Changes to Actor.anchor are only applied to the graphics component

[VaughanRSanders]

Changing the anchor of the Actor seem to intentionally only change the graphics component

private _handleAnchorChange(v: Vector) {
    if (this.graphics) {
      this.graphics.anchor = v;
    }
  }

This leads to the Actor having a physics component that is offset from the graphics - you can see in the screenshot the yellow box is the graphics bounds and the blue is the physics. The anchor for this Actor is vec(0.5, 1) and can be seen as the yellow dot.

Is there a way / should I be manually updating the physics bounds to match the graphics?

[Autsider666]

The easiest way to apply a new anchor to the collider of an actor outside of the constructor seems to be to create a new one using actor.collider.set(Shape.Box(width, height, newAnchor)).

You're running into this issue because the collider doesn't have any knowledge of the anchor of its entity.
It looks like the collider gets the anchor in the actor constructor, but the Box function only uses it to create the initial points of the PolygonCollider.

[Autsider666]

@eonarheim would it be possible to extract this logic from Shape.Box so it can be used to generate net points for an existing PolygonCollider in case the anchor of an actor gets changed? Running _calculateTransformation afterwards seems to be enough, but colliders are still mostly magic to me.

[eonarheim]

Thanks, agreed. I think the easiest way around this is to manage your collider anchor and graphics anchor separately.

Alternatively you could look at setting specific pixel offset on your collider and graphics if you know exact offsets

actor.graphics.offset = ex.vec(0, -100); // 100 pixels up

const collider = ex.Shape.Box(100, 100, ex.Vector.Half , ex.vec(0, -100)); // 100 pixels up
actor.collider.set(collider);

[eonarheim]

@eonarheim would it be possible to extract this logic from Shape.Box so it can be used to generate net points for an existing PolygonCollider in case the anchor of an actor gets changed? Running _calculateTransformation afterwards seems to be enough, but colliders are still mostly magic to me.

Totally, I was thinking we could probably do a convenience top level .offset on the ColliderComponent itself

[VaughanRSanders]

Thank you both for the reply. My thinking around using anchor rather than offset was I would like to be able to tell the actor to moveTo specific world positions and have the center of the feet arrive at that point - this seems like the correct way to setup that from a transform point of view.

I will manually set the collider 🙏