Window transparency doesn't work on Windows 10

[sbercx]

The DwmEnableBlurBehindWindow method for making windows transparent on Windows doesn't seem to work on Windows 10 anymore. On Windows 10 the DwmExtendFrameIntoClientArea function can be called with the margins set to -1 to make it fully transparent.

EDIT: The new method only works if the window decorations are disabled.

[LYP951018]

I'm trying to implement this by GetProcAddress in runtime. But should we cache kernel32 module handle in winit? Otherwise we may need to call LoadLibrary(or GetModuleHandle) every time the method is called.

[retep998]

Use lazy_static to lazily load kernel32.dll and keep the handle to it around and do the same for each of the function pointers. Never let go.

[haudan]

I will attempt to fix this as part of #568.

[subnomo]

I've enabled transparency using layered windows. It works with window decorations, as well. See my patch:

diff --git a/src/platform/windows/window.rs b/src/platform/windows/window.rs
index 259376f4..a227c090 100644
--- a/src/platform/windows/window.rs
+++ b/src/platform/windows/window.rs
@@ -905,6 +905,10 @@ unsafe fn init(
         ex_style |= winuser::WS_EX_NOREDIRECTIONBITMAP;
     }
 
+    if attributes.transparent {
+        ex_style |= winuser::WS_EX_LAYERED;
+    }
+
     // adjusting the window coordinates using the style
     winuser::AdjustWindowRectEx(&mut rect, style, 0, ex_style);
 
@@ -959,6 +963,11 @@ unsafe fn init(
                                               format!("{}", io::Error::last_os_error()))));
         }
 
+        if attributes.transparent {
+            let opacity = 100; // transparency value 0-255
+            winuser::SetLayeredWindowAttributes(handle, 0x0, opacity, winuser::LWA_ALPHA);
+        }
+
         WindowWrapper(handle)
     };

EDIT: This works if you just want a transparent window, it's not a replacement for DwmEnableBlurBehindWindow...