CI tests can exit directly after taking a screenshot (#19806)

# Objective

- Currently, CI tests take a screenshot at frame X and exits at frame Y
with X < Y, and both number fixed
- This means tests can take longer than they actually need when taking
the screenshot is fast, and can fail to take the screenshot when it's
taking too long

## Solution

- Add a new event `ScreenshotAndExit` that exit directly after the
screenshot is saved

crates/bevy_dev_tools/src/ci_testing/config.rs

@@ -37,6 +37,9 @@ pub enum CiTestingEvent {
     /// Takes a screenshot of the entire screen, and saves the results to
     /// `screenshot-{current_frame}.png`.
     Screenshot,
+    /// Takes a screenshot of the entire screen, saves the results to
+    /// `screenshot-{current_frame}.png`, and exits once the screenshot is taken.
+    ScreenshotAndExit,
     /// Takes a screenshot of the entire screen, and saves the results to
     /// `screenshot-{name}.png`.
     NamedScreenshot(String),

crates/bevy_dev_tools/src/ci_testing/systems.rs

@@ -21,6 +21,19 @@ pub(crate) fn send_events(world: &mut World, mut current_frame: Local<u32>) {
                 world.send_event(AppExit::Success);
                 info!("Exiting after {} frames. Test successful!", *current_frame);
             }
+            CiTestingEvent::ScreenshotAndExit => {
+                let this_frame = *current_frame;
+                world.spawn(Screenshot::primary_window()).observe(
+                    move |captured: On<bevy_render::view::screenshot::ScreenshotCaptured>,
+                          mut exit_event: EventWriter<AppExit>| {
+                        let path = format!("./screenshot-{}.png", this_frame);
+                        save_to_disk(path)(captured);
+                        info!("Exiting. Test successful!");
+                        exit_event.write(AppExit::Success);
+                    },
+                );
+                info!("Took a screenshot at frame {}.", *current_frame);
+            }
             CiTestingEvent::Screenshot => {
                 let path = format!("./screenshot-{}.png", *current_frame);
                 world

tools/example-showcase/src/main.rs

@@ -55,6 +55,12 @@ enum Action {
         /// This defaults to frame 250. Set it to 0 to not stop the example automatically.
         stop_frame: u32,
 
+        #[arg(long, default_value = "false")]
+        /// Automatically ends after taking a screenshot
+        ///
+        /// Only works if `screenshot-frame` is set to non-0, and overrides `stop-frame`.
+        auto_stop_frame: bool,
+
         #[arg(long)]
         /// Which frame to take a screenshot at. Set to 0 for no screenshot.
         screenshot_frame: u32,
@@ -150,6 +156,7 @@ fn main() {
         Action::Run {
             wgpu_backend,
             stop_frame,
+            auto_stop_frame,
             screenshot_frame,
             fixed_frame_time,
             in_ci,
@@ -183,11 +190,21 @@ fn main() {
 
             let mut extra_parameters = vec![];
 
-            match (stop_frame, screenshot_frame) {
+            match (stop_frame, screenshot_frame, auto_stop_frame) {
                 // When the example does not automatically stop nor take a screenshot.
-                (0, 0) => (),
+                (0, 0, _) => (),
+                // When the example automatically stops at an automatic frame.
+                (0, _, true) => {
+                    let mut file = File::create("example_showcase_config.ron").unwrap();
+                    file.write_all(
+                        format!("(setup: (fixed_frame_time: Some({fixed_frame_time})), events: [({screenshot_frame}, ScreenshotAndExit)])").as_bytes(),
+                    )
+                    .unwrap();
+                    extra_parameters.push("--features");
+                    extra_parameters.push("bevy_ci_testing");
+                }
                 // When the example does not automatically stop.
-                (0, _) => {
+                (0, _, false) => {
                     let mut file = File::create("example_showcase_config.ron").unwrap();
                     file.write_all(
                         format!("(setup: (fixed_frame_time: Some({fixed_frame_time})), events: [({screenshot_frame}, Screenshot)])").as_bytes(),
@@ -197,15 +214,25 @@ fn main() {
                     extra_parameters.push("bevy_ci_testing");
                 }
                 // When the example does not take a screenshot.
-                (_, 0) => {
+                (_, 0, _) => {
                     let mut file = File::create("example_showcase_config.ron").unwrap();
                     file.write_all(format!("(events: [({stop_frame}, AppExit)])").as_bytes())
                         .unwrap();
                     extra_parameters.push("--features");
                     extra_parameters.push("bevy_ci_testing");
                 }
+                // When the example both automatically stops at an automatic frame and takes a screenshot.
+                (_, _, true) => {
+                    let mut file = File::create("example_showcase_config.ron").unwrap();
+                    file.write_all(
+                        format!("(setup: (fixed_frame_time: Some({fixed_frame_time})), events: [({screenshot_frame}, ScreenshotAndExit)])").as_bytes(),
+                    )
+                    .unwrap();
+                    extra_parameters.push("--features");
+                    extra_parameters.push("bevy_ci_testing");
+                }
                 // When the example both automatically stops and takes a screenshot.
-                (_, _) => {
+                (_, _, false) => {
                     let mut file = File::create("example_showcase_config.ron").unwrap();
                     file.write_all(
                         format!("(setup: (fixed_frame_time: Some({fixed_frame_time})), events: [({screenshot_frame}, Screenshot), ({stop_frame}, AppExit)])").as_bytes(),