feat(windows): allow setting memory usage target level to reduce memo…

…ry consumption of inactive application (#1053)

* feat(windows): Allow setting memory usage target level

Signed-off-by: rhysd <[email protected]>

* chore(doc): clarify `WebviewExtWindows::set_low_memory_usage` does nothing with WebView2 earlier than v1.0.1020.30

Signed-off-by: rhysd <[email protected]>

* chore(doc): apply review suggestions by @FabianLars

Co-authored-by: Fabian-Lars <[email protected]>

* feat(windows): change the memory usage level to `MemoryUsageLevel` enum

Signed-off-by: rhysd <[email protected]>

* use en-us link

---------

Signed-off-by: rhysd <[email protected]>
Co-authored-by: Fabian-Lars <[email protected]>

.changes/add-api-to-set-memory-usage-for-windows.md

@@ -0,0 +1,5 @@
+---
+"wry": patch
+---
+
+Add `WebviewExtWindows::set_memory_usage_level` API to set the [memory usage target level](https://learn.microsoft.com/en-us/dotnet/api/microsoft.web.webview2.core.corewebview2memoryusagetargetlevel) on Windows. Setting 'Low' memory usage target level when an application is going to inactive can significantly reduce the memory consumption. Please read the [guide for WebView2](https://github.com/MicrosoftEdge/WebView2Feedback/blob/main/specs/MemoryUsageTargetLevel.md) for more details.

src/webview/mod.rs

@@ -1134,14 +1134,45 @@ pub fn webview_version() -> Result<String> {
   platform_webview_version()
 }
 
+/// The [memory usage target level][1]. There are two levels 'Low' and 'Normal' and the default
+/// level is 'Normal'. When the application is going inactive, setting the level to 'Low' can
+/// significantly reduce the application's memory consumption.
+///
+/// [1]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.web.webview2.core.corewebview2memoryusagetargetlevel
+#[cfg(target_os = "windows")]
+#[non_exhaustive]
+#[derive(Default, Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum MemoryUsageLevel {
+  /// The 'Normal' memory usage. Applications should set this level when they are becoming active.
+  #[default]
+  Normal,
+  /// The 'Low' memory usage. Applications can reduce memory comsumption by setting this level when
+  /// they are becoming inactive.
+  Low,
+}
+
 /// Additional methods on `WebView` that are specific to Windows.
 #[cfg(target_os = "windows")]
 pub trait WebviewExtWindows {
   /// Returns WebView2 Controller
   fn controller(&self) -> ICoreWebView2Controller;
 
-  // Changes the webview2 theme.
+  /// Changes the webview2 theme.
   fn set_theme(&self, theme: Theme);
+
+  /// Sets the [memory usage target level][1].
+  ///
+  /// When to best use this mode depends on the app in question. Most commonly it's called when
+  /// the app's visiblity state changes.
+  ///
+  /// Please read the [guide for WebView2][2] for more details.
+  ///
+  /// This method uses a WebView2 API added in Runtime version 114.0.1823.32. When it is used in
+  /// an older Runtime version, it does nothing.
+  ///
+  /// [1]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.web.webview2.core.corewebview2memoryusagetargetlevel
+  /// [2]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.web.webview2.core.corewebview2.memoryusagetargetlevel?view=webview2-dotnet-1.0.2088.41#remarks
+  fn set_memory_usage_level(&self, level: MemoryUsageLevel);
 }
 
 #[cfg(target_os = "windows")]
@@ -1153,6 +1184,10 @@ impl WebviewExtWindows for WebView {
   fn set_theme(&self, theme: Theme) {
     self.webview.set_theme(theme)
   }
+
+  fn set_memory_usage_level(&self, level: MemoryUsageLevel) {
+    self.webview.set_memory_usage_level(level);
+  }
 }
 
 /// Additional methods on `WebView` that are specific to Linux.

src/webview/webview2/mod.rs

@@ -7,7 +7,8 @@ mod resize;
 
 use crate::{
   webview::{
-    proxy::ProxyConfig, PageLoadEvent, RequestAsyncResponder, WebContext, WebViewAttributes, RGBA,
+    proxy::ProxyConfig, MemoryUsageLevel, PageLoadEvent, RequestAsyncResponder, WebContext,
+    WebViewAttributes, RGBA,
   },
   Error, Result,
 };
@@ -967,6 +968,19 @@ window.addEventListener('mousemove', (e) => window.chrome.webview.postMessage('_
   pub fn set_theme(&self, theme: Theme) {
     set_theme(&self.webview, theme);
   }
+
+  pub fn set_memory_usage_level(&self, level: MemoryUsageLevel) {
+    let Ok(webview) = self.webview.cast::<ICoreWebView2_19>() else {
+      return;
+    };
+    // https://learn.microsoft.com/en-us/dotnet/api/microsoft.web.webview2.core.corewebview2memoryusagetargetlevel
+    let level = match level {
+      MemoryUsageLevel::Normal => 0,
+      MemoryUsageLevel::Low => 1,
+    };
+    let level = COREWEBVIEW2_MEMORY_USAGE_TARGET_LEVEL(level);
+    let _ = unsafe { webview.SetMemoryUsageTargetLevel(level) };
+  }
 }
 
 unsafe fn prepare_web_request_response(