fix dropdown position for gtk backend

We need to position internal windows (dropdowns, tooltips) relative
to the content area.

Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>

Author: maurerdietmar

druid-shell/src/backend/gtk/window.rs

@@ -983,7 +983,19 @@ impl WindowHandle {
     pub fn set_position(&self, mut position: Point) {
         if let Some(state) = self.state.upgrade() {
             if let Some(parent_state) = &state.parent {
-                let pos = (*parent_state).get_position();
+                let pos = if let Some(parent_state) = parent_state.0.state.upgrade() {
+                    let parent_window = &(*parent_state).window;
+                    let (root_x, root_y) = match state.window.type_hint() {
+                        WindowTypeHint::Tooltip | WindowTypeHint::DropdownMenu => {
+                            // position relative to the content area
+                            parent_window.window().unwrap().position()
+                        }
+                        _ => parent_window.position(),
+                    };
+                    Point::new(root_x as f64, root_y as f64).to_dp(state.scale.get())
+                } else {
+                    (*parent_state).get_position()
+                };
                 position += (pos.x, pos.y)
             }
         };