Is it possible to turn on webview-level pinch-zoom gesture?

[hippietrail]

I can't find this anywhere except for a few people asking a few years ago the opposite, how to turn pinch-zoom off.

But I want to make a Tauri app that allows pinch-zoom just like browsers do, as part of the system. I know I can manually set it up in JavaScript but that's not what I'm looking for.

If it makes a difference I'm on macOS so I guess it's a Safari webview.

[FabianLars]

as far as i know, wkwebview has no easy toggle for this so as i understand it you or we have to use https://developer.apple.com/documentation/appkit/nsmagnificationgesturerecognizer to listen to the pinch event and then call https://docs.rs/tauri/latest/tauri/webview/struct.WebviewWindow.html#method.set_zoom (or its native objc equivalent) to actual zoom in/out :/

The "good" thing is that this should be possible to implement in the app directly, the "bad" thing is that using objective-c, especially in rust, isn't exactly easy.

[hippietrail]

Thank you! I used to think objective-c was horrible but now I see it as just another quaint quirky language.

[sunnypatell]

@hippietrail @FabianLars's suggestion works but there's a simpler path. WKWebView has a built-in allowsMagnification property (macOS only, defaults to false) that enables native pinch-zoom without gesture recognizer wiring.

tauri/wry doesn't expose it though. looking at wry's source, zoom() uses setPageZoom() (CSS-level) and there's no reference to allowsMagnification anywhere.

the quickest workaround is unsafe obj-c from your tauri setup:

use objc2::msg_send;

// after webview creation
let webview = window.webview().inner();
unsafe {
    let _: () = msg_send![webview, setAllowsMagnification: true];
}

if you want something without unsafe code, the CSS viewport approach handles most cases:

<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=5, user-scalable=yes">

the cleanest long-term fix would be a PR to wry adding with_magnification_enabled(bool) to WebViewBuilder that calls setAllowsMagnification: on macOS. it's a small change in src/wkwebview/mod.rs. note: allowsMagnification is macOS-only, iOS uses the viewport meta tag approach.

[FabianLars]

Weird that I missed that. Thanks for the correction.

[sunnypatell]

@hippietrail did the allowsMagnification route end up working for you? it skips all the gesture recognizer/objc wiring that @FabianLars mentioned since WKWebView handles the pinch natively. if it solved your case, marking one of these as the answer would help others searching for tauri pinch-zoom.

[hippietrail]

@hippietrail did the allowsMagnification route end up working for you? it skips all the gesture recognizer/objc wiring that @FabianLars mentioned since WKWebView handles the pinch natively. if it solved your case, marking one of these as the answer would help others searching for tauri pinch-zoom.

I haven't had a chance to try it. At the time I was trying out various GUI solutions for Rust and that was one of the features I wanted. I did manage to get pinch-zoom working with the trackpad in a webview, which is obviously not the same thing. I will surely play with this again though.