Added GDI+ to the package's Windows version: DLL loaded, initialized, and shut down. It will be used for drawing to Areas because using GDI itself is more complex than it needs to be.

common_windows.go

@@ -12,6 +12,7 @@ var (
 	kernel32 = syscall.NewLazyDLL("kernel32.dll")
 	gdi32 = syscall.NewLazyDLL("gdi32.dll")
 	comctl32 = syscall.NewLazyDLL("comctl32.dll")
+	gdiplus = syscall.NewLazyDLL("gdiplus.dll")
 )
 
 type _HANDLE uintptr

init_windows.go

@@ -11,6 +11,7 @@ import (
 var (
 	hInstance		_HANDLE
 	nCmdShow	int
+	gdiplusToken	uintptr
 )
 
 // TODO is this trick documented in MSDN?
@@ -56,6 +57,26 @@ func getWinMainnCmdShow() {
 	}
 }
 
+func initGDIPlus() (err error) {
+	var gdiplusInit struct {
+		GdiplusVersion				uint32
+		DebugEventCallback			uintptr
+		SuppressBackgroundThread	int32		// originally BOOL
+		SuppressExternalCodecs		int32		// originally BOOL
+	}
+
+	gdiplusInit.GdiplusVersion = 1		// required
+	// TODO suppress external codecs?
+	r1, _, err := gdiplus.NewProc("GdiplusStartup").Call(
+		uintptr(unsafe.Pointer(&gdiplusToken)),
+		uintptr(unsafe.Pointer(&gdiplusInit)),
+		uintptr(0))		// we use the GDI+ thread so no need for output info
+	if r1 != 0 {			// failure
+		return fmt.Errorf("error initializing GDI+ (GDI+ error code %d; windows last error %v)", r1, err)
+	}
+	return nil
+}
+
 func doWindowsInit() (err error) {
 	err = getWinMainhInstance()
 	if err != nil {
@@ -74,6 +95,14 @@ func doWindowsInit() (err error) {
 	if err != nil {
 		return fmt.Errorf("error initializing Common Controls (comctl32.dll): %v", err)
 	}
+	err = initGDIPlus()
+	if err != nil {
+		return fmt.Errorf("error initializing GDI+ (gdiplus.dll): %v", err)
+	}
 	// TODO others
 	return nil		// all ready to go
 }
+
+func doWindowsQuitStuff() {
+	gdiplus.NewProc("GdiplusShutdown").Call(gdiplusToken)		// returns void according to MSDN
+}

uitask_windows.go

@@ -84,6 +84,7 @@ func ui(main func()) error {
 		}
 	}
 
+	doWindowsQuitStuff()
 	return nil
 }