From d54e29d3758f8abd0f97508ff89de46e739a0931 Mon Sep 17 00:00:00 2001
From: Jim <jim.eckerlein@icloud.com>
Date: Thu, 20 Mar 2025 11:05:22 +0100
Subject: [PATCH] macOS: Add `movable_by_window_background` option to viewport
 (#5412)

Add an option called `movable_by_window_background` alongside a new
builder method. When set to true, the window is movable by dragging its
background ([Apple
Docs](https://developer.apple.com/documentation/appkit/nswindow/ismovablebywindowbackground))

This is exclusive to macOS systems, similar to `fullsize_content_view`.

* [x] I have followed the instructions in the PR template
---
 crates/egui-winit/src/lib.rs |  4 +++-
 crates/egui/src/viewport.rs  | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/crates/egui-winit/src/lib.rs b/crates/egui-winit/src/lib.rs
index e7c5ffe8..1c47d7eb 100644
--- a/crates/egui-winit/src/lib.rs
+++ b/crates/egui-winit/src/lib.rs
@@ -1615,6 +1615,7 @@ pub fn create_winit_window_attributes(
 
         // macOS:
         fullsize_content_view: _fullsize_content_view,
+        movable_by_window_background: _movable_by_window_background,
         title_shown: _title_shown,
         titlebar_buttons_shown: _titlebar_buttons_shown,
         titlebar_shown: _titlebar_shown,
@@ -1761,7 +1762,8 @@ pub fn create_winit_window_attributes(
             .with_title_hidden(!_title_shown.unwrap_or(true))
             .with_titlebar_buttons_hidden(!_titlebar_buttons_shown.unwrap_or(true))
             .with_titlebar_transparent(!_titlebar_shown.unwrap_or(true))
-            .with_fullsize_content_view(_fullsize_content_view.unwrap_or(false));
+            .with_fullsize_content_view(_fullsize_content_view.unwrap_or(false))
+            .with_movable_by_window_background(_movable_by_window_background.unwrap_or(false));
     }
 
     window_attributes
diff --git a/crates/egui/src/viewport.rs b/crates/egui/src/viewport.rs
index 791b34c7..9aba6991 100644
--- a/crates/egui/src/viewport.rs
+++ b/crates/egui/src/viewport.rs
@@ -291,6 +291,7 @@ pub struct ViewportBuilder {
 
     // macOS:
     pub fullsize_content_view: Option<bool>,
+    pub movable_by_window_background: Option<bool>,
     pub title_shown: Option<bool>,
     pub titlebar_buttons_shown: Option<bool>,
     pub titlebar_shown: Option<bool>,
@@ -432,6 +433,15 @@ impl ViewportBuilder {
         self
     }
 
+    /// macOS: Set to `true` to allow the window to be moved by dragging the background.
+    ///
+    /// Enabling this feature can result in unexpected behaviour with draggable UI widgets such as sliders.
+    #[inline]
+    pub fn with_movable_by_background(mut self, value: bool) -> Self {
+        self.movable_by_window_background = Some(value);
+        self
+    }
+
     /// macOS: Set to `false` to hide the window title.
     #[inline]
     pub fn with_title_shown(mut self, title_shown: bool) -> Self {
@@ -640,6 +650,7 @@ impl ViewportBuilder {
             visible: new_visible,
             drag_and_drop: new_drag_and_drop,
             fullsize_content_view: new_fullsize_content_view,
+            movable_by_window_background: new_movable_by_window_background,
             title_shown: new_title_shown,
             titlebar_buttons_shown: new_titlebar_buttons_shown,
             titlebar_shown: new_titlebar_shown,
@@ -825,6 +836,13 @@ impl ViewportBuilder {
             recreate_window = true;
         }
 
+        if new_movable_by_window_background.is_some()
+            && self.movable_by_window_background != new_movable_by_window_background
+        {
+            self.movable_by_window_background = new_movable_by_window_background;
+            recreate_window = true;
+        }
+
         if new_drag_and_drop.is_some() && self.drag_and_drop != new_drag_and_drop {
             self.drag_and_drop = new_drag_and_drop;
             recreate_window = true;