# compose

Why does onGloballyPosition run on the next composition, and is there any way to get layout coords immediately?

onPlaced should give you the coordinates before the drawing phase of the current frame. I think it might even do so before the placement phase of your children., but I'm not sure.

I tried that once, I think, lemme check again

Working on a hackathon thing at work, a smart video callbox with livekit 😛

Using compose for android, and compose multiplatform on ubuntu core for the box

Still seems to do it on next composition

It won't be available in composition until the next frame, because the layout and draw phases happen after the composition phase completes. So you can get it in the same frame, but there's no way to get it for the same composition - trying to do so means you're probably doing something in composition that should be done in a later phase.

What’s the best way to force a layout?

Or at least force this layout event?

What are you trying to do that you need to force a layout?

I’m trying to display a live webrtc feed in a textureview

Why do you need to force a layout to do that?

Because it sets the dimensions of the video feed to display

This is library code

Sounds like you could use onSizeChanged for that and get the result even sooner (measurement happens before placement)

Either that, or use BoxWithConstraints to get how big the parent layout is without dealing with callbacks

No, i don’t think you need BoxWithConstraints for this, that is expensive and has a whole bunch of other implications

Was contemplating BoxWithConstraints but that seemed hacky

Exactly

Only thing is onSizeChange yields a size

I don’t know how this ComposeVisibility class interacts with everything else. But because `AndroidView`’s update function runs before layout, you could probably store the view somewhere then tell it what size to use from the onSizeChanged callback. Or, subclass the view and just make that call directly inside the view’s measurement callback.

Because it sets the dimensions of the video feed to display

I assumed you just needed a size since “dimensions” usually implies size, not location.

onGloballyPositioned in that screenshot is what gets called with onGloballyPositioned modifier

Does view layout interop nicely with with compose layout?

Yes

There is ViewVisibility for the view system, so if that works, I’ll do it upon update

what is ViewVisibility? I’ve never heard of that Oh it’s from that library you’re using?

It’s part of livekit

yeah

😛

onSizeChanged also runs next composition as well, btw

Yes, the first composition that sees its value will be the one in the next frame. It's important to understand that composition isn't the only thing that happens in a compose ui frame though. It's the first of a few discreet phases that always happen in the same order.

The onSizeChanged callback is invoked as soon as the node it's registered on is measured. This happens before anything is placed in that layout pass, and before anything is drawn.

I understand that, yes

I guess my assumption is, that those modifiers notify of layout changes, it would fire off an event which you could then recompose afterwards for

But I see how that could also cause a loop, potentially

You can, but it doesn't change the ordering of the phases. After composition is done for the frame, it won't run again until the next frame (except for subcompositions potentially, which is a whole other can of worms)

The way those layout events will trigger currently is via changing of state

In most cases, the only things measurement should affect are layout and drawing. In your case, idk when the library needs to know the size, but if it needs to know before the view has been measured you're gonna have a bad time no matter what 😅

Uploaded in the wrong order, but that’s what happens once measurements are received

Also note that measurement, placement, drawing, and even AndroidView update blocks all have their own snapshot state observers, so any states that are read in those contexts will invalidate the corresponding phase for the next frame.

You're saying the first frame is effectively blank?

Yes

The camera is on, it’s receiving video and transmitting

But the video feeds havent been sized appropriately

So the library determines the size of the video feeds by querying that size method on VideoSinkVisibility? When does it do that?

Or are you pushing the size to the library somehow, eg via a setter?

Internally it uses an observer from what I can tell, notifyChanged should trigger an update

But, we pass in layout info using onGloballyPositioned, both kinds, the modifier, and the method from the library

I’m not really familiar with LiveKit but I assume you’re using this TextureViewRenderer? https://github.com/livekit/client-sdk-android/blob/main/livekit-android-sdk/src/main/java/io/livekit/android/renderer/TextureViewRenderer.kt Have you tried using org.webrtc.SurfaceViewRenderer? (making this change would have other implications but I’m curious if it would solve your problem)

Yes, I have

Whether or not it's a surface view or texture view doesn't really have any implications it's just whether or not it's drawn as a view or not, which the traditional view system supports anyway, and compose interops nicely

The difference is just in how the video is drawn. You’re seeing some delay in when frames are drawn? Does SurfaceViewRenderer have the same problem? This might be useful reading https://source.android.com/devices/graphics/architecture.html#high_level This also https://stackoverflow.com/questions/21305651/textureview-vs-glsurfaceview-or-how-to-use-glsurfaceview-with-egl14#21322600 Basically TextureView is a little slower than SurfaceView. All this might make no difference. I’m building a webrtc app using compose and I’ve had to go down the graphics architecture rabbit hole a bit for some features. Good luck

That's what I was saying but oversimplified for brevity sake haha

Both work, but after the first composition, perfectly infact. It's just a layout issue