Fix Windows transparency behavior to support fully-opaque regions

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Unreleased
 
 - On Android, calling `WindowEvent::Focused` now works properly instead of always returning false. 
+- On Windows, fix bug preventing windows with transparency enabled from having fully-opaque regions.
 
 # 0.23.0 (2020-10-02)
 

src/platform_impl/windows/window.rs

@@ -23,7 +23,6 @@ use winapi::{
         ole2,
         oleidl::LPDROPTARGET,
         shobjidl_core::{CLSID_TaskbarList, ITaskbarList2},
-        wingdi::{CreateRectRgn, DeleteObject},
         winnt::LPCWSTR,
         winuser,
     },
@@ -708,33 +707,19 @@ unsafe fn init<T: 'static>(
 
     // making the window transparent
     if attributes.transparent && !pl_attribs.no_redirection_bitmap {
-        let region = CreateRectRgn(0, 0, -1, -1); // makes the window transparent
-
         let bb = dwmapi::DWM_BLURBEHIND {
-            dwFlags: dwmapi::DWM_BB_ENABLE | dwmapi::DWM_BB_BLURREGION,
+            dwFlags: dwmapi::DWM_BB_ENABLE,
             fEnable: 1,
-            hRgnBlur: region,
+            hRgnBlur: ptr::null_mut(),
             fTransitionOnMaximized: 0,
         };
 
         dwmapi::DwmEnableBlurBehindWindow(real_window.0, &bb);
-        DeleteObject(region as _);
 
         if attributes.decorations {
-            // HACK: When opaque (opacity 255), there is a trail whenever
-            // the transparent window is moved. By reducing it to 254,
-            // the window is rendered properly.
-            let opacity = 254;
-
-            // The color key can be any value except for black (0x0).
-            let color_key = 0x0030c100;
-
-            winuser::SetLayeredWindowAttributes(
-                real_window.0,
-                color_key,
-                opacity,
-                winuser::LWA_ALPHA,
-            );
+            let opacity = 255;
+
+            winuser::SetLayeredWindowAttributes(real_window.0, 0, opacity, winuser::LWA_ALPHA);
         }
     }