Change Harness::run to run until no more repaints are requested (#5580

)

Previously, `Harness::run` just called `Harness::step` 3 times. If that
wasn't enough, tests would often call run multiple times so all
animations would finish properly.

Also, I introduced `HarnessBuilder::with_step_dt` to customize with how
big of a dt each frame is called. I set the default to 1.0 / 6.0 (~6fps)
so we don't waste cpu in tests waiting on animations.

`HarnessBuilder::max_steps` allows us to control how many steps
`Harness::run` should run before panicing.
The default is 6, so we run for up to 1.0 logical seconds (six frames at
6 fps), which should be enough to finish most animations.

Turns out a lot of snapshots where rendered before fully shown and had a
light opacity, those are now fixed.

* [x] I have followed the instructions in the PR template

crates/egui/src/context.rs

@@ -775,7 +775,7 @@ impl Context {
         writer(&mut self.0.write())
     }
 
-    /// Run the ui code for one 1.
+    /// Run the ui code for one frame.
     ///
     /// At most [`Options::max_passes`] calls will be issued to `run_ui`,
     /// and only on the rare occasion that [`Context::request_discard`] is called.

crates/egui_demo_app/tests/test_demo_app.rs

@@ -49,7 +49,7 @@ fn test_demo_app() {
             // Load a local image where we know it exists and loads quickly
             #[cfg(feature = "image_viewer")]
             Anchor::ImageViewer => {
-                harness.run();
+                harness.step();
 
                 harness
                     .get_by_role_and_label(Role::TextInput, "URI:")
@@ -65,7 +65,8 @@ fn test_demo_app() {
             _ => {}
         }
 
-        harness.run();
+        // Can't use Harness::run because fractal clock keeps requesting repaints
+        harness.run_steps(2);
 
         if let Err(e) = harness.try_snapshot(&anchor.to_string()) {
             results.push(e);

crates/egui_demo_lib/src/demo/demo_app_windows.rs

@@ -397,7 +397,7 @@ mod tests {
             harness.set_size(Vec2::new(size.width as f32, size.height as f32));
 
             // Run the app for some more frames...
-            harness.run();
+            harness.run_ok();
 
             let mut options = SnapshotOptions::default();
             // The Bézier Curve demo needs a threshold of 2.1 to pass on linux

crates/egui_demo_lib/src/demo/modals.rs

@@ -183,12 +183,13 @@ mod tests {
 
         harness.get_by_role(Role::ComboBox).click();
 
-        harness.run();
+        // Harness::run would fail because we keep requesting repaints to simulate progress.
+        harness.run_ok();
         assert!(harness.ctx.memory(|mem| mem.any_popup_open()));
         assert!(harness.state().user_modal_open);
 
         harness.press_key(Key::Escape);
-        harness.run();
+        harness.run_ok();
         assert!(!harness.ctx.memory(|mem| mem.any_popup_open()));
         assert!(harness.state().user_modal_open);
     }
@@ -238,17 +239,11 @@ mod tests {
         results.push(harness.try_snapshot("modals_1"));
 
         harness.get_by_label("Save").click();
-        // TODO(lucasmerlin): Remove these extra runs once run checks for repaint requests
-        harness.run();
-        harness.run();
-        harness.run();
+        harness.run_ok();
         results.push(harness.try_snapshot("modals_2"));
 
         harness.get_by_label("Yes Please").click();
-        // TODO(lucasmerlin): Remove these extra runs once run checks for repaint requests
-        harness.run();
-        harness.run();
-        harness.run();
+        harness.run_ok();
         results.push(harness.try_snapshot("modals_3"));
 
         for result in results {
@@ -272,14 +267,11 @@ mod tests {
             initial_state,
         );
 
-        // TODO(lucasmerlin): Remove these extra runs once run checks for repaint requests
-        harness.run();
-        harness.run();
-        harness.run();
+        harness.run_ok();
 
         harness.get_by_label("Yes Please").simulate_click();
 
-        harness.run();
+        harness.run_ok();
 
         // This snapshots should show the progress bar modal on top of the save modal.
         harness.snapshot("modals_backdrop_should_prevent_focusing_lower_area");

crates/egui_kittest/src/builder.rs

@@ -8,6 +8,8 @@ use std::marker::PhantomData;
 pub struct HarnessBuilder<State = ()> {
     pub(crate) screen_rect: Rect,
     pub(crate) pixels_per_point: f32,
+    pub(crate) max_steps: u64,
+    pub(crate) step_dt: f32,
     pub(crate) state: PhantomData<State>,
     pub(crate) renderer: Box<dyn TestRenderer>,
 }
@@ -19,6 +21,8 @@ impl<State> Default for HarnessBuilder<State> {
             pixels_per_point: 1.0,
             state: PhantomData,
             renderer: Box::new(LazyRenderer::default()),
+            max_steps: 4,
+            step_dt: 1.0 / 4.0,
         }
     }
 }
@@ -40,6 +44,26 @@ impl<State> HarnessBuilder<State> {
         self
     }
 
+    /// Set the maximum number of steps to run when calling [`Harness::run`].
+    ///
+    /// Default is 4.
+    /// With the default `step_dt`, this means 1 second of simulation.
+    #[inline]
+    pub fn with_max_steps(mut self, max_steps: u64) -> Self {
+        self.max_steps = max_steps;
+        self
+    }
+
+    /// Set the time delta for a single [`Harness::step`].
+    ///
+    /// Default is 1.0 / 4.0 (4fps).
+    /// The default is low so we don't waste cpu waiting for animations.
+    #[inline]
+    pub fn with_step_dt(mut self, step_dt: f32) -> Self {
+        self.step_dt = step_dt;
+        self
+    }
+
     /// Set the [`TestRenderer`] to use for rendering.
     ///
     /// By default, a [`LazyRenderer`] is used.