windows: add DWM window attribute related syscalls

https://docs.microsoft.com/en-us/windows/win32/api/dwmapi/nf-dwmapi-dwmgetwindowattribute
https://docs.microsoft.com/en-us/windows/win32/api/dwmapi/nf-dwmapi-dwmsetwindowattribute

Change-Id: I96a68f91f745601e93c0cc21cc4f1f4c5e7d8b9e
GitHub-Last-Rev: bdbe2cc
GitHub-Pull-Request: #123
Reviewed-on: https://go-review.googlesource.com/c/sys/+/399135
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Run-TryBot: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

Author: ToadKing

windows/syscall_windows.go

@@ -442,6 +442,10 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	RtlAddFunctionTable(functionTable *RUNTIME_FUNCTION, entryCount uint32, baseAddress uintptr) (ret bool) = ntdll.RtlAddFunctionTable
 //sys	RtlDeleteFunctionTable(functionTable *RUNTIME_FUNCTION) (ret bool) = ntdll.RtlDeleteFunctionTable
 
+// Desktop Window Manager API (Dwmapi)
+//sys	DwmGetWindowAttribute(hwnd HWND, attribute uint32, value unsafe.Pointer, size uint32) (ret error) = dwmapi.DwmGetWindowAttribute
+//sys	DwmSetWindowAttribute(hwnd HWND, attribute uint32, value unsafe.Pointer, size uint32) (ret error) = dwmapi.DwmSetWindowAttribute
+
 // syscall interface implementation for other packages
 
 // GetCurrentProcess returns the handle for the current process.

windows/types_windows.go

@@ -3232,3 +3232,29 @@ type GUIThreadInfo struct {
 	CaretHandle HWND
 	CaretRect   Rect
 }
+
+const (
+	DWMWA_NCRENDERING_ENABLED            = 1
+	DWMWA_NCRENDERING_POLICY             = 2
+	DWMWA_TRANSITIONS_FORCEDISABLED      = 3
+	DWMWA_ALLOW_NCPAINT                  = 4
+	DWMWA_CAPTION_BUTTON_BOUNDS          = 5
+	DWMWA_NONCLIENT_RTL_LAYOUT           = 6
+	DWMWA_FORCE_ICONIC_REPRESENTATION    = 7
+	DWMWA_FLIP3D_POLICY                  = 8
+	DWMWA_EXTENDED_FRAME_BOUNDS          = 9
+	DWMWA_HAS_ICONIC_BITMAP              = 10
+	DWMWA_DISALLOW_PEEK                  = 11
+	DWMWA_EXCLUDED_FROM_PEEK             = 12
+	DWMWA_CLOAK                          = 13
+	DWMWA_CLOAKED                        = 14
+	DWMWA_FREEZE_REPRESENTATION          = 15
+	DWMWA_PASSIVE_UPDATE_MODE            = 16
+	DWMWA_USE_HOSTBACKDROPBRUSH          = 17
+	DWMWA_USE_IMMERSIVE_DARK_MODE        = 20
+	DWMWA_WINDOW_CORNER_PREFERENCE       = 33
+	DWMWA_BORDER_COLOR                   = 34
+	DWMWA_CAPTION_COLOR                  = 35
+	DWMWA_TEXT_COLOR                     = 36
+	DWMWA_VISIBLE_FRAME_BORDER_THICKNESS = 37
+)