fix: Mirror selfies on Android

[mrousavy]

What

This PR automatically horizontally flips (= mirrors) images taken from the front camera.

It is achieved by decoding the received byte[] to a Bitmap, applying a Matrix with a scaleX of -1, then converting it back to a byte[]. I am not fully happy with that approach, as I'd like to avoid the byte[] -> Bitmap -> byte[] approach if possible.

Benchmarks show that horizontally flipping an image takes ~24ms on my Huawai P10.

Back camera (no flipping):

2021-05-03 18:57:54.478 31448-31448/com.mrousavy.camera.example I/CameraView.performance: Session configured in 200 ms! Camera: androidx.camera.lifecycle.LifecycleCamera@c475d4
2021-05-03 18:58:17.609 31448-31729/com.mrousavy.camera.example I/CameraView.performance: Finished creating temp file in 1ms
2021-05-03 18:58:18.028 31448-31448/com.mrousavy.camera.example I/CameraView.performance: Finished image capture in 413ms
2021-05-03 18:58:18.033 31448-31729/com.mrousavy.camera.example I/CameraView.performance: Finished image saving in 3ms
2021-05-03 18:58:18.035 31448-31448/com.mrousavy.camera.example I/CameraView.performance: Finished function execution in 444ms

Front camera (flipping):

2021-05-03 18:58:50.155 31448-31448/com.mrousavy.camera.example I/CameraView.performance: Session configured in 129 ms! Camera: androidx.camera.lifecycle.LifecycleCamera@4e5ccc6
2021-05-03 18:58:52.032 31448-31729/com.mrousavy.camera.example I/CameraView.performance: Finished creating temp file in 2ms
2021-05-03 18:58:52.345 31448-31448/com.mrousavy.camera.example I/CameraView.performance: Finished image capture in 314ms
2021-05-03 18:58:52.379 31448-31729/com.mrousavy.camera.example I/CameraView.performance: Flipping Image took 31 ms.
2021-05-03 18:58:52.380 31448-31729/com.mrousavy.camera.example I/CameraView.performance: Finished image saving in 33ms
2021-05-03 18:58:52.381 31448-31448/com.mrousavy.camera.example I/CameraView.performance: Finished function execution in 353ms

Changes

• Add flipImage to ImageProxy+save - a function that flips the given byte[].
• Call flipImage in ImageProxy+save when flipHorizontally ist true

Side-effects

• Taking selfies takes a few milliseconds longer (~24ms on my Huawai P10)

Tested on

• Huawai P10

Related issues

Closes #74