Merge pull request #17 from papplampe/master

added Center function to window + Windows implementation (thanks to @papplampe)

common_windows.go

@@ -91,6 +91,7 @@ var (
 	_setWindowPos       = user32.NewProc("SetWindowPos")
 	_setWindowText      = user32.NewProc("SetWindowTextW")
 	_showWindow         = user32.NewProc("ShowWindow")
+	_getWindowRect      = user32.NewProc("GetWindowRect")
 )
 
 type _MINMAXINFO struct {

sysdata_windows.go

@@ -685,3 +685,15 @@ func (s *sysData) repaintAll() {
 	}
 	<-ret
 }
+
+func (s *sysData) center() {
+	var ws _RECT
+	_getWindowRect.Call(uintptr(s.hwnd), uintptr(unsafe.Pointer(&ws)))
+	dw, _, _ := _getSystemMetrics.Call(_SM_CXFULLSCREEN)
+	dh, _, _ := _getSystemMetrics.Call(_SM_CYFULLSCREEN)
+	ww := ws.right - ws.left
+	wh := ws.bottom - ws.top
+	wx := (int32(dw) / 2) - (ww / 2)
+	wy := (int32(dh) / 2) - (wh / 2)
+	s.setRect(int(wx), int(wy), int(ww), int(wh), 0)
+}

window.go

@@ -120,3 +120,14 @@ func (w *Window) Hide() {
 
 	w.sysData.hide()
 }
+
+// Centers the window
+func (w *Window) Center() {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	if !w.created {
+		return
+	}
+	w.sysData.center()
+}

zconstants_windows_386.go

@@ -81,6 +81,8 @@ const _SIF_RANGE = 1
 const _SIF_TRACKPOS = 16
 const _SM_CXDOUBLECLK = 36
 const _SM_CYDOUBLECLK = 37
+const _SM_CXFULLSCREEN = 16
+const _SM_CYFULLSCREEN = 17
 const _SPI_GETNONCLIENTMETRICS = 41
 const _SRCCOPY = 13369376
 const _SS_LEFTNOWORDWRAP = 12

zconstants_windows_amd64.go

@@ -81,6 +81,8 @@ const _SIF_RANGE = 1
 const _SIF_TRACKPOS = 16
 const _SM_CXDOUBLECLK = 36
 const _SM_CYDOUBLECLK = 37
+const _SM_CXFULLSCREEN = 16
+const _SM_CYFULLSCREEN = 17
 const _SPI_GETNONCLIENTMETRICS = 41
 const _SRCCOPY = 13369376
 const _SS_LEFTNOWORDWRAP = 12