Can I use a `ComposeView` to draw a composition into a Canvas, off-screen? More or less this: ```val...

# compose

[Chris Fillmore]

Can I use a ComposeView to draw a composition into a Canvas, off-screen? More or less this:

val canvas = Canvas()
val composeView = ComposeView(context)
composeView.setContent {
  // Call composables here

  SideEffect {
    composeView.draw(canvas)
  }
}

Important to note that the ComposeView is never attached to a window / drawn in the UI. The view is created programmatically, as above.

I am ultimately trying to get the composition into a Bitmap for the purpose of drawing into an OpenGL texture. (If there is a better approach, I’m all ears.) Thanks for any help!

[romainguy]

There are better ways, by using a SurfaceTexture and getting a Canvas for the SurfaceTexture's Surface

[romainguy]

This bypasses the need to upload the Bitmap as a texture

[romainguy]

On recent API levels you can go further by using a HardwareRenderer

[Chris Fillmore]

Thanks for responding. Sorry I should have provided more detail. In my use case, we are capturing video from the camera and sending it out over webrtc. We allow the user to draw into the webrtc video frames.

[Chris Fillmore]

So I am already using SurfaceTexture with WebRTC, and I can draw into the frames using a Canvas. But I need to draw a structured hierarchy of views (i.e. View or @Composable), not just plain unstructured canvas drawing.

[Chris Fillmore]

And I would like to reuse some Composables I already have. Altogether I would like to do as much with Compose as possible

[romainguy]

Right my point was just that you should not get through a Bitmap ^^

[romainguy]

I'm not sure what a ComposeView needs exactly but you at least need to measure and layout it

[romainguy]

In addition views often rely on m being attached to a window to work properly.

[romainguy]

@Adam Powell probably knows more about the requirements to drive a ComposeView

[Adam Powell]

Yeah there are a couple ViewTreeFoo things ComposeView looks for

[Chris Fillmore]

@romainguy thanks for the feedback about the bitmap. I’ll take a look at that!

Putting aside Compose for a moment, basically what I’m trying to do is define a hierarchy of UI elements (whether View or Composable) off-screen, so that I can draw it into a GL texture.

[Chris Fillmore]

Just following up here, I was able to do roughly what I want by using a Presentation targeting a VirtualDisplay backed by a Surface(SurfaceTexture)

[romainguy]

👍