fix(macOS): fix incorrect window position on multi-monitor setups (#15250)

* fix(macOS): fix incorrect window position on multi-monitor setups

* avoid 'flash' on current monitor when targeting another display for fullscreen

* simplify fullscreen monitor selection

* change file

---------

Co-authored-by: Lucas Nogueira <lucas@tauri.app>

Author: polw1

.changes/fix-macos-initial-window-position.md

@@ -0,0 +1,6 @@
+---
+"tauri-runtime-wry": patch:bug
+"tauri": patch:bug
+---
+
+Fix initial window position when positioning it to another monitor.

crates/tauri-runtime-wry/src/lib.rs

@@ -692,6 +692,25 @@ impl From<Position> for PositionWrapper {
   }
 }
 
+#[cfg(desktop)]
+fn find_monitor_for_position(
+  monitors: impl Iterator<Item = MonitorHandle>,
+  window_position: TaoPosition,
+) -> Option<MonitorHandle> {
+  monitors.into_iter().find(|m| {
+    let monitor_pos = m.position();
+    let monitor_size = m.size();
+
+    // type annotations required for 32bit targets.
+    let window_position = window_position.to_physical::<i32>(m.scale_factor());
+
+    monitor_pos.x <= window_position.x
+      && window_position.x < monitor_pos.x + monitor_size.width as i32
+      && monitor_pos.y <= window_position.y
+      && window_position.y < monitor_pos.y + monitor_size.height as i32
+  })
+}
+
 #[derive(Debug, Clone)]
 pub struct UserAttentionTypeWrapper(pub TaoUserAttentionType);
 
@@ -4489,18 +4508,7 @@ fn create_window<T: UserEvent, F: Fn(RawWindow) + Send + 'static>(
   #[cfg(desktop)]
   if window_builder.prevent_overflow.is_some() || window_builder.center {
     let monitor = if let Some(window_position) = &window_builder.inner.window.position {
-      event_loop.available_monitors().find(|m| {
-        let monitor_pos = m.position();
-        let monitor_size = m.size();
-
-        // type annotations required for 32bit targets.
-        let window_position = window_position.to_physical::<i32>(m.scale_factor());
-
-        monitor_pos.x <= window_position.x
-          && window_position.x < monitor_pos.x + monitor_size.width as i32
-          && monitor_pos.y <= window_position.y
-          && window_position.y < monitor_pos.y + monitor_size.height as i32
-      })
+      find_monitor_for_position(event_loop.available_monitors(), *window_position)
     } else {
       event_loop.primary_monitor()
     };
@@ -4567,12 +4575,38 @@ fn create_window<T: UserEvent, F: Fn(RawWindow) + Send + 'static>(
     }
   };
 
+  #[cfg(any(target_os = "macos", target_os = "linux"))]
+  let (initial_position, is_fullscreen) = (
+    window_builder.inner.window.position,
+    window_builder.inner.window.fullscreen.is_some(),
+  );
+
+  // If fullscreen is requested with an explicit position, resolve the target
+  // monitor up front so the window is created fullscreen on that display.
+  #[cfg(any(target_os = "macos", target_os = "linux"))]
+  if let (true, Some(position)) = (is_fullscreen, initial_position) {
+    if let Some(target_monitor) =
+      find_monitor_for_position(event_loop.available_monitors(), position)
+    {
+      window_builder.inner.window.fullscreen = Some(Fullscreen::Borderless(Some(target_monitor)));
+    }
+  }
+
   let window = window_builder
     .inner
     .build(event_loop)
     .inspect_err(|e| log::error!("Error creating window: {e:?}"))
     .map_err(|_| Error::CreateWindow)?;
 
+  // On macOS, `with_position` uses the content origin; the title bar is added
+  // above it. `set_outer_position` is needed for precise window placement.
+  #[cfg(target_os = "macos")]
+  if !is_fullscreen {
+    if let Some(position) = initial_position {
+      window.set_outer_position(position);
+    }
+  }
+
   #[cfg(feature = "tracing")]
   {
     drop(window_create_span);