rusting_engine 2.0.2

Vulkan 3D game engine with GPU-accelerated physics for massive physics-heavy scenes
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129

use rusting_engine::prelude::*;

/// Ticks between two moves at the start, and the fastest pace later on.
const FIRST_STEP: u64 = 9;
const LAST_STEP: u64 = 5;
/// Right, down, left, up, in grid cells (rows grow downward).
const HEADINGS: [(i32, i32); 4] = [(1, 0), (0, 1), (-1, 0), (0, -1)];
/// Where the apples appear, in order.
const APPLES: [(i32, i32); 10] = [
    (12, 6),
    (12, 2),
    (4, 3),
    (15, 8),
    (8, 9),
    (17, 2),
    (2, 10),
    (10, 5),
    (16, 6),
    (6, 2),
];

/// World position of the center of cell (`column`, `row`) of the Arena,
/// whose top-left corner is at (-10, 6).
fn center((column, row): (i32, i32)) -> [f32; 3] {
    [-9.5 + column as f32, 5.5 - row as f32, 0.1]
}

fn cell_of(position: [f32; 3]) -> (i32, i32) {
    (
        (position[0] + 10.0).floor() as i32,
        (6.0 - position[1]).floor() as i32,
    )
}

fn part(index: i32) -> String {
    if index == 0 {
        "Head".to_owned()
    } else {
        format!("Segment {index}")
    }
}

fn steer(scene: &mut GameScene<'_>) {
    for (heading, action) in ["right", "down", "left", "up"].iter().enumerate()
    {
        if scene.pressed(action) {
            scene.set_counter("turn", heading as i32);
        }
    }
}

/// Moves the snake one cell. Returns false when it crashed.
fn step(scene: &mut GameScene<'_>) -> bool {
    let heading = scene.counter_value("heading");
    let turn = scene.counter_value("turn");
    // A snake cannot turn back into itself.
    let heading = if (turn - heading).abs() == 2 {
        heading
    } else {
        turn
    };
    scene.set_counter("heading", heading);
    let (dx, dy) = HEADINGS[heading as usize];
    let length = scene.counter_value("length");
    let body: Vec<(i32, i32)> = (0..=length)
        .map(|index| cell_of(scene.object(&part(index)).position()))
        .collect();
    let next = (body[0].0 + dx, body[0].1 + dy);
    // The tail moves out of the way this step, so the head may follow it.
    let bites = body[1..body.len() - 1].contains(&next);
    if bites || scene.tile("Arena", center(next)) == Some('#') {
        return false;
    }
    for index in (1..=length).rev() {
        scene
            .object(&part(index))
            .set_position(center(body[index as usize - 1]));
    }
    scene.object("Head").set_position(center(next));

    if cell_of(scene.object("Apple").position()) == next {
        let grown = length + 1;
        scene.spawn_copy(
            "Segment",
            part(grown).as_str(),
            center(body[length as usize]),
        );
        scene.set_visible(&part(grown), true);
        scene.add_to_counter("length", 1);
        scene.add_to_counter("apples", 1);
        let eaten = scene.counter_value("apples") as usize;
        let mut occupied = body;
        occupied.push(next);
        // ponytail: the next free spot in a fixed list; a snake covering
        // every listed spot leaves the apple where it was.
        if let Some(spot) = (0..APPLES.len())
            .map(|offset| APPLES[(eaten + offset) % APPLES.len()])
            .find(|spot| !occupied.contains(spot))
        {
            scene.object("Apple").set_position(center(spot));
        }
    }
    true
}

fn update(scene: &mut GameScene<'_>, time: &FrameTime) {
    if scene.pressed("restart") {
        scene.restart();
        return;
    }
    if scene.counter_complete("apples") || scene.counter_complete("crashed") {
        return;
    }
    steer(scene);
    let tick = time.fixed_tick;
    let next_step = scene.counter_value("next_step") as u64;
    if tick < next_step {
        return;
    }
    let pace = FIRST_STEP
        .saturating_sub(scene.counter_value("apples") as u64 / 2)
        .max(LAST_STEP);
    scene.set_counter("next_step", (tick + pace) as i32);
    if next_step > 0 && !step(scene) {
        scene.add_to_counter("crashed", 1);
    }
}

rusting_game!(update);