fix: center floating panes when width/height but no x/y are provided (#4607)

* fix: center floating panes when width/height but no x/y are provided

* rustfmt

* add pr

9 files changed, 334 insertions, 72 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f820019..92dc3a15 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 * feat: new `layout-manager` interface and plugin API commands (https://github.com/zellij-org/zellij/pull/4601)
 * fix: keep serializing sessions resurrected from the welcome screen (https://github.com/zellij-org/zellij/pull/4604)
 * fix: sanitize session names when deleting them from the CLI (https://github.com/zellij-org/zellij/pull/4583)
+* fix: properly center floating panes started with `--floating` when explicit width/height is provided (https://github.com/zellij-org/zellij/pull/4607)
 
 ## [0.43.1] - 2025-08-08
 * fix: pane rename backspace regression (https://github.com/zellij-org/zellij/pull/4346)
diff --git a/zellij-server/src/panes/floating_panes/mod.rs b/zellij-server/src/panes/floating_panes/mod.rs
index a52c78e7..18710c01 100644
--- a/zellij-server/src/panes/floating_panes/mod.rs
+++ b/zellij-server/src/panes/floating_panes/mod.rs
@@ -292,18 +292,14 @@ impl FloatingPanes {
         let mut position = floating_pane_grid
             .find_room_for_new_pane()
             .with_context(err_context)?;
-        if let Some(x) = &floating_pane_layout.x {
-            position.x = x.to_position(viewport.cols);
-        }
-        if let Some(y) = &floating_pane_layout.y {
-            position.y = y.to_position(viewport.rows);
-        }
-        if let Some(width) = &floating_pane_layout.width {
-            position.cols = Dimension::fixed(width.to_position(viewport.cols));
-        }
-        if let Some(height) = &floating_pane_layout.height {
-            position.rows = Dimension::fixed(height.to_position(viewport.rows));
-        }
+        position.apply_floating_pane_position(
+            floating_pane_layout.x.clone(),
+            floating_pane_layout.y.clone(),
+            floating_pane_layout.width.clone(),
+            floating_pane_layout.height.clone(),
+            viewport.cols,
+            viewport.rows,
+        );
         if let Some(is_pinned) = &floating_pane_layout.pinned {
             position.is_pinned = *is_pinned;
         }
diff --git a/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout-2.snap b/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout-2.snap
index 1394348a..0b88ec67 100644
--- a/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout-2.snap
+++ b/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout-2.snap
@@ -1,6 +1,5 @@
 ---
 source: zellij-server/src/tab/./unit/tab_integration_tests.rs
-assertion_line: 8040
 expression: snapshot
 ---
 00 (C): ┌ Pane #1 ──────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
@@ -8,19 +7,18 @@ expression: snapshot
 02 (C): │                                                                                                                       │
 03 (C): │                                                                                                                       │
 04 (C): │                                                                                                                       │
-05 (C): │ ┌ Pane #2 ─────────────────────────────────── PIN [ ] ┐    ┌ Pane #3 ─────────────────────────────────── PIN [ ] ┐    │
-06 (C): │ │                                                     │    │                                                     │    │
-07 (C): │ │                                                     │    │                                                     │    │
-08 (C): │ │                                                     │    │                                                     │    │
-09 (C): │ │                                                     │    │                                                     │    │
-10 (C): │ │                                                     │    │                                                     │    │
-11 (C): │ │                                                     │    │                                                     │    │
-12 (C): │ │                                                     │    │                                                     │    │
-13 (C): │ │                                                     │    │                                                     │    │
-14 (C): │ └─────────────────────────────────────────────────────┘    └─────────────────────────────────────────────────────┘    │
+05 (C): │┌ Pane #2 ────────────────────────────────── PIN [ ] ┐     ┌ Pane #3 ────────────────────────────────── PIN [ ] ┐      │
+06 (C): ││                                                    │     │                                                    │      │
+07 (C): ││                                                    │     │                                                    │      │
+08 (C): ││                                                    │     │                                                    │      │
+09 (C): ││                                                    │     │                                                    │      │
+10 (C): ││                                                    │     │                                                    │      │
+11 (C): ││                                                    │     │                                                    │      │
+12 (C): ││                                                    │     │                                                    │      │
+13 (C): ││                                                    │     │                                                    │      │
+14 (C): │└────────────────────────────────────────────────────┘     └────────────────────────────────────────────────────┘      │
 15 (C): │                                                                                                                       │
 16 (C): │                                                                                                                       │
 17 (C): │                                                                                                                       │
 18 (C): │                                                                                                                       │
 19 (C): └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
-
diff --git a/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout-3.snap b/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout-3.snap
index 13848a2b..07992d63 100644
--- a/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout-3.snap
+++ b/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout-3.snap
@@ -1,26 +1,24 @@
 ---
 source: zellij-server/src/tab/./unit/tab_integration_tests.rs
-assertion_line: 8043
 expression: snapshot
 ---
-00 (C): ┌ Pane #1 ──────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
-01 (C): │ ┌ Pane #2 ─────────────────────────────────── PIN [ ] ┐    ┌ Pane #3 ─────────────────────────────────── PIN [ ] ┐    │
-02 (C): │ │                                                     │    │                                                     │    │
-03 (C): │ │                                                     │    │                                                     │    │
-04 (C): │ │                                                     │    │                                                     │    │
-05 (C): │ │                                                     │    │                                                     │    │
-06 (C): │ │                                                     │    │                                                     │    │
-07 (C): │ │                                                     │    │                                                     │    │
-08 (C): │ │                                                     │    │                                                     │    │
-09 (C): │ │                                                     │    │                                                     │    │
-10 (C): │ └─────────────────────────────────────────────────────┘    └─────────────────────────────────────────────────────┘    │
-11 (C): │                             ┌ Pane #4 ─────────────────────────────────── PIN [ ] ┐                                   │
-12 (C): │                             │                                                     │                                   │
-13 (C): │                             │                                                     │                                   │
-14 (C): │                             │                                                     │                                   │
-15 (C): │                             │                                                     │                                   │
-16 (C): │                             │                                                     │                                   │
-17 (C): │                             │                                                     │                                   │
-18 (C): │                             │                                                     │                                   │
-19 (C): └─────────────────────────────└─────────────────────────────────────────────────────┘───────────────────────────────────┘
-
+00 (C): ┌┌ Pane #2 ────────────────────────────────── PIN [ ] ┐─────┌ Pane #3 ────────────────────────────────── PIN [ ] ┐──────┐
+01 (C): ││                                                    │     │                                                    │      │
+02 (C): ││                                                    │     │                                                    │      │
+03 (C): ││                                                    │     │                                                    │      │
+04 (C): ││                                                    │     │                                                    │      │
+05 (C): ││                                                    │     │                                                    │      │
+06 (C): ││                                                    │     │                                                    │      │
+07 (C): ││                                                    │     │                                                    │      │
+08 (C): ││                                                    │     │                                                    │      │
+09 (C): │└────────────────────────────────────────────────────┘     └────────────────────────────────────────────────────┘      │
+10 (C): │                                                                                                                       │
+11 (C): │                                ┌ Pane #4 ────────────────────────────────── PIN [ ] ┐                                 │
+12 (C): │                                │                                                    │                                 │
+13 (C): │                                │                                                    │                                 │
+14 (C): │                                │                                                    │                                 │
+15 (C): │                                │                                                    │                                 │
+16 (C): │                                │                                                    │                                 │
+17 (C): │                                │                                                    │                                 │
+18 (C): │                                │                                                    │                                 │
+19 (C): └────────────────────────────────└────────────────────────────────────────────────────┘─────────────────────────────────┘
diff --git a/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout.snap b/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout.snap
index 675409f8..2f15c3ca 100644
--- a/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout.snap
+++ b/zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__new_floating_pane_in_auto_layout.snap
@@ -1,6 +1,5 @@
 ---
 source: zellij-server/src/tab/./unit/tab_integration_tests.rs
-assertion_line: 8040
 expression: snapshot
 ---
 00 (C): ┌ Pane #1 ──────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
@@ -13,14 +12,13 @@ expression: snapshot
 07 (C): │                                                                                                                       │
 08 (C): │                                                                                                                       │
 09 (C): │                                                                                                                       │
-10 (C): │                                                            ┌ Pane #2 ──────────────────────────────────────── PIN [ ] ┐
-11 (C): │                                                            │                                                          │
-12 (C): │                                                            │                                                          │
-13 (C): │                                                            │                                                          │
-14 (C): │                                                            │                                                          │
-15 (C): │                                                            │                                                          │
-16 (C): │                                                            │                                                          │
-17 (C): │                                                            │                                                          │
-18 (C): │                                                            │                                                          │
-19 (C): └────────────────────────────────────────────────────────────└──────────────────────────────────────────────────────────┘
-
+10 (C): │                                                           ┌ Pane #2 ──────────────────────────────────────── PIN [ ] ┐│
+11 (C): │                                                           │                                                          ││
+12 (C): │                                                           │                                                          ││
+13 (C): │                                                           │                                                          ││
+14 (C): │                                                           │                                                          ││
+15 (C): │                                                           │                                                          ││
+16 (C): │                                                           │                                                          ││
+17 (C): │                                                           │                                                          ││
+18 (C): │                                                           │                                                          ││
+19 (C): └───────────────────────────────────────────────────────────└──────────────────────────────────────────────────────────┘┘
diff --git a/zellij-server/src/tab/unit/tab_integration_tests.rs b/zellij-server/src/tab/unit/tab_integration_tests.rs
index 6eb39eae..d80fb8b7 100644
--- a/zellij-server/src/tab/unit/tab_integration_tests.rs
+++ b/zellij-server/src/tab/unit/tab_integration_tests.rs
@@ -9405,7 +9405,7 @@ fn new_floating_pane_in_auto_layout() {
         stacked_resize,
     );
 
-    let mut expected_cursor_coordinates = vec![(62, 11), (62, 6), (31, 12)];
+    let mut expected_cursor_coordinates = vec![(61, 11), (61, 6), (34, 12)];
     for i in 0..3 {
         let new_pane_id = i + 2;
         tab.new_pane(
diff --git a/zellij-server/src/unit/screen_tests.rs b/zellij-server/src/unit/screen_tests.rs
index b305a28f..75b427c3 100644
--- a/zellij-server/src/unit/screen_tests.rs
+++ b/zellij-server/src/unit/screen_tests.rs
@@ -1497,6 +1497,229 @@ fn open_new_floating_pane_with_custom_coordinates_exceeding_viewport() {
 }
 
 #[test]
+fn floating_pane_auto_centers_horizontally_with_only_width() {
+    let size = Size {
+        cols: 120,
+        rows: 20,
+    };
+    let mut screen = create_new_screen(size, true);
+
+    new_tab(&mut screen, 1, 0);
+    let active_tab = screen.get_active_tab_mut(1).unwrap();
+    active_tab
+        .new_pane(
+            PaneId::Terminal(2),
+            None,
+            None,
+            false,
+            true,
+            NewPanePlacement::Floating(Some(FloatingPaneCoordinates {
+                x: None,
+                y: Some(SplitSize::Fixed(5)),
+                width: Some(SplitSize::Fixed(60)),
+                height: Some(SplitSize::Fixed(10)),
+                pinned: None,
+            })),
+            Some(1),
+            None,
+        )
+        .unwrap();
+    let active_pane = active_tab.get_active_pane(1).unwrap();
+    assert_eq!(active_pane.x(), 30, "x centered: (120-60)/2 = 30");
+    assert_eq!(active_pane.y(), 5, "y explicitly set");
+    assert_eq!(active_pane.cols(), 60, "width set");
+    assert_eq!(active_pane.rows(), 10, "height set");
+}
+
+#[test]
+fn floating_pane_auto_centers_vertically_with_only_height() {
+    let size = Size {
+        cols: 120,
+        rows: 40,
+    };
+    let mut screen = create_new_screen(size, true);
+
+    new_tab(&mut screen, 1, 0);
+    let active_tab = screen.get_active_tab_mut(1).unwrap();
+    active_tab
+        .new_pane(
+            PaneId::Terminal(2),
+            None,
+            None,
+            false,
+            true,
+            NewPanePlacement::Floating(Some(FloatingPaneCoordinates {
+                x: Some(SplitSize::Fixed(10)),
+                y: None,
+                width: Some(SplitSize::Fixed(50)),
+                height: Some(SplitSize::Fixed(20)),
+                pinned: None,
+            })),
+            Some(1),
+            None,
+        )
+        .unwrap();
+    let active_pane = active_tab.get_active_pane(1).unwrap();
+    assert_eq!(active_pane.x(), 10, "x explicitly set");
+    assert_eq!(active_pane.y(), 10, "y centered: (40-20)/2 = 10");
+    assert_eq!(active_pane.cols(), 50, "width set");
+    assert_eq!(active_pane.rows(), 20, "height set");
+}
+
+#[test]
+fn floating_pane_auto_centers_both_axes_with_only_size() {
+    let size = Size {
+        cols: 120,
+        rows: 40,
+    };
+    let mut screen = create_new_screen(size, true);
+
+    new_tab(&mut screen, 1, 0);
+    let active_tab = screen.get_active_tab_mut(1).unwrap();
+    active_tab
+        .new_pane(
+            PaneId::Terminal(2),
+            None,
+            None,
+            false,
+            true,
+            NewPanePlacement::Floating(Some(FloatingPaneCoordinates {
+                x: None,
+                y: None,
+                width: Some(SplitSize::Fixed(80)),
+                height: Some(SplitSize::Fixed(30)),
+                pinned: None,
+            })),
+            Some(1),
+            None,
+        )
+        .unwrap();
+    let active_pane = active_tab.get_active_pane(1).unwrap();
+    assert_eq!(active_pane.x(), 20, "x centered: (120-80)/2 = 20");
+    assert_eq!(active_pane.y(), 5, "y centered: (40-30)/2 = 5");
+    assert_eq!(active_pane.cols(), 80, "width set");
+    assert_eq!(active_pane.rows(), 30, "height set");
+}
+
+#[test]
+fn floating_pane_respects_explicit_coordinates_with_size() {
+    let size = Size {
+        cols: 120,
+        rows: 40,
+    };
+    let mut screen = create_new_screen(size, true);
+
+    new_tab(&mut screen, 1, 0);
+    let active_tab = screen.get_active_tab_mut(1).unwrap();
+    active_tab
+        .new_pane(
+            PaneId::Terminal(2),
+            None,
+            None,
+            false,
+            true,
+            NewPanePlacement::Floating(Some(FloatingPaneCoordinates {
+                x: Some(SplitSize::Fixed(15)),
+                y: Some(SplitSize::Fixed(8)),
+                width: Some(SplitSize::Fixed(80)),
+                height: Some(SplitSize::Fixed(30)),
+                pinned: None,
+            })),
+            Some(1),
+            None,
+        )
+        .unwrap();
+    let active_pane = active_tab.get_active_pane(1).unwrap();
+    assert_eq!(active_pane.x(), 15, "x explicitly set, not centered");
+    assert_eq!(active_pane.y(), 8, "y explicitly set, not centered");
+    assert_eq!(active_pane.cols(), 80, "width set");
+    assert_eq!(active_pane.rows(), 30, "height set");
+}
+
+#[test]
+fn floating_pane_centers_with_percentage_width() {
+    let size = Size {
+        cols: 120,
+        rows: 40,
+    };
+    let mut screen = create_new_screen(size, true);
+
+    new_tab(&mut screen, 1, 0);
+    let active_tab = screen.get_active_tab_mut(1).unwrap();
+    active_tab
+        .new_pane(
+            PaneId::Terminal(2),
+            None,
+            None,
+            false,
+            true,
+            NewPanePlacement::Floating(Some(FloatingPaneCoordinates {
+                x: None,
+                y: Some(SplitSize::Fixed(5)),
+                width: Some(SplitSize::Percent(50)),
+                height: Some(SplitSize::Fixed(20)),
+                pinned: None,
+            })),
+            Some(1),
+            None,
+        )
+        .unwrap();
+    let active_pane = active_tab.get_active_pane(1).unwrap();
+    let expected_width = ((50.0_f64 / 100.0) * 120.0).floor() as usize;
+    let expected_x = (120 - expected_width) / 2;
+    assert_eq!(active_pane.cols(), expected_width, "width is 50% of 120");
+    assert_eq!(
+        active_pane.x(),
+        expected_x,
+        "x centered based on calculated width"
+    );
+    assert_eq!(active_pane.y(), 5, "y explicitly set");
+}
+
+#[test]
+fn floating_pane_centers_large_pane_safely() {
+    let size = Size {
+        cols: 100,
+        rows: 30,
+    };
+    let mut screen = create_new_screen(size, true);
+
+    new_tab(&mut screen, 1, 0);
+    let active_tab = screen.get_active_tab_mut(1).unwrap();
+    active_tab
+        .new_pane(
+            PaneId::Terminal(2),
+            None,
+            None,
+            false,
+            true,
+            NewPanePlacement::Floating(Some(FloatingPaneCoordinates {
+                x: None,
+                y: None,
+                width: Some(SplitSize::Fixed(150)),
+                height: Some(SplitSize::Fixed(50)),
+                pinned: None,
+            })),
+            Some(1),
+            None,
+        )
+        .unwrap();
+    let active_pane = active_tab.get_active_pane(1).unwrap();
+    assert_eq!(
+        active_pane.x(),
+        0,
+        "x is 0 when pane larger than viewport (saturating_sub)"
+    );
+    assert_eq!(
+        active_pane.y(),
+        0,
+        "y is 0 when pane larger than viewport (saturating_sub)"
+    );
+    assert!(active_pane.cols() <= 100, "width clamped to viewport");
+    assert!(active_pane.rows() <= 30, "height clamped to viewport");
+}
+
+#[test]
 pub fn mouse_hover_effect() {
     let size = Size {
         cols: 130,
diff --git a/zellij-utils/src/input/layout.rs b/zellij-utils/src/input/layout.rs
index 8ba81159..ae7d85a1 100644
--- a/zellij-utils/src/input/layout.rs
+++ b/zellij-utils/src/input/layout.rs
@@ -73,6 +73,24 @@ pub enum SplitSize {
     Fixed(usize), // An absolute number of columns or rows
 }
 
+impl From<PercentOrFixed> for SplitSize {
+    fn from(pof: PercentOrFixed) -> Self {
+        match pof {
+            PercentOrFixed::Percent(p) => SplitSize::Percent(p),
+            PercentOrFixed::Fixed(f) => SplitSize::Fixed(f),
+        }
+    }
+}
+
+impl From<SplitSize> for PercentOrFixed {
+    fn from(ss: SplitSize) -> Self {
+        match ss {
+            SplitSize::Percent(p) => PercentOrFixed::Percent(p),
+            SplitSize::Fixed(f) => PercentOrFixed::Fixed(f),
+        }
+    }
+}
+
 impl SplitSize {
     pub fn to_fixed(&self, full_size: usize) -> usize {
         match self {
@@ -727,6 +745,14 @@ impl PercentOrFixed {
             },
         }
     }
+    pub fn to_fixed(&self, full_size: usize) -> usize {
+        match self {
+            PercentOrFixed::Percent(percent) => {
+                ((*percent as f64 / 100.0) * full_size as f64).floor() as usize
+            },
+            PercentOrFixed::Fixed(fixed) => *fixed,
+        }
+    }
 }
 
 impl PercentOrFixed {
diff --git a/zellij-utils/src/pane_size.rs b/zellij-utils/src/pane_size.rs
index 50c4229a..453e57c1 100644
--- a/zellij-utils/src/pane_size.rs
+++ b/zellij-utils/src/pane_size.rs
@@ -5,7 +5,7 @@ use std::{
 };
 
 use crate::data::FloatingPaneCoordinates;
-use crate::input::layout::{SplitDirection, SplitSize};
+use crate::input::layout::{PercentOrFixed, SplitDirection, SplitSize};
 use crate::position::Position;
 
 /// Contains the position and size of a [`Pane`], or more generally of any terminal, measured
@@ -250,23 +250,45 @@ impl PaneGeom {
             SplitDirection::Horizontal => self.rows.is_percent(),
         }
     }
+    pub fn apply_floating_pane_position(
+        &mut self,
+        x: Option<PercentOrFixed>,
+        y: Option<PercentOrFixed>,
+        width: Option<PercentOrFixed>,
+        height: Option<PercentOrFixed>,
+        viewport_cols: usize,
+        viewport_rows: usize,
+    ) {
+        if let Some(width) = &width {
+            self.cols = Dimension::fixed(width.to_fixed(viewport_cols));
+        }
+        if let Some(height) = &height {
+            self.rows = Dimension::fixed(height.to_fixed(viewport_rows));
+        }
+        self.x = match &x {
+            Some(x) => x.to_fixed(viewport_cols),
+            None if width.is_some() => viewport_cols.saturating_sub(self.cols.as_usize()) / 2,
+            None => self.x,
+        };
+        self.y = match &y {
+            Some(y) => y.to_fixed(viewport_rows),
+            None if height.is_some() => viewport_rows.saturating_sub(self.rows.as_usize()) / 2,
+            None => self.y,
+        };
+    }
     pub fn adjust_coordinates(
         &mut self,
         floating_pane_coordinates: FloatingPaneCoordinates,
         viewport: Viewport,
     ) {
-        if let Some(x) = floating_pane_coordinates.x {
-            self.x = x.to_fixed(viewport.cols);
-        }
-        if let Some(y) = floating_pane_coordinates.y {
-            self.y = y.to_fixed(viewport.rows);
-        }
-        if let Some(height) = floating_pane_coordinates.height {
-            self.rows = Dimension::from_split_size(height, viewport.rows);
-        }
-        if let Some(width) = floating_pane_coordinates.width {
-            self.cols = Dimension::from_split_size(width, viewport.cols);
-        }
+        self.apply_floating_pane_position(
+            floating_pane_coordinates.x.map(Into::into),
+            floating_pane_coordinates.y.map(Into::into),
+            floating_pane_coordinates.width.map(Into::into),
+            floating_pane_coordinates.height.map(Into::into),
+            viewport.cols,
+            viewport.rows,
+        );
         if self.x < viewport.x {
             self.x = viewport.x;
         } else if self.x > viewport.x + viewport.cols {