windows feature WS_EX_NOREDIRECTIONBITMAP (#575)

* set WS_EX_NOREDIRECTIONBITMAP

* add CHANGELOG.md

* more flexibility.

* Skip DwmEnableBlurBehindWindow if no_redirection_bitmap is enabled.

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Unreleased
 
+- Windows additionally has `WindowBuilderExt::with_no_redirection_bitmap`.
 - **Breaking:** Removed `VirtualKeyCode::LMenu` and `VirtualKeyCode::RMenu`; Windows now generates `VirtualKeyCode::LAlt` and `VirtualKeyCode::RAlt` instead.
 - On X11, exiting fullscreen no longer leaves the window in the monitor's top left corner.
 - **Breaking:** `Window::hidpi_factor` has been renamed to `Window::get_hidpi_factor` for better consistency. `WindowEvent::HiDPIFactorChanged` has been renamed to `WindowEvent::HiDpiFactorChanged`. DPI factors are always represented as `f64` instead of `f32` now.

src/os/windows.rs

@@ -55,6 +55,9 @@ pub trait WindowBuilderExt {
 
     /// This sets `ICON_BIG`. A good ceiling here is 256x256.
     fn with_taskbar_icon(self, taskbar_icon: Option<Icon>) -> WindowBuilder;
+
+    /// This sets `WS_EX_NOREDIRECTIONBITMAP`.
+    fn with_no_redirection_bitmap(self, flag: bool) -> WindowBuilder;
 }
 
 impl WindowBuilderExt for WindowBuilder {
@@ -69,6 +72,12 @@ impl WindowBuilderExt for WindowBuilder {
         self.platform_specific.taskbar_icon = taskbar_icon;
         self
     }
+
+    #[inline]
+    fn with_no_redirection_bitmap(mut self, flag: bool) -> WindowBuilder {
+        self.platform_specific.no_redirection_bitmap = flag;
+        self
+    }
 }
 
 /// Additional methods on `MonitorId` that are specific to Windows.

src/platform/windows/mod.rs

@@ -11,6 +11,7 @@ pub use self::window::Window;
 pub struct PlatformSpecificWindowBuilderAttributes {
     pub parent: Option<HWND>,
     pub taskbar_icon: Option<::Icon>,
+    pub no_redirection_bitmap: bool,
 }
 
 unsafe impl Send for PlatformSpecificWindowBuilderAttributes {}

src/platform/windows/window.rs

@@ -888,6 +888,9 @@ unsafe fn init(
     if attributes.always_on_top {
         ex_style |= winuser::WS_EX_TOPMOST;
     }
+    if pl_attribs.no_redirection_bitmap {
+        ex_style |= winuser::WS_EX_NOREDIRECTIONBITMAP;
+    }
 
     // adjusting the window coordinates using the style
     winuser::AdjustWindowRectEx(&mut rect, style, 0, ex_style);
@@ -999,7 +1002,7 @@ unsafe fn init(
     };
 
     // making the window transparent
-    if attributes.transparent {
+    if attributes.transparent && !pl_attribs.no_redirection_bitmap {
         let bb = dwmapi::DWM_BLURBEHIND {
             dwFlags: 0x1, // FIXME: DWM_BB_ENABLE;
             fEnable: 1,