Fixing `Node`'s `GlobalTransform`s | Bevy | Page 1

crimson trail Jul 19, 2025, 7:41 PM

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I have some Nodes creating a flexbox layout, and drawing the borders verifies they are laid out as expected. However, plotting the location of their computed GlobalTransforms seems to have them in an arbitrary location. I have one Node with children that are non-ui (Sprites) so ideally their location could be relative to their parent in some manner.

Thus, is it possible to specify some sort of "anchor" where the global transform of a node is relative to its UI box (e.g. top left), or is there some other method of making custom UI components position themselves properly?

compact hound Jul 19, 2025, 9:56 PM

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UI and World-space can't really be mixed like this. The GlobalTransform of the Node is in fact correct, bot it uses a different coordinate space, one fixed to the camera, so the UI stays fixed on the screen even if you move the camera around in the world.

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You may be able to convert the Node GlobalTransform with Camera::viewport_to_world/_2d but i'm not sure whether UI actually uses viewport coordinates or a third thing

crimson trail Jul 19, 2025, 9:58 PM

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Right, thanks

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Is there an idiomatic way this is supposed to be done then? Most of my game is non ui, I just have a few ui elements and wanted to add the rest of the game (almost like an iframe) to the flexbox

compact hound Jul 19, 2025, 9:59 PM

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Do you have a specific requirement which means you can't appraoch the UI as a overlay (which is the intended way)?

crimson trail Jul 19, 2025, 10:01 PM

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Not exactly, it's just more convenient because it ensures that no ui element will overlap (as all ui is outside the main game), centering is done properly, etc.

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so I will do that if there's no other option

compact hound Jul 19, 2025, 10:02 PM

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Well, there is the concept of sub-views where you can make a camera render to less area than the entire window

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https://bevy.org/examples/3d-rendering/camera-sub-view/

Camera sub view

Bevy is a refreshingly simple data-driven game engine built in Rust. It is free and open-source forever!

crimson trail Jul 19, 2025, 10:05 PM

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hmm, kinda, thanks for that resource

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I guess it's slightly different in that it's a puzzle game, so I want the whole puzzle rendered and it's not about framing the camera

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just about aligning the puzzle relative under ui

compact hound Jul 19, 2025, 10:10 PM

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hmm, another alternative would be using a camera which renders to texture for the game, and using that texture as a UI image

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thats a bit more involved as far as setup goes but its basically exactly what you want with extra steps

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though its not intended for this kind of thing, so things like picking (finding which entity your mouse is over) might need some extra work

crimson trail Jul 19, 2025, 10:13 PM

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That's a smart idea that might work well in my use case actually, thanks

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I'll give it a try and resolve this for now

compact hound Jul 19, 2025, 10:15 PM

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I'd imagine things like the Drag observer would be amazing for a puzzle game, so idk if it really does fit your usecase so well

crimson trail Jul 19, 2025, 10:16 PM

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the controls happen to be outside the game so it does here

#Fixing `Node`'s `GlobalTransform`s