Bouncing Balls

1// Bouncing Balls — click to add more balls.
2// Demonstrates state, frame timing, mouse input, and the drawing API.
3 
4state balls = []
5 
6let sw = float(screen_width())
7let sh = float(screen_height())
8let delta = dt()
9 
10// Seed with a few balls on first frame
11if len(balls) == 0 then
12    for i in range(0, 12) do
13        let f = float(i)
14        push(balls, {
15            x: 50.0 + f * 60.0,
16            y: 80.0 + f * 20.0,
17            vx: 80.0 + f * 15.0,
18            vy: 40.0 - f * 8.0,
19            r: 12.0 + f * 1.5,
20            cr: 80 + (i * 23) % 175,
21            cg: 120 + (i * 47) % 135,
22            cb: 200 - (i * 31) % 150
23        })
24    end
25end
26 
27// Add a ball on click
28if mouse_pressed(1) then
29    let mx = float(mouse_x())
30    let my = float(mouse_y())
31    push(balls, {
32        x: mx, y: my,
33        vx: random(-200.0, 200.0),
34        vy: random(-200.0, 0.0),
35        r: random(8.0, 28.0),
36        cr: int(random(80.0, 255.0)),
37        cg: int(random(80.0, 255.0)),
38        cb: int(random(80.0, 255.0))
39    })
40end
41 
42let gravity = 600.0
43 
44// Physics step
45let new_balls = []
46for b in balls do
47    let nvy = b.vy + gravity * delta
48    let nx = b.x + b.vx * delta
49    let ny = b.y + nvy * delta
50    let nvx = b.vx
51 
52    // Wall collisions
53    let final_vx = nvx
54    let final_x = nx
55    if nx - b.r < 0.0 then
56        final_x = b.r
57        final_vx = -nvx * 0.85
58    end
59    if nx + b.r > sw then
60        final_x = sw - b.r
61        final_vx = -nvx * 0.85
62    end
63 
64    let final_vy = nvy
65    let final_y = ny
66    if ny + b.r > sh then
67        final_y = sh - b.r
68        final_vy = -nvy * 0.85
69    end
70    if ny - b.r < 0.0 then
71        final_y = b.r
72        final_vy = -nvy * 0.85
73    end
74 
75    push(new_balls, {
76        x: final_x, y: final_y,
77        vx: final_vx, vy: final_vy,
78        r: b.r, cr: b.cr, cg: b.cg, cb: b.cb
79    })
80end
81balls = new_balls
82 
83// === Drawing ===
84clear(14, 16, 28)
85 
86for b in balls do
87    // soft outer halo
88    draw_circle(int(b.x), int(b.y), int(b.r + 3.0), b.cr / 4, b.cg / 4, b.cb / 4)
89    draw_circle(int(b.x), int(b.y), int(b.r), b.cr, b.cg, b.cb)
90    draw_circle(int(b.x - b.r * 0.3), int(b.y - b.r * 0.3), int(b.r * 0.35),
91                min(255, b.cr + 60), min(255, b.cg + 60), min(255, b.cb + 60))
92end
93 
94draw_text("Bouncing Balls — click to add", 16, 12, 14, 200, 200, 220)
95draw_text("count: " ++ str(len(balls)), 16, 32, 12, 150, 150, 180)