Phase 5 slice D3 — Curve editor + Bezier handles

[fernandotonon]

Overview

Final chunk of slice D from #260. Adds a curve editor view alongside the dope sheet: per-channel curves with Bezier handles, interpolation-mode-per-keyframe, multi-channel display with color coding.

This is the largest D-slice — landing it as one PR may be impractical. Plan to split into D3a (data model + read-only view) and D3b (handle-drag + interp modes + resample) if implementation grows too big.

Why a side-table?

Ogre's TransformKeyFrame stores translate, rotation, and scale at a time — but no Bezier tangent handles, no interpolation mode flag. We need to keep that data on the side and re-emit linear samples into the underlying TransformKeyFrame whenever the curve changes, so Ogre's existing playback path keeps working.

Scope

Data model (C++)

• New CurveEditModel class. Keyed by (skeleton, animationName, boneName, channelId, time) with channelId ∈ {tx, ty, tz, rw, rx, ry, rz, sx, sy, sz}.
• Per-keyframe entry: { inTangent: float, outTangent: float, mode: enum }.
• Modes: Bezier, Linear, Stepped, Auto (Catmull-Rom auto-tangents from neighbors).
• API:
  • tangentsAt(skel, anim, bone, channel, time) → {in, out, mode}
  • setTangent(skel, anim, bone, channel, time, in, out)
  • setMode(skel, anim, bone, channel, time, mode)
  • evaluate(skel, anim, bone, channel, time) → float — sample the curve
• Side-table is in-memory only in this slice. Persistence (sidecar JSON) is a follow-up issue.

Resampler

When a tangent or mode changes, resample N points per second across the affected segment(s) into the underlying TransformKeyFrame. N is adaptive to local curvature (more samples where the second derivative is large) to keep file size reasonable.

• Default N = 30 samples per second; bumped to 60 around high-curvature regions.
• Limit to ±200 keyframes per segment to bound worst-case insertion.

QML — AnimationCurveEditor.qml

• New QML view, hosted in the same dock area as the Dope Sheet (toggle between them, or a tab widget).
• X axis = time (seconds), Y axis = channel value.
• Renders the selected channels as colored curves (red/green/blue T, magenta+RGB R, orange-tinted RGB S — matches D2 sub-row colors).
• Each keyframe shows as a square; drag to retime + change value.
• Each keyframe has two handles (in / out tangent); drag to adjust curve shape.
• Per-keyframe interp-mode dropdown shown on hover.
• Wheel = zoom around cursor (X + Y independently); middle-drag = pan.

Selection integration

• Reuses Dope Sheet's selection state — selected keyframe diamonds in the Dope Sheet appear as selected squares in the Curve Editor.
• Multi-select / bulk-drag still operates time-only (consistent with D1).

Tests

• Pure-data: tangent storage round-trip; auto-tangent computation matches Catmull-Rom math; evaluate(t) at a keyframe equals stored value.
• Ogre-fixture: setting a Bezier handle resamples into TransformKeyFrames; the resampled animation matches the curve at sample points within tolerance.

Out of scope

• Sidecar persistence (separate issue).
• Multi-channel batch editing (e.g. set all selected to "Linear" at once) — natural follow-up.
• Per-channel marquee selection (mostly redundant with Dope Sheet's selection).

Acceptance criteria

• Curve editor toggleable from View menu next to Dope Sheet
• Selecting channels in Dope Sheet draws those channels' curves in the Editor
• Each keyframe shows in/out handles; drag adjusts curve shape
• Interp-mode dropdown per keyframe (Bezier / Linear / Stepped / Auto)
• After editing, playback in viewport reflects the new curve shape
• Linux CI: side-table + resampler tests pass

Plan (#260)

Follows: #373 (slice C), #375 (D1), #377 (D2). Last animation slice in Phase 5.