avm1: Implement getInstanceAtDepth

core/src/avm1/globals/movie_clip.rs

@@ -176,6 +176,7 @@ pub fn create_proto<'gc>(
         "getBounds" => get_bounds,
         "getBytesLoaded" => get_bytes_loaded,
         "getBytesTotal" => get_bytes_total,
+        "getInstanceAtDepth" => get_instance_at_depth,
         "getNextHighestDepth" => get_next_highest_depth,
         "getRect" => get_rect,
         "getURL" => get_url,
@@ -818,6 +819,41 @@ fn get_bytes_total<'gc>(
         .unwrap_or(Value::Undefined))
 }
 
+fn get_instance_at_depth<'gc>(
+    movie_clip: MovieClip<'gc>,
+    activation: &mut Activation<'_, 'gc, '_>,
+    args: &[Value<'gc>],
+) -> Result<Value<'gc>, Error<'gc>> {
+    if activation.current_swf_version() >= 7 {
+        let depth = if let Some(depth) = args.get(0) {
+            depth
+                .coerce_to_i32(activation)?
+                .wrapping_add(AVM_DEPTH_BIAS)
+        } else {
+            avm_error!(
+                activation,
+                "MovieClip.get_instance_at_depth: Too few parameters"
+            );
+            return Ok(Value::Undefined);
+        };
+        match movie_clip.child_by_depth(depth) {
+            Some(child) => {
+                // If the child doesn't have a corresponding AVM object, return mc itself.
+                // NOTE: this behavior was guessed from observing behavior for Text and Graphic;
+                // I didn't test other variants like Bitmap, MorphSpahe, Video
+                // or objects that weren't fully initialized yet.
+                match child.object() {
+                    Value::Undefined => Ok(movie_clip.object()),
+                    obj => Ok(obj),
+                }
+            }
+            None => Ok(Value::Undefined),
+        }
+    } else {
+        Ok(Value::Undefined)
+    }
+}
+
 fn get_next_highest_depth<'gc>(
     movie_clip: MovieClip<'gc>,
     activation: &mut Activation<'_, 'gc, '_>,

core/tests/regression_tests.rs

@@ -163,6 +163,7 @@ swf_tests! {
     (lessthan2_swf7, "avm1/lessthan2_swf7", 1),
     (logical_ops_swf4, "avm1/logical_ops_swf4", 1),
     (logical_ops_swf8, "avm1/logical_ops_swf8", 1),
+    (movieclip_get_instance_at_depth, "avm1/movieclip_get_instance_at_depth", 1),
     (movieclip_depth_methods, "avm1/movieclip_depth_methods", 3),
     (get_variable_in_scope, "avm1/get_variable_in_scope", 1),
     (movieclip_init_object, "avm1/movieclip_init_object", 1),

core/tests/swfs/avm1/movieclip_get_instance_at_depth/output.txt

@@ -0,0 +1,28 @@
+//_root.getInstanceAtDepth(-16384)
+undefined
+//_root.getInstanceAtDepth(-16384).getDepth()
+undefined
+//_root.getInstanceAtDepth(-16383)
+_level0
+//_root.getInstanceAtDepth(-16383).getDepth()
+-16384
+//_root.getInstanceAtDepth(-16382)
+_level0.instance1
+//_root.getInstanceAtDepth(-16382).getDepth()
+-16382
+//_root.getInstanceAtDepth(-16381)
+undefined
+//_root.getInstanceAtDepth(-16381).getDepth()
+undefined
+//_root.getInstanceAtDepth(-16380)
+_level0
+//_root.getInstanceAtDepth(-16380).getDepth()
+-16384
+//_root.getInstanceAtDepth(-16379)
+_level0.instance2
+//_root.getInstanceAtDepth(-16379).getDepth()
+-16379
+//this.getInstanceAtDepth(123)
+_level0.fromscript
+//_root.getInstanceAtDepth(123).getDepth()
+123