focused_column(&self) -> bool {
+        self.options.center_focused_column == CenterFocusedColumn::Always
+            || (self.options.always_center_single_column && self.columns.len() <= 1)
+    }
+
     pub fn advance_animations(&mut self, current_time: Duration) {
         if let Some(ViewOffsetAdjustment::Animation(anim)) = &mut self.view_offset_adj {
             anim.set_current_time(current_time);
@@ -750,6 +755,10 @@ impl<W: LayoutElement> Workspace<W> {
         idx: usize,
         prev_idx: Option<usize>,
     ) -> f64 {
+        if self.is_centering_focused_column() {
+            return self.compute_new_view_offset_for_column_centered(current_x, idx);
+        }
+
         match self.options.center_focused_column {
             CenterFocusedColumn::Always => {
                 self.compute_new_view_offset_for_column_centered(current_x, idx)
@@ -1399,7 +1408,7 @@ impl<W: LayoutElement> Workspace<W> {
             if let Some(resize) = resize {
                 // If this is an interactive resize commit of an active window, then we need to
                 // either preserve the view offset or adjust it accordingly.
-                let centered = self.options.center_focused_column == CenterFocusedColumn::Always;
+                let centered = self.is_centering_focused_column();
 
                 let width = self.data[col_idx].width;
                 let offset = if centered {
@@ -2550,7 +2559,7 @@ impl<W: LayoutElement> Workspace<W> {
         let left_strut = self.working_area.loc.x;
         let right_strut = self.view_size.w - self.working_area.size.w - self.working_area.loc.x;
 
-        if self.options.center_focused_column == CenterFocusedColumn::Always {
+        if self.is_centering_focused_column() {
             let mut col_x = 0.;
             for (col_idx, col) in self.columns.iter().enumerate() {
                 let col_w = col.width();
@@ -2651,7 +2660,7 @@ impl<W: LayoutElement> Workspace<W> {
 
         let mut new_col_idx = target_snap.col_idx;
 
-        if self.options.center_focused_column != CenterFocusedColumn::Always {
+        if !self.is_centering_focused_column() {
             // Focus the furthest window towards the direction of the gesture.
             if target_view_offset >= current_view_offset {
                 for col_idx in (new_col_idx + 1)..self.columns.len() {
@@ -2768,6 +2777,8 @@ impl<W: LayoutElement> Workspace<W> {
             return false;
         }
 
+        let is_centering = self.is_centering_focused_column();
+
         let col = self
             .columns
             .iter_mut()
@@ -2786,7 +2797,7 @@ impl<W: LayoutElement> Workspace<W> {
                 dx = -dx;
             };
 
-            if self.options.center_focused_column == CenterFocusedColumn::Always {
+            if is_centering {
                 dx *= 2.;
             }
 
@@ -3637,6 +3648,9 @@ impl<W: LayoutElement> Column<W> {
         &self,
         data: impl Iterator<Item = TileData>,
     ) -> impl Iterator<Item = Point<f64, Logical>> {
+        // FIXME: this should take into account always-center-single-column, which means that
+        // Column should somehow know when it is being centered due to being the single column on
+        // the workspace or some other reason.
         let center = self.options.center_focused_column == CenterFocusedColumn::Always;
         let gaps = self.options.gaps;
         let col_width = self.width();