Tutorials · Animation and Cutscenes · Chapter 7

Root motion

Crouch and slide

1. Choose View → Input map…. Type crouch into New action and press Add. With crouch selected, press Record a control and press S. Press Record a control again and press Down. Press Save, and close the window.
2. Select knight and click the Graph tab. In the Parameters list, type crouch into the name box, choose switch in the list of kinds and press Add. Type slide, choose trigger and press Add. The crouch row has a tick box, and it starts unticked.
3. In the row over the canvas, add three states, each with the State and Clip boxes filled in as crouch and crouch, slide and slide, and crouched and crouched, with Add state. Drag them to a row of their own under the others. The crouched clip is made in the next section; its name is all the state needs now.
4. Click idle, press Link and click crouch. In the new row, idle to crouch, choose Is and type crouch in the name box, and leave its box ticked: true. Press the + at the end of the row: a second test, which must hold as well. Choose Is, type grounded and leave it ticked. Press the row’s up arrow until its number reads 2: it then comes just after the two Any State arrows. (While idle is selected the list shows only its own arrows; the number is the arrow’s place in the whole list.)
5. Do the same for run to crouch: the same two tests, and its up arrow until its number reads 3.
6. Click crouch, press Link and click idle. Choose Is, type crouch and untick the box: false. Click crouch, press Link and click slide: choose Trigger and type slide.
7. Click slide, press Link and click crouched: choose Finished. Click crouched, press Link and click idle: choose Is, type crouch and untick the box. Click crouched again, press Link and click slide: choose Trigger and type slide. Every blend stays 0.
8. Press Save.

Switch

A kind of parameter: a tick box. It is on or off and stays as it was set, which is what a trigger is not. crouch starts off. A script sets it with set_param_flag, and a condition reads it with Is.

and

A row can hold several tests, one under another, which the + at the row’s end adds, joined by and: the edge fires only when every one holds. crouch is true and grounded is true is a crouch on the ground, so a crouch in mid-air is not one.

1. Select knight. In the Code tab, replace everything in knight.rgs with the script below, and press Ctrl+S.

/// The knight's orders: J or X slashes, unless he is hurt; crouched (S or
/// down), J slides instead. The spikes hurt him, and not again until his
/// hurt clip has played out; its recoil frame lifts him by the number it
/// carries.
component Knight : Area {
    /// Whether his hurt clip is still playing.
    #[hidden]
    hurting: bool = false,

    fn while_in() {
        if in_group(other, "spikes") && !hurting {
            hurting = true;
            trigger("hurt");
        }
    }

    fn on_signal() {
        if heard("frame:recoil") {
            set_number("CharacterBodyComponent", "velocity.y", -heard_value("frame:recoil"));
        }
        if heard("finished:hurt") {
            hurting = false;
        }
    }

    fn loop() {
        set_param_flag("crouch", held("crouch"));
        if pressed("attack") {
            if state() == "crouch" || state() == "crouched" {
                trigger("slide");
            } else if state() != "hurt" && state() != "slide" {
                trigger("slash");
            }
        }
    }
}

held

Whether the player is holding the action down, on every step. pressed is true for the one step the key goes down; held is true for as long as it stays down. held("crouch") is true while S or Down is.

set_param_flag

Sets the switch of that name that this node’s graph reads, from the next step. The script writes it on every step, so the switch always follows the key: down, it is on; let go, it is off, and the edges crouch → idle and crouched → idle stand him up.

state and trigger("slide")

The state the graph was in as the step began. In crouch or crouched, J raises slide and the graph takes it. Anywhere else, J raises slash, unless he is in hurt or already in slide. crouch → slide and crouched → slide are the two edges that read it.

Why the slide snaps back

Pivots as drift

1. Select knight, and in the Animation tab open the slide clip. In its Frames, click the first frame and set its pivot x to 0.25, y stays 1. Click the second and set 0.375. The third is already 0.5. Click the fourth and set 0.625.
2. Double-click art/knight.png in Assets. In the Sprite sheet tab, set Cell to 48 and 48 and Margin to 1929 and 0: the crouch strip’s third and last frame. Drag across the one cell, 0, 0: Selected 1 x 1. Press From selection; name it crouched, 12 fps, Loop; press Generate 1 and Clear.
3. In the Animation tab, open crouched and set its one frame’s pivot x to 0.625, the slide’s last. Press Save.

Root Motion

1. Select knight, press Add component and choose RootMotionComponent. Leave its fields as they come: Scale 1, 0 and Enabled ticked. Press Ctrl+S.

Scale

The Root Motion’s Scale: how much of the drift is applied, along each axis. 1, 0 applies all of the sideways drift and none of the vertical. The knight’s jump and fall frames change their pivots’ y, to keep his feet down, and that must not lift him, so y stays 0. A new Root Motion has 1, 0.

Enabled

The Root Motion’s Enabled: whether it applies right now. Ticked, the drift of the frame he is on is added to his move each step. Unticked, the frames still play and nothing carries him. It starts ticked.

1. Press F5. Hold S, press J and watch the slide carry him. In the Inspector, untick Enabled, and slide again: the frames play, and he does not move. Tick it again, and press F5 to stop.

Check it works