I am trying to use pixelcopy to capture the screen in a compose application, however, it asks for a view (which is kind of hidden in compose). What is the relationship between compose and views? How do I get the view currently being rendered by compose?

fun getScreenShotFromView(view: View, activity: Activity, callback: (Bitmap) -> Unit) {
    activity.window?.let { window ->
        val bitmap = Bitmap.createBitmap(view.width, view.height, Bitmap.Config.ARGB_8888)
        val locationOfViewInWindow = IntArray(2)
        view.getLocationInWindow(locationOfViewInWindow)
        try {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                PixelCopy.request(
                    window,
                    Rect(
                        locationOfViewInWindow[0],
                        locationOfViewInWindow[1],
                        locationOfViewInWindow[0] + view.width,
                        locationOfViewInWindow[1] + view.height
                    ), bitmap, { copyResult ->
                        if (copyResult == PixelCopy.SUCCESS) {
                            callback(bitmap) }
                        else {

                        }
                        // possible to handle other result codes ...
                    },
                    Handler()
                )
            }
        } catch (e: IllegalArgumentException) {
            // PixelCopy may throw IllegalArgumentException, make sure to handle it
            e.printStackTrace()
        }
    }
}

@Filip Pavlis might have a better recommendation here so pinging him… But the only view is the root view of the compose hierarchy, so you can send that one if you want. it is created in Activity.setContent. If you look at the source of that function you should be able to see how to get it off of the window

PixelCopy

does not need a

View

Are you doing this as part of tests? For such thing we have

findRoot().captureToBitmap()

which would capture your whole compose view for you. You can also capture individual composables if needed.

I am trying to use pixelcopy to capture the screen in a compose application

Can you just render the composable to a bitmap-backed

Canvas

and bypass all the "capture the screen" stuff?

Where is findRoot? I did not see it in the docs.

@Mark Murphy any hints on how to do that?

@Mantas Varnagiris I was hoping there was a Compose-direct option for this -- in the end, everything in Compose winds up on a

Canvas

, after all. Looking at

AndroidComposeView

, though, it appears as though "render to a `Canvas`" is intertwined with lots of other stuff. ☹️ That being said, calling

draw()

on a

View

is fairly simple. Given a layout like this:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="<http://schemas.android.com/apk/res/android>"
  xmlns:app="<http://schemas.android.com/apk/res-auto>"
  xmlns:tools="<http://schemas.android.com/tools>"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context=".MainActivity">

  <FrameLayout
    android:id="@+id/composeTarget"
    android:layout_width="0dp"
    android:layout_height="0dp"
    app:layout_constraintBottom_toTopOf="@id/capturedImage"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

  <ImageView
    android:id="@+id/capturedImage"
    android:layout_width="0dp"
    android:layout_height="0dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@id/composeTarget" />
</androidx.constraintlayout.widget.ConstraintLayout>

...then this code renders a composable into the

FrameLayout

and displays a captured

Bitmap

of that output into the

ImageView

class MainActivity : AppCompatActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    val binding = ActivityMainBinding.inflate(layoutInflater)

    setContentView(binding.root)

    binding.composeTarget.setContent(Recomposer.current()) {
      MaterialTheme {
        Text("hello, world!", modifier = Modifier.padding(8.dp))
      }
    }

    binding.composeTarget.doOnLayout {
      val bitmap = Bitmap.createBitmap(
        binding.composeTarget.width,
        binding.composeTarget.height,
        Bitmap.Config.ARGB_8888
      )
      val canvas = Canvas(bitmap)

      binding.root.draw(canvas)

      binding.capturedImage.setImageBitmap(bitmap)
    }
  }
}

This is super helpful. Thank you! 🙏

do you have an example of a failing scenario?

I will create a failing scenario later today. But just reading documentation on

View.drawToBitmap

which effectively does the same thing as code above, it says:

/**
 * Return a [Bitmap] representation of this [View].
 *
 * The resulting bitmap will be the same width and height as this view's current layout
 * dimensions. This does not take into account any transformations such as scale or translation.
 *
 * Note, this will use the software rendering pipeline to draw the view to the bitmap. This may
 * result with different drawing to what is rendered on a hardware accelerated canvas (such as
 * the device screen).
 *
 * If this view has not been laid out this method will throw a [IllegalStateException].
 *
 * @param config Bitmap config of the desired bitmap. Defaults to [Bitmap.Config.ARGB_8888].
 */

Seems like the issue is that

drawLayer

users hardware accelerated canvas that's why all transformations seem to be ignored for me. Now need to investigate if it's possible to capture pixels from hardware accelerated canvas.

findRoot

or now called

onRoot

is a testing API. if you don't need it for testing then my advise above does not apply (sorry for delay).

No, it's not for testing. I'll have to find another way. I could not find a way to capture bitmap from hardware accelerated layer

@Mantas Varnagiris Did you get it working? I would like to make a screenshot of composable and send it as a bitmap. On running app, not for testing

No in the end I gave up.