Correctly feature gate custom_cursor (#16093)

# Objective

Currently there's no way to change the window's cursor icon with the
`custom_cursor` feature **disabled**. You should still be able to set
system cursor icons.

Connections:

- https://github.com/bevyengine/bevy/pull/15649

## Solution

Move some `custom_cursor` feature gates around, as to expose the
`CursorIcon` type again.

Note this refactoring was mainly piloted by hunting after the compiler
warnings -- I shouldn't have missed anything, but FYI.

## Testing

Disabled the `custom_cursor` feature, ran the `window_settings` example.

crates/bevy_winit/src/converters.rs

@@ -6,7 +6,6 @@ use bevy_input::{
     ButtonState,
 };
 use bevy_math::{CompassOctant, Vec2};
-#[cfg(feature = "custom_cursor")]
 use bevy_window::SystemCursorIcon;
 use bevy_window::{EnabledButtons, WindowLevel, WindowTheme};
 use winit::keyboard::{Key, NamedKey, NativeKey};
@@ -630,7 +629,6 @@ pub fn convert_native_key(native_key: &NativeKey) -> bevy_input::keyboard::Nativ
     }
 }
 
-#[cfg(feature = "custom_cursor")]
 /// Converts a [`SystemCursorIcon`] to a [`winit::window::CursorIcon`].
 pub fn convert_system_cursor_icon(cursor_icon: SystemCursorIcon) -> winit::window::CursorIcon {
     match cursor_icon {

crates/bevy_winit/src/cursor.rs

@@ -2,11 +2,18 @@
 
 use crate::{
     converters::convert_system_cursor_icon,
-    state::{CursorSource, CustomCursorCache, CustomCursorCacheKey, PendingCursor},
+    state::{CursorSource, PendingCursor},
+};
+#[cfg(feature = "custom_cursor")]
+use crate::{
+    state::{CustomCursorCache, CustomCursorCacheKey},
     WinitCustomCursor,
 };
 use bevy_app::{App, Last, Plugin};
+#[cfg(feature = "custom_cursor")]
 use bevy_asset::{Assets, Handle};
+#[cfg(feature = "custom_cursor")]
+use bevy_ecs::system::Res;
 use bevy_ecs::{
     change_detection::DetectChanges,
     component::Component,
@@ -14,21 +21,27 @@ use bevy_ecs::{
     observer::Trigger,
     query::With,
     reflect::ReflectComponent,
-    system::{Commands, Local, Query, Res},
+    system::{Commands, Local, Query},
     world::{OnRemove, Ref},
 };
+#[cfg(feature = "custom_cursor")]
 use bevy_image::Image;
 use bevy_reflect::{std_traits::ReflectDefault, Reflect};
-use bevy_utils::{tracing::warn, HashSet};
+#[cfg(feature = "custom_cursor")]
+use bevy_utils::tracing::warn;
+use bevy_utils::HashSet;
 use bevy_window::{SystemCursorIcon, Window};
+#[cfg(feature = "custom_cursor")]
 use wgpu_types::TextureFormat;
 
 pub(crate) struct CursorPlugin;
 
 impl Plugin for CursorPlugin {
     fn build(&self, app: &mut App) {
+        #[cfg(feature = "custom_cursor")]
+        app.init_resource::<CustomCursorCache>();
+
         app.register_type::<CursorIcon>()
-            .init_resource::<CustomCursorCache>()
             .add_systems(Last, update_cursors);
 
         app.add_observer(on_remove_cursor_icon);
@@ -39,6 +52,7 @@ impl Plugin for CursorPlugin {
 #[derive(Component, Debug, Clone, Reflect, PartialEq, Eq)]
 #[reflect(Component, Debug, Default, PartialEq)]
 pub enum CursorIcon {
+    #[cfg(feature = "custom_cursor")]
     /// Custom cursor image.
     Custom(CustomCursor),
     /// System provided cursor icon.
@@ -57,12 +71,14 @@ impl From<SystemCursorIcon> for CursorIcon {
     }
 }
 
+#[cfg(feature = "custom_cursor")]
 impl From<CustomCursor> for CursorIcon {
     fn from(cursor: CustomCursor) -> Self {
         CursorIcon::Custom(cursor)
     }
 }
 
+#[cfg(feature = "custom_cursor")]
 /// Custom cursor image data.
 #[derive(Debug, Clone, Reflect, PartialEq, Eq, Hash)]
 pub enum CustomCursor {
@@ -90,8 +106,8 @@ pub enum CustomCursor {
 fn update_cursors(
     mut commands: Commands,
     windows: Query<(Entity, Ref<CursorIcon>), With<Window>>,
-    cursor_cache: Res<CustomCursorCache>,
-    images: Res<Assets<Image>>,
+    #[cfg(feature = "custom_cursor")] cursor_cache: Res<CustomCursorCache>,
+    #[cfg(feature = "custom_cursor")] images: Res<Assets<Image>>,
     mut queue: Local<HashSet<Entity>>,
 ) {
     for (entity, cursor) in windows.iter() {
@@ -100,6 +116,7 @@ fn update_cursors(
         }
 
         let cursor_source = match cursor.as_ref() {
+            #[cfg(feature = "custom_cursor")]
             CursorIcon::Custom(CustomCursor::Image { handle, hotspot }) => {
                 let cache_key = CustomCursorCacheKey::Asset(handle.id());
 
@@ -170,6 +187,7 @@ fn on_remove_cursor_icon(trigger: Trigger<OnRemove, CursorIcon>, mut commands: C
         ))));
 }
 
+#[cfg(feature = "custom_cursor")]
 /// Returns the image data as a `Vec<u8>`.
 /// Only supports rgba8 and rgba32float formats.
 fn image_to_rgba_pixels(image: &Image) -> Option<Vec<u8>> {

crates/bevy_winit/src/lib.rs

@@ -44,7 +44,6 @@ use crate::{
 
 pub mod accessibility;
 mod converters;
-#[cfg(feature = "custom_cursor")]
 pub mod cursor;
 mod state;
 mod system;
@@ -136,7 +135,6 @@ impl<T: Event> Plugin for WinitPlugin<T> {
             );
 
         app.add_plugins(AccessKitPlugin);
-        #[cfg(feature = "custom_cursor")]
         app.add_plugins(cursor::CursorPlugin);
 
         let event_loop = event_loop_builder

crates/bevy_winit/src/state.rs

@@ -158,19 +158,19 @@ pub enum CustomCursorCacheKey {
 #[derive(Debug, Clone, Default, Resource)]
 pub struct CustomCursorCache(pub HashMap<CustomCursorCacheKey, winit::window::CustomCursor>);
 
-#[cfg(feature = "custom_cursor")]
 /// A source for a cursor. Consumed by the winit event loop.
 #[derive(Debug)]
 pub enum CursorSource {
+    #[cfg(feature = "custom_cursor")]
     /// A custom cursor was identified to be cached, no reason to recreate it.
     CustomCached(CustomCursorCacheKey),
+    #[cfg(feature = "custom_cursor")]
     /// A custom cursor was not cached, so it needs to be created by the winit event loop.
     Custom((CustomCursorCacheKey, winit::window::CustomCursorSource)),
     /// A system cursor was requested.
     System(winit::window::CursorIcon),
 }
 
-#[cfg(feature = "custom_cursor")]
 /// Component that indicates what cursor should be used for a window. Inserted
 /// automatically after changing `CursorIcon` and consumed by the winit event
 /// loop.
@@ -560,6 +560,8 @@ impl<T: Event> ApplicationHandler<T> for WinitAppRunnerState<T> {
                 self.run_app_update();
                 #[cfg(feature = "custom_cursor")]
                 self.update_cursors(event_loop);
+                #[cfg(not(feature = "custom_cursor"))]
+                self.update_cursors();
                 self.ran_update_since_last_redraw = true;
             } else {
                 self.redraw_requested = true;
@@ -787,15 +789,23 @@ impl<T: Event> WinitAppRunnerState<T> {
             .send_batch(buffered_events);
     }
 
+    fn update_cursors(&mut self, #[cfg(feature = "custom_cursor")] event_loop: &ActiveEventLoop) {
         #[cfg(feature = "custom_cursor")]
-    fn update_cursors(&mut self, event_loop: &ActiveEventLoop) {
         let mut windows_state: SystemState<(
             NonSendMut<WinitWindows>,
             ResMut<CustomCursorCache>,
             Query<(Entity, &mut PendingCursor), Changed<PendingCursor>>,
         )> = SystemState::new(self.world_mut());
+        #[cfg(feature = "custom_cursor")]
         let (winit_windows, mut cursor_cache, mut windows) =
             windows_state.get_mut(self.world_mut());
+        #[cfg(not(feature = "custom_cursor"))]
+        let mut windows_state: SystemState<(
+            NonSendMut<WinitWindows>,
+            Query<(Entity, &mut PendingCursor), Changed<PendingCursor>>,
+        )> = SystemState::new(self.world_mut());
+        #[cfg(not(feature = "custom_cursor"))]
+        let (winit_windows, mut windows) = windows_state.get_mut(self.world_mut());
 
         for (entity, mut pending_cursor) in windows.iter_mut() {
             let Some(winit_window) = winit_windows.get_window(entity) else {
@@ -806,6 +816,7 @@ impl<T: Event> WinitAppRunnerState<T> {
             };
 
             let final_cursor: winit::window::Cursor = match pending_cursor {
+                #[cfg(feature = "custom_cursor")]
                 CursorSource::CustomCached(cache_key) => {
                     let Some(cached_cursor) = cursor_cache.0.get(&cache_key) else {
                         error!("Cursor should have been cached, but was not found");
@@ -813,6 +824,7 @@ impl<T: Event> WinitAppRunnerState<T> {
                     };
                     cached_cursor.clone().into()
                 }
+                #[cfg(feature = "custom_cursor")]
                 CursorSource::Custom((cache_key, cursor)) => {
                     let custom_cursor = event_loop.create_custom_cursor(cursor);
                     cursor_cache.0.insert(cache_key, custom_cursor.clone());

examples/window/window_settings.rs

@@ -1,12 +1,14 @@
 //! Illustrates how to change window settings and shows how to affect
 //! the mouse pointer in various ways.
 
+#[cfg(feature = "custom_cursor")]
+use bevy::winit::cursor::CustomCursor;
 use bevy::{
     core::FrameCount,
     diagnostic::{FrameTimeDiagnosticsPlugin, LogDiagnosticsPlugin},
     prelude::*,
     window::{CursorGrabMode, PresentMode, SystemCursorIcon, WindowLevel, WindowTheme},
-    winit::cursor::{CursorIcon, CustomCursor},
+    winit::cursor::CursorIcon,
 };
 
 fn main() {
@@ -152,12 +154,16 @@ fn toggle_theme(mut window: Single<&mut Window>, input: Res<ButtonInput<KeyCode>
 #[derive(Resource)]
 struct CursorIcons(Vec<CursorIcon>);
 
-fn init_cursor_icons(mut commands: Commands, asset_server: Res<AssetServer>) {
+fn init_cursor_icons(
+    mut commands: Commands,
+    #[cfg(feature = "custom_cursor")] asset_server: Res<AssetServer>,
+) {
     commands.insert_resource(CursorIcons(vec![
         SystemCursorIcon::Default.into(),
         SystemCursorIcon::Pointer.into(),
         SystemCursorIcon::Wait.into(),
         SystemCursorIcon::Text.into(),
+        #[cfg(feature = "custom_cursor")]
         CustomCursor::Image {
             handle: asset_server.load("branding/icon.png"),
             hotspot: (128, 128),