iw4L/docs/ANIM.md

Animation: what lives where

Three floors, deliberately different: the curve facts (pure mathematics), the runtime tree (pose state) and who picked which clip (the game).

anim_iw4 — facts only, #![no_std], no clock and no allocator

• XAnimParts — curve storage, unpacking of half_quat / full_quat and quantized translations (XAnimCalcParts); translations are deltas;
• span/sample/time_to_frame — a pure function of (clip, time);
• the blend rule bind + scale * Δ, rotation replaced (DObjCompose);
• DObj — how model, skeleton and attachments compose (0x9c, prefix mapped out);
• XBoneInfo — the OBBs for bone hits (DObjGeom_RayBones);
• PartBits — the six-word requested/ignore mask (DObjCalcAnimInternal);
• PlayerAnimValue — 10-bit legsAnim / torsoAnim, a 9-bit index and the 0x200 "restart" bit: a restart changes only that bit, not the index;
• the leaf time step and the goal-weight ramp are measured IW4 constants;
• script name tables: ANIM_MT_NAMES, ANIM_BODY_PART_NAMES, ANIM_COND_NAMES.

No Vec, no AnimationClip, no glam matrices and no playback clock here.

xmodel_runtime — a runtime without Bevy and without ECS

A pure evaluator, used by both the authority and the client:

• XAnimTreeDefinition (the immutable hierarchy) + XAnimTreeRuntime (state; leaf time normalized into [0,1], update is the per-leaf advance);
• DObjAnimRuntime — update / pose_request / compose; DObj reuse is equality of (eType, model*), not "always a fresh one";
• RetainedModelCapability — pose, XBoneInfo, collSurf/collTris for hitscan;
• build_body_head_weapon_dobj — body + head on j_spine4 + weapon on its tag.

A missing clip never turns into the bind pose; additive nodes are a typed gap, not "ordinary blending".

Who picks the clip

• sim — player_anim_script.rs, mantle_xanim.rs, anim_script_gap.rs: what animation the player is in, and it travels into the snapshot as semantics, not as a tree;
• assets — XAnimParts → owning clips;
• render_frontend/adapters/anim/ + render_anim — the viewmodel (fpv*.rs, viewmodel_controller.rs), third person (third_person.rs, remote_body.rs), kick and sway (view_kick.rs, view_sway.rs), items and projectiles. FPV actions come from the presented weapAnim, never from the keyboard; the identity of the FPV mesh is weapon_iw4::bg_get_viewmodel_weapon_index.

To watch it live: IW4L_PERF=1 / PERF.md.