Blend animation states

An Animator mixes imported clips by weight, each on its own clock, with every weight easing toward a target. Drive them from code through app.animation(), each frame, on the entity that draws the model.

A clip may come from another model with the same bone names. Animations downloaded from Mixamo without skin import as skeletons with one clip each, named mixamo.com, and play on the character they were made for:

const walk = eggy.AssetRef(.animation).init("resources/models/animations/Walking.fbx/mixamo.com");

blendAlong is a 1D blend space. Place clips along an axis, such as ground speed, and the two either side of the value share the pose. Every other whole-body state fades out, so calling it each frame on the ground also ends a jump.

try app.animation().blendAlong(mesh, &.{
    .{ .clip = idle, .at = 0 },
    .{ .clip = walk, .at = 1.7 },
    .{ .clip = run, .at = 3.5 },
}, ground_speed_m_per_s, 0.2, .{ .root_motion = .in_place });

fadeToState moves to one state alone, such as a jump. Give start_s to start the clip there; leave it out on later frames so the clip carries on. setState sets one state's weight and leaves the others alone.

try app.animation().fadeToState(mesh, jump, 0.1, .{ .start_s = 0.45, .repeat = .once, .root_motion = .pinned });

A state given a bone is a layer: it moves only that bone and those below it, over what the other states make. Drawing a gun on mixamorig:Spine leaves the legs walking. stateEnded says when a once clip has finished, to fade its layer back out:

if (drew) try app.animation().setState(mesh, draw_gun, 1, 0.2, .{ .start_s = 0, .repeat = .once, .bone = "mixamorig:Spine" });
if (app.animation().stateEnded(mesh, draw_gun, &app.graphics.clips)) try app.animation().setState(mesh, draw_gun, 0, 0.2, .{ .repeat = .once, .bone = "mixamorig:Spine" });

root_motion decides what a clip does with its hips when the game moves the body itself. .in_place takes out a walk's travel and keeps its sway, and .pinned holds the hips still, leaving the lift of a jump to physics.

Weights of whole-body states are shared out when they add up to more than 1. Below 1, the Animator's model clip shows through; without one the states share the whole pose, so a T-pose never shows mid-fade. Set the model clip to the idle in the scene and the model stands idle in the editor and on the game's first frame too. An Animator holds eight states at once, and a state that fades out to nothing frees its slot.