Is there an equivalent to this in `Canvas` using Compose I m

Question

Is there an equivalent to this in `Canvas` using Compose I m looking to do this ``` override fun onDraw canvas Canvas super onDraw canvas calculatePropagation canvas let render postInvalidateDelayed 20 ``` But I can t seem to find an equivalent for repeatedly drawing to Canvas I ve done a tonne of digging through docs and on here can anyone chime in

Bacho Kurtanidze · Answer

```fun Modifier drawBehind onDraw Density canvas Canvas size PxSize gt Unit = this + DrawBackgroundModifier onDraw ```

Bacho Kurtanidze · Answer

have you tried this modifier

Adam Bennett · Answer

No I haven t thanks I ll look into this

Adam Bennett · Answer

Is there a way with this modifier to call draw repeatedly with a delay of some form I haven t had much experience with modifiers so trying to wrap my head around it

Bacho Kurtanidze · Answer

I think you can request recomposition manually with recompose method so Recompose and simple Handler delay could do the trick for reference look at this link <https github com Foso Jetpack Compose Playground blob master mkdocs compose recompose md>

Adam Bennett · Answer

Aha I think this was the method I was missing

Adam Bennett · Answer

Thank you so much

Timo Drick · Answer

Maybe you should also consider use an animated state variable to trigger the recomposition automatically Because it only makes sense to redraw when you draw something different the second time

Bacho Kurtanidze · Answer

< Adam Bennett> Glad I managed to help

Adam Powell · Answer

There s a `Canvas` composable function that will take up some layout space for you to draw into You should separate the time pulse code from your drawing code though

Adam Powell · Answer

The Canvas composable uses that modifier from above as its implementation

Adam Bennett · Answer

Interesting thank you I think I ve got everything I need

Adam Powell · Answer

Nice post resulting from this slightly smiling face

Adam Bennett · Answer

Thank you If there s a more idiomatic way of achieving this I d love to know

Adam Powell · Answer

You had the right of it in terms of driving it from data updates You could get a bit more efficient in the data structures used after that given the use case but the single value state update is a good start here

Adam Powell · Answer

In particular you can have it skip composition entirely using the approach you arrived at since compose knows the difference between state read by a composable function and state read by drawing code

Adam Bennett · Answer

Interesting feedback thank you I didn t know that compose could distinguish where the state was being read from that s clever Would be interested to see how others would approach the same problem within the compose framework

Adam Powell · Answer

yep we maintain different observation scopes Composable functions have a local observation scope within the function body and we also have separate observation scopes for measurement layout and drawing of different elements

Adam Powell · Answer

so we can tell the difference between what part of the UI needs to do work Much easier than trying to track manual `requestLayout ` `invalidate ` everywhere we record when you read state instead and infer what scopes need to invalidate from there

Adam Bennett · Answer

That makes a tonne of sense Brilliant thanks so much for chiming in

Adam Powell · Answer

thanks for the cool demo I m sure Fabian and Romain will get a kick out of it too slightly smiling face

Adam Bennett · Answer

I hope so