bevy_ui compilation (#19858)

# Objective

- `bevy_ui` has errors and warnings when building independently

## Solution

- properly use the `bevy_ui_picking_backend` feature

## Testing

`cargo build -p bevy_ui`

crates/bevy_ui/src/focus.rs

@@ -1,7 +1,4 @@
-use crate::{
-    picking_backend::clip_check_recursive, ui_transform::UiGlobalTransform, ComputedNode,
-    ComputedNodeTarget, Node, UiStack,
-};
+use crate::{ui_transform::UiGlobalTransform, ComputedNode, ComputedNodeTarget, Node, UiStack};
 use bevy_ecs::{
     change_detection::DetectChangesMut,
     entity::{ContainsEntity, Entity},
@@ -322,3 +319,27 @@ pub fn ui_focus_system(
         }
     }
 }
+
+/// Walk up the tree child-to-parent checking that `point` is not clipped by any ancestor node.
+pub fn clip_check_recursive(
+    point: Vec2,
+    entity: Entity,
+    clipping_query: &Query<'_, '_, (&ComputedNode, &UiGlobalTransform, &Node)>,
+    child_of_query: &Query<&ChildOf>,
+) -> bool {
+    if let Ok(child_of) = child_of_query.get(entity) {
+        let parent = child_of.0;
+        if let Ok((computed_node, transform, node)) = clipping_query.get(parent) {
+            if !computed_node
+                .resolve_clip_rect(node.overflow, node.overflow_clip_margin)
+                .contains(transform.inverse().transform_point2(point))
+            {
+                // The point is clipped and should be ignored by picking
+                return false;
+            }
+        }
+        return clip_check_recursive(point, parent, clipping_query, child_of_query);
+    }
+    // Reached root, point unclipped by all ancestors
+    true
+}

crates/bevy_ui/src/picking_backend.rs

@@ -24,7 +24,7 @@
 
 #![deny(missing_docs)]
 
-use crate::{prelude::*, ui_transform::UiGlobalTransform, UiStack};
+use crate::{clip_check_recursive, prelude::*, ui_transform::UiGlobalTransform, UiStack};
 use bevy_app::prelude::*;
 use bevy_ecs::{prelude::*, query::QueryData};
 use bevy_math::Vec2;
@@ -252,27 +252,3 @@ pub fn ui_picking(
         output.write(PointerHits::new(*pointer, picks, order));
     }
 }
-
-/// Walk up the tree child-to-parent checking that `point` is not clipped by any ancestor node.
-pub fn clip_check_recursive(
-    point: Vec2,
-    entity: Entity,
-    clipping_query: &Query<'_, '_, (&ComputedNode, &UiGlobalTransform, &Node)>,
-    child_of_query: &Query<&ChildOf>,
-) -> bool {
-    if let Ok(child_of) = child_of_query.get(entity) {
-        let parent = child_of.0;
-        if let Ok((computed_node, transform, node)) = clipping_query.get(parent) {
-            if !computed_node
-                .resolve_clip_rect(node.overflow, node.overflow_clip_margin)
-                .contains(transform.inverse().transform_point2(point))
-            {
-                // The point is clipped and should be ignored by picking
-                return false;
-            }
-        }
-        return clip_check_recursive(point, parent, clipping_query, child_of_query);
-    }
-    // Reached root, point unclipped by all ancestors
-    true
-}

crates/bevy_ui/src/widget/viewport.rs

@@ -2,22 +2,32 @@ use bevy_asset::Assets;
 use bevy_ecs::{
     component::Component,
     entity::Entity,
-    event::EventReader,
     query::{Changed, Or},
     reflect::ReflectComponent,
-    system::{Commands, Query, Res, ResMut},
+    system::{Query, ResMut},
+};
+#[cfg(feature = "bevy_ui_picking_backend")]
+use bevy_ecs::{
+    event::EventReader,
+    system::{Commands, Res},
 };
 use bevy_image::{Image, ToExtents};
-use bevy_math::{Rect, UVec2};
+#[cfg(feature = "bevy_ui_picking_backend")]
+use bevy_math::Rect;
+use bevy_math::UVec2;
 #[cfg(feature = "bevy_ui_picking_backend")]
 use bevy_picking::{
     events::PointerState,
     hover::HoverMap,
     pointer::{Location, PointerId, PointerInput, PointerLocation},
 };
+#[cfg(feature = "bevy_ui_picking_backend")]
 use bevy_platform::collections::HashMap;
 use bevy_reflect::Reflect;
-use bevy_render::camera::{Camera, NormalizedRenderTarget};
+use bevy_render::camera::Camera;
+#[cfg(feature = "bevy_ui_picking_backend")]
+use bevy_render::camera::NormalizedRenderTarget;
+#[cfg(feature = "bevy_ui_picking_backend")]
 use bevy_transform::components::GlobalTransform;
 #[cfg(feature = "bevy_ui_picking_backend")]
 use uuid::Uuid;