Tutorials · Animation and Cutscenes · Chapter 6

Tweens

Squash on landing

1. In Assets, press Create, choose New script, type squash, and press Enter. In the Code tab, replace everything in squash.rgs with the script below, and press Ctrl+S.

/// Squashes the knight as he lands, the harder the faster he fell, then
/// springs him back.
component Squash : Body {
    /// How fast he was falling the step before he landed.
    #[hidden]
    falling: f32 = 0.0,

    fn on_land() {
        let amount = ease(.OutQuad, clamp(falling / 900.0, 0.0, 1.0));
        await anneal_scale(vec2(1.0 + 0.3 * amount, 1.0 - 0.3 * amount), 0.05, .OutQuad);
        anneal_scale(vec2(1.0, 1.0), 0.25, .OutBack);
    }

    fn loop() {
        if !grounded() {
            falling = velocity().y;
        }
    }
}

1. Select knight, press Add component and choose Squash. Its one field, falling, is hidden: the script keeps it, and it starts 0.

component Squash : Body

A script with a Body base: it goes on a node that has a Character Body, which the knight has, and it hears the body’s events.

on_land

A Body hook. It runs on the step the body touches the ground after being in the air: once for each landing.

grounded and velocity

grounded() is whether the body stood on something as the step began. velocity() is how fast it was moving then, in world units a second, and down is positive. loop keeps velocity().y in falling on every step he is in the air.

clamp

clamp(falling / 900.0, 0.0, 1.0) is the fall speed as a share of the body’s terminal speed, 900, kept between 0 and 1: a standing fall is 0, the fastest fall 1.

ease

Runs a number from 0 to 1 through a curve and gives back where it lands, at once, with no waiting. ease(.OutQuad, …) bends the share so that a middling fall already counts for most of it: a jump lands at about 620, a share of 0.69, which comes out as 0.9.

vec2

Builds a Vec2, a pair of numbers, from two: here a scale, in squash.rgs, and an offset, in bob.rgs. vec2(1.0, 1.0) is his own size: no squash at all.

anneal_scale

Scales this node to the Vec2 it is given, over the seconds it is given, along a curve. The knight’s node stands on his feet, so he is flattened onto the boards, not into them. vec2(1.0 + 0.3 * amount, 1.0 - 0.3 * amount) is wider by up to three tenths and shorter by the same.

await

In front of an anneal it stops the hook until the anneal has finished, and then carries on. The squash is awaited, so the spring back starts only when it is done. The spring back is not: the hook ends there, and the anneal runs on by itself.

.OutQuad and .OutBack

Curves, written with a leading point. .OutQuad ends slow: the squash gets to its depth quickly and eases into it. .OutBack overshoots and settles: the knight springs past his height by a little and comes back to it.

A lever that snaps

1. Copy creak1.ogg above into audio, and press Refresh in Assets.
2. Select lever. In its SignalComponent, press the + beside Connections twice more. Open the second row and set Signal to pulled and To to lever_handle. Open the third, set Signal to pulled and To to platform: the third is for the last section.
3. Select lever_handle, press Add component and choose AudioSourceComponent. Leave Bus on Sfx. Press the + beside Triggers, open the new row, set Name to creak and Clip to creak1.ogg.
4. In Assets, press Create, choose New script, type handle, and press Enter. In the Code tab, replace everything in handle.rgs with the script below, and press Ctrl+S. Then select lever_handle, press Add component and choose Handle.

/// The lever's handle: thrown over when the lever is pulled, past its mark
/// and back, with a creak.
component Handle {
    fn on_signal() {
        if heard("pulled") {
            play_sound("creak");
            anneal_turn(-1.0, 0.4, .OutBack);
        }
    }
}

anneal_turn

Turns this node by an amount in radians, over the seconds it is given, along a curve. -1.0 is one radian, about 57 degrees, anticlockwise: the handle starts tilted 28.65 degrees to the right, and ends up as far to the left. .OutBack takes it past that, and back.

heard("pulled")

The same signal the trapdoor heard in chapter 5: all three nodes the lever’s Signal names get it, on the same step, and each script reacts in its own way. play_sound plays the creak trigger.

A platform that bobs

1. In Assets, press Create, choose New script, type bob, and press Enter. In the Code tab, replace everything in bob.rgs with the script below, and press Ctrl+S. Then select platform, press Add component and choose Bob, and press Ctrl+S.

/// The platform bobs up and down for good, until the lever is pulled: then
/// it stops where it stands.
component Bob {
    fn on_create() {
        pulse_by(vec2(0.0, -24.0), 1.5, .InOutSine);
    }

    fn on_signal() {
        if heard("pulled") {
            quench();
        }
    }
}

on_create

Runs once, on the first step the node exists: for a node in the room, the first step after you press Play.

pulse_by

Moves this node by a Vec2 and back, forever, taking the seconds it is given each way. vec2(0.0, -24.0) is 24 units up, since y grows downward, and 1.5 seconds each way makes a cycle of 3. .InOutSine is soft at both ends, so the platform slows as it turns.

quench

Stops every anneal and pulse on this node, wherever each stands. The platform stays wherever it was when the signal arrived, anywhere between its lowest and its top, and does not return.

The curves

The scene, as the chapter leaves it

Check it works