Windows: Support setting ICoreWebView2EnvironmentOptions8::ScrollBarStyle

[Themayu]

Is your feature request related to a problem? Please describe.

I need a way to set the WebView2 instance on Windows to use Fluent-style overlay scrollbars in Tauri. A member of the project has informed me on Discord that Wry exposes a way to set some platform-specific attributes by use of PlatformSpecificWebViewAttributes that are then used to configure settings in the WebView2 options and environment options.

Describe the solution you'd like

I propose adding a new field to PlatformSpecificWebViewAttributes on Windows, and a setter method to WebViewBuilderExtWindows to update this field. I'm unsure whether to use a boolean where true = fluent overlay scrollbars and false = default scrollbars, or an enum that exposes both Default and FluentOverlay. I feel the latter would be better for extensibility if Microsoft extend the list of scrollbar styles in the future.

I expect the API would look something like this (documentation omitted for brevity):

#[cfg(windows)]
#[derive(Clone, Copy, Default)]
pub enum ScrollbarStyle {
  #[default]
  Default,
  FluentOverlay,
}

...

#[cfg(windows)]
#[derive(Clone)]
pub(crate) struct PlatformSpecificWebViewAttributes {
  ...
  scrollbar_style: ScrollbarStyle,
}

#[cfg(windows)]
impl Default for PlatformSpecificWebViewAttributes {
  fn default() -> Self {
    Self {
      ...
      scrollbar_style: ScrollbarStyle::Default,
    }
  }
}

#[cfg(windows)]
pub trait WebViewBuilderExtWindows {
  ...
  fn with_scrollbar_style(self, style: ScrollbarStyle) -> Self;
}

#[cfg(windows)]
impl WebViewBuilderExtWindows for WebViewBuilder<'_> {
  ...
  fn with_scrollbar_style(self, style: ScrollbarStyle) -> Self {
    self.platform_specific.scrollbar_style = style;
    self
  }
}

Describe alternatives you've considered

I cannot use a browser flag for this, as per the Microsoft Documentation on WebView2 browser flags where it says that browser feature flags are subject to being removed or altered at any time.

Also, it was either this or adding and exposing a Windows-specific wrapper around all of ICoreWebView2EnvironmentOptions*. I feel that for now, this will do.

[amrbashir]

I'm unsure whether to use a boolean where true = fluent overlay scrollbars and false = default scrollbars, or an enum that exposes both Default and FluentOverlay. I feel the latter would be better for extensibility if Microsoft extend the list of scrollbar styles in the future.

An enum sounds fine

Do you plan to work on this in a PR? I can assign the issue to you in that case.

[Themayu]

I'm fine with adding this myself.

[Themayu]

Ah. I think I've encountered a bit of a problem: I can't figure out how I am going to expose this in Tauri, given that this is Windows-specific functionality with an enum that only exists in Wry when compiling for Windows.

[amrbashir]

one step at a time, you only need to worry about exposing it as a method on WebviewBuilderExtWindows, then later we can open a PR in Tauri, that will call this method.

[Themayu]

I have it exposed on WebviewBuilderExtWindows in my wry fork already, on the feat/windows-add-scrollbar-style-option branch. The reason I'm trying to figure out how to expose it in Tauri right now is so that I can test it, and make sure it's actually doing what I want it to.

[amrbashir]

you can see this commit for inspiration tauri-apps/tauri@3dc38b1

[Themayu]

...I just realised I don't need to expose it in Tauri to test it just yet. I can just do something dirty - force it inside a local patch of tauri_runtime_wry, then revert that when I'm done.

[Themayu]

...

Well that's... very annoying.

Turns out that despite them being exposed, and despite the Microsoft documentation for ICoreWebView2EnvironmentOptions clearly showing the ability to cast CoreWebView2EnvironmentOptions to ICoreWebView2EnvironmentOptions4 and above, it turns out that webview2-com doesn't actually reflect the implementations of ICoreWebView2EnvironmentOptions4 or above on CoreWebView2EnvironmentOptions. So everything lines up according to the C++ documentation, but I'm completely unable to actually cast to ICoreWebView2EnvironmentOptions8 in order to set the scrollbar style.

I'm going to submit a request for the missing COM interfaces to be added.

[amrbashir]

webview2-com does have that https://docs.rs/webview2-com/latest/webview2_com/Microsoft/Web/WebView2/Win32/struct.ICoreWebView2EnvironmentOptions8.html , we just haven't updated the version in wry, probably because we need to update windows-sys and windows crate across our repos

gonna start working on that today

[Themayu]

It has the interface defined. So does the version we are using here. It does not appear to have an implementation of that interface reflected on CoreWebView2EnvironmentOptions, which means we cannot cast to it.

[amrbashir]

I see, it is missing in https://github.com/wravery/webview2-rs/blob/2a4d92c91002f91b49fd282abbbe8ec8d3318339/crates/webview2-com/src/options.rs#L26-L31

[Themayu]

I've opened a request in webview2-com: wravery/webview2-rs#30

[Themayu]

@amrbashir Good news: The missing COM interface implementations were added to CoreWebView2EnvironmentOptions in [email protected], so this can go forward once Wry updates to the latest version.

Also, it turned out that the raw ICoreWebView2EnvironmentOptions4 had a problem, so it was replaced with a custom-made IFixedEnvironmentOptions4 instead.

[amrbashir]

webview2-com is updated in #1341

[Themayu]

Alright. I'll rebase onto that commit once it lands, then open a PR for both this and moving to using the CoreWebView2EnvironmentOptions API directly.