Fix Android default zoom ratio

[jfversluis]

Summary

• Fix Android ZoomFactor mapping so the default value (0) resolves to 1x zoom, matching Apple/Windows behavior
• Avoid using CameraX SetLinearZoom(0) as the default because on logical multi-camera devices such as Pixel 7 the minimum zoom ratio can select an ultrawide/fixed-focus physical camera
• Keep higher ZoomFactor values mapped from 1x to the camera's max zoom ratio

Fixes #315.

Thanks @sbrunaugh for testing the first artifact. That ruled out the explicit continuous-AF approach and pointed back to the 0.8.2 → 0.9.0 regression. The key change in that range was the new Android zoom path: default ZoomFactor = 0 started calling SetLinearZoom(0), unlike 0.8.2 which never applied zoom and unlike Apple/Windows which treat 0 as 1x. On Pixel 7, CameraX minimum zoom can switch to the ultrawide/fixed-focus lens, which matches the blurry/no-continuous-focus behavior.

Once the updated PR build artifacts are available, please try the new artifacts and let us know whether the preview/scanning focus behavior is back to the 0.8.2 behavior on your Pixel 7.

Validation

• dotnet test ZXing.Net.MAUI.Tests/ZXing.Net.MAUI.Tests.csproj --no-restore --verbosity minimal
• dotnet build ZXing.Net.MAUI/ZXing.Net.MAUI.csproj -f net10.0-android --no-restore --verbosity minimal

[sbrunaugh]

Hi, tested artifact build \ci28429682816\ (0.999.0-ci28429682816) on a Pixel 7 running Android — unfortunately the autofocus behavior is identical to 0.10.x. The camera preview shows but focus does not continuously adjust; it behaves exactly like the regression we reported in #315.

For reference, 0.8.2 (on our \develop\ branch) still works correctly on the same device, so the regression is still present with this PR's changes.

Happy to test follow-up builds if you want to try a different approach. The fallback idea mentioned in #315 (periodic \CancelFocusAndMetering\ + \AutoFocus()\ for devices that don't honor \CONTINUOUS_PICTURE\ via \Camera2Interop) might be worth exploring.

[jfversluis]

Thanks for testing the first build, @sbrunaugh. I took another hard look specifically at 0.8.2 → 0.9.0 since you confirmed 0.8.2 still works.

The likely regression is the Android zoom change added in that range: the default ZoomFactor = 0 was being applied with CameraX SetLinearZoom(0). On Pixel 7/logical multi-camera devices that can mean the minimum zoom ratio, which may select the ultrawide/fixed-focus physical camera. That would explain why continuous AF changes did not help.

I pushed an updated fix that maps Android ZoomFactor = 0 to 1x, matching Apple/Windows and the pre-zoom Android behavior. Once the new PR artifacts are available, could you try those and let us know whether the focus behavior matches 0.8.2 again?

[sbrunaugh]

@jfversluis that worked! Barcodes are scanning cleanly like in 0.8.2. I look forward to integrating this fix once it's merged.

[jfversluis]

@sbrunaugh thanks! Should be released as 0.10.2 shortly!