Tutorials · Animation and Cutscenes · Chapter 11

Cutting the strings

A body for every bone

1. In the Hierarchy, make sure the whole rig shows under marionette. Select torso, then Ctrl-click the thirteen bones under it: head, upper_arm_left, lower_arm_left, hand_left, upper_arm_right, lower_arm_right, hand_right, upper_leg_left, lower_leg_left, foot_left, upper_leg_right, lower_leg_right and foot_right. Fourteen nodes are selected.
2. Click Add component and choose PhysicalBoneComponent. It goes on all fourteen.
3. With the fourteen still selected, set Gravity to 1200 and Damping to 0.5. What you set now is set on all of them. Limp stays unticked.
4. Select torso alone and set its Size to 16, 16. Select head and set 14, 14.
5. Select upper_arm_left, then Ctrl-click upper_arm_right, hand_left and hand_right, and set Size to 6, 6.
6. Select both lower arms and set Size to 5, 5. Select both upper legs: 7, 7. Select both lower legs: 6, 6. Select both feet: 10, 12.

Size

A Physical Bone’s Size: the box the bone has as a body while it is limp, in world units, centred on its joint and about as thick as the limb. It is a box on the joint, not the picture along the bone, so a bone that lies down rests on the boards at its own thickness. A new one is 8, 8. The torso’s is 16, 16, the head’s 14, 14, the limbs’ between 5 and 7, and the feet’s 10, 12.

Gravity

How hard a Physical Bone’s body is pulled down while it is limp, in world units a second a second. Down counts as positive here: a positive number pulls the bone to the boards. A new one is 900; the marionette’s is 1200, a brisk fall.

Damping

How much of its motion against its parent bone, and of its swing, a limp bone loses each step, from 0 to 1. 0 lets a limb swing on and on; 1 holds it dead against its parent. It is what settles a fallen rig instead of leaving it twitching. A new one is 0.2; the marionette’s is 0.5.

Limp

The switch. Ticked, the bone falls as a body pinned to its parent bone, and nothing else moves it; unticked, it is the rig’s again, and it stands back at its Bone’s rest pose. A scene keeps it unticked, and a script turns it on: the ragdoll call below does it for every bone at once.

A rest pose to stand up in

1. Look at the Hierarchy: torso has a warning mark beside it, and the status bar at the bottom of the window says 1 problem. Click it: the Problems tab opens in the bottom dock.

1. Select torso. In its Bone, press Capture rest pose. The 1 problem in the status bar goes, and so does the warning. If you left Record on, leave it: it keys only what you edit in a row, never a button.

Capture rest pose and Reset to rest

Two buttons in a Bone, each acting on every bone at or under the node it is pressed on. Capture rest pose copies where each bone stands now, its Position, Rotation and Scale, into its rest fields. Reset to rest does the opposite and puts each bone back at its captured pose, which is how you tidy a rig you have been posing by hand. Both are one undo step.

Rest Position

The Bone’s Rest Position: where the bone sits, in its parent’s space, when nothing is driving it. Capture copies the node’s Position into it, so torso’s is 0, -55.3, up from the marionette’s feet, and each limb’s is its joint’s place on its parent. A new Bone’s is 0, 0, which is why an uncaptured rig stands up in a heap. Nobody types it.

Rest Rotation

The Bone’s Rest Rotation, the rotation of its rest pose, shown in radians, the unit it is stored in; the node’s own Rotation, above it, shows degrees. torso’s is 1.5708, a quarter turn, the 90° above it; head’s is 3.1416, half a turn. Radians are degrees times about 0.01745.

Rest Scale

The Bone’s Rest Scale, the scale of its rest pose. It is 1, 1 on every bone of this rig, so Capture leaves it where it was, and a Bone starts there too.

The cut

1. Select marionette, click Add component and choose AreaComponent. Set its Shape’s Size to 24, 64 and its Offset to 0, -32. That is a box 24 wide and 64 high standing on the boards where the marionette stands. Its other rows stay as they come.
2. Click Add component again and choose AudioSourceComponent. Leave Bus on Sfx and Autoplay off. Press + beside Triggers, open the new row, set Name to snap, and drag chop.ogg from Assets onto its Clip, as you did for the footsteps.

1. Open marionette.rgs in the Code tab, replace everything in it with the script below, and press Ctrl+S.
2. Select marionette. Its Marionette component has a new Strings row, empty. Click it and choose strings from the list, or drag strings from the Hierarchy onto the slot. The row shows the node’s name.

/// The marionette's puppeteer: it rests three seconds, then dances three,
/// turn and turn about. A blade that reaches it cuts its strings: it falls
/// limp, and five seconds later it is strung up again, at rest.
component Marionette : Area {
    /// Seconds into this turn.
    #[hidden]
    clock: f32 = 0.0,
    /// Whether it dances this turn.
    #[hidden]
    dancing: bool = false,
    /// The strings a cut takes away.
    #[node_path]
    strings: i32 = 0,
    /// Whether its strings are cut.
    #[hidden]
    cut: bool = false,

    fn on_enter(other: NodeId) {
        if in_group(other, "blade") && !cut {
            cut = true;
            play_sound("snap");
            set_visible(node(strings), false);
            ragdoll(true);
            await wait(5.0);
            ragdoll(false);
            set_visible(node(strings), true);
            cut = false;
        }
    }

    fn loop() {
        clock += dt;
        if clock >= 3.0 {
            clock = 0.0;
            dancing = !dancing;
            set_param_flag("dancing", dancing);
        }
    }
}

ragdoll

Turns every Physical Bone on this node and under it limp with true, and stands them back up with false. The run carries it out as the step ends, so the bones are bodies from the next step. ragdoll(false) also puts every Bone under the node back at its rest pose at once, so the rig is upright and at rest on the step it is called, not eased there.

wait

Suspends the hook for that many seconds, then carries on from the same line. It is awaited: await wait(5.0). While the hook waits, loop keeps running, and the hook is not entered again: a second blade that reaches the marionette while it is down starts nothing.

set_visible

Shows or hides another node, here the one node(strings) names, and the nodes under it go with it: the three strings. The node is hidden from the step the call runs on.

node

Turns the pick a #[node_path] field holds into the node the other calls take. A field with nothing picked is 0, which names nobody. The scene file keeps the pick as the node’s number, 31 for strings.

Down, and back up

The bones, the rest pose and the cut

Check it works