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ryan ab5c79ab6a feat: Implement draggable torso and head IK targets in the test harness

- Added draggable handles for the torso and head to the test harness.
- Updated `IK_HANDLE_PATHS` to include new entries for "Head" and "Torso".
- Implemented distinct colors for the torso (magenta) and head (yellow) markers.
- Added a visual aid (aim line) to indicate the head's LookAt target direction.
- Ensured that dragging the torso moves only the torso marker, allowing for limb stretching towards stationary targets.

2026-08-21 12:39:31 -04:00

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Phase 9 Round 4 — Bugfix: Head Position vs. the Editor's Silhouette Guide

Overview

User report: the head is too high in the harness. Reference: the editor's silhouette guide head is a circle; the bottom of the mounted head shape must line up with the bottom of that circle relative to the torso bone, so the head overlaps the torso some.

Guide geometry (source of truth, `scripts/whole_stickman_preview.gd`)

Constant	Value
`GUIDE_JOINTS["Neck"]` (`:61`)	`(0, −391.5)` — the Head bone origin
`GUIDE_JOINTS["Head"]` (`:62`)	`(0, −463.5)` — the head circle center
`GUIDE_HEAD_RADIUS` (`:49`)	`100.0`

→ The guide's head circle bottom = −463.5 + 100 = −363.5 — 28 px below the neck, overlapping the torso's top region (torso spans 0 → −391.5) by 28 px.

Current behavior (wrong)

Round 3 zeroes the Head driver's local position, so Body/Head sits on the Head bone origin (the neck, y = −391.5); the mounted chin is the local origin → the chin lands at the neck and the head floats above the torso with no overlap.

Required behavior

The mounted head's bottom (chin) must land at y = −363.5 — i.e. the mounted head geometry gets a +28 px local Y offset so the chin sits 28 px below the neck joint, matching the guide circle's bottom and overlapping the torso.

Fix specification — `scripts/stk_rig_adapter.gd`

Add const HEAD_CHIN_DROP := 28.0 with a doc comment deriving the value (guide head circle bottom −363.5 − neck −391.5 = 28; the guide circle has radius 100 centered at the Head joint (0, −463.5)).
In the head branch of the mount (where θ = 0, s = 1), after transforming the points, translate them by Vector2(0.0, HEAD_CHIN_DROP) — the chin (local origin) ends up 28 px below the node origin (the neck).
The flip anchor rule from Round 3 is unchanged (a flipped head still attaches at its cap top; the drop applies identically).
Nothing else changes (no driver/overlay/serialization changes).

Note: the offset is applied after the part scale/rotation composition (it is a rig-space fixture position, not part geometry), so a 180°-rotated head drops by the same 28 px.

Files modified

File	Changes
`scripts/stk_rig_adapter.gd`	`HEAD_CHIN_DROP` const + head-points translation.
`docs/phase9_round4_bugfix_spec.md`	This file.

Test plan

Parse check: ..\Godot_v4.7.1-stable_win64_console.exe . --headless --check-only --quit.
Headless smoke test (spawn break.stk, stack enabled, 2 frames):
- Body/Head world position ≈ (0, −391.5) (node still at the neck).
- Mounted head chin point ≈ local (0, +28); world chin ≈ (0, −363.5).
- Head top ≈ world (0, −363.5 − 219) ≈ (0, −582); the head now overlaps the torso's top region (torso top at −391.5) by ≈ 28 px.
- Regression: the head's other Round 3 properties (scale ≈160 face, one node per shape, IK following, flip behavior) unchanged.
Manual harness check (F6): head bottom aligned with the guide circle's bottom; head overlaps the torso.

Design decisions

#	Decision	Justification
D1	Fixed `+28 px` rig-space offset (not relative to the head's drawn size)	The guide circle is a fixed rig fixture; the requirement is to align to its bottom.
D2	Offset applied to the mounted points (not the driver)	The Head driver's zeroing stays (rotation about the neck with the LookAt); a driver offset would swing with the bone rotation.

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