ETC2 Usage without ETC1
We started to use only ETC2+Alpha without ETC1.
ETC1 works with OpenGL ES 1.0 and all android devices supporting it.
ETC2 works with OpenGL ES 3.0+ and new devices should support it.
Old devices with no support to OpenGL ES 3.0 should not be able to download the game. So we add this tag to application.xml:
<uses-feature android:glEsVersion="0x00030000" android:required="true" />
Now only OpenGL ES 3.0 supported with game. So we are safe to use ETC2 only. This enables Google Play Store to only allow devices with OpenGL ES 3.0+ to our game. So no bad reviews due to lack of ETC1.
JXR Usage
Using JXR increases application size in an unexpected way.
Example:
When you use ETC2+A you get a ATF file with 4 MB size.
When you use ETC2+A+JXR you get ATF file with 1.2 MB size.
This looks like JXR decreased the file size in the end. However when AAB/APK created final compressed sizes:
Compressed: ETC2+A ATF file decreases from 4 MB to 800 KB
Compressed: ETC2+A+JXR ATF file decreases from 1.2 MB to 1.1 MB
So JXR usage did not made a decrease to download size, instead increased it, so we don't use JXR.