Added scrollbars to Areas on Windows; they seem to respond properly to resize events, but since we're not handling scroll events, the scroll position won't change yet. (We're also not drawing with scrolling just yet.)

area_windows.go

@@ -11,7 +11,7 @@ import (
 )
 
 const (
-	areastyle = 0 | controlstyle
+	areastyle = _WS_HSCROLL | _WS_VSCROLL | controlstyle
 	areaxstyle = 0 | controlxstyle
 )
 
@@ -139,12 +139,69 @@ func paintArea(s *sysData) {
 		uintptr(unsafe.Pointer(&ps)))
 }
 
+var (
+	_getWindowRect = user32.NewProc("GetWindowRect")
+)
+
+func getAreaControlSize(hwnd _HWND) (width int, height int) {
+	var rect _RECT
+
+	r1, _, err := _getWindowRect.Call(
+		uintptr(hwnd),
+		uintptr(unsafe.Pointer(&rect)))
+	if r1 == 0 {		// failure
+		panic(fmt.Errorf("error getting size of actual Area control: %v", err))
+	}
+	return int(rect.Right - rect.Left),
+		int(rect.Bottom - rect.Top)
+}
+
+func adjustAreaScrollbars(hwnd _HWND) {
+	var si _SCROLLINFO
+
+	cwid, cht := getAreaControlSize(hwnd)
+
+	// the trick is we want a page to be the width/height of the visible area
+	// so the scroll range would go from [0..image_dimension - control_dimension]
+	// but judging from the sample code on MSDN, we don't need to do this; the scrollbar will do it for us
+
+	// have to do horizontal and vertical separately
+	si.cbSize = uint32(unsafe.Sizeof(si))
+	si.fMask = _SIF_RANGE | _SIF_PAGE
+	si.nMin = 0
+	si.nMax = int32(320)
+	si.nPage = uint32(cwid)
+	_setScrollInfo.Call(
+		uintptr(hwnd),
+		uintptr(_SB_HORZ),
+		uintptr(unsafe.Pointer(&si)),
+		uintptr(_TRUE))			// redraw the scroll bar
+
+	si.cbSize = uint32(unsafe.Sizeof(si))			// MSDN sample code does this a second time; let's do it too to be safe
+	si.fMask = _SIF_RANGE | _SIF_PAGE
+	si.nMin = 0
+	si.nMax = int32(240)
+	si.nPage = uint32(cht)
+	_setScrollInfo.Call(
+		uintptr(hwnd),
+		uintptr(_SB_VERT),
+		uintptr(unsafe.Pointer(&si)),
+		uintptr(_TRUE))			// redraw the scroll bar
+}
+
 func areaWndProc(s *sysData) func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam _LPARAM) _LRESULT {
 	return func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam _LPARAM) _LRESULT {
 		switch uMsg {
 		case _WM_PAINT:
 			paintArea(s)
 			return _LRESULT(0)
+		case _WM_HSCROLL:
+			fallthrough	// TODO
+		case _WM_VSCROLL:
+			fallthrough	// TODO
+		case _WM_SIZE:
+			adjustAreaScrollbars(hwnd)		// don't use s.hwnd; this message can be sent before that's loaded
+			return 0
 		default:
 			r1, _, _ := defWindowProc.Call(
 				uintptr(hwnd),

controls_windows.go

@@ -420,3 +420,88 @@ const (
 	_STN_ENABLE = 2
 	_STN_DISABLE = 3
 )
+
+// SetScrollPos/GetScrollPos scrollbar identifiers.
+const (
+	// from winuser.h
+	_SB_HORZ = 0
+	_SB_VERT = 1
+	_SB_CTL = 2
+	_SB_BOTH = 3
+)
+
+// Scrollbar event types.
+const (
+	// from winuser.h
+	_SB_LINEUP = 0
+	_SB_LINELEFT = 0
+	_SB_LINEDOWN = 1
+	_SB_LINERIGHT = 1
+	_SB_PAGEUP = 2
+	_SB_PAGELEFT = 2
+	_SB_PAGEDOWN = 3
+	_SB_PAGERIGHT = 3
+	_SB_THUMBPOSITION = 4
+	_SB_THUMBTRACK = 5
+	_SB_TOP = 6
+	_SB_LEFT = 6
+	_SB_BOTTOM = 7
+	_SB_RIGHT = 7
+	_SB_ENDSCROLL = 8
+)
+
+// ScrollWindowEx flags.
+const (
+	// from winuser.h
+	_SW_SCROLLCHILDREN = 0x0001
+	_SW_INVALIDATE = 0x0002
+	_SW_ERASE = 0x0004
+)
+
+// Scrollbar messages.
+const (
+	// from winuser.h
+	_SBM_SETPOS = 0x00E0
+	_SBM_GETPOS = 0x00E1
+	_SBM_SETRANGE = 0x00E2
+	_SBM_SETRANGEREDRAW = 0x00E6
+	_SBM_GETRANGE = 0x00E3
+	_SBM_ENABLE_ARROWS = 0x00E4
+	_SBM_SETSCROLLINFO = 0x00E9
+	_SBM_GETSCROLLINFO = 0x00EA
+	_SBM_GETSCROLLBARINFO = 0x00EB
+)
+
+// Scrollbar notifications. (These are actually sent to the parent window.)
+const (
+	// from winuser.h
+	_WM_HSCROLL = 0x0114
+	_WM_VSCROLL = 0x0115
+)
+
+// SCROLLINFO flags.
+const (
+	// from winuser.h
+	_SIF_RANGE = 0x0001
+	_SIF_PAGE = 0x0002
+	_SIF_POS = 0x0004
+	_SIF_DISABLENOSCROLL = 0x0008
+	_SIF_TRACKPOS = 0x0010
+	_SIF_ALL = (_SIF_RANGE | _SIF_PAGE | _SIF_POS | _SIF_TRACKPOS)
+)
+
+var (
+	_getScrollPos = user32.NewProc("GetScrollPos")
+	_setScrollInfo = user32.NewProc("SetScrollInfo")
+	_scrollWindowEx = user32.NewProc("ScrollWindowEx")
+)
+
+type _SCROLLINFO struct {
+	cbSize		uint32
+	fMask		uint32
+	nMin			int32		// originally int
+	nMax		int32		// originally int
+	nPage		uint32
+	nPos			int32		// originally int
+	nTrackPos	int32		// originally int
+}