What is the best approach to get the bounds of a c...

# compose-android

[Konstantin Klassen]

What is the best approach to get the bounds of a composable in the coordinates space of another composable up the tree? e.g.: What are the bounds of B in the coordinates space of Box?

Box(Modifier.fillMaxSize()) {
    Column(Modifier.padding(left = 100.dp)) {
        A()
        B()
    }
}

What I do is I get LayoutCoordinates of Box and B in their respective onGloballyPositioned callback and do the conversion once I have both of the LayoutCoordinates. There must be a better way.

I thought about using LookaheadScope inside Box, because that gives me lookaheadScopeCoordinates during the placement of B. Might be overkill though?

[Stylianos Gakis]

If Column has the same bounds as Box, you can add a onPlaced{} modifier on your item and do .positionInParent or something like that

[Stylianos Gakis]

In your case since you have a 100.dp padding you can offset that yourself in the calculation.

[Konstantin Klassen]

This should have been just an example. B could be any indirect child of Box deep down the tree

[Jonathan]

Out of curiosity what are you trying to achieve? I do not see why the LayoutCoordinates.parentLayoutCoordinates does not give you exactly what you want.

[Konstantin Klassen]

Because that are the layout coordinates of the direct parent. I want to climb higher up the tree. You could chain parentLayoutCoordines but I not sure how I would know when to stop traversing

[Jonathan]

Do you mind sharing what you’re trying to build? Maybe there is a simpler way to achieve it.

[Konstantin Klassen]

Would be useful for spotlights and particle systems. I built something working for https://github.com/KlassenKonstantin/ComposePhysicsLayout but was curious how other people would approach this