feat(webview2): add theme API, closes #806 (#809)

.changes/webview2-theme.md

@@ -0,0 +1,5 @@
+---
+"wry": "patch"
+---
+
+On Windows, Add `WebviewBuilderExtWindows::with_theme` and `WebviewExtWindows::set_theme` to change webview2 theme.

src/webview/mod.rs

@@ -256,16 +256,19 @@ impl Default for WebViewAttributes {
 }
 
 #[cfg(windows)]
+#[derive(Clone)]
 pub(crate) struct PlatformSpecificWebViewAttributes {
   additional_browser_args: Option<String>,
   browser_accelerator_keys: bool,
+  theme: Option<Theme>,
 }
 #[cfg(windows)]
 impl Default for PlatformSpecificWebViewAttributes {
   fn default() -> Self {
     Self {
       additional_browser_args: None,
       browser_accelerator_keys: true, // This is WebView2's default behavior
+      theme: None,
     }
   }
 }
@@ -610,6 +613,11 @@ pub trait WebViewBuilderExtWindows {
   ///
   /// https://learn.microsoft.com/en-us/microsoft-edge/webview2/reference/winrt/microsoft_web_webview2_core/corewebview2settings#arebrowseracceleratorkeysenabled
   fn with_browser_accelerator_keys(self, enabled: bool) -> Self;
+
+  /// Specifies the theme of webview2. This affects things like `prefers-color-scheme`.
+  ///
+  /// Defaults to [`Theme::Auto`] which will follow the OS defaults.
+  fn with_theme(self, theme: Theme) -> Self;
 }
 
 #[cfg(windows)]
@@ -623,6 +631,11 @@ impl WebViewBuilderExtWindows for WebViewBuilder<'_> {
     self.platform_specific.browser_accelerator_keys = enabled;
     self
   }
+
+  fn with_theme(mut self, theme: Theme) -> Self {
+    self.platform_specific.theme = Some(theme);
+    self
+  }
 }
 
 /// The fundamental type to present a [`WebView`].
@@ -796,13 +809,20 @@ pub fn webview_version() -> Result<String> {
 pub trait WebviewExtWindows {
   /// Returns WebView2 Controller
   fn controller(&self) -> ICoreWebView2Controller;
+
+  // Changes the webview2 theme.
+  fn set_theme(&self, theme: Theme);
 }
 
 #[cfg(target_os = "windows")]
 impl WebviewExtWindows for WebView {
   fn controller(&self) -> ICoreWebView2Controller {
     self.webview.controller.clone()
   }
+
+  fn set_theme(&self, theme: Theme) {
+    self.webview.set_theme(theme)
+  }
 }
 
 /// Additional methods on `WebView` that are specific to Linux.
@@ -858,6 +878,13 @@ impl WebviewExtAndroid for WebView {
   }
 }
 
+#[derive(Debug, Clone, Copy)]
+pub enum Theme {
+  Dark,
+  Light,
+  Auto,
+}
+
 #[cfg(test)]
 mod tests {
   use super::*;

src/webview/webview2/mod.rs

@@ -42,6 +42,8 @@ use webview2_com::{Microsoft::Web::WebView2::Win32::*, *};
 use crate::application::{platform::windows::WindowExtWindows, window::Window};
 use http::Request;
 
+use super::Theme;
+
 impl From<webview2_com::Error> for Error {
   fn from(err: webview2_com::Error) -> Self {
     Error::WebView2Error(err)
@@ -69,17 +71,9 @@ impl InnerWebView {
     let file_drop_handler = attributes.file_drop_handler.take();
     let file_drop_window = window.clone();
 
-    let browser_accelerator_keys = pl_attrs.browser_accelerator_keys;
-    let env = Self::create_environment(&web_context, pl_attrs)?;
+    let env = Self::create_environment(&web_context, pl_attrs.clone())?;
     let controller = Self::create_controller(hwnd, &env)?;
-    let webview = Self::init_webview(
-      window,
-      hwnd,
-      attributes,
-      &env,
-      &controller,
-      browser_accelerator_keys,
-    )?;
+    let webview = Self::init_webview(window, hwnd, attributes, &env, &controller, pl_attrs)?;
 
     if let Some(file_drop_handler) = file_drop_handler {
       let mut controller = FileDropController::new();
@@ -198,11 +192,16 @@ impl InnerWebView {
     mut attributes: WebViewAttributes,
     env: &ICoreWebView2Environment,
     controller: &ICoreWebView2Controller,
-    browser_accelerator_keys: bool,
+    pl_attrs: super::PlatformSpecificWebViewAttributes,
   ) -> webview2_com::Result<ICoreWebView2> {
     let webview =
       unsafe { controller.CoreWebView2() }.map_err(webview2_com::Error::WindowsError)?;
 
+    // theme
+    if let Some(theme) = pl_attrs.theme {
+      set_theme(&webview, theme);
+    }
+
     // background color
     if !attributes.transparent {
       if let Some(background_color) = attributes.background_color {
@@ -255,7 +254,7 @@ impl InnerWebView {
           .SetAreDevToolsEnabled(true)
           .map_err(webview2_com::Error::WindowsError)?;
       }
-      if !browser_accelerator_keys {
+      if !pl_attrs.browser_accelerator_keys {
         if let Ok(settings3) = settings.cast::<ICoreWebView2Settings3>() {
           settings3
             .SetAreBrowserAcceleratorKeysEnabled(false)
@@ -828,6 +827,10 @@ window.addEventListener('mousemove', (e) => window.chrome.webview.postMessage('_
     let url = encode_wide(url);
     let _ = unsafe { self.webview.Navigate(PCWSTR::from_raw(url.as_ptr())) };
   }
+
+  pub fn set_theme(&self, theme: Theme) {
+    set_theme(&self.webview, theme);
+  }
 }
 
 fn encode_wide(string: impl AsRef<std::ffi::OsStr>) -> Vec<u16> {
@@ -858,6 +861,21 @@ pub fn set_background_color(
   }
 }
 
+fn set_theme(webview: &ICoreWebView2, theme: Theme) {
+  unsafe {
+    let _ = webview
+      .cast::<ICoreWebView2_13>()
+      .unwrap()
+      .Profile()
+      .unwrap()
+      .SetPreferredColorScheme(match theme {
+        Theme::Dark => COREWEBVIEW2_PREFERRED_COLOR_SCHEME_DARK,
+        Theme::Light => COREWEBVIEW2_PREFERRED_COLOR_SCHEME_LIGHT,
+        Theme::Auto => COREWEBVIEW2_PREFERRED_COLOR_SCHEME_AUTO,
+      });
+  }
+}
+
 pub fn platform_webview_version() -> Result<String> {
   let mut versioninfo = PWSTR::null();
   unsafe { GetAvailableCoreWebView2BrowserVersionString(PCWSTR::null(), &mut versioninfo) }