Simple Windows GUI application written in Go

win32.go

package main

import (
	"log"
	"syscall"
	"unsafe"
)

var (
	kernel32 = syscall.NewLazyDLL("kernel32.dll")

	pGetModuleHandleW = kernel32.NewProc("GetModuleHandleW")
)

func getModuleHandle() (syscall.Handle, error) {
	ret, _, err := pGetModuleHandleW.Call(uintptr(0))
	if ret == 0 {
		return 0, err
	}
	return syscall.Handle(ret), nil
}

var (
	user32 = syscall.NewLazyDLL("user32.dll")

	pCreateWindowExW  = user32.NewProc("CreateWindowExW")
	pDefWindowProcW   = user32.NewProc("DefWindowProcW")
	pDestroyWindow    = user32.NewProc("DestroyWindow")
	pDispatchMessageW = user32.NewProc("DispatchMessageW")
	pGetMessageW      = user32.NewProc("GetMessageW")
	pLoadCursorW      = user32.NewProc("LoadCursorW")
	pPostQuitMessage  = user32.NewProc("PostQuitMessage")
	pRegisterClassExW = user32.NewProc("RegisterClassExW")
	pTranslateMessage = user32.NewProc("TranslateMessage")
)

const (
	cSW_SHOW        = 5
	cSW_USE_DEFAULT = 0x80000000
)

const (
	cWS_MAXIMIZE_BOX = 0x00010000
	cWS_MINIMIZEBOX  = 0x00020000
	cWS_THICKFRAME   = 0x00040000
	cWS_SYSMENU      = 0x00080000
	cWS_CAPTION      = 0x00C00000
	cWS_VISIBLE      = 0x10000000

	cWS_OVERLAPPEDWINDOW = 0x00CF0000
)

func createWindow(className, windowName string, style uint32, x, y, width, height int32, parent, menu, instance syscall.Handle) (syscall.Handle, error) {
	ret, _, err := pCreateWindowExW.Call(
		uintptr(0),
		uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(className))),
		uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(windowName))),
		uintptr(style),
		uintptr(x),
		uintptr(y),
		uintptr(width),
		uintptr(height),
		uintptr(parent),
		uintptr(menu),
		uintptr(instance),
		uintptr(0),
	)
	if ret == 0 {
		return 0, err
	}
	return syscall.Handle(ret), nil
}

const (
	cWM_DESTROY = 0x0002
	cWM_CLOSE   = 0x0010
)

func defWindowProc(hwnd syscall.Handle, msg uint32, wparam, lparam uintptr) uintptr {
	ret, _, _ := pDefWindowProcW.Call(
		uintptr(hwnd),
		uintptr(msg),
		uintptr(wparam),
		uintptr(lparam),
	)
	return uintptr(ret)
}

func destroyWindow(hwnd syscall.Handle) error {
	ret, _, err := pDestroyWindow.Call(uintptr(hwnd))
	if ret == 0 {
		return err
	}
	return nil
}

type tPOINT struct {
	x, y int32
}

type tMSG struct {
	hwnd    syscall.Handle
	message uint32
	wParam  uintptr
	lParam  uintptr
	time    uint32
	pt      tPOINT
}

func dispatchMessage(msg *tMSG) {
	pDispatchMessageW.Call(uintptr(unsafe.Pointer(msg)))
}

func getMessage(msg *tMSG, hwnd syscall.Handle, msgFilterMin, msgFilterMax uint32) (bool, error) {
	ret, _, err := pGetMessageW.Call(
		uintptr(unsafe.Pointer(msg)),
		uintptr(hwnd),
		uintptr(msgFilterMin),
		uintptr(msgFilterMax),
	)
	if int32(ret) == -1 {
		return false, err
	}
	return int32(ret) != 0, nil
}

const (
	cIDC_ARROW = 32512
)

func loadCursorResource(cursorName uint32) (syscall.Handle, error) {
	ret, _, err := pLoadCursorW.Call(
		uintptr(0),
		uintptr(uint16(cursorName)),
	)
	if ret == 0 {
		return 0, err
	}
	return syscall.Handle(ret), nil
}

func postQuitMessage(exitCode int32) {
	pPostQuitMessage.Call(uintptr(exitCode))
}

const (
	cCOLOR_WINDOW = 5
)

type tWNDCLASSEXW struct {
	size       uint32
	style      uint32
	wndProc    uintptr
	clsExtra   int32
	wndExtra   int32
	instance   syscall.Handle
	icon       syscall.Handle
	cursor     syscall.Handle
	background syscall.Handle
	menuName   *uint16
	className  *uint16
	iconSm     syscall.Handle
}

func registerClassEx(wcx *tWNDCLASSEXW) (uint16, error) {
	ret, _, err := pRegisterClassExW.Call(
		uintptr(unsafe.Pointer(wcx)),
	)
	if ret == 0 {
		return 0, err
	}
	return uint16(ret), nil
}

func translateMessage(msg *tMSG) {
	pTranslateMessage.Call(uintptr(unsafe.Pointer(msg)))
}

func main() {
	className := "testClass"

	instance, err := getModuleHandle()
	if err != nil {
		log.Println(err)
		return
	}

	cursor, err := loadCursorResource(cIDC_ARROW)
	if err != nil {
		log.Println(err)
		return
	}

	fn := func(hwnd syscall.Handle, msg uint32, wparam, lparam uintptr) uintptr {
		switch msg {
		case cWM_CLOSE:
			destroyWindow(hwnd)
		case cWM_DESTROY:
			postQuitMessage(0)
		default:
			ret := defWindowProc(hwnd, msg, wparam, lparam)
			return ret
		}
		return 0
	}

	wcx := tWNDCLASSEXW{
		wndProc:    syscall.NewCallback(fn),
		instance:   instance,
		cursor:     cursor,
		background: cCOLOR_WINDOW + 1,
		className:  syscall.StringToUTF16Ptr(className),
	}
	wcx.size = uint32(unsafe.Sizeof(wcx))

	if _, err = registerClassEx(&wcx); err != nil {
		log.Println(err)
		return
	}

	_, err = createWindow(
		className,
		"Test Window",
		cWS_VISIBLE|cWS_OVERLAPPEDWINDOW,
		cSW_USE_DEFAULT,
		cSW_USE_DEFAULT,
		cSW_USE_DEFAULT,
		cSW_USE_DEFAULT,
		0,
		0,
		instance,
	)
	if err != nil {
		log.Println(err)
		return
	}

	for {
		msg := tMSG{}
		gotMessage, err := getMessage(&msg, 0, 0, 0)
		if err != nil {
			log.Println(err)
			return
		}

		if gotMessage {
			translateMessage(&msg)
			dispatchMessage(&msg)
		} else {
			break
		}
	}
}

I got a build error on this. .\win32.go:223: constant 2147483648 overflows int32. It's around "Test Window".

I also received the same error:
at line 223, file main.goconstant 2147483648 overflows int32

running go1.6 windows/amd64

Changing int32to int64in line 53 solves this (might not be the best solution):

x, y, width, height int32 --> x, y, width, height int64

@mrichman

I'm sorry for off topic, but what editor is that? Looks pretty :)

@waspoza i'm pretty sure it is atom (from github) with go-plus plugin

Yup atom for sure @waspoza

I don't know GO, but 2147483648 is 0x80000000, if an unsigned 32 bit integer (or even signed, if larger, eg. int64).

Presumably the setting of cSW_USE_DEFAULT = 0x80000000 is meant to be equivalent tocSW_USE_DEFAULT = -1 (or maybe -0 or -2147483647).

The locations it is used (specifying x, y, width, height, etc. are signed int32's (again suggesting that -1 means default).
I would assume that rather than inserting the bit pattern 0x80000000 (i.e. "10000000000000000000000000000000" where the leftmost bit is the sign flag, the checker at least (and maybe the interpreter/compiler) is either: type guessing and storing the no-type-specified constant (lines 37-39) cSW_USE_DEFAULT = 0x80000000 as either uint32 or int64 and therefore choking on assigning it to an int32 when it gets to the function, or: converting it to a number 2147483648 in some intermediary representation and then checking if that will fit into the int32 (which it won't, thus overflow).

Try changing cSW_USE_DEFAULT = 0x80000000 to cSW_USE_DEFAULT = -1 or casting the constant as an uint32.

I expect somewhere there is documentation that says something along the lines of "Values specified in hex default to unsigned int64" or "... unsigned int of the minimum size to hold the value" or something like that.

Pretty cool.

Using the windows api documentation, a more complex gui app is possible.

Changing int32to int64in line 53 solves this (might not be the best solution):

x, y, width, height int32 --> x, y, width, height int64

x, y, width, height int32 --> x, y, width, height uint32 looks like it works too

I confirmed that both of them had worked well.

x, y, width, height int32 --> x, y, width, height uint32

x, y, width, height int32 --> x, y, width, height int64

Anyway this is just what I want to know, Cool.

Awesome! Thanks for posting this. It's working fine. The only change required was updating int32 to int64 for parameter within CreateWindow function.