Add max-rows

Scrolling left the overlay's height entirely derived — as many rows as fit
in 90% of the display — so with enough windows it is always nearly
full-height, and there was no way to ask for a compact strip instead.
max-rows caps the viewport and scrolls the rest, which makes it the
symmetric partner to max-columns; rows are also the natural unit when
tiles are a fixed size, where a height in ppt would flip the row count
about as the tile size changes.

Measured on a 1280x1440 display with 14 tiles at 18ppt: uncapped gives a
981px surface showing 3 of 4 rows, max-rows = 2 gives 657px, and 1 gives
333px — each a row's pitch apart.

The test I wrote for it was wrong before the code was: four tiles make a
2x2 grid under the ceil(sqrt(n)) rule, not the 4x1 I had assumed.

src/cli.rs

@@ -53,7 +53,9 @@ config:
 
     tile-width     = 18ppt        # how big a thumbnail is
     tile-height    = 20ppt        # defaults to the display's aspect
-    max-columns    = 4            # rows beyond the screen scroll
+    max-columns    = 4
+    max-rows       = 3            # default: as many as the display fits;
+                                  # rows beyond that scroll
 
     font           = monospace    # also --font
     font-size      = 13.3
@@ -159,6 +161,7 @@ impl Args {
             tile_w: tile_w.max(1),
             tile_h: tile_h.max(1),
             max_cols: cfg.max_columns.unwrap_or(base.max_cols).max(1),
+            max_rows: cfg.max_rows.map(|r| r.max(1)).or(base.max_rows),
             labels: self.labels.or(cfg.labels).unwrap_or(base.labels),
             font: self
                 .font

src/config.rs

@@ -88,6 +88,7 @@ pub struct Config {
     pub tile_width: Option<Length>,
     pub tile_height: Option<Length>,
     pub max_columns: Option<i32>,
+    pub max_rows: Option<i32>,
     pub font: Option<String>,
     pub font_size: Option<f32>,
     pub labels: Option<bool>,
@@ -140,9 +141,8 @@ impl Config {
             "border-width" => self.border_width = Some(Length::parse(value)?),
             "tile-width" => self.tile_width = Some(Length::parse(value)?),
             "tile-height" => self.tile_height = Some(Length::parse(value)?),
-            "max-columns" => {
-                self.max_columns = Some(number(value)?);
-            }
+            "max-columns" => self.max_columns = Some(number(value)?),
+            "max-rows" => self.max_rows = Some(number(value)?),
             "font" => self.font = Some(value.to_string()),
             "font-size" => self.font_size = Some(number(value)?),
             "labels" => self.labels = Some(boolean(value)?),
@@ -230,6 +230,7 @@ border-width = 2px
 
 tile-width = 18ppt
 max-columns = 4
+max-rows = 3
 
 live = current
 fps = 30
@@ -242,6 +243,7 @@ labels = no
         assert_eq!(cfg.border_width, Some(Length::Px(2)));
         assert_eq!(cfg.tile_width, Some(Length::Ppt(18.0)));
         assert_eq!(cfg.max_columns, Some(4));
+        assert_eq!(cfg.max_rows, Some(3));
         assert_eq!(cfg.fps, Some(30));
         assert_eq!(cfg.labels, Some(false));
         assert!(cfg.live.is_some());

src/theme.rs

@@ -25,6 +25,9 @@ pub struct Theme {
     /// Margin between the grid and the window edge.
     pub margin: i32,
     pub max_cols: i32,
+    /// Cap on rows shown at once. Without it the viewport is as tall as the
+    /// display allows; with it the grid stays compact and scrolls sooner.
+    pub max_rows: Option<i32>,
     /// Gap between a thumbnail and its label (rasi `element { spacing }`).
     pub spacing: i32,
     /// Label font family, resolved against the system's fonts. The default is
@@ -53,6 +56,7 @@ impl Default for Theme {
             gap: 15,
             margin: 12,
             max_cols: 4,
+            max_rows: None,
             spacing: 10,
             font: crate::text::SYSTEM_MONO.to_string(),
             font_px: 13.3,
@@ -111,7 +115,8 @@ impl Layout {
         let fit_cols = ((room_w + t.gap) / (elem_w + t.gap)).max(1);
         cols = cols.clamp(1, t.max_cols.min(fit_cols)).max(1);
         let rows = (n + cols - 1) / cols;
-        let visible_rows = ((room_h + t.gap) / (elem_h + t.gap)).clamp(1, rows.max(1));
+        let fits = (room_h + t.gap) / (elem_h + t.gap);
+        let visible_rows = fits.min(t.max_rows.unwrap_or(fits)).clamp(1, rows.max(1));
 
         Self {
             cols,
@@ -472,6 +477,26 @@ mod tests {
         );
     }
 
+    #[test]
+    fn max_rows_keeps_the_grid_compact() {
+        let mut t = Theme::default();
+        let full = Layout::new(&t, 30, (1280, 1440));
+        t.max_rows = Some(2);
+        let capped = Layout::new(&t, 30, (1280, 1440));
+        assert!(
+            capped.visible_rows == 2 && full.visible_rows > 2,
+            "{capped:?}"
+        );
+        assert!(capped.height < full.height, "a shorter overlay");
+        assert!(capped.scrollable());
+        // The cap cannot invent rows: four tiles make a 2x2 grid, and a cap of
+        // five leaves it alone.
+        t.max_rows = Some(5);
+        let few = Layout::new(&t, 4, (1280, 1440));
+        assert_eq!((few.cols, few.rows, few.visible_rows), (2, 2, 2), "{few:?}");
+        assert!(!few.scrollable());
+    }
+
     #[test]
     fn revealing_moves_the_viewport_as_little_as_possible() {
         let t = Theme::default();