Add Impeller migration step for camera plugin authors (#11008)

_Description of what this PR is changing or adding, and why:_ 
Adds a note to the Impeller Android plugins migration to clarify that
plugin authors that create a camera preview may additionally need to
correct the rotation of the preview due to rotation information of
produced `Surface`s being lost.

_Issues fixed by this PR (if any):_ 
N/A

_PRs or commits this PR depends on (if any):_ 
Should land after flutter/packages#6856 as this
is mentioned as an example.

cc @navaronbracke

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---------

Co-authored-by: Parker Lougheed <[email protected]>
Co-authored-by: Shams Zakhour (ignore Sfshaza) <[email protected]>

src/content/release/breaking-changes/android-surface-plugins.md

@@ -75,6 +75,36 @@ surfaceProducer.setCallback(
 A full example of using this new API can be found in [PR 6989][] for the
 `video_player_android` plugin.
 
+## Note on camera previews
+
+If your plugin implements a camera preview, your migration might also require
+fixing the rotation of that preview. This is because `Surface`s produced by the
+`SurfaceProducer` might not contain the transformation information that Android
+libraries need to correctly rotate the preview automatically.
+
+In order to correct the rotation, you need to rotate the preview with
+respect to the camera sensor orientation and the device orientation according
+to the equation:
+
+```plaintext
+rotation = (sensorOrientationDegrees - deviceOrientationDegrees * sign + 360) % 360
+```
+
+where `deviceOrientationDegrees` is counterclockwise degrees and `sign` is 1 for
+front-facing cameras and -1 for back-facing cameras. 
+
+To calculate this rotation,
+- Retrieve the sensor orientation degrees by retrieving the value of
+[`CameraCharacteristics.SENSOR_ORIENTATION`][].
+- Retrieve the device orientation degrees in one of the ways that the
+[Android orientation calculation documentation][] details.
+
+To apply this rotation, you can use a [`RotatedBox`][] widget.
+
+For more information on this calculation, check out the
+[Android orientation calculation documentation][]. For a full example of making
+this fix, check out [this `camera_android_camerax` PR][].
+
 ## Timeline
 
 Landed in version: 3.22
@@ -116,7 +146,11 @@ Relevant PRs:
 [`createSurfaceProducer`]: {{site.api}}/javadoc/io/flutter/view/TextureRegistry.html#createSurfaceProducer()
 [`createSurfaceTexture`]: {{site.api}}/javadoc/io/flutter/view/TextureRegistry.html#createSurfaceTexture()
 [`getSurface()`]: {{site.api}}/javadoc/io/flutter/view/TextureRegistry.SurfaceProducer.html#getSurface()
-[`setCallback`]: https://main-api.flutter.dev/javadoc/io/flutter/view/TextureRegistry.SurfaceProducer.html#setCallback(io.flutter.view.TextureRegistry.SurfaceProducer.Callback)
+[`setCallback`]: {{site.api}}/javadoc/io/flutter/view/TextureRegistry.SurfaceProducer.html#setCallback(io.flutter.view.TextureRegistry.SurfaceProducer.Callback)
+[`CameraCharacteristics.SENSOR_ORIENTATION`]: {{site.android-dev}}/reference/android/hardware/camera2/CameraCharacteristics#SENSOR_ORIENTATION
+[`RotatedBox`]: {{site.api}}/flutter/widgets/RotatedBox-class.html
+[Android orientation calculation documentation]: {{site.android-dev}}/media/camera/camera2/camera-preview#orientation_calculation
+[this`camera_android_camerax` PR]: {{site.repo.flutter}}/packages/pull/7044
 [Issue 139702]: {{site.repo.flutter}}/issues/139702
 [Issue 145930]: {{site.repo.flutter}}/issues/145930
 [PR 51061]: {{site.repo.engine}}/pull/51061