Add SetOutlineDepth component.

src/computed.rs

@@ -6,7 +6,15 @@ pub struct ComputedOutlineDepth {
     pub(crate) origin: Vec3,
 }
 
-/// A component which specifies that this entity lies at the same depth as its parent.
+/// A component which specifies how the outline depth should be computed.
+#[derive(Clone, Component)]
+#[non_exhaustive]
+pub enum SetOutlineDepth {
+    /// A flat plane facing the camera and intersecting the specified point in model-space.
+    Flat { model_origin: Vec3 },
+}
+
+/// A component which specifies that this outline lies at the same depth as its parent.
 #[derive(Clone, Component, Default)]
 pub struct InheritOutlineDepth;
 
@@ -17,6 +25,7 @@ pub(crate) fn compute_outline_depth(
             &mut ComputedOutlineDepth,
             &GlobalTransform,
             Changed<GlobalTransform>,
+            Option<(&SetOutlineDepth, Changed<SetOutlineDepth>)>,
             Option<(&Children, Changed<Children>)>,
         ),
         Without<InheritOutlineDepth>,
@@ -24,17 +33,28 @@ pub(crate) fn compute_outline_depth(
     mut computed_query: Query<(&mut ComputedOutlineDepth, Changed<InheritOutlineDepth>)>,
     child_query: Query<(&Children, Changed<Children>)>,
 ) {
-    for (mut computed, transform, changed_transform, children) in root_query.iter_mut() {
+    for (mut computed, transform, changed_transform, set_depth, children) in root_query.iter_mut() {
-        if changed_transform {
+        let mut changed = changed_transform;
+        if changed {
+            let origin = if let Some((sd, sd_changed)) = set_depth {
+                changed |= sd_changed;
+                match sd {
+                    SetOutlineDepth::Flat {
+                        model_origin: origin,
+                    } => *origin,
+                }
+            } else {
+                Vec3::ZERO
+            };
             let matrix = transform.compute_matrix();
-            computed.origin = matrix.project_point3(Vec3::ZERO);
+            computed.origin = matrix.project_point3(origin);
         }
         if let Some((cs, changed_children)) = children {
-            let changed2 = changed_children || changed_transform;
+            changed |= changed_children;
             for child in cs.iter() {
                 propagate_outline_depth(
                     &computed,
-                    changed2,
+                    changed,
                     *child,
                     &mut computed_query,
                     &child_query,
@@ -46,21 +66,22 @@ pub(crate) fn compute_outline_depth(
 
 fn propagate_outline_depth(
     root_computed: &ComputedOutlineDepth,
-    changed: bool,
+    mut changed: bool,
     entity: Entity,
     computed_query: &mut Query<(&mut ComputedOutlineDepth, Changed<InheritOutlineDepth>)>,
     child_query: &Query<(&Children, Changed<Children>)>,
 ) {
     if let Ok((mut computed, changed_inherit)) = computed_query.get_mut(entity) {
-        if changed_inherit || changed {
+        changed |= changed_inherit;
+        if changed {
             *computed = root_computed.clone();
         }
         if let Ok((cs, changed_children)) = child_query.get(entity) {
-            let changed2 = changed_children || changed_inherit || changed;
+            changed |= changed_children;
             for child in cs.iter() {
                 propagate_outline_depth(
                     root_computed,
-                    changed2,
+                    changed,
                     *child,
                     computed_query,
                     child_query,