[FR]: Support double-tap zoom

[herbeth1u]

Is there an existing issue for this?

• I have searched the existing issues

Describe the problem

As of now, Zoomable supports a "double-tap + drag" zoom. Is it possible to support the arguably more usual "double-tap" zoom?
For example, it's a feature supported by PhotoView or Discord's image viewer.

Describe the solution

How it works:

• Double-tap once: scale = max scale / 2
• Double-tap again: scale = max scale
• Double-tap again: resets zoom
  See https://github.com/Baseflow/PhotoView/blob/master/photoview/src/main/java/com/github/chrisbanes/photoview/PhotoViewAttacher.java#L231

Thanks.

[usuiat]

Thanks for the proposal. @herbeth1u
I agree that a double-tap zoom would be useful.

However, is the 3-step behaviour like PhotoView necessary?
I think the following 2-step behaviour is enough.

• Double-tap once: scale = 2.0
• Double-tap again: resets zoom

I checked the behavior of Google Photo, Twitter, Facebook, Discord, etc.
They all implement this 2-step behavior.

[herbeth1u]

How about making the number of steps configurable? If this is too overkill, settling on the 2-step behavior like most popular apps sounds like a reasonable plan as well.

[usuiat]

Noted.
We will consider how to implement it.

[cacato86]

How is the state of this feature? The library is awesome, but I'm missing this functionality 😞

[usuiat]

Thank you for waiting.

I have been busy with my personal life recently and implementation has stopped.
I hope to resume in June.

I will push the source code of the implementation in progress, so please take a look if you like.
Your comments are also welcome.