Game state

Screenshot

Before we add any more functionality to our game it’s time for some refactoring. To make it easier to keep track of the game state we’ll add an enum called GameState with variants to differentiate between the game being played and the game being over. This will allows us to remove the gameover variable, and we can add states for showing a start menu and pausing the game.

Implementation

Game state enum

Begin by adding an enum called GameState below the Shape implementation. It should contain all four possible game states: MainMenu, Playing, Paused, and GameOver.

enum GameState {
    MainMenu,
    Playing,
    Paused,
    GameOver,
}

Game state variable

Replace the line that declares the gameover variable with a line that instantiates a game_state variable set to GameState::MainMenu.

    let mut game_state = GameState::MainMenu;

Match on GameState

We’ll replace the old code in the game loop with code that uses the match control flow construct on the game_state variable. It has to match on all four states in the enum. Later on we’ll add back code from the earlier chapter within the matching arms. Keep the call to clearing the screen at the start of the loop, and the call to next_frame().await at the end.

        clear_background(DARKPURPLE);

        match game_state {
            GameState::MainMenu => {
                ...
            }
            GameState::Playing => {
                ...
            }
            GameState::Paused => {
                ...
            }
            GameState::GameOver => {
                ...
            }
        }

        next_frame().await

Now let’s add back code into the match arms to handle each game state. When the game is started, the state will be GameState::MainMenu. We’ll start by quitting the game if the Escape key is pressed. If the player presses the space key we’ll set the game_state to the new state GameState::Playing. We’ll also reset all the game variables. We will also draw the text “Press space” in the middle of the screen.

            GameState::MainMenu => {
                if is_key_pressed(KeyCode::Escape) {
                    std::process::exit(0);
                }
                if is_key_pressed(KeyCode::Space) {
                    squares.clear();
                    bullets.clear();
                    circle.x = screen_width() / 2.0;
                    circle.y = screen_height() / 2.0;
                    score = 0;
                    game_state = GameState::Playing;
                }
                let text = "Press space";
                let text_dimensions = measure_text(text, None, 50, 1.0);
                draw_text(
                    text,
                    screen_width() / 2.0 - text_dimensions.width / 2.0,
                    screen_height() / 2.0,
                    50.0,
                    WHITE,
                );
            },

Playing the game

Let’s add back the code for playing the game to the matching arm for the state GameState::Playing. It’s the same code as most of the game loop from the last chapter. However, don’t add back the code that handles Game Over as it will be added in the matching arm for the GameState::GameOver.

We’ll also add a code that checks if the player presses the Escape key and change the state to GameState::Paused. This will ensure that the game will be paused in the next iteration of the game loop.

            GameState::Playing => {
                let delta_time = get_frame_time();
                if is_key_down(KeyCode::Right) {
                    circle.x += MOVEMENT_SPEED * delta_time;
                }
                if is_key_down(KeyCode::Left) {
                    circle.x -= MOVEMENT_SPEED * delta_time;
                }
                if is_key_down(KeyCode::Down) {
                    circle.y += MOVEMENT_SPEED * delta_time;
                }
                if is_key_down(KeyCode::Up) {
                    circle.y -= MOVEMENT_SPEED * delta_time;
                }
                if is_key_pressed(KeyCode::Space) {
                    bullets.push(Shape {
                        x: circle.x,
                        y: circle.y,
                        speed: circle.speed * 2.0,
                        size: 5.0,
                        collided: false,
                    });
                }
                if is_key_pressed(KeyCode::Escape) {
                    game_state = GameState::Paused;
                }

                // Clamp X and Y to be within the screen
                circle.x = clamp(circle.x, 0.0, screen_width());
                circle.y = clamp(circle.y, 0.0, screen_height());

                // Generate a new square
                if rand::gen_range(0, 99) >= 95 {
                    let size = rand::gen_range(16.0, 64.0);
                    squares.push(Shape {
                        size,
                        speed: rand::gen_range(50.0, 150.0),
                        x: rand::gen_range(size / 2.0, screen_width() - size / 2.0),
                        y: -size,
                        collided: false,
                    });
                }

                // Movement
                for square in &mut squares {
                    square.y += square.speed * delta_time;
                }
                for bullet in &mut bullets {
                    bullet.y -= bullet.speed * delta_time;
                }

                // Remove shapes outside of screen
                squares.retain(|square| square.y < screen_height() + square.size);
                bullets.retain(|bullet| bullet.y > 0.0 - bullet.size / 2.0);

                // Remove collided shapes
                squares.retain(|square| !square.collided);
                bullets.retain(|bullet| !bullet.collided);

                // Check for collisions
                if squares.iter().any(|square| circle.collides_with(square)) {
                    if score == high_score {
                        fs::write("highscore.dat", high_score.to_string()).ok();
                    }
                    game_state = GameState::GameOver;
                }
                for square in squares.iter_mut() {
                    for bullet in bullets.iter_mut() {
                        if bullet.collides_with(square) {
                            bullet.collided = true;
                            square.collided = true;
                            score += square.size.round() as u32;
                            high_score = high_score.max(score);
                        }
                    }
                }

                // Draw everything
                for bullet in &bullets {
                    draw_circle(bullet.x, bullet.y, bullet.size / 2.0, RED);
                }
                draw_circle(circle.x, circle.y, circle.size / 2.0, YELLOW);
                for square in &squares {
                    draw_rectangle(
                        square.x - square.size / 2.0,
                        square.y - square.size / 2.0,
                        square.size,
                        square.size,
                        GREEN,
                    );
                }
                draw_text(
                    format!("Score: {}", score).as_str(),
                    10.0,
                    35.0,
                    25.0,
                    WHITE,
                );
                let highscore_text = format!("High score: {}", high_score);
                let text_dimensions = measure_text(highscore_text.as_str(), None, 25, 1.0);
                draw_text(
                    highscore_text.as_str(),
                    screen_width() - text_dimensions.width - 10.0,
                    35.0,
                    25.0,
                    WHITE,
                );
            },

Pause the game

Many games have the option to pause the action, so we’ll add support for that in our game, too. When the game is paused, we’ll check if the player presses the Space key and change the game state to GameState::Playing so that the game can continue. We’ll also draw a text on the screen showing that the game is paused.

The changed game state will only come into effect in the next iteration of the game loop, so even if it has been changed we need to display the text during the current frame.

            GameState::Paused => {
                if is_key_pressed(KeyCode::Space) {
                    game_state = GameState::Playing;
                }
                let text = "Paused";
                let text_dimensions = measure_text(text, None, 50, 1.0);
                draw_text(
                    text,
                    screen_width() / 2.0 - text_dimensions.width / 2.0,
                    screen_height() / 2.0,
                    50.0,
                    WHITE,
                );
            },

Game Over

Finally we will handle what happens when the game is over. If the player presses the space bar we’ll change the state to GameState::MainMenu to allow the player to start a new game or quit the game. We’ll also draw the “GAME OVER!” text to the screen as we did in the last chapter.

            GameState::GameOver => {
                if is_key_pressed(KeyCode::Space) {
                    game_state = GameState::MainMenu;
                }
                let text = "GAME OVER!";
                let text_dimensions = measure_text(text, None, 50, 1.0);
                draw_text(
                    text,
                    screen_width() / 2.0 - text_dimensions.width / 2.0,
                    screen_height() / 2.0,
                    50.0,
                    RED,
                );
            },

Note

Since the states for GameState::Playing and GameState::GameOver are separated, the squares and circles will not be shown when the game is paused.

Challenge

Now that we have a main menu, you could come up with a name for your game and display it in a large font at the top of the screen in the state GameState::MainMenu.

You could also try drawing all the circles and squares even when the game is paused without moving them.

Full source code

Click to show the the full source code

use macroquad::prelude::*;

use std::fs;

struct Shape {
    size: f32,
    speed: f32,
    x: f32,
    y: f32,
    collided: bool,
}

impl Shape {
    fn collides_with(&self, other: &Self) -> bool {
        self.rect().overlaps(&other.rect())
    }

    fn rect(&self) -> Rect {
        Rect {
            x: self.x - self.size / 2.0,
            y: self.y - self.size / 2.0,
            w: self.size,
            h: self.size,
        }
    }
}

enum GameState {
    MainMenu,
    Playing,
    Paused,
    GameOver,
}

#[macroquad::main("My game")]
async fn main() {
    const MOVEMENT_SPEED: f32 = 200.0;

    rand::srand(miniquad::date::now() as u64);
    let mut squares = vec![];
    let mut bullets: Vec<Shape> = vec![];
    let mut circle = Shape {
        size: 32.0,
        speed: MOVEMENT_SPEED,
        x: screen_width() / 2.0,
        y: screen_height() / 2.0,
        collided: false,
    };
    let mut score: u32 = 0;
    let mut high_score: u32 = fs::read_to_string("highscore.dat")
        .map_or(Ok(0), |i| i.parse::<u32>())
        .unwrap_or(0);
    let mut game_state = GameState::MainMenu;

    loop {
        clear_background(DARKPURPLE);

        match game_state {
            GameState::MainMenu => {
                if is_key_pressed(KeyCode::Escape) {
                    std::process::exit(0);
                }
                if is_key_pressed(KeyCode::Space) {
                    squares.clear();
                    bullets.clear();
                    circle.x = screen_width() / 2.0;
                    circle.y = screen_height() / 2.0;
                    score = 0;
                    game_state = GameState::Playing;
                }
                let text = "Press space";
                let text_dimensions = measure_text(text, None, 50, 1.0);
                draw_text(
                    text,
                    screen_width() / 2.0 - text_dimensions.width / 2.0,
                    screen_height() / 2.0,
                    50.0,
                    WHITE,
                );
            },
            GameState::Playing => {
                let delta_time = get_frame_time();
                if is_key_down(KeyCode::Right) {
                    circle.x += MOVEMENT_SPEED * delta_time;
                }
                if is_key_down(KeyCode::Left) {
                    circle.x -= MOVEMENT_SPEED * delta_time;
                }
                if is_key_down(KeyCode::Down) {
                    circle.y += MOVEMENT_SPEED * delta_time;
                }
                if is_key_down(KeyCode::Up) {
                    circle.y -= MOVEMENT_SPEED * delta_time;
                }
                if is_key_pressed(KeyCode::Space) {
                    bullets.push(Shape {
                        x: circle.x,
                        y: circle.y,
                        speed: circle.speed * 2.0,
                        size: 5.0,
                        collided: false,
                    });
                }
                if is_key_pressed(KeyCode::Escape) {
                    game_state = GameState::Paused;
                }

                // Clamp X and Y to be within the screen
                circle.x = clamp(circle.x, 0.0, screen_width());
                circle.y = clamp(circle.y, 0.0, screen_height());

                // Generate a new square
                if rand::gen_range(0, 99) >= 95 {
                    let size = rand::gen_range(16.0, 64.0);
                    squares.push(Shape {
                        size,
                        speed: rand::gen_range(50.0, 150.0),
                        x: rand::gen_range(size / 2.0, screen_width() - size / 2.0),
                        y: -size,
                        collided: false,
                    });
                }

                // Movement
                for square in &mut squares {
                    square.y += square.speed * delta_time;
                }
                for bullet in &mut bullets {
                    bullet.y -= bullet.speed * delta_time;
                }

                // Remove shapes outside of screen
                squares.retain(|square| square.y < screen_height() + square.size);
                bullets.retain(|bullet| bullet.y > 0.0 - bullet.size / 2.0);

                // Remove collided shapes
                squares.retain(|square| !square.collided);
                bullets.retain(|bullet| !bullet.collided);

                // Check for collisions
                if squares.iter().any(|square| circle.collides_with(square)) {
                    if score == high_score {
                        fs::write("highscore.dat", high_score.to_string()).ok();
                    }
                    game_state = GameState::GameOver;
                }
                for square in squares.iter_mut() {
                    for bullet in bullets.iter_mut() {
                        if bullet.collides_with(square) {
                            bullet.collided = true;
                            square.collided = true;
                            score += square.size.round() as u32;
                            high_score = high_score.max(score);
                        }
                    }
                }

                // Draw everything
                for bullet in &bullets {
                    draw_circle(bullet.x, bullet.y, bullet.size / 2.0, RED);
                }
                draw_circle(circle.x, circle.y, circle.size / 2.0, YELLOW);
                for square in &squares {
                    draw_rectangle(
                        square.x - square.size / 2.0,
                        square.y - square.size / 2.0,
                        square.size,
                        square.size,
                        GREEN,
                    );
                }
                draw_text(
                    format!("Score: {}", score).as_str(),
                    10.0,
                    35.0,
                    25.0,
                    WHITE,
                );
                let highscore_text = format!("High score: {}", high_score);
                let text_dimensions = measure_text(highscore_text.as_str(), None, 25, 1.0);
                draw_text(
                    highscore_text.as_str(),
                    screen_width() - text_dimensions.width - 10.0,
                    35.0,
                    25.0,
                    WHITE,
                );
            },
            GameState::Paused => {
                if is_key_pressed(KeyCode::Space) {
                    game_state = GameState::Playing;
                }
                let text = "Paused";
                let text_dimensions = measure_text(text, None, 50, 1.0);
                draw_text(
                    text,
                    screen_width() / 2.0 - text_dimensions.width / 2.0,
                    screen_height() / 2.0,
                    50.0,
                    WHITE,
                );
            },
            GameState::GameOver => {
                if is_key_pressed(KeyCode::Space) {
                    game_state = GameState::MainMenu;
                }
                let text = "GAME OVER!";
                let text_dimensions = measure_text(text, None, 50, 1.0);
                draw_text(
                    text,
                    screen_width() / 2.0 - text_dimensions.width / 2.0,
                    screen_height() / 2.0,
                    50.0,
                    RED,
                );
            },
        }

        next_frame().await
    }
}

Quiz

Try your knowledge by answering the following quiz before you move on to the next chapter.

Game development in Rust with Macroquad

Game state

Implementation

Game state enum

Game state variable

Match on GameState

Main menu

Playing the game

Pause the game

Game Over

Full source code

Quiz