Avoid undefined behaviour in GTK animation frames

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

@@ -29,7 +29,7 @@ use cairo::Surface;
 use gdk::{EventKey, EventMask, ModifierType, ScrollDirection, WindowExt, WindowTypeHint};
 use gio::ApplicationExt;
 use gtk::prelude::*;
-use gtk::{AccelGroup, ApplicationWindow, DrawingArea, SettingsExt};
+use gtk::{AccelGroup, ApplicationWindow, ContainerExt, DrawingArea, SettingsExt};
 use tracing::{error, warn};
 
 #[cfg(feature = "raw-win-handle")]
@@ -177,6 +177,9 @@ pub(crate) struct WindowState {
     click_counter: ClickCounter,
     active_text_input: Cell<Option<TextFieldToken>>,
     deferred_queue: RefCell<Vec<DeferredOp>>,
+
+    request_animation: Cell<bool>,
+    in_draw: Cell<bool>,
 }
 
 #[derive(Clone, PartialEq)]
@@ -296,6 +299,8 @@ impl WindowBuilder {
             click_counter: ClickCounter::default(),
             active_text_input: Cell::new(None),
             deferred_queue: RefCell::new(Vec::new()),
+            request_animation: Cell::new(false),
+            in_draw: Cell::new(false),
         });
 
         self.app
@@ -361,6 +366,33 @@ impl WindowBuilder {
             );
         }
 
+        win_state
+            .drawing_area
+            .connect_realize(clone!(handle => move |drawing_area| {
+                if let Some(clock) = drawing_area.get_frame_clock() {
+                    clock.connect_before_paint(clone!(handle => move |_clock|{
+                        if let Some(state) = handle.state.upgrade() {
+                            state.in_draw.set(true);
+                        }
+                    }));
+                    clock.connect_after_paint(clone!(handle => move |_clock|{
+                        if let Some(state) = handle.state.upgrade() {
+                            state.in_draw.set(false);
+                            if state.request_animation.get() {
+                                state.request_animation.set(false);
+                                let vbox = state.window.get_children().first().unwrap().clone()
+                                    .downcast::<gtk::Box>()
+                                    .unwrap();
+                                let first_child = vbox.get_children().last().unwrap().clone();
+                                if first_child.is::<gtk::DrawingArea>() {
+                                    first_child.queue_draw();
+                                }
+                            }
+                        }
+                    }));
+                }
+            }));
+
         win_state.drawing_area.connect_draw(clone!(handle => move |widget, context| {
             if let Some(state) = handle.state.upgrade() {
                 let mut scale = state.scale.get();
@@ -780,7 +812,22 @@ impl WindowState {
     /// Queues a call to `prepare_paint` and `paint`, but without marking any region for
     /// invalidation.
     fn request_anim_frame(&self) {
-        self.window.queue_draw();
+        if self.in_draw.get() {
+            self.request_animation.set(true);
+        } else {
+            let vbox = &self
+                .window
+                .get_children()
+                .first()
+                .unwrap()
+                .clone()
+                .downcast::<gtk::Box>()
+                .unwrap();
+            let first_child = vbox.get_children().last().unwrap().clone();
+            if first_child.is::<gtk::DrawingArea>() {
+                first_child.queue_draw();
+            }
+        }
     }
 
     /// Invalidates a rectangle, given in display points.
@@ -1165,10 +1212,10 @@ impl WindowHandle {
                 .downcast::<gtk::Box>()
                 .unwrap();
 
-            let first_child = &vbox.get_children()[0];
+            let first_child = vbox.get_children().first().unwrap().clone();
             if let Some(old_menubar) = first_child.downcast_ref::<gtk::MenuBar>() {
                 old_menubar.deactivate();
-                vbox.remove(first_child);
+                vbox.remove(old_menubar);
             }
             let menubar = menu.into_gtk_menubar(self, &accel_group);
             vbox.pack_start(&menubar, false, false, 0);