core: Add flag for display objects which were placed by AS3.

In AS3. objects placed by scripts *cannot* be removed by `RemoveObject` tags. This enforces that in Ruffle.

core/src/display_object.rs

@@ -358,6 +358,18 @@ impl<'gc> DisplayObjectBase<'gc> {
         }
     }
 
+    fn placed_by_script(&self) -> bool {
+        self.flags.contains(DisplayObjectFlags::PlacedByScript)
+    }
+
+    fn set_placed_by_script(&mut self, value: bool) {
+        if value {
+            self.flags.insert(DisplayObjectFlags::PlacedByScript);
+        } else {
+            self.flags.remove(DisplayObjectFlags::PlacedByScript);
+        }
+    }
+
     fn swf_version(&self) -> u8 {
         self.parent
             .map(|p| p.swf_version())
@@ -736,6 +748,16 @@ pub trait TDisplayObject<'gc>:
         false
     }
 
+    /// Whether this display object has been created by ActionScript 3.
+    /// When this flag is set, changes from SWF `RemoveObject` tags are
+    /// ignored.
+    fn placed_by_script(&self) -> bool;
+
+    /// Sets whether this display object has been created by ActionScript 3.
+    /// When this flag is set, changes from SWF `RemoveObject` tags are
+    /// ignored.
+    fn set_placed_by_script(&self, context: MutationContext<'gc, '_>, value: bool);
+
     /// Executes and propagates the given clip event.
     /// Events execute inside-out; the deepest child will react first, followed by its parent, and
     /// so forth.
@@ -1123,6 +1145,12 @@ macro_rules! impl_display_object_sansbounds {
                 .$field
                 .set_transformed_by_script(value)
         }
+        fn placed_by_script(&self) -> bool {
+            self.0.read().$field.placed_by_script()
+        }
+        fn set_placed_by_script(&self, context: gc_arena::MutationContext<'gc, '_>, value: bool) {
+            self.0.write(context).$field.set_placed_by_script(value)
+        }
         fn instantiate(
             &self,
             gc_context: gc_arena::MutationContext<'gc, '_>,
@@ -1255,6 +1283,10 @@ enum DisplayObjectFlags {
     /// Whether this object has been transformed by ActionScript.
     /// When this flag is set, changes from SWF `PlaceObject` tags are ignored.
     TransformedByScript,
+
+    /// Whether this object has been placed on the timeline by ActionScript 3.
+    /// When this flag is set, changes from SWF `RemoveObject` tags are ignored.
+    PlacedByScript,
 }
 
 pub struct ChildIter<'gc> {

core/src/display_object/movie_clip.rs

@@ -1198,7 +1198,9 @@ impl<'gc> MovieClip<'gc> {
                     .children
                     .insert(depth, child);
                 if let Some(prev_child) = prev_child {
-                    self.remove_child_from_exec_list(context, prev_child);
+                    if !prev_child.placed_by_script() {
+                        self.remove_child_from_exec_list(context, prev_child);
+                    }
                 }
                 self.0
                     .write(context.gc_context)
@@ -1275,8 +1277,10 @@ impl<'gc> MovieClip<'gc> {
                 })
                 .collect();
             for (depth, child) in children {
-                self.0.write(context.gc_context).children.remove(&depth);
+                if !child.placed_by_script() {
-                self.remove_child_from_exec_list(context, child);
+                    self.0.write(context.gc_context).children.remove(&depth);
+                    self.remove_child_from_exec_list(context, child);
+                }
             }
             true
         } else {
@@ -1704,9 +1708,11 @@ impl<'gc> MovieClip<'gc> {
             // Don't do this for rewinds, because they conceptually
             // start from an empty display list, and we also want to examine
             // the old children to decide if they persist (place_frame <= goto_frame).
-            let child = self.0.write(context.gc_context).children.remove(&depth);
+            if let Some(child) = self.0.read().children.get(&depth).cloned() {
-            if let Some(child) = child {
+                if !child.placed_by_script() {
-                self.remove_child_from_exec_list(context, child);
+                    self.0.write(context.gc_context).children.remove(&depth);
+                    self.remove_child_from_exec_list(context, child);
+                }
             }
         }
         Ok(())
@@ -2944,14 +2950,14 @@ impl<'gc, 'a> MovieClip<'gc> {
         } else {
             reader.read_remove_object_2()
         }?;
-        let child = self
+
-            .0
+        if let Some(child) = self.0.read().children.get(&remove_object.depth.into()).cloned() {
-            .write(context.gc_context)
+            if !child.placed_by_script() {
-            .children
+                self.0.write(context.gc_context).children.remove(&remove_object.depth.into());
-            .remove(&remove_object.depth.into());
+                self.remove_child_from_exec_list(context, child);
-        if let Some(child) = child {
+            }
-            self.remove_child_from_exec_list(context, child);
         }
+        
         Ok(())
     }