Take example screenshots in CI

.github/example-run/breakout.ron

@@ -1,3 +1,5 @@
 (
-    exit_after: Some(900)
+    exit_after: Some(900),
+    frame_time: Some(0.03),
+    screenshot_frames: [200],
 )

.github/example-run/load_gltf.ron

@@ -1,3 +1,5 @@
 (
-    exit_after: Some(300)
+    exit_after: Some(300),
+    frame_time: Some(0.03),
+    screenshot_frames: [100],
 )

.github/workflows/ci.yml

@@ -199,13 +199,23 @@ jobs:
             echo "running $example_name - "`date`
             time TRACE_CHROME=trace-$example_name.json CI_TESTING_CONFIG=$example xvfb-run cargo run --example $example_name --features "bevy_ci_testing,trace,trace_chrome"
             sleep 10
+            if [ `find ./ -maxdepth 1 -name 'screenshot-*.png' -print -quit` ]; then
+              mkdir screenshots-$example_name
+              mv screenshot-*.png screenshots-$example_name/
+            fi
           done
           zip traces.zip trace*.json
+          zip -r screenshots.zip screenshots-*
       - name: save traces
         uses: actions/upload-artifact@v3
         with:
           name: example-traces.zip
           path: traces.zip
+      - name: save screenshots
+        uses: actions/upload-artifact@v3
+        with:
+          name: screenshots.zip
+          path: screenshots.zip
       - name: Save PR number
         if: ${{ failure() && github.event_name == 'pull_request' }}
         run: |

crates/bevy_app/src/ci_testing.rs

@@ -1,3 +1,5 @@
+//! Utilities for testing in CI environments.
+
 use crate::{app::AppExit, App, Update};
 use serde::Deserialize;
 
@@ -13,6 +15,11 @@ use bevy_utils::tracing::info;
 pub struct CiTestingConfig {
     /// The number of frames after which Bevy should exit.
     pub exit_after: Option<u32>,
+    /// The time in seconds to update for each frame.
+    pub frame_time: Option<f32>,
+    /// Frames at which to capture a screenshot.
+    #[serde(default)]
+    pub screenshot_frames: Vec<u32>,
 }
 
 fn ci_testing_exit_after(

crates/bevy_app/src/lib.rs

@@ -10,7 +10,7 @@ mod plugin_group;
 mod schedule_runner;
 
 #[cfg(feature = "bevy_ci_testing")]
-mod ci_testing;
+pub mod ci_testing;
 
 pub use app::*;
 pub use bevy_derive::DynamicPlugin;

crates/bevy_internal/Cargo.toml

@@ -73,7 +73,7 @@ subpixel_glyph_atlas = ["bevy_text/subpixel_glyph_atlas"]
 webgl = ["bevy_core_pipeline?/webgl", "bevy_pbr?/webgl", "bevy_render?/webgl"]
 
 # enable systems that allow for automated testing on CI
-bevy_ci_testing = ["bevy_app/bevy_ci_testing", "bevy_render?/ci_limits"]
+bevy_ci_testing = ["bevy_app/bevy_ci_testing", "bevy_time/bevy_ci_testing", "bevy_render?/bevy_ci_testing", "bevy_render?/ci_limits"]
 
 # Enable animation support, and glTF animation loading
 animation = ["bevy_animation", "bevy_gltf?/bevy_animation"]

crates/bevy_render/Cargo.toml

@@ -17,6 +17,7 @@ jpeg = ["image/jpeg"]
 bmp = ["image/bmp"]
 webp = ["image/webp"]
 dds = ["ddsfile"]
+bevy_ci_testing = ["bevy_app/bevy_ci_testing"]
 
 # For ktx2 supercompression
 zlib = ["flate2"]

crates/bevy_render/src/view/window/screenshot.rs

@@ -102,7 +102,35 @@ impl Plugin for ScreenshotPlugin {
         if let Ok(render_app) = app.get_sub_app_mut(RenderApp) {
             render_app.init_resource::<SpecializedRenderPipelines<ScreenshotToScreenPipeline>>();
         }
+
+        #[cfg(feature = "bevy_ci_testing")]
+        if app
+            .world
+            .contains_resource::<bevy_app::ci_testing::CiTestingConfig>()
+        {
+            app.add_systems(bevy_app::Update, ci_testing_screenshot_at);
+        }
+    }
+}
+
+#[cfg(feature = "bevy_ci_testing")]
+fn ci_testing_screenshot_at(
+    mut current_frame: bevy_ecs::prelude::Local<u32>,
+    ci_testing_config: bevy_ecs::prelude::Res<bevy_app::ci_testing::CiTestingConfig>,
+    mut screenshot_manager: ResMut<ScreenshotManager>,
+    main_window: Query<Entity, With<bevy_window::PrimaryWindow>>,
+) {
+    if ci_testing_config
+        .screenshot_frames
+        .contains(&*current_frame)
+    {
+        info!("Taking a screenshot at frame {}.", *current_frame);
+        let path = format!("./screenshot-{}.png", *current_frame);
+        screenshot_manager
+            .save_screenshot_to_disk(main_window.single(), path)
+            .unwrap();
     }
+    *current_frame += 1;
 }
 
 pub(crate) fn align_byte_size(value: u32) -> u32 {

crates/bevy_time/Cargo.toml

@@ -11,6 +11,7 @@ keywords = ["bevy"]
 [features]
 default = []
 serialize = ["serde"]
+bevy_ci_testing = ["bevy_app/bevy_ci_testing"]
 
 [dependencies]
 # bevy

crates/bevy_time/src/lib.rs

@@ -47,6 +47,19 @@ impl Plugin for TimePlugin {
             .init_resource::<FixedTime>()
             .add_systems(First, time_system.in_set(TimeSystem))
             .add_systems(RunFixedUpdateLoop, run_fixed_update_schedule);
+
+        #[cfg(feature = "bevy_ci_testing")]
+        if let Some(ci_testing_config) = app
+            .world
+            .get_resource::<bevy_app::ci_testing::CiTestingConfig>()
+        {
+            if let Some(frame_time) = ci_testing_config.frame_time {
+                app.world
+                    .insert_resource(TimeUpdateStrategy::ManualDuration(Duration::from_secs_f32(
+                        frame_time,
+                    )));
+            }
+        }
     }
 }
 
@@ -60,7 +73,7 @@ pub enum TimeUpdateStrategy {
     Automatic,
     // Update [`Time`] with an exact `Instant` value
     ManualInstant(Instant),
-    // Update [`Time`] with the current time + a specified `Duration`
+    // Update [`Time`] with the last update time + a specified `Duration`
     ManualDuration(Duration),
 }
 
@@ -107,7 +120,8 @@ fn time_system(
         TimeUpdateStrategy::Automatic => time.update_with_instant(new_time),
         TimeUpdateStrategy::ManualInstant(instant) => time.update_with_instant(*instant),
         TimeUpdateStrategy::ManualDuration(duration) => {
-            time.update_with_instant(Instant::now() + *duration);
+            let last_update = time.last_update().unwrap_or_else(|| time.startup());
+            time.update_with_instant(last_update + *duration);
         }
     }
 }