Store offscreen element id on Mapped instead of user data

We don't need user data for this.

src/niri.rs

@@ -29,7 +29,7 @@ use smithay::backend::renderer::element::utils::{
     select_dmabuf_feedback, Relocate, RelocateRenderElement,
 };
 use smithay::backend::renderer::element::{
-    default_primary_scanout_output_compare, Id, Kind, PrimaryScanoutOutput, RenderElementStates,
+    default_primary_scanout_output_compare, Kind, PrimaryScanoutOutput, RenderElementStates,
 };
 use smithay::backend::renderer::gles::GlesRenderer;
 use smithay::backend::renderer::sync::SyncPoint;
@@ -503,9 +503,6 @@ pub enum CenterCoords {
     Both,
 }
 
-#[derive(Default)]
-pub struct WindowOffscreenId(pub RefCell<Option<Id>>);
-
 impl RedrawState {
     fn queue_redraw(self) -> Self {
         match self {
@@ -3796,12 +3793,7 @@ impl Niri {
 
         for mapped in self.layout.windows_for_output(output) {
             let win = &mapped.window;
-            let offscreen_id = win
+            let offscreen_id = mapped.offscreen_element_id().clone();
-                .user_data()
-                .get_or_insert(WindowOffscreenId::default)
-                .0
-                .borrow();
-            let offscreen_id = offscreen_id.as_ref();
 
             win.with_surfaces(|surface, states| {
                 let surface_primary_scanout_output = states
@@ -3811,7 +3803,7 @@ impl Niri {
                     .lock()
                     .unwrap()
                     .update_from_render_element_states(
-                        offscreen_id.cloned().unwrap_or_else(|| surface.into()),
+                        offscreen_id.clone().unwrap_or_else(|| surface.into()),
                         output,
                         render_element_states,
                         |_, _, output, _| output,

src/window/mapped.rs

@@ -1,4 +1,4 @@
-use std::cell::{Cell, RefCell};
+use std::cell::{Cell, Ref, RefCell};
 use std::time::Duration;
 
 use niri_config::{Color, CornerRadius, GradientInterpolation, WindowRule};
@@ -24,7 +24,6 @@ use crate::layout::{
     ConfigureIntent, InteractiveResizeData, LayoutElement, LayoutElementRenderElement,
     LayoutElementRenderSnapshot,
 };
-use crate::niri::WindowOffscreenId;
 use crate::niri_render_elements;
 use crate::render_helpers::border::BorderRenderElement;
 use crate::render_helpers::renderer::NiriRenderer;
@@ -71,6 +70,11 @@ pub struct Mapped {
     /// resizes immediately, without waiting for a 1 second throttled callback.
     needs_frame_callback: bool,
 
+    /// Id of the offscreen element rendered in place of this window.
+    ///
+    /// If `None`, then the window is not offscreened.
+    offscreen_element_id: RefCell<Option<Id>>,
+
     /// Whether this window has the keyboard focus.
     is_focused: bool,
 
@@ -188,6 +192,7 @@ impl Mapped {
             need_to_recompute_rules: false,
             needs_configure: false,
             needs_frame_callback: false,
+            offscreen_element_id: RefCell::new(None),
             is_focused: false,
             is_active_in_column: true,
             is_floating: false,
@@ -252,6 +257,10 @@ impl Mapped {
         self.credentials.as_ref()
     }
 
+    pub fn offscreen_element_id(&self) -> Ref<Option<Id>> {
+        self.offscreen_element_id.borrow()
+    }
+
     pub fn is_focused(&self) -> bool {
         self.is_focused
     }
@@ -743,11 +752,7 @@ impl LayoutElement for Mapped {
     }
 
     fn set_offscreen_element_id(&self, id: Option<Id>) {
-        let data = self
+        self.offscreen_element_id.replace(id);
-            .window
-            .user_data()
-            .get_or_insert(WindowOffscreenId::default);
-        data.0.replace(id);
     }
 
     fn set_activated(&mut self, active: bool) {