Fix recurring C++ timers

* sixtyfps_timer_start needs to *take* the timer id out of the Rust
  timer to avoid that the subsequent drop stops the timer again
* For the Qt event loop, call `timer_event()` once before entering
  QCoreApplication::exec(), to schedule any timers that were started
  beforehand.
* Added a way to quit the event loop gently, in order to use that
  from the C++ unit test.

api/sixtyfps-cpp/include/sixtyfps.h

@@ -670,6 +670,11 @@ void run_event_loop()
     cbindgen_private::sixtyfps_run_event_loop();
 }
 
+void quit_event_loop()
+{
+    cbindgen_private::sixtyfps_quit_event_loop();
+}
+
 /// Registers a font by the specified path. The path must refer to an existing
 /// TrueType font font.
 /// \returns an empty optional on success, otherwise an error string

api/sixtyfps-cpp/lib.rs

@@ -37,6 +37,11 @@ pub unsafe extern "C" fn sixtyfps_run_event_loop() {
     crate::backend().run_event_loop();
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn sixtyfps_quit_event_loop() {
+    crate::backend().quit_event_loop();
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn sixtyfps_register_font_from_path(
     path: &sixtyfps_corelib::SharedString,

api/sixtyfps-cpp/tests/datastructures.cpp

@@ -8,6 +8,7 @@
     Please contact info@sixtyfps.io for more information.
 LICENSE END */
 
+#include <chrono>
 #define CATCH_CONFIG_MAIN
 #include "catch2/catch.hpp"
 
@@ -64,3 +65,12 @@ TEST_CASE("Property Tracker")
     REQUIRE(tracker2.is_dirty());
     REQUIRE(!tracker1.is_dirty());
 }
+
+TEST_CASE("C++ Timers")
+{
+    using namespace sixtyfps;
+
+    Timer testTimer(std::chrono::milliseconds(16), []() { sixtyfps::quit_event_loop(); });
+
+    sixtyfps::run_event_loop();
+}

sixtyfps_runtime/corelib/backend.rs

@@ -24,6 +24,9 @@ pub trait Backend: Send + Sync {
     /// Spins an event loop and renders the visible windows.
     fn run_event_loop(&'static self);
 
+    /// Exits the event loop.
+    fn quit_event_loop(&'static self);
+
     /// This function can be used to register a custom TrueType font with SixtyFPS,
     /// for use with the `font-family` property. The provided slice must be a valid TrueType
     /// font.

sixtyfps_runtime/corelib/timers.rs

@@ -340,7 +340,7 @@ pub(crate) mod ffi {
         timer.start(TimerMode::Repeated, core::time::Duration::from_millis(duration), move || {
             (wrap.callback)(wrap.user_data)
         });
-        timer.id.get().map(|x| x as i64).unwrap_or(-1)
+        timer.id.take().map(|x| x as i64).unwrap_or(-1)
     }
 
     /// Execute a callback with a delay in milisecond

sixtyfps_runtime/rendering_backends/gl/eventloop.rs

@@ -110,6 +110,7 @@ pub enum CustomEvent {
     #[cfg(target_arch = "wasm32")]
     WakeUpAndPoll,
     UpdateWindowProperties(Weak<Window>),
+    Exit,
 }
 
 /// Runs the event loop and renders the items in the provided `component` in its
@@ -400,6 +401,10 @@ pub fn run() {
                     window.upgrade().map(|window| window.update_window_properties());
                 }
 
+                winit::event::Event::UserEvent(CustomEvent::Exit) => {
+                    *control_flow = winit::event_loop::ControlFlow::Exit;
+                }
+
                 _ => (),
             }
 

sixtyfps_runtime/rendering_backends/gl/lib.rs

@@ -1487,6 +1487,12 @@ impl sixtyfps_corelib::backend::Backend for Backend {
         crate::eventloop::run();
     }
 
+    fn quit_event_loop(&'static self) {
+        crate::eventloop::with_window_target(|event_loop| {
+            event_loop.event_loop_proxy().send_event(crate::eventloop::CustomEvent::Exit).ok();
+        })
+    }
+
     fn register_font_from_memory(
         &'static self,
         data: &[u8],

sixtyfps_runtime/rendering_backends/qt/build.rs

@@ -59,4 +59,5 @@ fn main() {
     println!("cargo:rerun-if-changed=qt_window.rs");
     println!("cargo:rerun-if-changed=widgets.rs");
     println!("cargo:rerun-if-changed=qttypes.rs");
+    println!("cargo:rerun-if-changed=lib.rs");
 }

sixtyfps_runtime/rendering_backends/qt/lib.rs

@@ -114,6 +114,8 @@ impl sixtyfps_corelib::backend::Backend for Backend {
     fn run_event_loop(&'static self) {
         #[cfg(not(no_qt))]
         {
+            // Schedule any timers with Qt that were set up before this event loop start.
+            crate::qt_window::timer_event();
             use cpp::cpp;
             cpp! {unsafe [] {
                 qApp->exec();
@@ -121,6 +123,16 @@ impl sixtyfps_corelib::backend::Backend for Backend {
         };
     }
 
+    fn quit_event_loop(&'static self) {
+        #[cfg(not(no_qt))]
+        {
+            use cpp::cpp;
+            cpp! {unsafe [] {
+                qApp->quit();
+            } }
+        };
+    }
+
     fn register_font_from_memory(
         &'static self,
         _data: &[u8],

sixtyfps_runtime/rendering_backends/qt/qt_window.rs

@@ -1080,7 +1080,7 @@ thread_local! {
 }
 
 /// Called by C++'s TimerHandler::timerEvent, or everytime a timer might have been started
-fn timer_event() {
+pub(crate) fn timer_event() {
     sixtyfps_corelib::animations::update_animations();
     sixtyfps_corelib::timers::TimerList::maybe_activate_timers();
 
@@ -1113,6 +1113,7 @@ fn timer_event() {
     };
     if let Some(timeout) = timeout {
         cpp! { unsafe [timeout as "int"] {
+            ensure_initialized();
             TimerHandler::instance().timer.start(timeout, &TimerHandler::instance());
         }}
     }