basics/
basics.rs

1//! Basic example: a bouncing ball with camera shake and tweening.
2//!
3//! Run with: `cargo run --example basics`
4
5use game_gem::prelude::*;
6
7struct BouncingBall {
8    position: Vec2,
9    velocity: Vec2,
10    radius: f32,
11    color: Color,
12    trail: Vec<(Vec2, f32)>, // (position, alpha)
13}
14
15impl BouncingBall {
16    fn new() -> Self {
17        Self {
18            position: vec2(400.0, 300.0),
19            velocity: vec2(250.0, -180.0),
20            radius: 30.0,
21            color: Color::GOLD,
22            trail: Vec::with_capacity(60),
23        }
24    }
25}
26
27struct BasicsExample {
28    ball: BouncingBall,
29    hue: f32,
30    click_count: u32,
31}
32
33impl GameState for BasicsExample {
34    fn on_enter(&mut self, ctx: &mut Context) {
35        // Register input actions
36        let mut jump = InputAction::new("shake");
37        jump.bind_key(KeyCode::Space);
38        ctx.input.register_action(jump);
39
40        // Set up camera with follow
41        ctx.graphics.camera.follow(self.ball.position, 0.05);
42    }
43
44    fn update(&mut self, ctx: &mut Context) {
45        let dt = ctx.time.delta() as f32;
46
47        // --- Ball physics ---
48        self.ball.velocity.y += 600.0 * dt; // Gravity
49        self.ball.position += self.ball.velocity * dt;
50
51        // Bounce off walls
52        let w = ctx.screen_width();
53        let h = ctx.screen_height();
54
55        if self.ball.position.x - self.ball.radius < 0.0 {
56            self.ball.position.x = self.ball.radius;
57            self.ball.velocity.x = self.ball.velocity.x.abs();
58        }
59        if self.ball.position.x + self.ball.radius > w {
60            self.ball.position.x = w - self.ball.radius;
61            self.ball.velocity.x = -self.ball.velocity.x.abs();
62        }
63        if self.ball.position.y - self.ball.radius < 0.0 {
64            self.ball.position.y = self.ball.radius;
65            self.ball.velocity.y = self.ball.velocity.y.abs();
66        }
67        if self.ball.position.y + self.ball.radius > h {
68            self.ball.position.y = h - self.ball.radius;
69            self.ball.velocity.y = -self.ball.velocity.y.abs() * 0.95; // Damping
70        }
71
72        // Update trail
73        self.ball.trail.push((self.ball.position, 1.0));
74        if self.ball.trail.len() > 60 {
75            self.ball.trail.remove(0);
76        }
77        for (_, alpha) in &mut self.ball.trail {
78            *alpha -= dt * 2.0;
79        }
80        self.ball.trail.retain(|(_, a)| *a > 0.0);
81
82        // --- Input ---
83        if ctx.input.is_action_pressed("shake") {
84            ctx.graphics.camera.shake(10.0, 0.3);
85        }
86
87        if ctx.input.mouse.is_pressed(MouseButton::Left) {
88            self.click_count += 1;
89            // Change ball color
90            self.hue = (self.hue + 30.0) % 360.0;
91            self.ball.color = Color::from_hsla(self.hue, 0.8, 0.6, 1.0);
92            // Boost ball toward click
93            let dir = ctx.input.mouse.position - self.ball.position;
94            self.ball.velocity += dir.normalize_or_zero() * 200.0;
95        }
96
97        // Zoom with scroll
98        let zoom = ctx.graphics.camera.zoom + ctx.input.mouse.scroll.y * 0.1;
99        ctx.graphics.camera.set_zoom(zoom);
100
101        // Escape to quit
102        if ctx.input.keyboard.is_pressed(KeyCode::Escape) {
103            ctx.quit();
104        }
105
106        // Update camera follow target
107        ctx.graphics.camera.follow(self.ball.position, 0.05);
108    }
109
110    fn render(&mut self, ctx: &mut Context) {
111        ctx.graphics.clear(ctx.window.clear_color);
112
113        // Draw trail
114        for &(pos, alpha) in &self.ball.trail {
115            ctx.graphics.draw_circle(
116                pos.x, pos.y,
117                self.ball.radius * 0.5 * alpha,
118                self.ball.color.with_alpha(alpha * 0.5),
119            );
120        }
121
122        // Draw ball
123        ctx.graphics.draw_circle(
124            self.ball.position.x,
125            self.ball.position.y,
126            self.ball.radius,
127            self.ball.color,
128        );
129
130        // Draw HUD
131        ctx.graphics.reset_camera();
132        ctx.graphics.draw_text(
133            &format!("FPS: {:.0}", ctx.time.fps()),
134            10.0, 10.0, 18.0, Color::WHITE,
135        );
136        ctx.graphics.draw_text(
137            &format!("Clicks: {}", self.click_count),
138            10.0, 35.0, 18.0, Color::WHITE,
139        );
140        ctx.graphics.draw_text(
141            "Space = shake | Click = change color | Scroll = zoom | Esc = quit",
142            10.0, 60.0, 14.0, Color::LIGHT_GRAY,
143        );
144    }
145}
146
147fn main() {
148    let example = BasicsExample {
149        ball: BouncingBall::new(),
150        hue: 0.0,
151        click_count: 0,
152    };
153
154    Game::new()
155        .window_title("game-gem: Basics Example")
156        .window_size(800, 600)
157        .clear_color(Color::from_hex("#0F0F23").unwrap())
158        .run(example);
159}
basics/basics.rs

basics/
basics.rs
