Add debug save states

Reviewed-on: #5
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

.gitea/workflows/ci.yml

@@ -10,7 +10,7 @@ on:
 jobs:
   build-and-test:
     runs-on: ubuntu-latest
-    timeout-minutes: 15
+    timeout-minutes: 30
     steps:
       - name: Check out source
         uses: actions/checkout@v4
@@ -20,7 +20,13 @@ jobs:
           curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
             sh -s -- -y --profile minimal
           echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
-          "$HOME/.cargo/bin/rustup" toolchain install nightly --profile minimal
+          "$HOME/.cargo/bin/rustup" toolchain install nightly-2026-09-14 --profile minimal
+
+      - name: Cache Rust dependencies and build artifacts
+        uses: Swatinem/rust-cache@779680da715d629ac1d338a641029a2f4372abb5 # v2.8.2
+        with:
+          shared-key: linux-nightly
+          cache-bin: false
 
       - name: Install Linux dependencies
         run: |
@@ -39,7 +45,7 @@ jobs:
             pkg-config
 
       - name: Build
-        run: cargo build --locked -j 4
+        run: RUSTFLAGS="-D warnings" cargo build --locked -j 4
 
       - name: Run unit tests
         run: cargo test --locked --lib -j 4

rust-toolchain.toml

@@ -1,2 +1,2 @@
 [toolchain]
-channel = "nightly"
+channel = "nightly-2026-09-14"

src/debug_tools.rs

@@ -3,16 +3,19 @@
 use std::{collections::HashMap, time::Duration};
 
 use bevy::{
+    input::InputSystems,
     prelude::*,
     settings::{ReflectSettingsGroup, SaveSettingsDeferred, SettingsGroup},
 };
 use bevy_egui::{EguiContexts, EguiPrimaryContextPass, egui};
-use bevy_ggrs::RollbackFrameRate;
+use bevy_ggrs::{RollbackFrameRate, RunGgrsSystems};
 use enum_cycling::EnumCycle;
 use enum_cycling_derive::EnumCycle;
 
 use crate::{AppState, player::Player, replay::StopReplayRecording};
 
+mod save_state;
+
 pub const PLAYER_DEBUG_ROW_COUNT: usize = 6;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Reflect)]
@@ -48,7 +51,7 @@ impl PresentationMotionMode {
     }
 }
 
-#[derive(EnumCycle, Reflect)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, EnumCycle, Reflect)]
 pub enum GameSpeedDebug {
     Full,
     Half,
@@ -114,6 +117,7 @@ enum DebugFlag {
     Hurtboxes,
     Camera,
     DrawThroughGeometry,
+    FrameStepping,
 }
 
 #[derive(Clone, Copy)]
@@ -174,6 +178,10 @@ const WORLD_MENU: &[DebugMenuEntry] = &[
     DebugMenuEntry::GameSpeed {
         label: "Game speed",
     },
+    DebugMenuEntry::Toggle {
+        label: "Frame stepping",
+        flag: DebugFlag::FrameStepping,
+    },
 ];
 
 const DIAGNOSTICS_MENU: &[DebugMenuEntry] = &[DebugMenuEntry::Toggle {
@@ -233,6 +241,8 @@ pub struct DebugSettings {
     selections: Vec<usize>,
     #[reflect(ignore)]
     pub player_rows: HashMap<usize, [FighterDebugRowKind; PLAYER_DEBUG_ROW_COUNT]>,
+    #[reflect(ignore)]
+    pub frame_stepping: bool,
     pub network: bool,
     pub ecb: bool,
     pub stage_collision: bool,
@@ -253,6 +263,7 @@ impl Default for DebugSettings {
             pages: vec![DebugMenuPage::Static(ROOT_MENU)],
             selections: vec![0],
             player_rows: HashMap::new(),
+            frame_stepping: false,
             network: false,
             ecb: false,
             stage_collision: false,
@@ -325,6 +336,7 @@ impl DebugSettings {
             DebugFlag::Hurtboxes => self.hurtboxes,
             DebugFlag::DrawThroughGeometry => self.draw_through_geometry,
             DebugFlag::Camera => self.camera,
+            DebugFlag::FrameStepping => self.frame_stepping,
         }
     }
 
@@ -340,6 +352,7 @@ impl DebugSettings {
                 self.draw_through_geometry = !self.draw_through_geometry
             }
             DebugFlag::Camera => self.camera = !self.camera,
+            DebugFlag::FrameStepping => self.frame_stepping = !self.frame_stepping,
         }
     }
 
@@ -356,9 +369,35 @@ impl DebugSettings {
 
 pub struct DebugToolsPlugin;
 
+#[derive(Resource, Default)]
+struct FrameStepState {
+    requested: bool,
+    time_backup: Option<Time>,
+    last_step_time: Time
+}
+
 impl Plugin for DebugToolsPlugin {
     fn build(&self, app: &mut App) {
         app.init_resource::<DebugSettings>()
+            .init_resource::<FrameStepState>()
+            .init_resource::<save_state::DebugSaveState>()
+            .add_systems(OnEnter(AppState::InMatch), save_state::clear)
+            .add_systems(OnExit(AppState::InMatch), save_state::clear)
+            .add_systems(
+                PreUpdate,
+                prepare_frame_step
+                    .after(InputSystems)
+                    .before(RunGgrsSystems)
+                    .run_if(in_state(AppState::InMatch)),
+            )
+            .add_systems(
+                PreUpdate,
+                save_state::save_or_restore
+                    .after(InputSystems)
+                    .before(RunGgrsSystems)
+                    .run_if(in_state(AppState::InMatch)),
+            )
+            .add_systems(PreUpdate, restore_frame_step_time.after(RunGgrsSystems))
             .add_systems(
                 Update,
                 (handle_palette_input, sync_gizmo_depth_bias)
@@ -387,6 +426,141 @@ fn page_len(page: DebugMenuPage, player_handles: &[usize]) -> usize {
     }
 }
 
+fn queue_settings_save(commands: &mut Commands) {
+    commands.queue(SaveSettingsDeferred(Duration::from_secs_f32(0.1)));
+}
+
+fn frame_step_duration(frame_rate: usize) -> Duration {
+    Duration::from_nanos(1_000_000_000u64 / frame_rate as u64)
+}
+
+fn prepare_frame_step(
+    settings: Res<DebugSettings>,
+    gamepads: Query<&Gamepad>,
+    key: Res<ButtonInput<KeyCode>>,
+    mut state: ResMut<FrameStepState>,
+    mut time: ResMut<Time>,
+    frame_rate: Res<RollbackFrameRate>,
+) {
+    if !settings.frame_stepping {
+        state.requested = false;
+        return;
+    }
+
+    let pressed = gamepads
+        .iter()
+        .any(|gamepad| gamepad.pressed(GamepadButton::DPadDown));
+
+    let just_pressed = gamepads
+            .iter()
+            .any(|gamepad| gamepad.just_pressed(GamepadButton::DPadDown));
+
+    let just_pressed = key.just_pressed(KeyCode::F4) || just_pressed;
+    let pressed = key.pressed(KeyCode::F4) || pressed;
+
+    if just_pressed {
+        state.last_step_time = time.clone();
+    }
+
+    let can_repress = pressed && (time.elapsed() - state.last_step_time.elapsed()).as_millis() > 500;
+
+    if !settings.menu_open && (just_pressed || can_repress)
+    {
+        state.requested = true;
+    }
+
+    state.time_backup = Some(*time);
+    let delta = if state.requested {
+        frame_step_duration(**frame_rate)
+    } else {
+        Duration::ZERO
+    };
+    time.advance_by(delta);
+}
+
+fn restore_frame_step_time(mut state: ResMut<FrameStepState>, mut time: ResMut<Time>) {
+    if let Some(backup) = state.time_backup.take() {
+        *time = backup;
+        state.requested = false;
+    }
+}
+
+fn activate_selected(
+    settings: &mut DebugSettings,
+    page_len: usize,
+    player_handles: &[usize],
+    commands: &mut Commands,
+) {
+    if page_len == 0 {
+        return;
+    }
+
+    match settings.page() {
+        DebugMenuPage::Static(entries) => match entries[settings.selected()] {
+            DebugMenuEntry::StopRecording { .. } => {
+                commands.insert_resource(StopReplayRecording);
+            }
+            DebugMenuEntry::Toggle { flag, .. } => {
+                settings.toggle_flag(flag);
+                if !matches!(flag, DebugFlag::FrameStepping) {
+                    queue_settings_save(commands);
+                }
+            }
+            DebugMenuEntry::Submenu { entries, .. } => {
+                settings.push_page(DebugMenuPage::Static(entries));
+            }
+            DebugMenuEntry::PlayerSlots { .. } => settings.push_page(DebugMenuPage::PlayerList),
+            DebugMenuEntry::MotionSampling { .. } => {
+                settings.cycle_motion_sampling();
+                queue_settings_save(commands);
+            }
+            DebugMenuEntry::GameSpeed { .. } => {
+                commands.insert_resource(RollbackFrameRate(settings.game_speed.frame_rate()));
+                queue_settings_save(commands);
+            }
+        },
+        DebugMenuPage::PlayerList => {
+            let handle = player_handles[settings.selected()];
+            settings.rows_mut(handle);
+            settings.push_page(DebugMenuPage::PlayerRows(handle));
+        }
+        DebugMenuPage::PlayerRows(_) => {}
+    }
+}
+
+fn cycle_selected_value(settings: &mut DebugSettings, direction: i8, commands: &mut Commands) {
+    match settings.page() {
+        DebugMenuPage::Static(entries) => {
+            if let Some(entry) = entries.get(settings.selected()) {
+                match entry {
+                    DebugMenuEntry::MotionSampling { .. } => {
+                        settings.cycle_motion_sampling();
+                        queue_settings_save(commands);
+                    }
+                    DebugMenuEntry::GameSpeed { .. } => {
+                        settings.game_speed = if direction > 0 {
+                            settings.game_speed.up()
+                        } else {
+                            settings.game_speed.down()
+                        };
+                        commands
+                            .insert_resource(RollbackFrameRate(settings.game_speed.frame_rate()));
+                        queue_settings_save(commands);
+                    }
+                    _ => {}
+                }
+            }
+        }
+        DebugMenuPage::PlayerRows(handle) => {
+            let selected = settings.selected();
+            let rows = settings.rows_mut(handle);
+            rows[selected] = rows[selected].cycle(direction);
+            queue_settings_save(commands);
+        }
+        DebugMenuPage::PlayerList => {}
+    }
+}
+
 fn handle_palette_input(
     keyboard: Res<ButtonInput<KeyCode>>,
     gamepads: Query<(Entity, &Gamepad)>,
@@ -398,6 +572,15 @@ fn handle_palette_input(
         settings.toggle_flag(DebugFlag::DrawThroughGeometry);
     }
 
+    if keyboard.just_pressed(KeyCode::F3) {
+        settings.menu_open = !settings.menu_open;
+        settings.controller = None;
+        if settings.menu_open {
+            settings.reset_navigation();
+        }
+        return;
+    }
+
     if !settings.menu_open {
         for (entity, gamepad) in &gamepads {
             if gamepad.just_pressed(GamepadButton::Start) && gamepad.pressed(GamepadButton::DPadUp)
@@ -411,14 +594,15 @@ fn handle_palette_input(
         return;
     }
 
-    let Some(controller) = settings.controller else {
+    let gamepad = if let Some(controller) = settings.controller {
-        settings.menu_open = false;
+        let Ok((_, gamepad)) = gamepads.get(controller) else {
-        return;
+            settings.menu_open = false;
-    };
+            settings.controller = None;
-    let Ok((_, gamepad)) = gamepads.get(controller) else {
+            return;
-        settings.menu_open = false;
+        };
-        settings.controller = None;
+        Some(gamepad)
-        return;
+    } else {
+        None
     };
     let player_handles = player_handles(&players);
     let page = settings.page();
@@ -428,95 +612,51 @@ fn handle_palette_input(
         *settings.selected_mut() = 0;
     }
 
-    if gamepad.just_pressed(GamepadButton::DPadUp) && page_len != 0 {
+    if (gamepad.is_some_and(|pad| pad.just_pressed(GamepadButton::DPadUp))
+        || keyboard.just_pressed(KeyCode::ArrowUp)
+        || keyboard.just_pressed(KeyCode::KeyW))
+        && page_len != 0
+    {
         let selected = settings.selected_mut();
         *selected = selected.checked_sub(1).unwrap_or(page_len - 1);
     }
-    if gamepad.just_pressed(GamepadButton::DPadDown) && page_len != 0 {
+    if (gamepad.is_some_and(|pad| pad.just_pressed(GamepadButton::DPadDown))
+        || keyboard.just_pressed(KeyCode::ArrowDown)
+        || keyboard.just_pressed(KeyCode::KeyS))
+        && page_len != 0
+    {
         let selected = settings.selected_mut();
         *selected = (*selected + 1) % page_len;
     }
 
-    let direction = if gamepad.just_pressed(GamepadButton::DPadLeft) {
+    let direction = if gamepad.is_some_and(|pad| pad.just_pressed(GamepadButton::DPadLeft))
+        || keyboard.just_pressed(KeyCode::ArrowLeft)
+        || keyboard.just_pressed(KeyCode::KeyA)
+    {
         Some(-1)
-    } else if gamepad.just_pressed(GamepadButton::DPadRight) {
+    } else if gamepad.is_some_and(|pad| pad.just_pressed(GamepadButton::DPadRight))
+        || keyboard.just_pressed(KeyCode::ArrowRight)
+        || keyboard.just_pressed(KeyCode::KeyD)
+    {
         Some(1)
     } else {
         None
     };
 
     if let Some(direction) = direction {
-        match page {
+        cycle_selected_value(&mut settings, direction, &mut commands);
-            DebugMenuPage::Static(entries) => {
-                if let Some(entry) = entries.get(settings.selected()) {
-                    match entry {
-                        DebugMenuEntry::StopRecording { .. } => {}
-                        DebugMenuEntry::MotionSampling { .. } => settings.cycle_motion_sampling(),
-                        DebugMenuEntry::GameSpeed { .. } => {
-                            if direction > 0 {
-                                settings.game_speed = settings.game_speed.up();
-                            } else {
-                                settings.game_speed = settings.game_speed.down();
-                            }
-
-                            commands.insert_resource(RollbackFrameRate(
-                                settings.game_speed.frame_rate(),
-                            ));
-                        }
-                        _ => {}
-                    }
-                }
-            }
-            DebugMenuPage::PlayerList => todo!(),
-            DebugMenuPage::PlayerRows(_) => {
-                let DebugMenuPage::PlayerRows(handle) = page else {
-                    unreachable!("player row navigation must have a player row page")
-                };
-                let selected = settings.selected();
-                let rows = settings.rows_mut(handle);
-                rows[selected] = rows[selected].cycle(direction);
-
-                commands.queue(SaveSettingsDeferred(Duration::from_secs_f32(0.1)));
-            }
-        }
     }
-
+    if (gamepad.is_some_and(|pad| pad.just_pressed(GamepadButton::South))
-    if matches!(page, DebugMenuPage::PlayerRows(_)) {
+        || keyboard.just_pressed(KeyCode::Enter)
-        let direction = if gamepad.just_pressed(GamepadButton::DPadLeft) {
+        || keyboard.just_pressed(KeyCode::Space))
-            Some(-1)
+        && page_len != 0
-        } else if gamepad.just_pressed(GamepadButton::DPadRight) {
+    {
-            Some(1)
+        activate_selected(&mut settings, page_len, &player_handles, &mut commands);
-        } else {
-            None
-        };
-        if let Some(_direction) = direction {}
     }
-    if gamepad.just_pressed(GamepadButton::South) {
+    if (gamepad.is_some_and(|pad| pad.just_pressed(GamepadButton::West))
-        match page {
+        || keyboard.just_pressed(KeyCode::Escape))
-            DebugMenuPage::Static(entries) if page_len != 0 => match entries[settings.selected()] {
+        && !settings.pop_page()
-                DebugMenuEntry::StopRecording { .. } => {
+    {
-                    commands.insert_resource(StopReplayRecording);
-                }
-                DebugMenuEntry::Toggle { flag, .. } => {
-                    settings.toggle_flag(flag);
-                    commands.queue(SaveSettingsDeferred(Duration::from_secs_f32(0.1)));
-                }
-                DebugMenuEntry::Submenu { entries, .. } => {
-                    settings.push_page(DebugMenuPage::Static(entries));
-                }
-                DebugMenuEntry::PlayerSlots { .. } => settings.push_page(DebugMenuPage::PlayerList),
-                DebugMenuEntry::MotionSampling { .. } => settings.cycle_motion_sampling(),
-                DebugMenuEntry::GameSpeed { .. } => {}
-            },
-            DebugMenuPage::PlayerList if page_len != 0 => {
-                let handle = player_handles[settings.selected()];
-                settings.rows_mut(handle);
-                settings.push_page(DebugMenuPage::PlayerRows(handle));
-            }
-            _ => {}
-        }
-    }
-    if gamepad.just_pressed(GamepadButton::West) && !settings.pop_page() {
         settings.menu_open = false;
         settings.controller = None;
     }
@@ -538,8 +678,9 @@ fn sync_gizmo_depth_bias(settings: Res<DebugSettings>, mut configs: ResMut<Gizmo
 
 fn draw_palette(
     mut contexts: EguiContexts,
-    settings: Res<DebugSettings>,
+    mut settings: ResMut<DebugSettings>,
     players: Query<&Player>,
+    mut commands: Commands,
 ) -> Result {
     if !settings.menu_open {
         return Ok(());
@@ -547,7 +688,7 @@ fn draw_palette(
 
     let player_handles = player_handles(&players);
     let page = settings.page();
-    let selected = settings.selected();
+    let page_len = page_len(page, &player_handles);
     egui::Window::new("Debug")
         .anchor(egui::Align2::RIGHT_TOP, egui::vec2(-12.0, 12.0))
         .resizable(false)
@@ -556,38 +697,113 @@ fn draw_palette(
             match page {
                 DebugMenuPage::Static(entries) => {
                     for (index, entry) in entries.iter().enumerate() {
-                        let marker = if index == selected { ">" } else { " " };
+                        ui.horizontal(|ui| {
-                        match entry {
+                            ui.label(if index == settings.selected() {
-                            DebugMenuEntry::StopRecording { label } => {
+                                ">"
-                                ui.label(format!("{marker} {label}"));
+                            } else {
+                                " "
+                            });
+                            match entry {
+                                DebugMenuEntry::StopRecording { label } => {
+                                    if ui.button(*label).clicked() {
+                                        *settings.selected_mut() = index;
+                                        activate_selected(
+                                            &mut settings,
+                                            page_len,
+                                            &player_handles,
+                                            &mut commands,
+                                        );
+                                    }
+                                }
+                                DebugMenuEntry::Toggle { label, flag } => {
+                                    let mut value = settings.flag(*flag);
+                                    if ui.checkbox(&mut value, *label).changed() {
+                                        settings.toggle_flag(*flag);
+                                        if !matches!(flag, DebugFlag::FrameStepping) {
+                                            queue_settings_save(&mut commands);
+                                        }
+                                    }
+                                }
+                                DebugMenuEntry::Submenu { label, .. }
+                                | DebugMenuEntry::PlayerSlots { label } => {
+                                    if ui.button(format!("{label} >")).clicked() {
+                                        *settings.selected_mut() = index;
+                                        activate_selected(
+                                            &mut settings,
+                                            page_len,
+                                            &player_handles,
+                                            &mut commands,
+                                        );
+                                    }
+                                }
+                                DebugMenuEntry::MotionSampling { label } => {
+                                    let old = settings.motion_sampling;
+                                    egui::ComboBox::from_id_salt(("debug-motion", index))
+                                        .width(180.0)
+                                        .selected_text(format!("{label}: {}", old.label()))
+                                        .show_ui(ui, |ui| {
+                                            ui.selectable_value(
+                                                &mut settings.motion_sampling,
+                                                PresentationMotionMode::Interpolation,
+                                                "Interpolation",
+                                            );
+                                            ui.selectable_value(
+                                                &mut settings.motion_sampling,
+                                                PresentationMotionMode::Extrapolation,
+                                                "Extrapolation",
+                                            );
+                                        });
+                                    if settings.motion_sampling != old {
+                                        queue_settings_save(&mut commands);
+                                    }
+                                }
+                                DebugMenuEntry::GameSpeed { label } => {
+                                    let old = settings.game_speed;
+                                    egui::ComboBox::from_id_salt(("debug-speed", index))
+                                        .width(180.0)
+                                        .selected_text(format!("{label}: {}", old.label()))
+                                        .show_ui(ui, |ui| {
+                                            for speed in [
+                                                GameSpeedDebug::Full,
+                                                GameSpeedDebug::Half,
+                                                GameSpeedDebug::Quarter,
+                                            ] {
+                                                ui.selectable_value(
+                                                    &mut settings.game_speed,
+                                                    speed,
+                                                    speed.label(),
+                                                );
+                                            }
+                                        });
+                                    if settings.game_speed != old {
+                                        commands.insert_resource(RollbackFrameRate(
+                                            settings.game_speed.frame_rate(),
+                                        ));
+                                        queue_settings_save(&mut commands);
+                                    }
+                                }
                             }
-                            DebugMenuEntry::Toggle { label, flag } => {
+                        });
-                                let state = if settings.flag(*flag) { "on" } else { "off" };
-                                ui.label(format!("{marker} {label}: {state}"));
-                            }
-                            DebugMenuEntry::Submenu { label, .. }
-                            | DebugMenuEntry::PlayerSlots { label } => {
-                                ui.label(format!("{marker} {label} >"));
-                            }
-                            DebugMenuEntry::MotionSampling { label } => {
-                                ui.label(format!(
-                                    "{marker} {label}: {}",
-                                    settings.motion_sampling.label()
-                                ));
-                            }
-                            DebugMenuEntry::GameSpeed { label } => {
-                                ui.label(format!(
-                                    "{marker} {label}: {}",
-                                    settings.game_speed.label()
-                                ));
-                            }
-                        }
                     }
                 }
                 DebugMenuPage::PlayerList => {
                     for (index, handle) in player_handles.iter().enumerate() {
-                        let marker = if index == selected { ">" } else { " " };
+                        ui.horizontal(|ui| {
-                        ui.label(format!("{marker} Player {} >", handle + 1));
+                            ui.label(if index == settings.selected() {
+                                ">"
+                            } else {
+                                " "
+                            });
+                            if ui.button(format!("Player {} >", handle + 1)).clicked() {
+                                *settings.selected_mut() = index;
+                                activate_selected(
+                                    &mut settings,
+                                    page_len,
+                                    &player_handles,
+                                    &mut commands,
+                                );
+                            }
+                        });
                     }
                     if player_handles.is_empty() {
                         ui.label("No players in match");
@@ -600,16 +816,30 @@ fn draw_palette(
                         .unwrap_or([FighterDebugRowKind::None; PLAYER_DEBUG_ROW_COUNT]);
                     ui.label(format!("Player {}", handle + 1));
                     for (index, row) in rows.iter().enumerate() {
-                        let marker = if index == selected { ">" } else { " " };
+                        ui.horizontal(|ui| {
-                        ui.label(format!("{marker} Row {}: {}", index + 1, row.label()));
+                            ui.label(if index == settings.selected() {
+                                ">"
+                            } else {
+                                " "
+                            });
+                            egui::ComboBox::from_id_salt(("debug-row", handle, index))
+                                .width(180.0)
+                                .selected_text(format!("Row {}: {}", index + 1, row.label()))
+                                .show_ui(ui, |ui| {
+                                    let rows = settings.rows_mut(handle);
+                                    for kind in FighterDebugRowKind::ALL {
+                                        ui.selectable_value(&mut rows[index], kind, kind.label());
+                                    }
+                                });
+                        });
                     }
                 }
             }
             ui.separator();
             let controls = if matches!(page, DebugMenuPage::PlayerRows(_)) {
-                "D-pad: select/change   B: back"
+                "Arrows/WASD: select/change   Escape/B: back"
             } else {
-                "D-pad: select   A: enter/toggle   Left/right: change   B: back"
+                "Arrows/WASD: select   Enter/A: activate   Escape/B: back"
             };
             ui.label(controls);
         });
@@ -699,4 +929,29 @@ mod tests {
         mode.cycle();
         assert_eq!(mode, PresentationMotionMode::Interpolation);
     }
+
+    #[test]
+    fn game_speed_has_expected_frame_rates() {
+        assert_eq!(GameSpeedDebug::Full.frame_rate(), 60);
+        assert_eq!(GameSpeedDebug::Half.frame_rate(), 30);
+        assert_eq!(GameSpeedDebug::Quarter.frame_rate(), 15);
+    }
+
+    #[test]
+    fn frame_stepping_is_disabled_by_default_and_uses_game_speed_timestep() {
+        let settings = DebugSettings::default();
+
+        assert!(!settings.frame_stepping);
+        assert_eq!(frame_step_duration(60), Duration::from_nanos(16_666_666));
+        assert_eq!(frame_step_duration(30), Duration::from_nanos(33_333_333));
+    }
+
+    #[test]
+    fn empty_player_list_does_not_activate() {
+        let mut settings = DebugSettings::default();
+        settings.push_page(DebugMenuPage::PlayerList);
+
+        assert_eq!(page_len(settings.page(), &[]), 0);
+        assert_eq!(settings.selected(), 0);
+    }
 }

src/debug_tools/save_state.rs

@@ -0,0 +1,196 @@
+use bevy::prelude::*;
+
+use crate::{
+    camera::MatchCamera,
+    fighter::{
+        FighterECB, FighterFacingDirection, FighterHitboxes, FighterHitstop,
+        FighterPreviousFacingDirection, FighterPreviousTranslation, FighterTranslation,
+        FighterVelocity, Grounded,
+        animation::FighterAnimationFrame,
+        attack::{
+            FighterDamage, FighterKnockbackVelocity, FighterPendingHitReaction,
+            FighterReceivedAttacks, FighterSolvedHurtboxes, FighterStaleMoveQueue,
+        },
+        baked_animation::FighterBoneMatrices,
+        state::FighterState,
+    },
+    input::FighterInput,
+    player::Player,
+    stage::line::StageCollision,
+};
+
+#[derive(Resource, Default)]
+pub(super) struct DebugSaveState {
+    checkpoint: Option<Checkpoint>,
+}
+
+#[derive(Clone)]
+struct Checkpoint {
+    fighters: Vec<FighterCheckpoint>,
+    stage_collision: StageCollision,
+}
+
+#[derive(Clone)]
+struct FighterCheckpoint {
+    entity: Entity,
+    handle: usize,
+    ecb: FighterECB,
+    previous_ecb: crate::fighter::ecb::FighterPreviousECB,
+    velocity: FighterVelocity,
+    translation: FighterTranslation,
+    previous_translation: FighterPreviousTranslation,
+    facing: FighterFacingDirection,
+    previous_facing: FighterPreviousFacingDirection,
+    animation: FighterAnimationFrame,
+    state: FighterState,
+    input: FighterInput,
+    damage: FighterDamage,
+    pending_hit_reaction: FighterPendingHitReaction,
+    hitstop: FighterHitstop,
+    knockback_velocity: FighterKnockbackVelocity,
+    stale_moves: FighterStaleMoveQueue,
+    hitboxes: FighterHitboxes,
+    received_attacks: FighterReceivedAttacks,
+    solved_hurtboxes: FighterSolvedHurtboxes,
+    bone_matrices: FighterBoneMatrices,
+    grounded: bool,
+}
+
+pub(super) fn save_or_restore(world: &mut World) {
+    if world.resource::<super::DebugSettings>().menu_open {
+        return;
+    }
+
+    let left = world
+        .query::<&Gamepad>()
+        .iter(world)
+        .any(|gamepad| gamepad.just_pressed(GamepadButton::DPadLeft));
+    let right = world
+        .query::<&Gamepad>()
+        .iter(world)
+        .any(|gamepad| gamepad.just_pressed(GamepadButton::DPadRight));
+
+    if left == right {
+        return;
+    }
+
+    let Some(roster) = world
+        .get_resource::<crate::fighter::FighterRoster>()
+        .map(|roster| roster.0.clone())
+    else {
+        return;
+    };
+    if roster.len() != 1 {
+        warn!("Save states are only available in single-player matches");
+        return;
+    }
+
+    if left {
+        let Some(stage_collision) = world.get_resource::<StageCollision>().cloned() else {
+            return;
+        };
+        let mut checkpoint_fighters = Vec::with_capacity(roster.len());
+        for entity in roster.iter().copied() {
+            let Some(checkpoint) = capture_fighter(world, entity) else {
+                warn!("Could not save the current fighter state");
+                return;
+            };
+            checkpoint_fighters.push(checkpoint);
+        }
+        world.resource_mut::<DebugSaveState>().checkpoint = Some(Checkpoint {
+            fighters: checkpoint_fighters,
+            stage_collision,
+        });
+        info!("Saved debug game state");
+        return;
+    }
+
+    let Some(checkpoint) = world.resource::<DebugSaveState>().checkpoint.clone() else {
+        warn!("No debug game state has been saved");
+        return;
+    };
+    if checkpoint.fighters.len() != roster.len()
+        || checkpoint
+            .fighters
+            .iter()
+            .zip(roster.iter())
+            .any(|(saved, current)| saved.entity != *current)
+    {
+        warn!("Saved debug game state belongs to another match");
+        return;
+    }
+
+    for saved in &checkpoint.fighters {
+        let Some(player) = world.entity(saved.entity).get::<Player>() else {
+            warn!("Could not restore the saved fighter state");
+            return;
+        };
+        if player.handle != saved.handle {
+            warn!("Saved debug game state belongs to another match");
+            return;
+        }
+
+        let mut entity = world.entity_mut(saved.entity);
+        entity.insert(saved.ecb);
+        entity.insert(saved.previous_ecb);
+        entity.insert(saved.velocity);
+        entity.insert(saved.translation);
+        entity.insert(saved.previous_translation);
+        entity.insert(saved.facing);
+        entity.insert(saved.previous_facing);
+        entity.insert(saved.animation);
+        entity.insert(saved.state.clone());
+        entity.insert(saved.input);
+        entity.insert(saved.damage);
+        entity.insert(saved.pending_hit_reaction.clone());
+        entity.insert(saved.hitstop);
+        entity.insert(saved.knockback_velocity);
+        entity.insert(saved.stale_moves.clone());
+        entity.insert(saved.hitboxes.clone());
+        entity.insert(saved.received_attacks.clone());
+        entity.insert(saved.solved_hurtboxes.clone());
+        entity.insert(saved.bone_matrices.clone());
+        if saved.grounded {
+            entity.insert(Grounded);
+        } else {
+            entity.remove::<Grounded>();
+        }
+    }
+    world.insert_resource(checkpoint.stage_collision);
+    for mut match_camera in world.query::<&mut MatchCamera>().iter_mut(world) {
+        match_camera.needs_snap = true;
+    }
+    info!("Restored debug game state");
+}
+
+fn capture_fighter(world: &World, entity: Entity) -> Option<FighterCheckpoint> {
+    let fighter = world.entity(entity);
+    Some(FighterCheckpoint {
+        entity,
+        handle: fighter.get::<Player>()?.handle,
+        ecb: *fighter.get::<FighterECB>()?,
+        previous_ecb: *fighter.get::<crate::fighter::ecb::FighterPreviousECB>()?,
+        velocity: *fighter.get::<FighterVelocity>()?,
+        translation: *fighter.get::<FighterTranslation>()?,
+        previous_translation: *fighter.get::<FighterPreviousTranslation>()?,
+        facing: *fighter.get::<FighterFacingDirection>()?,
+        previous_facing: *fighter.get::<FighterPreviousFacingDirection>()?,
+        animation: *fighter.get::<FighterAnimationFrame>()?,
+        state: fighter.get::<FighterState>()?.clone(),
+        input: *fighter.get::<FighterInput>()?,
+        damage: *fighter.get::<FighterDamage>()?,
+        pending_hit_reaction: fighter.get::<FighterPendingHitReaction>()?.clone(),
+        hitstop: *fighter.get::<FighterHitstop>()?,
+        knockback_velocity: *fighter.get::<FighterKnockbackVelocity>()?,
+        stale_moves: fighter.get::<FighterStaleMoveQueue>()?.clone(),
+        hitboxes: fighter.get::<FighterHitboxes>()?.clone(),
+        received_attacks: fighter.get::<FighterReceivedAttacks>()?.clone(),
+        solved_hurtboxes: fighter.get::<FighterSolvedHurtboxes>()?.clone(),
+        bone_matrices: fighter.get::<FighterBoneMatrices>()?.clone(),
+        grounded: fighter.contains::<Grounded>(),
+    })
+}
+
+pub(super) fn clear(mut save_state: ResMut<DebugSaveState>) {
+    save_state.checkpoint = None;
+}