http://stackoverflow.com/questions/12414669

/*
  file: testwinapi.go

  go! winapi test using "go-winapi":
    http://github.com/lxn/go-winapi
*/

// this package
package main

// package imports
import (
    "fmt"
    "github.com/lxn/go-winapi"
    "os"
    "syscall"
    "unsafe"
)

// variables
var (
    oldWndProc winapi.HWND
)

// constants
const (
    winWidth       int32 = 300
    winHeight      int32 = 200
    SIZE_MAXIMIZED       = 2
)

// string to int16(utf) helper function
func _S(_srt string) *uint16 {
    return syscall.StringToUTF16Ptr(_srt)
}

// window procedure
func WndProc(hwnd winapi.HWND, msg uint32, wparam uintptr, lparam uintptr) uintptr {
    switch msg {
    case winapi.WM_SIZE:
        if wparam == SIZE_MAXIMIZED {
            fmt.Println("Changed!")
        }
    }
    // call original procedure
    return winapi.CallWindowProc(uintptr(oldWndProc), hwnd, msg, wparam, lparam)
}

// main
func main() {
    var message winapi.MSG
    var hwnd winapi.HWND
    var wproc uintptr

    // create an edit window
    hwnd = winapi.CreateWindowEx(
        winapi.WS_EX_CLIENTEDGE,
        _S("EDIT"),
        _S("test window"),
        winapi.WS_OVERLAPPEDWINDOW,
        (winapi.GetSystemMetrics(winapi.SM_CXSCREEN)-winWidth)>>1,
        (winapi.GetSystemMetrics(winapi.SM_CYSCREEN)-winHeight)>>1,
        winWidth,
        winHeight,
        0,
        0,
        winapi.GetModuleHandle(nil),
        unsafe.Pointer(nil))

    // create callback, set procedure, show window
    wproc = syscall.NewCallback(WndProc)
    oldWndProc = winapi.HWND(winapi.SetWindowLong(hwnd, winapi.GWL_WNDPROC, int32(wproc)))
    winapi.ShowWindow(hwnd, winapi.SW_SHOWDEFAULT)

    // dispatch message
    for {
        if winapi.GetMessage(&message, 0, 0, 0) == 0 {
            break
        }
        winapi.TranslateMessage(&message)
        winapi.DispatchMessage(&message)
    }

    // print handle and exit
    fmt.Println("hwnd =", hwnd)
    os.Exit(int(message.WParam))
}