How to wrap a component?

[st-pasha]

Suppose I have a component X which is already mounted somewhere in a component tree: A->B->...->V->X. What I want is to wrap X into another component W, so that the component tree becomes A->B->...->V->W(X). The component W should assume X's identity: the priority and the place in the rendering sequence.

At first, I thought this would be as simple as X.parent.replaceChild(X, W(X)), but there is no replaceChild() function or anything remotely similar.

Do you guys have any suggestions for how to achieve this?

[spydon]

Edit: this was solved by #906 and component.changeParent

Good idea! This should be pretty easy to implement.
With replaceChild I would expect W to fully take X place in the tree though, and not wrap X, but maybe that is what you meant with the W(X) notation, that X is added to W there already?
I'm guessing we need quite a lot of optional parameters for the method too, since for a PositionComponent you might want it to take the position, size, scale or angle of the component that it replaces too.

Right now you would have to do something like this:

v.remove(x);
w.changePriorityWithoutResorting(x.priority);
// wait for next tick
x.shouldRemove = false;
w.addChild(x);
v.add(w);

After #906 you could do this instead:

w.changePriorityWithoutResorting(x.priority);
v.add(w);
x.changeParent(w);

So with this suggestion it would be something like this?

v.replaceChild(x, w, inheritPriority: true, inheritPosition: true ...);
w.add(x);

[st-pasha]

Well, I was thinking of a simple component like

class W extends Component {
  final Component _wrapped;
  W(this._wrapped);
  
  @override
  void update(double dt) { /* do something here */ }
  @override
  void render(Canvas canvas) { /* or maybe do something here */ }
}

Examples where this could be useful:

• cast slow, or freeze time on an NPC by passing a fraction of the real time dt;
• modify canvas before drawing, i.e. apply a blend effect, or use a Layer as a component, or apply a canvas transform if for whatever reason the regular transform is not enough;
• draw a special effect under or over a component, e.g. a visual for a spell effect;
• render X and then post-process the image, such as adding blur or outline;
• temporarily replace X with completely different visual, and then revert back after some time.

[st-pasha]

After #906 you could do this instead:

w.changePriorityWithoutResorting(x.priority);
v.add(w);
x.changeParent(w);```

There could be a problem if the components in the tree have the default priority. For example, Root has 3 children [A, B, C] all at the same default priority 0. If I now add W and reparent A, then root's children will be [B, C, W->A], and so W did not take A's place properly.

[spydon]

Alright, so we have two different things that are discussed here then:

• component.replaceChild
• A wrap component

Do you mean that W would live in Flame? If so then that could handle the transfer of the component to its own tree.

But I wonder if this solution is suitable, it seems like there would be a lot of tree modifications when a component is wrapped in many components that are added and removed. Maybe a new set, similar to children could be introduced which runs before the components own update/render functions? Not fully satisfied with such a solution either though, but it would be more efficient.

[spydon]

After #906 you could do this instead:

w.changePriorityWithoutResorting(x.priority);
v.add(w);
x.changeParent(w);```

There could be a problem if the components in the tree have the default priority. For example, Root has 3 children [A, B, C] all at the same default priority 0. If I now add W and reparent A, then root's children will be [B, C, W->A], and so W did not take A's place properly.

True, this is something that would need to be implemented in the OrderedSet then.

[st-pasha]

Do you mean that W would live in Flame?

W is just any component. You could replace X with anything you want. Maybe a pawn becomes a Queen, or an enemy corpse turns into a Zombie. Some kinds of wrappers can be provided by Flame too, similar to Effects.