fix(input): start games with the plus key

Match the recovered Win16 registration flow: the first plus press creates Player 1 and additional presses add Players 2 through 4 until the initial launch. Down now belongs only to charging and releasing the plunger.

Test Plan:
- cargo fmt --check
- cargo test
- cargo clippy --all-targets --all-features -- -D warnings
- live: verify Down cannot leave attract mode
- live: start with plus, add Player 2, hold Down through partial/full plunger frames, and release onto the table
- git diff --check

tdkpin-rs/README.md

@@ -35,8 +35,8 @@ command-line tools.
 
 | Action | Original key | Additional modern key |
 | --- | --- | --- |
-| Choose 1-4 players | `+` | `=` |
-| Start game / charge launcher | Hold Down arrow, release to launch | Enter starts a game |
+| Start game / add up to 4 players | `+` | `=` or Enter starts one player |
+| Charge launcher | Hold Down arrow, release to launch | - |
 | Left flipper | Left Ctrl | `A` or Left arrow |
 | Right flipper | Keypad Enter | Right Ctrl, `D`, or Right arrow |
 | Nudge | Space, either Shift, keypad `3` | - |

tdkpin-rs/src/app.rs

@@ -28,7 +28,6 @@ pub struct App {
     screen: Screen,
     return_screen: Screen,
     game: Option<Game>,
-    player_count: usize,
     setting_row: usize,
     loading_until: f64,
     last_help_click: f64,
@@ -53,7 +52,6 @@ impl App {
             screen: Screen::Loading,
             return_screen: Screen::Attract,
             game: None,
-            player_count: 1,
             setting_row: 0,
             loading_until: get_time() + 1.1,
             last_help_click: -1.0,
@@ -131,18 +129,25 @@ impl App {
     }
 
     fn update_attract(&mut self) {
-        if is_key_pressed(KeyCode::KpAdd) || is_key_pressed(KeyCode::Equal) {
-            self.player_count = self.player_count % 4 + 1;
-            self.assets.play(2012, self.saved.settings.sounds);
-        }
-        if is_key_pressed(KeyCode::Down) || is_key_pressed(KeyCode::Enter) {
-            self.game = Some(Game::new(self.player_count));
+        if is_key_pressed(KeyCode::KpAdd)
+            || is_key_pressed(KeyCode::Equal)
+            || is_key_pressed(KeyCode::Enter)
+        {
+            self.game = Some(Game::new(1));
             self.screen = Screen::Playing;
             self.assets.play(2008, self.saved.settings.sounds);
         }
     }
 
     fn update_game(&mut self) {
+        if (is_key_pressed(KeyCode::KpAdd) || is_key_pressed(KeyCode::Equal))
+            && self
+                .game
+                .as_mut()
+                .is_some_and(Game::add_player_before_launch)
+        {
+            self.assets.play(2012, self.saved.settings.sounds);
+        }
         let left_flipper = is_key_down(KeyCode::LeftControl)
             || is_key_down(KeyCode::A)
             || is_key_down(KeyCode::Left);
@@ -350,20 +355,14 @@ impl App {
         draw_panel(342.0, 72.0, 267.0, 144.0);
         draw_centered_at("TDK PINBALL MACHINE", 475.5, 107.0, 22, BLACK);
         draw_centered_at(
-            "PRESS DOWN ARROW",
+            "PRESS + TO START",
             475.5,
             139.0,
             22,
             Color::from_rgba(0, 72, 102, 255),
         );
-        draw_centered_at("TO START BALL", 475.5, 165.0, 18, BLACK);
-        draw_centered_at(
-            &format!("PLAYERS: {}   [+] CHANGE", self.player_count),
-            475.5,
-            196.0,
-            16,
-            BLACK,
-        );
+        draw_centered_at("PRESS + AGAIN TO ADD PLAYERS", 475.5, 165.0, 15, BLACK);
+        draw_centered_at("THEN HOLD DOWN TO LAUNCH", 475.5, 196.0, 16, BLACK);
         draw_text(
             "F1 HELP   F2 SETTINGS   F3 HIGHSCORES   F12 SOUND",
             322.0,

tdkpin-rs/src/game.rs

@@ -92,6 +92,12 @@ pub struct Ball {
     pub in_launcher: bool,
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum PlayerEntry {
+    Open,
+    Closed,
+}
+
 impl Default for Ball {
     fn default() -> Self {
         Self {
@@ -128,6 +134,7 @@ pub struct Game {
     nudge_meter: f32,
     stalled_for: f32,
     launcher_was_down: bool,
+    player_entry: PlayerEntry,
 }
 
 impl Game {
@@ -157,6 +164,7 @@ impl Game {
             nudge_meter: 0.0,
             stalled_for: 0.0,
             launcher_was_down: false,
+            player_entry: PlayerEntry::Open,
         }
     }
 
@@ -168,12 +176,21 @@ impl Game {
         LAUNCHER_FRAME_THRESHOLDS.partition_point(|threshold| self.launcher_charge >= *threshold)
     }
 
+    pub fn add_player_before_launch(&mut self) -> bool {
+        if self.player_entry == PlayerEntry::Closed || self.players.len() >= 4 {
+            return false;
+        }
+        self.players.push(Player::default());
+        true
+    }
+
     fn fire_launcher(&mut self) {
         let launch_speed = LAUNCH_SPEED_MIN + self.launcher_charge * LAUNCH_SPEED_RANGE;
         self.ball.in_launcher = false;
         self.ball.velocity = vec2(0.0, -launch_speed);
         self.launcher_charge = 0.0;
         self.launcher_was_down = false;
+        self.player_entry = PlayerEntry::Closed;
         self.stalled_for = 0.0;
     }
 
@@ -626,6 +643,22 @@ mod tests {
         assert_eq!(Game::new(99).players.len(), 4);
     }
 
+    #[test]
+    fn plus_adds_players_only_before_the_first_launch() {
+        let mut game = Game::new(1);
+
+        assert!(game.add_player_before_launch());
+        assert!(game.add_player_before_launch());
+        assert!(game.add_player_before_launch());
+        assert!(!game.add_player_before_launch());
+        assert_eq!(game.players.len(), 4);
+
+        let mut game = Game::new(1);
+        launch_ball(&mut game, 1);
+        assert!(!game.add_player_before_launch());
+        assert_eq!(game.players.len(), 1);
+    }
+
     #[test]
     fn ball_starts_in_the_recovered_shooter_lane() {
         let game = Game::new(1);