GrapheneOS
Zoom buttons like Google Camera
Google Camera has zoom buttons for 0.6x, 1x, and 2x. If you long press the buttons you can slide either left/right (or down/up in landscape) to zoom out/in. These buttons are always visible, allowing you to zoom with 1 finger.
Their zoom levels vary based on what the device supports. 0.6x, 1x and 2x is what they use on 5th generation Pixels where 0.6x is the wide angle camera without zoom, 1x is the main camera without zoom and 2x is 2x digital zoom with the main camera.
On the 6th generation devices, the main camera has a wider field of field so the wide angle camera button is 0.7x and there's a 4x telephoto camera too.
The issue with this feature proposal is that we do not want to hard-wire the zoom levels for the cameras used by different devices. It's possible that the Camera2 multi-camera API can be used to retrieve the values, but currently very few devices implement this. Only devices implementing the multi-camera API and CONTROL_ZOOM_RATIO such as Pixels have support for automatically switching between zoom levels. It would defeat the purpose of that API if we hard-wired the zoom levels to provide buttons for certain devices. CameraX doesn't currently expose an API for retrieving this information so this cannot be implemented in a portable way, and we want our camera app to be portable instead of hard-wired to work fully with only certain devices.
The buttons wouldn't have to be hard wired for certain devices, but general buttons such as 0.5x, 1x, and 3x zoom.
Or they could be programmable buttons that users can set to their desired zoom level. I think many devices have "ultra-wide", "standard", and "telephoto" lens. You could implement buttons for these three zoom levels and the specific level of each could be user adjustable in settings.
Important to note that the 4x telephoto camera on the Pixel 6 Pro and Pixel 7 Pro is not actually triggered at 4x in many cases. It triggers at a dynamic zoom value based on the available light. Quite often, it doesn't switch until around 4.7x to 5x zoom and it may not trigger at all in very low light.