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

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 ());