Character animation (skeleton, clips, Animator)

A model with a skeleton (FBX or glTF/GLB with bones and weights) comes alive with the Animator component: it plays clips, blends between them and deforms the model every frame. Textures, shaders and shadows work as for any model.

Quick start

1. Put a character model in the scene (.fbx, .glb).
2. Add component → Animator. The clip list shows every clip of the model. The animation plays in the Scene view, without starting the game.
3. In a script:

let monster = ctx.find("Counter").unwrap();
ctx.play_animation(monster, "Walk_Nervous");   // cross-fades from the current clip
ctx.set_animation_speed(monster, 1.4);         // steps in time with the real speed
let clips = ctx.animation_clips(monster);      // what the model offers

Full access goes through the component: ctx.get_mut_of::<Animator>(e) (clip, speed, looping, playing, fade; read-only time and clips).

Where clips come from

• The file. Every FBX animation (Rig|Walk becomes Walk) and glTF animation. Walking clips are made "in place": the hips' straight forward drift is removed (the sway stays), because a script moves the object.
• Procedural clips for humanoids. When bones have familiar names (hips/pelvis, spine, chest, neck, head, upper_arm, forearm, hand, thigh, shin, foot, sides as .L/.R, _left/_right, Left…; Mixamo works), the model gets the clips its file lacks:

Clip	What it does
Idle	breathing, weight shift, glances
Walk, Run	stride with arm and torso motion
Talk	nods and hand gestures
Wave	waves
Sit	sits (lower the object to the seat height)
Wipe	wipes a counter
Look	looks around

The character's axes (up, right, forward) come from the rest pose, and arms in a T- or A-pose are brought down first, so the clips fit any model with such bones.

Blending and accuracy

• Changing clip blends over fade seconds (0 is instant).
• looping = false holds the last frame (a strike, a fall).
• Skinning uses up to four bones per vertex, on the CPU: a few thousand vertices take microseconds.
• The rest pose matches the unanimated model exactly (checked by cargo test -p kvas_engine --test skeletal).

Example: LAST SERVICE

• MonsterAi picks the clip from the monster's state: Idle_Watchful, Walk_Nervous, Run_Frantic, Scream at the first sighting, Attack_Lunge when it catches you; the clip speed follows the movement speed.
• The Npc script on Anna and Pavel: work (Wipe, Anna wipes the counter; Look, Pavel looks around), turning to the player with Idle when close, Talk while one of that character's lines plays, Sit at the end.

IK: feet on the ground and looking

The CharacterIk component next to an Animator (humanoids only):

• feet: feet stand on the real colliders under them. On stairs, slopes and kerbs the hips drop for the lower leg and the knees bend (two-bone IK, the knee stays in its plane); the clip's own foot lift is kept. max_step is how far a foot may go up or down. Works in the running game (it needs physics).
• look_at: the name of an object to look at, or a point from a script. The chest, neck and head turn (20 / 30 / 50 %) within look_limit degrees, smoothly; a target behind the back is let go.

let eyes = ctx.find("Eyes").map(|e| ctx.world_matrix_of(e).w_axis.truncate());
ctx.look_at_point(npc, eyes);   // look at the player
ctx.look_at_point(npc, None);   // let go

Ragdoll

The Ragdoll component (or ctx.ragdoll(entity, impulse)): the character's body becomes physics capsules (pelvis, chest, head, upper arms, forearms, thighs, shins) on ball joints. They start exactly in the clip's pose, get the object's velocity and the impulse on the chest, and collide with the world but not with each other. The skeleton follows the bodies; hands and feet ride on the forearms and shins.

ctx.ragdoll(enemy, hit_dir * 40.0); // fall from a hit
ctx.stop_ragdoll(enemy);            // remove the bodies, the clip plays again

mass is the total mass (shared out over the parts), damping how stiff the joints feel.

In LAST SERVICE Anna and Pavel meet Lida's eyes when she is close; the Counter follows her with its head and plants its feet on the floor, and at the bus stop at the end it goes limp and falls.