Changed AreaHandler.Key() to return a boolean value indicating if the event was handled; implemented this on Windows. It does sledgehammer some edge cases I wanted to avoid, but it also avoids fussing about scrolling and focus and what not.

redo/area.go

@@ -74,10 +74,10 @@ type AreaHandler interface {
 	Mouse(e MouseEvent)
 
 	// Key is called when the Area receives a keyboard event.
-	// You are allowed to do nothing in this handler (to ignore keyboard events).
+	// Return true to indicate that you handled the event; return false to indicate that you did not and let the system handle the event.
+	// You are allowed to do nothing in this handler (to ignore keyboard events); in this case, return false.
 	// See KeyEvent for details.
-	// After handling the key event, package ui will decide whether to perform platform-dependent event chain continuation based on that platform's designated action (so it is not possible to override global key events, such as Alt-Tab, this way).
-	Key(e KeyEvent)
+	Key(e KeyEvent) (handled bool)
 }
 
 // MouseEvent contains all the information for a mous event sent by Area.Mouse.
@@ -140,7 +140,7 @@ func (e MouseEvent) HeldBits() (h uintptr) {
 // on US English QWERTY keyboards; see Key for details.
 //
 // If a key is pressed that is not supported by Key, ExtKey,
-// or Modifiers, no KeyEvent will be produced.
+// or Modifiers, no KeyEvent will be produced and package ui will behave as if false was returned from the event handler.
 type KeyEvent struct {
 	// Key is a byte representing a character pressed
 	// in the typewriter section of the keyboard.

redo/area_windows.c

@@ -380,19 +380,10 @@ static LRESULT CALLBACK areaWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM
 		heldButtons = (uintptr_t) GET_KEYSTATE_WPARAM(wParam);
 		areaMouseEvent(hwnd, data, which, TRUE, heldButtons, lParam);
 		return TRUE;
-	case WM_KEYDOWN:
-		areaKeyEvent(data, FALSE, wParam, lParam);
-		return 0;
-	case WM_KEYUP:
-		areaKeyEvent(data, TRUE, wParam, lParam);
-		return 0;
-	// Alt+[anything] and F10 send these instead and require us to return to DefWindowProc() so global keystrokes such as Alt+Tab can be processed
-	case WM_SYSKEYDOWN:
-		areaKeyEvent(data, FALSE, wParam, lParam);
-		return DefWindowProcW(hwnd, uMsg, wParam, lParam);
-	case WM_SYSKEYUP:
-		areaKeyEvent(data, TRUE, wParam, lParam);
-		return DefWindowProcW(hwnd, uMsg, wParam, lParam);
+	case msgAreaKeyDown:
+		return (LRESULT) areaKeyEvent(data, FALSE, wParam, lParam);
+	case msgAreaKeyUp:
+		return (LRESULT) areaKeyEvent(data, TRUE, wParam, lParam);
 	case msgAreaSizeChanged:
 		adjustAreaScrollbars(hwnd, data);
 		repaintArea(hwnd);		// this calls for an update

redo/area_windows.go

@@ -152,7 +152,7 @@ func finishAreaMouseEvent(data unsafe.Pointer, cbutton C.DWORD, up C.BOOL, heldB
 }
 
 //export areaKeyEvent
-func areaKeyEvent(data unsafe.Pointer, up C.BOOL, wParam C.WPARAM, lParam C.LPARAM) {
+func areaKeyEvent(data unsafe.Pointer, up C.BOOL, wParam C.WPARAM, lParam C.LPARAM) C.BOOL {
 	var ke KeyEvent
 
 	a := (*area)(data)
@@ -180,10 +180,14 @@ func areaKeyEvent(data unsafe.Pointer, up C.BOOL, wParam C.WPARAM, lParam C.LPAR
 		ke.ExtKey = xke.ExtKey
 	} else if ke.Modifiers == 0 {
 		// no key, extkey, or modifiers; do nothing
-		return
+		return C.FALSE
 	}
 	ke.Up = up != C.FALSE
-	a.handler.Key(ke)
+	handled := a.handler.Key(ke)
+	if handled {
+		return C.TRUE
+	}
+	return C.FALSE
 }
 
 // all mappings come from GLFW - https://github.com/glfw/glfw/blob/master/src/win32_window.c#L152

redo/uitask_windows.c

@@ -8,9 +8,31 @@
 // this also assumes WC_TABCONTROL is longer than areaWindowClass
 #define NCLASSNAME (sizeof WC_TABCONTROL / sizeof WC_TABCONTROL[0])
 
-void uimsgloop_area(MSG *msg)
+void uimsgloop_area(HWND active, HWND focus, MSG *msg)
 {
+	MSG copy;
+
+	copy = *msg;
+	switch (copy.message) {
+	case WM_KEYDOWN:
+	case WM_SYSKEYDOWN:			// Alt+[anything] and F10 send these instead
+		copy.message = msgAreaKeyDown;
+		break;
+	case WM_KEYUP:
+	case WM_SYSKEYUP:
+		copy.message = msgAreaKeyUp;
+		break;
+	default:
+		goto notkey;
+	}
+	// if we handled the key, don't do the default behavior
 	// don't call TranslateMessage(); we do our own keyboard handling
+	if (DispatchMessage(&copy) != FALSE)
+		return;
+	// TODO move this under notkey?
+	if (IsDialogMessage(active, msg) != 0)
+		return;
+notkey:
 	DispatchMessage(msg);
 }
 
@@ -70,7 +92,7 @@ void uimsgloop(void)
 			if (GetClassNameW(focus, classchk, NCLASSNAME) == 0)
 				xpanic("error getting name of focused window class for Area check", GetLastError());
 			if (wcscmp(classchk, areaWindowClass) == 0) {
-				uimsgloop_area(&msg);
+				uimsgloop_area(active, focus, &msg);
 				continue;
 			} else if (wcscmp(classchk, WC_TABCONTROL) == 0) {
 				uimsgloop_tab(active, focus, &msg);

redo/winapi_windows.h

@@ -34,6 +34,8 @@ enum {
 	msgTabCurrentTabHasChildren,
 	msgBeginModal,
 	msgEndModal,
+	msgAreaKeyDown,
+	msgAreaKeyUp,
 };
 
 // uitask_windows.c

redo/zz_test.go

@@ -63,14 +63,16 @@ type testwin struct {
 	wsmall	Window
 }
 
-type areaHandler struct{}
+type areaHandler struct {
+	handled	bool
+}
 func (a *areaHandler) Paint(r image.Rectangle) *image.RGBA {
 	i := image.NewRGBA(r)
 	draw.Draw(i, r, &image.Uniform{color.RGBA{128,0,128,255}}, image.ZP, draw.Src)
 	return i
 }
 func (a *areaHandler) Mouse(me MouseEvent) { fmt.Printf("%#v\n", me) }
-func (a *areaHandler) Key(ke KeyEvent) { fmt.Printf("%#v %q\n", ke, ke.Key) }
+func (a *areaHandler) Key(ke KeyEvent) bool { fmt.Printf("%#v %q\n", ke, ke.Key); return a.handled }
 
 func (tw *testwin) addfe() {
 	tw.festart = NewButton("Start")
@@ -169,7 +171,7 @@ func (tw *testwin) make(done chan struct{}) {
 	tw.nt.Append("Tab 2", Space())
 	tw.t.Append("Tab", tw.nt)
 	tw.t.Append("Space", Space())
-	tw.a = NewArea(200, 200, &areaHandler{})
+	tw.a = NewArea(200, 200, &areaHandler{false})
 	tw.t.Append("Area", tw.a)
 	tw.spw = NewHorizontalStack(
 		NewButton("hello"),
@@ -233,7 +235,7 @@ func (tw *testwin) make(done chan struct{}) {
 			NewVerticalStack(
 				NewButton("Small"),
 				NewButton("Small 2"),
-				NewArea(200, 200, &areaHandler{})))
+				NewArea(200, 200, &areaHandler{true})))
 		tw.wsmall.Show()
 	}
 }