Tutorials · Ship Evader · Chapter 5

Firing

The laser’s script

1. In Assets, press Create, choose New script, type laser, and press Enter. The editor writes laser.rgs into the project folder.
2. Click the Code tab, then laser.rgs in its Scripts list, replace everything in it with the script below, and press Ctrl+S.

/// A laser: it flies up the field, and removes itself once it is 100 units
/// past the top.
component Laser {
    /// How fast the laser flies.
    #[suffix("u/s")]
    speed: f32 = 900.0,

    fn loop(dt: f32) {
        // Up is toward negative y: the world's y grows downward.
        translate(vec2(0.0, -speed * dt));
        // camera_view().y is the top edge of the field.
        if position().y < camera_view().y - 100.0 {
            destroy_self();
        }
    }
}

Make the laser once

1. Click the Viewport tab, select ship, and drag art/laserBlue01.png from Assets into the Viewport. It lands beside the ship, under Game.
2. Double-click its row in the Hierarchy, type laser, and press Enter.
3. Set its Position to 0 and 0. A copy is placed wherever the ship asks for it, so the laser itself sits at the world’s origin.
4. Leave its Sprite’s Size at the picture’s own 9 by 54, and set Sort Layer to -1, so a laser leaving the ship draws under its nose rather than over it.
5. Press Add component and choose Laser. Its Speed is 900.

Save it as an artifact

1. Right-click laser in the Hierarchy and choose Save as artifact….
2. In the save dialog, make a folder called artifacts, open it, and save the file as laser.artifact.
3. Delete the laser left in the scene: select it, press Delete, and choose Delete. It is a copy of that file now, and the game makes copies of its own.

The ship’s Spawner

1. Select ship, press Add component, and choose SpawnerComponent.
2. Press + beside Entries, and open the new [0] row.
3. Type laser as the new entry’s Name, and drag artifacts/laser.artifact from Assets onto its Artifact.

Fire while Space is held

/// The player's ship: it flies where `move` points, never leaves the field,
/// and fires lasers while `fire` is held.
component Ship {
    /// How fast the ship flies.
    #[suffix("u/s")]
    speed: f32 = 420.0,
    /// How close the ship's centre may come to an edge of the field.
    #[suffix("u")]
    margin: f32 = 50.0,
    /// Seconds between two lasers while fire is held.
    #[suffix("s")]
    fire_interval: f32 = 0.16,
    /// Seconds until the ship can fire again.
    #[hidden]
    cooldown: f32 = 0.0,

    fn loop(dt: f32) {
        let view = camera_view();
        let next = position() + direction("move").normalized() * (speed * dt);
        move_to(vec2(
            clamp(next.x, view.x + margin, view.z - margin),
            clamp(next.y, view.y + margin, view.w - margin),
        ));

        if cooldown > 0.0 {
            cooldown -= dt;
        }
        if held("fire") && cooldown <= 0.0 {
            // 50 units above the ship's centre: up is toward negative y.
            spawn("laser", position() + vec2(0.0, -50.0));
            cooldown = fire_interval;
        }
    }
}

held

Whether an action’s key is down on this step. held("fire") stays true for as long as Space is held.

spawn

Makes a copy of the artifact the Spawner calls laser, at a point in the world: 50 units above the ship’s centre. The copy is a node of its own at the top of the scene, so it does not follow the ship; its own script flies it.

cooldown

Seconds until the ship may fire again. #[hidden] keeps it out of the Inspector: it is the script’s own counting, not something to tune. Each step takes dt off it, and a laser fires once it has run out and fire is held, setting it to fire_interval again.

Check it works