avm2: Implement `DisplayObjectContainer.getChildAt`.

This test doesn't work yet because it needs `avm2-domainscope` to get merged in.

core/src/avm2/globals/flash/display/displayobjectcontainer.rs

@@ -4,9 +4,11 @@ use crate::avm2::activation::Activation;
 use crate::avm2::class::Class;
 use crate::avm2::method::Method;
 use crate::avm2::names::{Namespace, QName};
-use crate::avm2::object::Object;
+use crate::avm2::object::{Object, TObject};
+use crate::avm2::traits::Trait;
 use crate::avm2::value::Value;
 use crate::avm2::Error;
+use crate::display_object::TDisplayObject;
 use gc_arena::{GcCell, MutationContext};
 
 /// Implements `flash.display.DisplayObjectContainer`'s instance constructor.
@@ -27,9 +29,34 @@ pub fn class_init<'gc>(
     Ok(Value::Undefined)
 }
 
+/// Implements `DisplayObjectContainer.getChildAt`
+pub fn get_child_at<'gc>(
+    activation: &mut Activation<'_, 'gc, '_>,
+    this: Option<Object<'gc>>,
+    args: &[Value<'gc>],
+) -> Result<Value<'gc>, Error> {
+    if let Some(dobj) = this.and_then(|this| this.as_display_object()) {
+        let id = args
+            .get(0)
+            .cloned()
+            .unwrap_or(Value::Undefined)
+            .coerce_to_i32(activation)?;
+        let child = dobj.get_child_by_id(id).ok_or_else(|| {
+            format!(
+                "RangeError: Display object container has no child with id {}",
+                id
+            )
+        })?;
+
+        return Ok(child.object2());
+    }
+
+    Ok(Value::Undefined)
+}
+
 /// Construct `DisplayObjectContainer`'s class.
 pub fn create_class<'gc>(mc: MutationContext<'gc, '_>) -> GcCell<'gc, Class<'gc>> {
-    Class::new(
+    let class = Class::new(
         QName::new(
             Namespace::package("flash.display"),
             "DisplayObjectContainer",
@@ -38,5 +65,14 @@ pub fn create_class<'gc>(mc: MutationContext<'gc, '_>) -> GcCell<'gc, Class<'gc>
         Method::from_builtin(instance_init),
         Method::from_builtin(class_init),
         mc,
-    )
+    );
+
+    let mut write = class.write(mc);
+
+    write.define_instance_trait(Trait::from_method(
+        QName::new(Namespace::public_namespace(), "getChildAt"),
+        Method::from_builtin(get_child_at),
+    ));
+
+    class
 }

core/src/display_object.rs

@@ -675,6 +675,11 @@ pub trait TDisplayObject<'gc>:
         None
     }
 
+    /// Get a child display object by it's depth.
+    fn get_child_by_id(&self, _id: Depth) -> Option<DisplayObject<'gc>> {
+        None
+    }
+
     /// Get another level by level name.
     ///
     /// Since levels don't have instance names, this function instead parses

core/src/display_object/button.rs

@@ -440,6 +440,10 @@ impl<'gc> TDisplayObject<'gc> for Button<'gc> {
         }
         self.set_removed(context.gc_context, true);
     }
+
+    fn get_child_by_id(&self, id: Depth) -> Option<DisplayObject<'gc>> {
+        self.0.read().children.get(&id).cloned()
+    }
 }
 
 impl<'gc> ButtonData<'gc> {

core/src/display_object/movie_clip.rs

@@ -1950,6 +1950,10 @@ impl<'gc> TDisplayObject<'gc> for MovieClip<'gc> {
     fn on_focus_changed(&self, context: MutationContext<'gc, '_>, focused: bool) {
         self.0.write(context).has_focus = focused;
     }
+
+    fn get_child_by_id(&self, id: Depth) -> Option<DisplayObject<'gc>> {
+        self.0.read().children.get(&id).cloned()
+    }
 }
 
 impl<'gc> MovieClipData<'gc> {

core/tests/regression_tests.rs

@@ -411,6 +411,7 @@ swf_tests! {
     (as3_movieclip_constr, "avm2/movieclip_constr", 1),
     (as3_lazyinit, "avm2/lazyinit", 1),
     (as3_trace, "avm2/trace", 1),
+    (as3_displayobjectcontainer_getchildat, "avm2/displayobjectcontainer_getchildat", 1),
 }
 
 // TODO: These tests have some inaccuracies currently, so we use approx_eq to test that numeric values are close enough.

core/tests/swfs/avm2/displayobjectcontainer_getchildat/output.txt

@@ -0,0 +1,4 @@
+//this.getChildAt(0)
+[object ChildClip_1]
+//this.getChildAt(0).child_method()
+//Child method called