Windows sysData has been adjusted to deal with child controls. Rather than storing the parent window, it is passed as an argument to sysData.make(), which does the child ID allocation. Child IDs are now window-local, getting rid of that restriction.

restrictions.md

@@ -2,4 +2,3 @@ This is a file to keep track of API restrictions that simplify the implementatio
 
 - Once you open a window, the controls are finalized: you cannot change the window's control or add/remove controls to layouts.
 - Once you open a window, you cannot change its event channels or its controls's event channels.
-- [Windows] At most 65535 controls can be made, period. This is because child window IDs are alloted by the UI library application-global, not window-local, and BN_CLICKED only stores the control ID in a word (and I start counting at 1 to be safe). If I keep the first restriction and amend it such that you can only set the control of a window at the time of first open (somehow; split create and open?), I can easily make them window-local.

sysdata_windows.go

@@ -12,7 +12,9 @@ type sysData struct {
 	cSysData
 
 	hwnd			_HWND
-	cid				_HMENU
+	children			map[_HMENU]*sysData
+	nextChildID		_HMENU
+	childrenLock		sync.Mutex
 	shownAlready		bool
 }
 
@@ -36,30 +38,32 @@ var classTypes = [nctypes]*classData{
 		name:	"BUTTON",
 		style:	_BS_PUSHBUTTON | controlstyle,
 		xstyle:	0 | controlxstyle,
-		mkid:	true,
 	},
 }
 
-var (
-	cid _HMENU = 0
-	cidLock sync.Mutex
-)
-
-func nextID() _HMENU {
-	cidLock.Lock()
-	defer cidLock.Unlock()
-	cid++
-	return cid
+func (s *sysData) addChild(chlid *sysData) _HMENU {
+	s.childrenLock.Lock()
+	defer s.childrenLock.Unlock()
+	s.nextChildID++		// start at 1
+	s.children[s.nextChildID] = child
+	return s.nextChildID
 }
 
-func (s *sysData) make(initText string, initWidth int, initHeight int) (err error) {
+func (s *sysData) delChild(id _HMENU) {
+	s.childrenLock.Lock()
+	defer s.childrenLock.Unlock()
+	delete(s.children, id)
+}
+
+func (s *sysData) make(initText string, initWidth int, initHeight int, window *sysData) (err error) {
 	ret := make(chan uiret)
 	defer close(ret)
 	ct := classTypes[s.ctype]
+	cid := _HMENU(0)
 	pwin := uintptr(_NULL)
-	if ct.mkid {
-		s.cid = nextID()
-		pwin = uintptr(s.parentWindow.hwnd)
+	if window != nil {		// this is a child control
+		cid = window.addChild(s)
+		pwin = uintptr(window.hwnd)
 	}
 	uitask <- &uimsg{
 		call:		_createWindowEx,	
@@ -73,7 +77,7 @@ func (s *sysData) make(initText string, initWidth int, initHeight int) (err erro
 			uintptr(initWidth),
 			uintptr(initHeight),
 			pwin,
-			uintptr(s.cid),
+			uintptr(cid),
 			uintptr(hInstance),
 			uintptr(_NULL),
 		},
@@ -81,13 +85,12 @@ func (s *sysData) make(initText string, initWidth int, initHeight int) (err erro
 	}
 	r := <-ret
 	if r.ret == 0 {		// failure
+		if window != nil {
+			window.delChild(cid)
+		}
 		return r.err
 	}
 	s.hwnd = _HWND(r.ret)
-	addSysData(s.hwnd, s)
-	if ct.mkid {
-		addSysDataID(s.cid, s)
-	}
 	return nil
 }