On Windows, add option to customize window class name (#2978)

CHANGELOG.md

@@ -8,6 +8,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 
 # Unreleased
 
+- On Windows, added `WindowBuilderExtWindows::with_class_name` to customize the internal class name.
 - On iOS, always wake the event loop when transitioning from `ControlFlow::Poll` to `ControlFlow::Poll`.
 - **Breaking:** `ActivationTokenDone` event which could be requested with the new `startup_notify` module, see its docs for more.
 - On Wayland, make double clicking and moving the CSD frame more reliable.

FEATURES.md

@@ -119,6 +119,7 @@ If your PR makes notable changes to Winit's features, please update this section
 
 ## Platform
 ### Windows
+* Setting the name of the internal window class
 * Setting the taskbar icon
 * Setting the parent window
 * Setting a menu bar

src/platform/windows.rs

@@ -223,6 +223,9 @@ pub trait WindowBuilderExtWindows {
     /// Whether show or hide the window icon in the taskbar.
     fn with_skip_taskbar(self, skip: bool) -> WindowBuilder;
 
+    /// Customize the window class name.
+    fn with_class_name<S: Into<String>>(self, class_name: S) -> WindowBuilder;
+
     /// Shows or hides the background drop shadow for undecorated windows.
     ///
     /// The shadow is hidden by default.
@@ -267,6 +270,12 @@ impl WindowBuilderExtWindows for WindowBuilder {
         self
     }
 
+    #[inline]
+    fn with_class_name<S: Into<String>>(mut self, class_name: S) -> WindowBuilder {
+        self.platform_specific.class_name = class_name.into();
+        self
+    }
+
     #[inline]
     fn with_undecorated_shadow(mut self, shadow: bool) -> WindowBuilder {
         self.platform_specific.decoration_shadow = shadow;

src/platform_impl/windows/mod.rs

@@ -30,6 +30,7 @@ pub struct PlatformSpecificWindowBuilderAttributes {
     pub no_redirection_bitmap: bool,
     pub drag_and_drop: bool,
     pub skip_taskbar: bool,
+    pub class_name: String,
     pub decoration_shadow: bool,
 }
 
@@ -42,6 +43,7 @@ impl Default for PlatformSpecificWindowBuilderAttributes {
             no_redirection_bitmap: false,
             drag_and_drop: true,
             skip_taskbar: false,
+            class_name: "Window Class".to_string(),
             decoration_shadow: false,
         }
     }

src/platform_impl/windows/window.rs

@@ -1100,7 +1100,8 @@ where
 {
     let title = util::encode_wide(&attributes.title);
 
-    let class_name = register_window_class::<T>();
+    let class_name = util::encode_wide(&pl_attribs.class_name);
+    register_window_class::<T>(&class_name);
 
     let mut window_flags = WindowFlags::empty();
     window_flags.set(WindowFlags::MARKER_DECORATIONS, attributes.decorations);
@@ -1187,9 +1188,7 @@ where
     Ok(initdata.window.unwrap())
 }
 
-unsafe fn register_window_class<T: 'static>() -> Vec<u16> {
-    let class_name = util::encode_wide("Window Class");
-
+unsafe fn register_window_class<T: 'static>(class_name: &[u16]) {
     let class = WNDCLASSEXW {
         cbSize: mem::size_of::<WNDCLASSEXW>() as u32,
         style: CS_HREDRAW | CS_VREDRAW,
@@ -1210,8 +1209,6 @@ unsafe fn register_window_class<T: 'static>() -> Vec<u16> {
     // Also since there is no weird element in the struct, there is no reason for this
     //  call to fail.
     RegisterClassExW(&class);
-
-    class_name
 }
 
 struct ComInitialized(*mut ());