app: add support for system cursors

Signed-off-by: pierre <pierre.curto@gmail.com>

app/internal/window/os_windows.go

@@ -45,6 +45,7 @@ type window struct {
 	height      int
 	stage       system.Stage
 	pointerBtns pointer.Buttons
+	cursor      syscall.Handle
 
 	mu        sync.Mutex
 	animating bool
@@ -105,6 +106,9 @@ func NewWindow(window Callbacks, opts *Options) error {
 		windows.ShowWindow(w.hwnd, windows.SW_SHOWDEFAULT)
 		windows.SetForegroundWindow(w.hwnd)
 		windows.SetFocus(w.hwnd)
+		// Since the window class for the cursor is null,
+		// set it here to show the cursor.
+		w.SetCursor(pointer.CursorDefault)
 		if err := w.loop(); err != nil {
 			panic(err)
 		}
@@ -120,17 +124,16 @@ func initResources() error {
 		return err
 	}
 	resources.handle = hInst
-	curs, err := windows.LoadCursor(windows.IDC_ARROW)
+	c, err := loadCursor(pointer.CursorDefault)
 	if err != nil {
 		return err
 	}
-	resources.cursor = curs
+	resources.cursor = c
 	wcls := windows.WndClassEx{
 		CbSize:        uint32(unsafe.Sizeof(windows.WndClassEx{})),
 		Style:         windows.CS_HREDRAW | windows.CS_VREDRAW | windows.CS_OWNDC,
 		LpfnWndProc:   syscall.NewCallback(windowProc),
 		HInstance:     hInst,
-		HCursor:       curs,
 		LpszClassName: syscall.StringToUTF16Ptr("GioWindow"),
 	}
 	cls, err := windows.RegisterClassEx(&wcls)
@@ -299,6 +302,8 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 				Y: w.minmax.maxHeight + w.deltas.height,
 			}
 		}
+	case windows.WM_SETCURSOR:
+		windows.SetCursor(w.cursor)
 	}
 
 	return windows.DefWindowProc(hwnd, msg, wParam, lParam)
@@ -552,6 +557,37 @@ func (w *window) writeClipboard(s string) error {
 	return nil
 }
 
+func (w *window) SetCursor(name pointer.CursorName) {
+	c, err := loadCursor(name)
+	if err != nil {
+		c = resources.cursor
+	}
+	w.cursor = c
+}
+
+func loadCursor(name pointer.CursorName) (syscall.Handle, error) {
+	var curID uint16
+	switch name {
+	default:
+		fallthrough
+	case pointer.CursorDefault:
+		return resources.cursor, nil
+	case pointer.CursorText:
+		curID = windows.IDC_IBEAM
+	case pointer.CursorPointer:
+		curID = windows.IDC_HAND
+	case pointer.CursorCrossHair:
+		curID = windows.IDC_CROSS
+	case pointer.CursorColResize:
+		curID = windows.IDC_SIZEWE
+	case pointer.CursorRowResize:
+		curID = windows.IDC_SIZENS
+	case pointer.CursorNone:
+		return 0, nil
+	}
+	return windows.LoadCursor(curID)
+}
+
 func (w *window) ShowTextInput(show bool) {}
 
 func (w *window) HDC() syscall.Handle {